U.S. patent application number 09/800272 was filed with the patent office on 2002-01-31 for fire detector and housing.
This patent application is currently assigned to Fire Sentry Corporation. Invention is credited to Castleman, David A..
Application Number | 20020011570 09/800272 |
Document ID | / |
Family ID | 46254485 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020011570 |
Kind Code |
A1 |
Castleman, David A. |
January 31, 2002 |
Fire detector and housing
Abstract
A process and system for flame detection includes a
microprocessor-controlled detector with at least three sensors. A
wide band infrared sensor is used as the primary detector, with
near band and visible band sensors serving to detect false-alarm
energy from nonfire sources. Digital signal processing is used to
analyze sensed data and discriminate against false alarms. A
multistage alarm system can be provided, which is selectively
triggered by the microprocessor. Spectral recording and analysis of
prefire data is provided for. The detector can be housed in an
enclosed, sealed, removable, plastic housing that may include an
integral plastic window lens.
Inventors: |
Castleman, David A.;
(Coarsegold, CA) |
Correspondence
Address: |
IRELL & MANELLA LLP
1800 AVENUE OF THE STARS
SUITE 900
LOS ANGELES
CA
90067
US
|
Assignee: |
Fire Sentry Corporation
Brea
CA
|
Family ID: |
46254485 |
Appl. No.: |
09/800272 |
Filed: |
March 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09800272 |
Mar 5, 2001 |
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09384808 |
Aug 27, 1999 |
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6239435 |
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09384808 |
Aug 27, 1999 |
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08866029 |
May 30, 1997 |
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6064064 |
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08866029 |
May 30, 1997 |
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08690067 |
Jul 31, 1996 |
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6046452 |
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08690067 |
Jul 31, 1996 |
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08609740 |
Mar 1, 1996 |
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5773826 |
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Current U.S.
Class: |
250/339.15 ;
250/339.04; 250/339.05; 340/578 |
Current CPC
Class: |
G08B 29/24 20130101;
G08B 25/002 20130101; G08B 29/22 20130101; G08B 17/12 20130101 |
Class at
Publication: |
250/339.15 ;
250/339.04; 250/339.05; 340/578 |
International
Class: |
G01J 005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 1997 |
US |
PCT/US97/03327 |
Claims
What is claimed is:
1. A fire detector, comprising: a wide band infrared sensor; means
for detecting when a level of wide band infrared radiant energy
detected by the wide band infrared sensor exceeds an energy level
threshold; and means responsive to said detecting means for
initiating a fire response protocol.
2. The fire detector of claim 1, wherein said means for detecting
when a level of wide band infrared radiant energy detected by the
wide band infrared sensor exceeds an energy level threshold
comprises a filter connected to the wide band infrared sensor for
measuring the level of wide band infrared radiant energy, and a
comparator connected to an output of said filter and to said energy
level threshold.
3. The fire detector of claim 2, wherein said means for detecting
when a level of wide band infrared radiant energy detected by the
wide band infrared sensor exceeds an energy level threshold further
comprises a visible band sensor connected to a second filter for
measuring a level of visible band radiant energy, and a subtractor
whereby said level of visible band radiant energy is subtracted
from the output of the filter connected to the wide band infrared
sensor prior to said comparator.
4. The fire detector of claim 1, further comprising a near band
infrared sensor, wherein said energy level threshold is set as a
function of a level of energy detected by the near band infrared
sensor.
5. A fire detection system, comprising: a sensor array for
providing sensor signals, said sensor array including a false-alarm
sensor for detecting visible band energy, a false-alarm sensor for
detecting near band infrared energy, and a primary sensor for
detecting wide band infrared energy; a temperature sensor for
providing signals indicative of ambient temperature conditions; and
a controller for processing said sensor signals, said controller
coupled to said sensor array and said temperature sensor for
receiving said sensor signals from said sensor array and said
signals from said temperature sensor, said controller calibrating
operation parameters for said fire detection system in accordance
with said signals from said temperature sensor and said sensor
signals.
6. The fire detection system of claim 5, further comprising a
multistage alarm system coupled to said controller, said controller
selectively activating a select one of a plurality of relays of
said multistage alarm system depending upon one of a plurality of
conditions sensed by said controller.
7. The fire detection system of claim 6, wherein said plurality of
relays comprises two relays and said plurality of conditions
comprises two conditions.
8. The fire detection system of claim 6, wherein said plurality of
relays comprises three relays and said plurality of conditions
comprises three conditions.
9. The fire detection system of claim 5, further comprising means
for storing spectral information associated with a detected fire
event.
10. The fire detection system of claim 9, wherein said means for
storing comprises nonvolatile RAM.
11. The fire detection system of claim 5, further comprising means
for storing spectral information preceding a detected fire
event.
12. The fire detection system of claim 11, wherein said means for
storing comprises nonvolatile RAM.
13. The fire detection system of claim 5, further comprising an
enclosed, sealed, removable housing containing said sensor array,
said temperature sensor, and said controller, said housing
including a window lens.
14. The fire detection system of claim 13, wherein said window lens
is integral with said housing.
15. The fire detection system of claim 14, wherein said window lens
is thinner than the remaining part of said housing.
16. The fire detection system of claim 13, wherein said window lens
is embedded in said housing.
17. The fire detection system of claim 13, wherein said housing is
heat sealed.
18. The fire detection system of claim 17, further comprising a
plastic-coated, electrical power cable, said housing being heat
sealed to said cable.
19. A fire detection system, comprising: a sensor array including a
primary fire sensor for detecting wide band infrared energy, a
first false-alarm sensor for detecting near band infrared energy,
and a second false-alarm sensor for detecting visible band energy;
a temperature sensor; a microprocessor configured to receive
signals from said sensor array and said temperature sensor, said
microprocessor calibrating operation parameters for said fire
detection system in accordance with said signals received from said
sensor array and said temperature sensor; a multistage alarm system
coupled to said microprocessor, said microprocessor selectively
activating a select one of a plurality of relays of said multistage
alarm system depending upon one of a plurality of conditions sensed
by said microprocessor; an enclosed, sealed, removable housing
containing said sensor array, said temperature sensor, and said
microprocessor, said housing including a window lens integral
thereto; and a nonvolatile storage medium for storing spectral data
associated with a detected fire event, said nonvolatile storage
medium coupled to said microprocessor.
20. A method of detecting a spark, flame, or fire, comprising the
steps of: sensing wide band infrared energy, near band infrared
energy, and visible band energy; eliminating false-alarm, nonfires
based upon the sensed near band infrared energy and visible band
energy; and detecting a spark, flame, or fire based upon the sensed
wide band infrared energy.
21. The method of claim 20, further comprising the step of storing
the detected energy.
22. The method of claim 20, further comprising the step of varying
the response to the results of said detecting step based upon the
results of said detecting step.
23. The method of claim 22, wherein said varying step comprises
first and second sequentially performed steps, said first step
comprising initiating an alarm signal when the results of said
detecting step exceed a first predetermined energy threshold, said
second step comprising releasing a suppressing agent when the
results of said detecting step exceed a second predetermined energy
threshold, said second threshold greater in magnitude than said
first threshold.
24. The method of claim 22, wherein said varying step comprises
first, second, and third sequentially performed steps, said first
step comprising initiating an alarm signal when the results of said
detecting step exceed a first predetermined energy threshold, said
second step comprising shutting off electric power when the results
of said detecting step indicate that a fire remains burning for a
predetermined time after performance of said initiating step, said
third step comprising releasing a suppressing agent when the
results of said detecting step exceed a second predetermined energy
threshold, said second threshold greater in magnitude than said
first threshold.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 09/384,808, filed on Aug. 27, 1999, which is a continuation
application of U.S. application Ser. No. 08/866,029, filed on May
30, 1997, now U.S. Pat. No. 6,064,064, which is a
continuation-in-part of U.S. application Ser. No. 08/690,067, filed
on Jul. 31, 1996, now U.S. Pat. No. 6,046,452, which is a
continuation-in-part of U.S. application Ser. No. 08/609,740, filed
on Mar. 1, 1996, now U.S. Pat. No. 5,773,826, and also claims
priority to PCT International application Ser. No. PCT/U.S.
97/03327, filed on Feb. 28, 1997. Each of the foregoing
applications is hereby incorporated by reference as if set forth
fully herein.
1. FIELD OF THE INVENTION
[0002] The field of the present invention pertains to apparatus and
methods for detecting sparks, flames, or fire. More particularly,
the invention relates to a process and system for detecting a
spark, flame, or fire with increased sensitivity, faster processing
and response times, intelligence for discriminating against false
alarms, and selective actuation of multi-stage alarm relays.
2. BACKGROUND
[0003] To prevent fires, and the resulting loss of life and
property, the use of flame detectors or flame detection systems is
not only voluntarily adopted in many situations, but is also
required by the appropriate authority for implementing the National
Fire Protection Association's (NFPA) codes, standards, and
regulations. Facilities faced with a constant threat of fire, such
as petrochemical facilities and refineries, semiconductor
fabrication plants, paint facilities, co-generation plants,
aircraft hangers, silane gas storage facilities, gas turbines and
power plants, gas compressor stations, munitions plants, airbag
manufacturing plants, and so on are examples of environments that
typically require constant monitoring and response to fires and
potential fire hazard situations.
[0004] To convey the significance of the fire detection system and
process proposed by this patent application, an exemplary
environment, in which electrostatic coating or spraying operations
are performed, is explained in some detail. However, it should be
understood that the present invention may be practiced in any
environment faced with a threat of fire.
[0005] Electrostatic coating or spraying is a popular technique for
large scale application of paint, as for example, in a production
painting line for automobiles and large appliances. Electrostatic
coating or spraying involves the movement of very small droplets of
electrically charged "liquid" paint or particles of electrically
charged "Powder" paint from an electrically charged (40 to 120,000
volts) nozzle to the surface of a part to be coated.
[0006] While facilitating efficiency, environmental benefits, and
many production advantages, electrostatic coating of parts in a
production paint line, presents an environment fraught with fire
hazards and safety concerns. For example, sparks are common from
improperly grounded workpieces or faulty spray guns. In instances
where the coating material is a paint having a volatile solvent,
the danger of a fire from sparking, or arcing, is, in fact, quite
serious. Fires are also a possibility if electrical arcs occur
between charged objects and a grounded conductor in the vicinity of
flammable vapors.
[0007] Flame detectors have routinely been located at strategic
positions in spray booths, to monitor any fires that may occur and
to shut down the electrostatics, paint flow to the gun, and
conveyors in order to cut off the contributing factors leading to
the fire.
[0008] Three primary contributing factors to a fire are: (1) fuel,
such as atomized paint spray, solvents, and paint residues; (2)
heat such as derived from electrostatic corona discharges,
sparking, and arcing from ungrounded workpieces, and so on; and (3)
oxygen. If the fuel is heated above its ignition temperature (or
"flash point") in the presence of oxygen, then a fire will
occur.
[0009] An electrical spark can cause the temperature of a fuel to
exceed its ignition temperature. For example, in a matter of
seconds, a liquid spray gun fire can result from an ungrounded
workpiece producing sparks, as the spray gun normally operates at
very high voltages (in the 40,000 to 120,000 volt range). An
electrical spark can cause the paint (fuel) to exceed its ignition
temperature. The resulting spray gun fire can quickly produce
radiant thermal energy sufficient to raise the temperature of the
nearby paint residue on the booth walls or floor, causing the fire
to quickly spread throughout the paint booth.
[0010] A fire may self-extinguish if one of the three above
mentioned factors is eliminated. Thus, if the fuel supply of the
fire is cut off, the fire typically stops. If a fire fails to
self-extinguish, flame detectors are expected to activate
suppression agents to extinguish the fire and thereby prevent major
damage.
[0011] Flame detectors, which are an integral part of industrial
operations such as the one described above, must meet standards set
by the NFPA, which standards are becoming increasingly stringent.
Thus, increased sensitivity, faster reaction times, and fewer false
alarms are not only desirable, but are now a requirement.
[0012] Previous flame detectors have had many drawbacks. The
drawbacks of these previous devices have led to false alarms which
unnecessarily stop production or activate fire suppression systems
when no fire is present. These prior flame detectors have also
failed to detect fires upon occasion, resulting in damage to the
facilities in which they have been deployed and/or financial
repercussions due to work stoppage or damaged inventory and
equipment caused by improper release of the fire suppressant.
[0013] One drawback of the most common types of flame detectors is
that they can only sense radiant energy in one or more of either
the ultraviolet, visible, near band infrared (IR), or carbon
dioxide (CO.sub.2) 4.3 micron band spectra. Such flame detectors
tend to be unreliable and can fail to distinguish false alarms,
including those caused by non-fire radiant energy sources (such as
industrial ovens), or controlled fire sources that are not
dangerous (such as a lighter). Disrupting an automated process in
response to a false alarm can, as noted, have tremendous financial
setbacks.
[0014] Another drawback of previous fire detectors is their lack of
reliability, which can be viewed as largely stemming from their
approach to fire detection. The most advanced fire detectors
available tend to involve simple microprocessor controls and
processing software of roughly the same complexity as those used
for controlling microwave ovens. The sensitivity levels of these
previous devices are usually calibrated only once, during
manufacture. However, the sensitivity levels often change as time
passes, causing such conventional flame detectors to fail to detect
real fires or to false alarm.
[0015] Many of the conventional flame detectors also are limited by
their utilization of pyroelectric sensors, which detect only the
change in radiant heat emitted from a fire. Such pyroelectric
sensors depend upon temperature changes caused by radiant energy
fluctuations, and are susceptible to premature aging and degraded
sensitivity and stability with the passage of time. In addition,
such pyroelectric sensors do not take into account natural
temperature variations resulting from environmental temperature
changes that occur, typically during the day, as a result of
seasonal changes or prevailing climatic conditions.
[0016] Other types of conventional flame detectors identify fires
by relying primarily on the ability to detect a unique narrow band
spectral emissions radiated from hot CO.sub.2 (carbon dioxide)
fumes produced by the fire. Hot CO.sub.2 gas from a fire emits a
narrow band of radiant energy at a wavelength of approximately 4.3
microns. However, cold CO.sub.2 (a common fire suppression agent)
absorbs energy at 4.3 microns, and can therefore absorb a hot
CO.sub.2 spike emission generated by a fire. In such situations,
conventional CO.sub.2-based flame detectors can miss detecting a
fire.
[0017] Another type of conventional IR flame detector monitors
radiant energy in two infrared frequency bands, typically the 4.3
micron frequency band and the 3.8 micron frequency band, while
others use as many as three infrared frequency bands. The dual IR
frequency band flame detector commonly utilizes an analog signal
subtraction technique for subtracting a reference sensor reading at
approximately 3.8 microns from the sensed reading of CO.sub.2 at
approximately 4.3 microns. The triple IR frequency band flame
detector uses an analogous technique, with an additional reference
band at approximately 5 microns. These types of multiband flame
detectors can false alarm when cold CO.sub.2 obscures the fire
source from the flame detector, thereby misleading the detector
into believing that a strong CO.sub.2 emission spike from a fire is
detected, when, in fact, a negative absorption spike (caused by
e.g., a CO.sub.2 suppression agent discharge or leak) has been
detected.
[0018] Conventional flame detectors using ultraviolet ("UV")
sensors also exist, but these too have drawbacks. Flame detectors
with UV sensors may be sensitive to electrostatic spray gun flashes
and corona discharges from waterborne coatings, which can cause
false alarms and needlessly shut down production in paint spray
booths. Also, because arc welding produces copious amounts of
intense ultraviolet energy which can be reflected or transmitted
over long distances, UV flame detectors can generate false alarms
from such UV energy sources, even when the non-fire UV energy is
located at a far distance from the spray booth. Moreover, after
deployment, conventional UV detectors eventually can become highly
de-sensitized as a result of absorbing smoke from a fire and/or
solvent mist, causing the UV detector to become blinded. As a
result, UV detectors can provide a false sense of security that
they are operating at their optimum performance levels, when, in
fact, the facility may be vulnerable to a costly fire.
[0019] As an additional disadvantage, UV flame detectors generally
require a relatively clean viewing window lens for the UV sensor,
and can therefore become blinded or degraded by the presence of
paint or oil contaminants on the viewing window lens. Moreover, the
sensing techniques utilized with conventional UV detectors usually
do not take into account the effects of such types of
degradation.
[0020] Besides problems with flame detection, many or all
conventional flame detectors also have limitations or drawbacks
relating to their housing and/or mounting that can affect their
performance or longevity, in addition to being relatively expensive
to manufacture. For example, most optical flame detectors have been
built with metal housing made from costly aluminum, stainless
steel, or similar materials. Such housings can be heavy, difficult
to mount and may not be suitable for certain corrosive environments
such as "wet-benches" used in semiconductor fabrication facilities
for manufacturing silicon chips and the like.
[0021] Further, most or all optical flame detector housings require
a window lens (necessary for high optical transmission in the
spectral bands used, and typically made of glass, quartz, sapphire,
etc.), but it is usually quite difficult to obtain a tight seal of
the window lens to metal housings, particularly in chemical
manufacturing, or integrated circuit manufacturing or other
applications having extremely rigorous environmental requirements.
If the flame detector is not tightly sealed, then corrosive
chemicals can leak into the electronic circuitry and degrade or
destroy the unit.
[0022] In flame detectors that detect UV energy, the protective
window lens must be constructed from highly expensive quartz,
sapphire, or other similar material that does not block UV energy.
Moreover, the quartz or sapphire window lenses are typically placed
in a metal detector housing, and are collectors of dust and
contaminants due to the electrostatic effect of the high voltage
field (around 300 to 400 volts) used in the UV detectors. To ensure
that the UV detector's sensor(s) can "see through" the window lens,
complex and costly "through the lens" tests are necessary. To
conduct built-in "through the lens" window lens tests, a UV source
tube is generally required to generate a UV test signal. Such UV
source tubes require a high voltage for gas discharge sources
and/or a large current for incandescent sources. Also, UV source
tubes are subject to high failure rates. In sum, these self tests
are expensive, require extra power and space, and are prone to
breakdowns.
[0023] There is a need for a sensitive, reliable, fully enclosed,
inexpensive, light-weight, intelligent, and effective method and
system for detecting sparks, flames, or fire with little or no
interruptions caused by false alarms.
SUMMARY OF THE INVENTION
[0024] The present invention is directed in various aspects to a
sensitive, reliable, fully enclosed, inexpensive, light-weight,
intelligent, and effective method and system for detecting sparks,
flames, or fire with little or no interruptions caused by false
alarms. According to one embodiment of the present invention, a
process and system for flame detection includes a sensor array for
providing sensor signals, a temperature sensor for providing
signals indicative of ambient temperature conditions, and either
internal or external signal processing electronics for processing
the sensor signals and generating a response, if necessary.
[0025] In a first aspect of the invention, a
microprocessor-controlled detector advantageously includes at least
three sensors. Preferably, a wide band infrared sensor is used as
the primary detector, with near band and visible band sensors
serving to detect false-alarm energy from nonfire sources. The
system may comprise a single or a series of detector units with
wide spectrum sensing capabilities (quantum sensors) located within
a desired facility such as, e.g., inside a paint spray booth.
[0026] In a second, separate aspect of the invention, a multistage
alarm system is provided. In a preferred embodiment, the multistage
alarm system is selectively triggered by a microprocessor. Sensor
data captured at detector units can be interfaced to either
internal or external signal processing electronics which process
and analyze the sensor data, and selectively trigger multistage
(e.g., two- or three-stage) alarm relays. The signal processing
electronics and the relays may advantageously be located within the
detector unit, or can be remotely located in a controller unit.
[0027] In a third, separate aspect of the invention, digital signal
processing is used to analyze sensed data and discriminate against
false alarms. False alarms also are avoided through periodic
conduction of comprehensive diagnostic evaluations of the system
components. The system programs parameters for its system
components and varies the parameters depending upon ambient
conditions. Algorithms and techniques for eliminating false alarms
are employed, thereby providing effective detection of any sign of
a spark, flame, or fire.
[0028] In a fourth, separate aspect of the invention, prefire
spectral data is recorded both before and after a fire situation.
The recorded spectral data may be later analyzed to identify the
cause of the fire and thereby help eliminate the occurrence of
future fires. Sensor data is captured, processed, and analyzed at
the detection location. Preferably, the spectra of the radiated
detected energy from a fire or potential fire is stored in memory,
providing a comprehensive record of sensor array spectral data
(processed or unprocessed). This information may be retrieved after
a fire occurs for analysis.
[0029] In a fifth, separate aspect of the invention, a fire
detector is preferably housed in a sealed, self-contained housing.
The housing may include a window region to protect the sensors
wherein the window region is constructed from a different material
than the housing material. The housing may be placed within a wall,
workbench, wet-bench, or other suitable mounting structure, and
sealed therewith, welded or similarly attached thereto. In another
embodiment, the housing comprises a base portion and a removable
upper lid portion. Attached to the upper lid portion is a module
containing the sensors and sensitive electronic circuitry used in
the flame detector. The removable upper lid portion of the housing
allows relatively quick and easy replacement of the primary
detection components of the fire detector.
[0030] Further embodiments and variations of the invention are also
disclosed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a diagrammatic illustration of an electrostatic
coating booth, in which a fire detector according to the present
invention may be employed.
[0032] FIG. 2 is a graphical representation of the wide spectrum
sensitivity afforded by the process and system of FIG. 1, in which
the protective cover has the same transmittance characteristics as
the detector.
[0033] FIG. 3 is a graphical representation of the sensitivity of a
flame detector having wide band IR, near band IR and visible band
sensors.
[0034] FIG. 4 is a perspective view of one housing embodiment in
accordance with certain aspects of the present invention.
[0035] FIG. 4a is a perspective view of a protective cover with
wide spectrum transmittance characteristics.
[0036] FIG. 4b is a diagrammatic illustration of a fire/flame
detector having a fiber optic cable assembly with a protective
cover to facilitate use in confined or unaccessible areas.
[0037] FIG. 4c is a cross-sectional view taken along line 4d-4d
through FIGS. 4 and 4a.
[0038] FIG. 5 is a graph illustrating the regions of sensitivity of
a particular wideband sensor array in accordance with various
aspects of the present invention.
[0039] FIG. 6 is a diagrammatic illustration of an enclosed,
removable, self-contained module for optical fire/flame
detectors.
[0040] FIG. 7a is a diagrammatic side view illustration of a
plastic, sealed housing with an integral window lens.
[0041] FIG. 7b is a top view of the housing of FIG. 7a.
[0042] FIG. 8 is a diagrammatic illustration of a side view of a
plastic, sealed housing with a thin window-lens area for high
transmittance.
[0043] FIG. 9 is a diagrammatic illustration of a side view of a
plastic, sealed housing with an embedded window lens made of such
materials as quartz or sapphire.
[0044] FIG. 10 is a diagrammatic illustration of a side view of
housing that is heat welded to a plastic cable.
[0045] FIG. 11 is a block diagram representation of one embodiment
of a flame/fire detection system in accordance with various aspects
of the present invention, wherein a single or a series of flame
detector components are located inside a desired facility, such as
a paint booth, and a controller component of the system is located
outside the facility for processing data captured by the
sensors.
[0046] FIG. 12 is a block diagram representation of an alternative
embodiment of a flame/fire detection system, wherein a single or a
series of detectors incorporate a microprocessor and process data
captured by the system in the detector component.
[0047] FIGS. 13a and 13b depict a table comparing fire/flame
temperature and radiant energy calculations in various spectral
regions.
[0048] FIG. 14 is a graph of radiant energy as a function of fire
temperature.
[0049] FIGS. 15 and 16 are graphs comparing a detected radiant
energy for a wide band spectral detector versus a narrow band 4.3
micron infrared detector as a function of fire temperature.
[0050] FIG. 17 is a graph illustrating relative radiant emittance
at various wavelengths for a 2500 K degree fire.
[0051] FIG. 18 is an illustration of a record and fields of data
that may be stored upon occurrence of a fire.
[0052] FIG. 19 is a diagram of an event log generated by the system
upon detection of a fire signature warranting an "alert"
condition.
[0053] FIG. 19a is an exemplary fire signature which upon
observation would result in an "alert" condition being
declared.
[0054] FIG. 20 is a diagram of an event log generated by the system
upon detection of a fire signature warranting a "fire early
warning" condition.
[0055] FIG. 20a is an exemplary fire signature which upon
observation would cause a "fire early warning" condition to be
declared.
[0056] FIG. 21 is a diagram of an event log generated by the system
upon detection of a fire signature warranting an "alarm"
condition.
[0057] FIG. 21a is an exemplary fire signature which upon
observation would cause an "alarm" condition to be declared.
[0058] FIG. 22 is a logic flow diagram of processing as may be
embodied in the present system, illustrating diagnostic evaluations
or tests performed by the system.
[0059] FIG. 23 is a logic flow diagram of processing as may be
embodied in the present system, illustrating a lens test performed
by the system.
[0060] FIG. 24 is a portion of a logic flow diagram of processing
as may be embodied in the present system, illustrating a preferred
logic flow and sequence of steps performed during overall operation
of the system.
[0061] FIG. 25 is a portion of a logic flow diagram of processing
as may be embodied in the present system, illustrating a logic flow
and continued sequence of steps for detecting an "alert"
condition.
[0062] FIG. 26 is a portion of the logic flow diagram of processing
as may be embodied in the present system, illustrating a logic flow
and continued sequence of steps for detecting a "fire early
warning" condition and an "alarm" condition.
[0063] FIG. 27 is a logic flow diagram illustrating operation of a
system with a two-stage alarm relay.
[0064] FIG. 28 is a functional diagram illustrating a preferred
fire discrimination algorithm.
[0065] FIG. 29 is a graph showing filtered sensor outputs after
processing through two filters with different time response
characteristics.
[0066] FIG. 30 is a graph showing a compensation made to a slow
filter output of the wide band IR sensor.
[0067] FIG. 31 is a diagram illustrating the effect of asymmetrical
digital filtering on the visible band sensor output for the purpose
of rejecting certain false alarm sources such as a flashlight.
[0068] FIG. 32 is a diagram illustrating operation of a flicker
detection algorithm for rejection of other false alarm sources.
[0069] FIG. 33 is a diagram illustrating an algorithm for rejecting
false alarm sources such as industrial ovens.
[0070] FIG. 34 is a diagram of a circuit for processing a sensor
input signal.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0071] A process and system for detecting sparks, flames, or fire
in accordance with a preferred embodiment of the present invention
is described herein. It should be noted that the terms "fire
detector," "flame detector" and "fire/flame detector" are used
interchangeably in the present text and refer generally to any
process and/or system for detecting sparks, flames, or fires,
including explosive type fires or fireballs and other dangerous
heat-energy phenomena.
[0072] A particular embodiment of a process and system for fire
detection is described in conjunction with an exemplary situation
of an electrostatic coating operation. However, it should be
understood that the process and system may be effectively utilized
in any environment facing a threat from sparks, flames, or fire.
For example, the process and system may be used in such
applications as petrochemical facilities and refineries,
semiconductor fabrication plants, co-generation plants, aircraft
hangars, gas storage facilities, gas turbines and power plants, gas
compressor stations, munitions plants, airbag manufacturing plants,
and so on.
[0073] FIG. 1 illustrates an exemplary environment 10, as for
example, a coating zone, such as a spray or paint booth or
enclosure, in which electrostatic coating operations are routinely
performed. As illustrated in FIG. 1, parts 12 are transported
through the spray booth 14 by a conveyor 16 connected to a
reference potential or ground 18. The direction in which the
conveyor moves is indicated by an arrow 20. The parts 12 are
typically supported from the conveyor by a conductive hook-like
support or hanger 22. The parts 12 are passed proximate a high
voltage source 13 with a high voltage antenna 15. The high voltage
source 13 may be one available from Nordson as Model number EPU-9.
Electrical charge is transferred from the high voltage source,
which may operate between 60,000-120,000 volts, to the parts 12 to
be coated.
[0074] The electrostatic coating system illustrated in FIG. 1
represents an air electrostatic spray system of a type used in many
industrial operations. A typical industrial spray system 24
includes a spray gun 26 coupled to a power supply 27, a paint
supply container 28 (for example, a pressure tank), and some form
of spray control mechanism 30. The spray control mechanism 30 may
include an air compressor and an air regulator (not separately
shown).
[0075] A single flame detector component 32 is located at a
strategic position within the spray booth 14. The detector
component 32 can be advantageously manufactured from a
substantially explosion-proof material, as discussed in greater
detail below. Depending upon the size of the spray booth 14 or
other facility, a plurality of such flame detector components 32
may be strategically located throughout the spray booth 14 or other
facility.
[0076] Referring also to FIG. 4, the flame detector 32 embodying
features in accordance with a preferred embodiment of the present
invention is sensitive to radiant energy in the visible (VIS) band,
near band infrared (NIR), and wide band infrared (including middle
band infrared (MIR)) spectra. The flame detector 32 preferably has
a spectrum sensitivity for infrared energy, within a range from
roughly 700 to 5000 nanometers (0.7 to 5 microns), and for visible
energy, within a range from approximately 400 to 700 nanometers.
The flame detector 32 is preferably enclosed within a protective
housing 132. The type of housing 132 (i.e., shape, material and/or
configuration) may vary depending upon application and such things
as environmental factors. Various housings are discussed in more
detail hereinafter.
[0077] The housing 132 of the flame detector 32 is, in a particular
embodiment, constructed with a viewing window 132b disposed over
the sensors of the flame detector. The viewing window 132b is
advantageously provided where one or more IR sensors (by itself or
in conjunction with other sensors) are used so that the flame
detector may detect IR frequency bands. In such embodiments, the
viewing window 132b would be comprised of an IR-transparent
material. In such embodiments, the viewing window 132b may be
quartz, sapphire, glass or a plastic material such as hydrocarbon
or fluorocarbon polymer, for example. Other embodiments of housings
are also disclosed herein that do not utilize a viewing window that
is constructed from a material that is different from the housing
material.
[0078] In one embodiment, the flame detector 32 has a protective
cover 132a disposed over it that is conformed to fit snugly over
the protective housing 132. The protective cover 132a is preferably
constructed from a relatively inexpensive material such as a
plastic, such as polypropylene or polyvinyl chloride, that is
transmissive with respect to IR and visible wavelengths. Thus, the
protective cover 132a may be easily disposed, recycled, or reused,
as desired. To avoid accumulation of paint and grime on a viewing
window 132b, the protective cover 132a can be configured to slip
easily over the housing 132 of the flame detector 32.
[0079] So as not to obstruct the wide spectrum sensitivity of the
flame detector 32, the protective cover 132a (see FIG. 4a)
preferably has wide spectrum transmittance characteristics that
enable optimum sensing of any flame, spark or ignition that may
occur. The transmittance characteristics of the protective cover
132a are also illustrated in FIG. 2.
[0080] Referring to FIGS. 4, 4a, and 4c, the protective cover 132a,
which appears somewhat like a top hat, is preferably configured to
conform around a cylindrical protruding portion 272 of the housing
132 of the flame detector 32. In order to prevent accumulation of
spray paint, grime, oil contaminants, or the like on a viewing
window 132b of the flame detector housing 132, the protective cover
132a should completely cover the viewing window 132b. Preferably,
the protective cover 132a has a planar face 270 and a cylindrical
body 271. The cylindrical body 271 extends sufficiently along the
protruding portion 272 and is sufficiently detached from the
protruding portion 272 to prevent any movement of airborne paint
particles toward the viewing window 132b.
[0081] As specifically illustrated in FIGS. 4 and 4a, the
cylindrical body 271, at its base 273, terminates in a
perpendicularly projecting flange 274. The flange 274 also serves
to prevent airborne paint particles from moving toward the viewing
window 132b. A centrally located groove 275 runs along its
circumference, almost contacting the protruding portion 272 of the
housing 132 of the flame detector 32, which serves to further
prevent airborne paint particles from reaching the viewing window
132b. Slight pressure applied on the protective cover 132a, to ease
the protective cover 132a over the housing 132 of the flame
detector 32, causes the groove 275 to slide over a locking
mechanism 278 of the housing 132 of the flame detector 32 (best
illustrated in FIG. 4c). The groove 275 serves to hold the
protective cover 132a, albeit flexibly, in place.
[0082] The flange 274 has a plurality of reinforcing members 276
projecting outwardly toward its outer periphery. The reinforcing
members 276 preferably lend the flange 274 enough rigidity to allow
a person to easily pull it off the flame detector housing 32 when
replacing the flame detector 32.
[0083] The protective cover 132a may be constructed from any
suitable material having the required transmittance
characteristics. The material used in the illustrated embodiment is
relatively inexpensive, has some rigidity, yet is also resilient.
In the illustrated embodiment of the protective cover 132a, a clear
polyvinyl chloride (PVC), with an "ORVIS.RTM.-K" coating to serve
as an anti-static agent, is used. The protective cover 132a is
preferably fabricated from clear PVC with a starting gauge of 20
mil, which is vacuum drawn over a machined, metal mold to yield
thin, flexible protective covers. The protective cover 132a may
alternatively be fabricated from materials such as LEXAN.RTM.,
which may be injection molded. Other plastics with similar
transmittance characteristics may alternatively be used. The
illustrated protective cover 132a may be easily disposed, recycled,
or reused after cleaning, as desired.
[0084] Alternatively, the protective cover 132a may be configured
as a bag or a planar surface in any shape or form necessary to
cover the viewing window 132b, with a string or wire to fasten the
protective cover 132a to the protruding portion 272 of the housing
132 of the flame detector 32. Additionally, although the protective
cover is preferably constructed from a light weight, inexpensive
and disposable material, any material that transmits radiant energy
having wavelengths between 700-5000 nanometers is appropriate.
[0085] Referring now to an embodiment shown in FIG. 4b, the
protective cover 132a may vary in dimensions to suit various
applications. Flame detectors are routinely used in confined areas,
such as cabinets, processing equipment (including mixers of
explosive materials), extruders, and the like. For example, a
small, almost miniature, version of the protective cover 132a, as
illustrated in FIG. 4b, may be used at a viewing end 277 of a fiber
optic cable 279, which is attached at a second end 280 to a flame
detector 320. Use of the fiber optic cable 279 can facilitate
remote location of the flame detector 320 and enable transmission
of the radiant energy patterns detected to the flame detector
320.
[0086] Sensor data captured by the flame detector 32 can be relayed
to a central control system 34 (see FIG. 1), which, in paint spray
booth applications, may be located outside the spray booth 14. The
central control system 34 may take the form of a computer with a
central microprocessing unit, a display monitor, a suitable memory,
and printing capabilities. The central control system 34 may
coordinate functioning of the flame detectors 32 with other
detection systems, as for ungrounded parts or the like.
[0087] The housing 132 of the flame detector 32 also can be
constructed from polypropylene, which is inert to harsh chemical
environments and beneficial for transmittance of infrared spectra.
In addition to these advantages, use of polypropylene may permit
the housing to be heat-sealed so as to create a sealed, watertight
environment. The housing may incorporate structural elements or be
otherwise reinforced to enable it to withstand explosions and to
give it an explosion proof rating. Potting resins can be added to
reduce cavities that typically trap gases or fumes.
[0088] The flame detector 32 preferably operates by searching for
radiant energy characteristics or patterns of a flame or fire. A
continuous stream of spectral data from a sensor array 38 (as
illustrated in FIG. 11 or 12 and described hereinafter) may be
analyzed by a controller (microprocessor, or microcomputer) unit 39
or the controller (or microprocessor, or microcomputer) 36. In a
preferred embodiment, an Intel 8051 microprocessor or microcomputer
is utilized.
[0089] In another embodiment, a removable, enclosed, self-contained
electro-optical module 220, illustrated in FIG. 6, is used for
optical fire/flame detection. The electro-optics and electronics of
the optical fire/flame detector 220 (whether analog, digital, or a
combination thereof) preferably comprise one or more sensors
operating in one or more of the ultraviolet band, visible band,
near band infrared, wide band infrared, or narrow band infrared
(such as a 4.3 micron narrow band IR).
[0090] FIG. 6 shows a surface-mountable flame detector 220
constructed according to the present invention, having a structure
particularly well suited to ease of replacement of the electronics
and electro-optical components of the flame detector without having
to re-mount an entirely new flame detection unit. The flame
detector 220 comprises a detector housing base 222 having a
relatively flat back portion or plate 214 which may be placed flush
against a surface to which the flame detector 220 is mounted (e.g.,
a wall). The back plate 214 of the detector housing base 222 has
mounting holes 215 placed at appropriate locations to secure the
detector housing base 222 to the mounting surface, and may be
mounted to a swivel assembly or hard-mounted to a surface.
[0091] The detector housing base 222 is connected to one or more
conduits 210 which contain signal and power wires 226, as
illustrated in FIG. 6 through the cut-away portion of the detector
housing base 222. The signal and power wires 226 are connected to a
removable plug-in connector 213. The detector housing base 222 is
preferably cylindrical in shape, and has circular threadings 216
around its outer, upper periphery, as illustrated in FIG. 6. A
threaded detector housing lid 227, having a cylindrical shape, is
adapted to fit over the detector housing base 222 and has
threadings on its interior portion that allow it to be placed
snugly over the detector housing base 222 in a manner similar to a
threaded nut and screw. The detector housing lid 227 has a solid,
relatively flat upper surface or plate 217 on one side so as to
enclose an inner detector module 224 when the detector housing lid
227 is placed securely over the detector housing base 222.
[0092] The inner detector module 224 comprises the electronics and
electro-optics, including the sensors 225 of the flame detector
220. The inner detector module 224 from a physical standpoint
comprises an enclosed chamber in which the sensitive electronics
reside, and can be self-contained in the sense that the flame
detection circuitry and other components reside within the enclosed
chamber. In the alternative, the sensors are enclosed within the
enclosed chamber and the processing circuitry can be external to
the enclosed chamber. The inner detector module 224 is physically
attached directly to the detector housing lid 227, and more
specifically to the upper plate 217 of the detector housing lid
227, such that when the detector housing lid 227 is removed the
inner detector module 224 removes along with it. The sensors 225
are preferably located adjacent to the upper plate 217, as
illustrated in FIG. 6.
[0093] The detector housing lid 227 may optionally be provided with
a viewing window 212. Alternatively, the detector housing lid 227
need not have a viewing window 212. In such a case, the upper plate
217 of the detector housing lid 227 (and possibly the entire
detector housing lid 227 as well as the detector housing base 222)
is preferably comprised of a material that has low bulk adsorption
characteristics for radiant energy having frequency components
between approximately 400-5000 nanometers, such as glass,
polypropylene or other suitable plastic material.
[0094] If it is desired to replace the flame detection unit 220 to
perform maintenance or tests on the unit, or because of a
functional problem in the sensors or circuitry, or for any other
reason, the electronics and electro-optical components may be
relatively easily replaced by unscrewing the detector housing lid
227 and replacing it with another detector housing lid 227. Because
the inner detector module 224 is connected to the detector housing
lid 227, the key components of the flame detector can be relatively
quickly and easily replaced without having to re-mount the flame
detector to the surface. The same detector housing base 222 that
was used for the old detector housing lid 227 continues to remain
operable for the new one. The removable plug-in connector 213 also
facilitates rapid and relatively easy substitution of the new unit
for the old one.
[0095] There are a number of advantages associated with the housing
structure of the flame detector embodiment shown in FIG. 6. For
example, sensitive detector electronics and electro-optics which
form a part of the inner detector module 224 are better protected
from handling-induced electrostatic discharge and physical handling
damage. Also, as noted above, the critical components of the flame
detector 220 can be replaced easily and quickly in the field
without removing or dismantling the detector housing base 222,
which would otherwise necessitate detaching the back plate 214 from
the surface to which it is mounted as well as detaching the
attached conduit(s) 210. Because the sensitive electronics are
largely protected within the inner detector module 224, the
installation process can in many instances be quickly and easily
performed, once the detector housing base 222 is secured and
connected to the conduit piping. Benefits may also be achieved in
testing, storing and shipping the flame detector 220 with less
concern for electrostatic discharge damage at either the factory or
the distributor/integrator facility.
[0096] The detector housing lid 227 and detector housing base 222
can be of any shape or size, so long as the detector housing lid
227 fits securely within the detector housing base 222. Further,
the detector housing lid 227 and detector housing base 222 need not
necessarily be threaded so as to attach by screwing together, but
may also snap together or be secured by other suitable or
conventional means. Also, the detector housing lid 227 and detector
housing base 222 can be made from plastic, metal, or any other
suitable material, or any combination thereof.
[0097] A second embodiment of a flame detector with a housing is
illustrated in various angles, cross-sectionals and details in
FIGS. 7a, 7b, 8, 9 and 10. Referring first to FIG. 7a, a
self-contained, sealed housing 230 encloses the electronics and
electro-optical components of a flame detector. At least one
printed circuit board (PCB) 233 is mounted to one or more walls of
the sealed housing 230. On the PCB 233 integrated chips could be
mounted which comprise the electronic circuitry and/or
electro-optical circuitry of the flame detector. Also on the PCB
233 a sensor 236 or array of sensors for detecting radiant light
can be mounted. The sealed housing 232 can be made from a variety
of materials and may comprise a window region 232 that is formed of
thinner housing material or material different from the housing.
Advantageously, the window region 232 is integral with the housing
230, thereby allowing the housing 230 to be constructed of lighter
and less costly material than conventional metal housings.
Depending upon the environment in which the detector will be used,
different materials may be used to construct the housing. For
example, in environments that may subject the housing to corrosive
chemicals, such as acids, polypropylene may be utilized. In
environments in which greasy hydrocarbons are present such as an
oil rig, Teflon may be appropriate. In other environments, ceramic
or metal housings may be desirable. In addition, the housing may be
constructed of a first material and then coated with a second
material that provides the best protection for the device in the
intended environment.
[0098] As a result of the fact that no UV sensors are necessary to
practice the present invention, the window region 232 of the
housing 230 need not be a quartz or sapphire lens as is required in
flame detectors that rely upon UV sensors. Historically, quartz or
sapphire windows have been necessary with UV sensors because these
two materials have low bulk absorption characteristics for UV
wavelengths. However, since the present invention utilizes infrared
and visible wavelengths, any material that does not significantly
absorb the desired IR and visible wavelengths can be used as a
window for the IR sensors. In addition some materials such as
Teflon or polypropylene are resistant to the accumulation of
contaminants. Accordingly, the housing 230 is preferably
constructed of a corrosion-resistant and contamination-resistant
material such as Teflon or polypropylene, or some similar material
or hybrid. Use of such a contamination-resistant material largely
eliminates the need for conventional "through the lens" testing as
is commonly required for prior flame detectors (particularly those
using UV sensors) having a glass, quartz or sapphire window lens
that is not contamination-resistant.
[0099] Further, use of a wideband infrared sensor or sensor array
(spanning a light frequency band from about 0.7 microns to 5
microns) as a primary sensor in the flame detector, and elimination
of UV sensors, results in a construction wherein the wideband
infrared sensors are able to effectively "see through" the housing
230 due to the longer wavelengths detected by such sensors. The
wide band infrared sensor or sensors should be able to "see
through" most contaminants because most contaminants do not absorb
significant amounts of infrared energy.
[0100] Therefore, the flame detector housing 230 can be
manufactured from a material such as polypropylene, polyvinyl
chloride, ABS plastic, Teflon, glass, fiberglass, spun glass, or a
combination of several materials and/or additives. The integral
window region 232 can be made from the same material as the housing
230, SO that sealing and mounting problems associated with prior
art flame detectors that required quartz, or sapphire window lenses
can be provided. The housing 230 may be heat sealed or sealed with
an "O" ring 239, as illustrated in FIG. 7a. A shielded cable 238
may be welded or otherwise connected to the housing 230, as further
described hereinafter in more detail with respect to FIG. 10.
[0101] In an alternate embodiment, shown in FIG. 8, the detector
housing 230 can be constructed from a combination of polypropylene,
polyvinyl chloride, ABS plastic, Teflon, fiberglass, spun glass,
quartz, glass, sapphire, etc., or a combination of several
materials and/or additives. The outer integral window region 232 of
the housing 230 can be made from the same material as the housing
body 230 and reinforced under the window region 232 with a suitable
material such as polypropylene or glass, so that sealing and
mounting problems associated with conventional glass, quartz, or
sapphire window lenses are eliminated.
[0102] A Teflon housing 230 with a thin area immediately adjacent
to the window lens area 232 is used for the embodiment shown in
FIG. 8. Because the bulk absorption of Teflon is relatively high
for longer (infrared) wavelengths, the area of the window region
232 is preferably thin so that the absorption of the desired
wavelengths is minimized. A reinforcing plug 234 of low absorption
material can be screwed in, snapped in, molded in (e.g., in the
injection molding process), heat welded, or otherwise attached to
the housing 230 as shown in FIG. 8 in the hollow space caused by
the thin window region 232, such that the thin window region 232 is
more resistant to puncture or physical damage. The reinforcing plug
can be constructed from any material having low bulk absorption
characteristics for the desired wavelengths, including the
materials mentioned above.
[0103] In another alternate embodiment, illustrated in FIG. 9, the
detector housing 230 is made from a combination of polypropylene,
polyvinyl chloride, ABS plastic, Teflon, fiberglass, spun glass,
quartz, glass, sapphire, etc., or a combination of several
materials and/or additives. The window region 232 can be made from
any different material, which material is secured or embedded
(e.g., by heat sealing) into the plastic housing 230 during the
injection molding process, or is heat sealed into the material
after the housing fabrication. Thus, problems associated with
sealing and mounting problems glass, quartz, or sapphire window
lenses are eliminated.
[0104] As discussed above, few contaminants will adhere to the
housing 230 when constructed of Teflon, polypropylene or another of
the preferred corrosion-resistant and contamination-resistant
materials. The use of such contaminant-resistant materials, without
the need for a window lens of sapphire, quartz or other
UV-transparent material, is made possible by the present flame
detectors which do not require UV detectors. The housing for the
present flame detectors are easier to maintain than conventional
types of flame detectors, particularly those detectors that use UV
sensors, which require regular and frequent cleaning of the sensor
window lens to remove contaminants. In addition, because plastics
are generally lighter than metal, quartz and sapphire, mounting and
installation costs can be reduced. The preferred, light-weight,
low-cost, sealed, plastic detector housing 230 is constructed so as
to fall within NEMA 4, 12, etc. outdoor ratings and hazardous
ratings such as Class I and II and Divisions 1 and 2. These ratings
are necessary for operating the optical detector in a hazardous,
corrosive, and/or outdoor environment.
[0105] In another embodiment, the self-contained housing 230 is
sealed using one or more "O" rings and screws, rivets, etc. The
preferred method of sealing is heat sealing, which melts the
housing materials (e.g., plastic or glass) into essentially one
solid piece. The optical flame/fire detectors can use various
sensors 236, including wide band IR, nearband IR, visible band, or
narrow band IR (such as 4.3 micron infrared, for example), with one
or more IR rejection bands for multiple frequency IR detection. The
optical transmittance of the window region 232 should be high
enough for the selected sensors 236 to sense radiant energy in
their respective light frequency detection bands.
[0106] The window region 232 for an all-plastic or all fiberglass
detector housing 230 for example, can be thinner than the rest of
the housing 230 so as to decrease the bulk absorption losses of the
window region. In a an embodiment using a combination of wide band
IR, near band IR and visible light sensors, preferably the window
region 232 has a low bulk absorption for wavelengths in the range
of approximately 0.4 to 5 microns, or about 400 to 5000 nanometers.
Preferably, various reinforcement techniques may be used such as
ribbing or braces, or the high-optical-transmittance plug described
previously with respect to FIG. 8.
[0107] As an additional advantage, manufacture of the housing 230
from a material such as polypropylene, Teflon, fiberglass and the
like (with or without additives, if desired) can render the
preferred detector housing 230 resistant to corrosion and/or acid.
The detector housing 230 can be machined out of the bulk material,
injection molded or blow molded, for example, and is preferably
heat sealed to ensure complete isolation of the internal
electro-optics and electronic from any corrosive elements that
could leak through conventional sealing techniques such as "O"
rings and screws.
[0108] A power and signal cable 238 connects to the housing 230 and
can be made from the same material as the housing 230. The
power/signal cable 238 can be sealed to the housing 230 with clamps
or "O" rings, for example, or can be heat sealed to the housing 230
itself, as illustrated in FIG. 10. For example, in an embodiment in
which the housing 230 and power/signal cable 238 are made from
polypropylene, the housing/cable interface can be heat sealed for
optimum sealing because the cable 238 and housing 230 can be melted
into an integral piece. In addition, in an acidic environment such
as a semiconductor wet-process bench, one or more protective
sleeves are advantageously placed around the power/signal cable 238
to add further protection to the electronic wires enclosed within
the power/signal cable 238.
[0109] There is currently a need to deploy fire/flame detectors in
hostile, caustic, acidic environments, both indoors and outdoors.
In a preferred embodiment suitable for many such environments, a
flame detector is physically installed within a wall, workbench, or
similar structure. Preferably, the flame detector housing is such
as described for any of the embodiments shown in FIGS. 7a, 7b, 8, 9
and 10. For example, a self-contained, sealed flame detector
housing made of polypropylene can be installed inside the corrosive
compartments of a semiconductor clean-room chemical wet-process
bench. Installing a sealed, corrosion-proof, plastic-housed optical
fire/flame detector inside the wet bench compartments has the
advantage of reducing exposure to contaminants and placing the
detector closer to the potential fire source for improved fire
response. Also, the flame detector housing itself is less likely to
become a repository of miscellaneous contaminants present in the
worksite.
[0110] A sealed, corrosion-proof, plastic-housed optical fire/flame
detector can similarly be used on an offshore oil platform where
maintenance costs are high and low weight is important. Preferably,
the housing is constructed from or coated with Teflon, which is
highly resistant to the accumulation of oil deposits. In addition,
because the flame detector does not require frequent maintenance,
i.e., window-lens cleaning, as do conventional fire detectors,
substantial cost savings from reduced maintenance can be
realized.
[0111] FIGS. 11 and 12 are block diagrams depicting embodiments of
a flame detector utilizing wide band IR detection. In accordance
with one embodiment of the present system, a single flame detector
32 located at a particular location, indicated by reference letters
FD1, or a plurality of flame detectors, located at a plurality of
different locations, indicated by reference letter FDN, may be
located, for example, inside the spray booth 14 (see FIG. 1). A
power supply 46, typically operating at 24 volts, supplies power to
the flame detector 32.
[0112] In addition to the sensor array 38, the flame detector 32
may include an analog to digital (A/D) converter 50, which receives
a continuous stream of analog sensor signals from each of the
sensors 40, 42, 44 of the sensor array 38, and converts the analog
signals into digital signals for storage and selective processing
by a microprocessor 36 or a controller 39, or both. A temperature
sensor 52 located within the flame detector 32 serves to indicate
ambient temperature values for calibration purposes. A memory
component 54 within the flame detector 32 comprises ROM (Read Only
Memory) and RAM (Random Access Memory) for temporary and permanent
storage of data, as for storing instructions for the microprocessor
36, for performing intermediate calculations, or the like. In a
preferred embodiment, the sensor array 38 preferably has a sensor
40 for sensing radiant energy within the visible band spectrum, a
sensor 42 for sensing radiant energy within the near band infrared
spectrum, and a sensor 44 for sensing radiant energy within a wide
band infrared (WBIR, or MIR) spectrum.
[0113] Referring now to FIG. 2, the first sensor 40 searches for
and detects radiant energy within the visible band range extending
from about 400 nanometers to approximately 700 nanometers,
indicated in FIG. 2 by the frequency band designated as "VIS." The
second sensor 42 searches for and detects radiant energy within the
near band infrared range extending from roughly 700 nanometers to
about 1100 nanometers, indicated in FIG. 2 by the frequency band
designated as "NEAR BAND IR." The third sensor 44 searches for and
detects radiant energy within a wide band infrared range extending
from about 700 nanometers to about 5000 nanometers, indicated in
FIG. 2 by the frequency band designated as "WIDE IR SPECTRUM."
[0114] In a preferred embodiment, wide band IR (WBIR) is used as
the primary sensor in the optical fire/flame detectors. The WBIR
sensor preferably detects radiant energy over a spectral band from
about the end of the visible spectrum (about 0.7 microns) to the
band comprising the longer IR wavelengths (up to about 3.5
microns). The WBIR sensor 44 can, however, be susceptible to
various false-alarm sources, including sunlight, bright lights,
ovens, and other sources of wideband IR radiation. In order to
successfully use WBIR as the primary sensor without false alarms
from broadband energy sources, information obtained from sensing
energy in the visible band (VB) (from about 0.4 to 0.7 microns)
and/or the near band IR (NBIR) (from about 0.7 to about 1.5
microns) is used in conjunction with signal processing algorithms
to prevent false triggering. A preferred process and system
therefore comprises an "intelligent" multi-spectral approach to
optical fire/flame detection.
[0115] In a preferred embodiment, compensating digital signal
processing algorithms are performed in the optical fire/flame
detectors by the microprocessor 36 or controller 39 to distinguish
between actual fires and non-fire energy sources. Such algorithms
preferably include time correlation of the sensor signals along
with VB and NBIR energy bands and a comparison of relative energy
levels in the different energy bands.
[0116] In order to rapidly detect all types of fires, whether
hydrocarbon and nonhydrocarbon in nature, a preferred optical
fire/flame detector senses energy over a wide, continuous spectral
band of infrared radiant energy. Preferably, the energy band
observed by the fire/flame detector covers the range from about 0.4
to about 5 microns (i.e., spectral ranges in the VB, NBIR, and
WBIR) to ensure that virtually all types of fires are detected.
This spectral range constitutes the bulk of the radiant heat energy
generated by an unwanted fire, including, for example, burning
polypropylene or PVC plastic.
[0117] FIG. 17 is a graph illustrating the energy emitted at
various wavelengths by an exemplary fire source. As shown in FIG.
17, a large portion of the energy emitted by a typical fire occurs
at wavelengths other than the 4.3 micron range. Accordingly, fire
detections that rely solely on observing a CO.sub.2 spike in the
narrow 4.3 micron band are in effect observing only a small
fraction of a fire's total energy radiation. In contrast, the
preferred fire/flame detector observes a much wider portion of the
energy emitted by a fire. However, because nonfire sources such as
sunlight and artificial light may also be observed by the
fire/flame detector, a mechanism for discrimination between fire
and non-fire energy sources is desireable.
[0118] The discriminator in the fire/flame detector can be
programmed or otherwise configured to make advantageous use of
known or observed characteristics of different types of fires, in
order to more readily distinguish fire and non-fire energy sources.
By way of general background, all materials that burn in the
condition known as an unwanted fire, which can be described as
uncontrolled rapid oxidation, emit wideband blackbody radiant
energy and molecular narrow band line emissions, such as the 4.3
micron CO.sub.2 spike. (The term blackbody refers to a material's
emissivity, and not its color.) The blackbody radiant emissions of
a fire are always present and predictable because they are a
function of the temperature of the materials being consumed by the
fire, the temperature of the fire's gaseous flames and solid
particulates, and the average emissivity of the flames,
particulates, and burning material. Radiant emissions are the
transfer of heat from one body to another without a temperature
change in the medium; they are electromagnetic in nature and travel
at the speed of light. They are, for example, the physical
mechanism that transfers energy (heat) from the sun to the earth
through airless outer space.
[0119] Blackbody radiant emissions are the primary reason that a
fire feels hot at a distance. Because Kirchoff's Law states that a
good emitter is also a good absorber for each wavelength, a
blackbody may be defined as an ideal body that completely absorbs
all radiant energy striking it, and therefore, appears perfectly
black at all wavelengths. Emissivity may be defined as the ratio of
an object's radiance to that emitted by a blackbody radiator at the
same temperature and at the same wavelength. A perfect blackbody
has an emissivity of one. Highly reflective surfaces have a low
emissivity, but most materials that burn easily have emissivities
of 0.5 or greater. The radiation emitted by a blackbody is referred
to as Planck's Blackbody Radiation Law.
[0120] FIGS. 13a, 13b, 14, 15 and 16 can be used to compare the
amount of energy emitted at different energy bands by fires of
different temperatures, and therefore the amount of energy that can
be detected by sensors operating at different energy bands. FIGS.
13a and 13b are tables containing data comparing the heat of a fire
(in degrees Kelvin), its total radiant energy (in watts/cm.sup.2)
over the visible, nearband IR and wideband IR ranges, its radiant
energy in the narrowband IR range, and the relative percentages of
narrowband versus the composite of nearband IR, visible and
wideband IR. FIGS. 14, 15 and 16 are graphs illustrating the
information in the table of FIGS. 13a and 13b. The table and graphs
of FIGS. 13a, 13b, 14, 15 and 16 indicate that a fire emits far
more energy in the wideband energy spectra than in the narrowband
IR band.
[0121] FIG. 14 is a graph showing total radiant energy as a
function of a fire's temperature. As shown in FIG. 14, the total
radiant energy generally increases as a function of the fire's
temperature. FIGS. 15 and 16 compare in different aspects the
amount of the fire's energy observable by a wideband detector
versus a narrowband detector. FIG. 15 compares the percentage of
radiant energy detected by a wideband detector and a narrowband
detector as a function of the fire's temperature, while FIG. 16 is
a graph showing a plot of the relative increase in energy detected
by a wideband detector over a narrowband detector, as a function of
the fire's temperature.
[0122] The information appearing in FIGS. 13a, 13b, 14, 15 and 16
has been derived as follows. First, the formula for calculating the
total heat radiation at all wavelengths from a perfect blackbody is
known as the Stefan-Boltzmann Law:
W=.sigma.T.sup.4 (1)
[0123] where W is the total radiation emitted in watts/m.sup.2, T
is the absolute temperature in .degree.K (degrees Kelvin), and
.sigma. is the Stefan-Boltzmann constant, 5.67.times.10.sup.-8
watt/m.sup.2K.sup.4. The Stefan-Boltzmann Law indicates that the
total radiant emitted energy from a surface is proportional to the
fourth power of its absolute temperature; consequently, the hotter
the body is, the greater the wide-band infrared radiation that is
emitted. To obtain a more precise value of W, the total radiant
blackbody energy emitted using equation (1), W can be multiplied by
the average emissivity of the burning materials, which can be
approximated by 0.5.
[0124] Planck's Radiation Law may be used to calculate the
continuous radiant energy distribution among the various
wavelengths. For all the wavelengths from 0 to 100 microns, the
radiated energy should be equal to the total radiated energy
calculated by the Stefan-Boltzmann Law. The detected percentage of
radiated energy is found by calculating the energy in the
wavelength span covered by an optical fire detector with the total
energy radiated by the fire using the Stefan-Boltzmann Law.
Planck's formula for calculating the total radiated energy between
first and second wavelengths .lambda.1 and .lambda.2 is as
follows:
W.sub..lambda.1-.lambda.2=.intg.((2.pi.hc.sup.2)d.lambda.)/.lambda..sup.5(-
e.sup.hc/.lambda.(kT)-1)) (2)
[0125] where
[0126] h=Planck's constant, 6.63.times.10.sup.-34 joule-sec.,
[0127] c=speed of light, 3.00.times.10.sup.10 cm/sec.,
[0128] .lambda.=wavelength in cm (10-2 meters),
[0129] T=absolute temperature in degrees Kelvin, and
[0130] k=Boltzmann constant, 1.38.times.10.sup.-23
joules/.degree.K.
[0131] Using equation (2) and integrating over the wavelength range
from 0.4 to 3.5 microns, it can be determined that an "ideal"
optical fire detector with a wide band spectral range of 0.4 to 3.5
microns is theoretically capable of sensing, for example, about
88.23% of the total radiated energy at a fire/flame temperature of
2500 degrees Kelvin (K) (2226.85 degrees Celsius), as appears in
the information contained in the tables of FIGS. 13a and 13b. For
reference, the temperature of a typical clean burning flame
generally varies from between 1400 and 3500 degrees K.
[0132] There is another kind of infrared (IR) radiation that is
discontinuous and made up of individual, very narrow emission
lines. An example is the line spectrum produced by a heated gas,
such as carbon dioxide, which is a by-product of hydrocarbon fires.
This phenomenon is related to the excitation or heating of certain
types of gases. The atoms or molecules of a gas have certain
natural frequencies of vibration and rotation depending upon their
structure, bonding forces, and masses. If certain gases are
suitably excited (i.e., heated), they will emit a line emission
spectrum characteristic of the particular gas. Such gases can also
absorb radiation in the same line spectrum (i.e., according to
application of Kirchoff's Law). For CO.sub.2 gas, these narrow band
line emissions and absorption regions include the 4.3 micron band.
Nonhydrocarbon fires, however, such as silane and hydrogen fires,
do not produce CO.sub.2 gas as a by-product because no carbon atoms
are involved in the combustion process.
[0133] Thus, fires that are not oxidizing carbon based materials
may not emit CO.sub.2 gas or have a narrow band line emission at
4.3 microns. The CO.sub.2 gas emission line from an uncontrolled
fire is therefore unpredictable. Moreover, the total radiant energy
of line emissions represents a very small fraction of the total
blackbody radiant energy and does not measurably affect the total
radiant energy output. Using Planck's Radiation Law, Equation (2),
with a wavelength range from 4.2 to 4.4 microns to calculate the
energy in the 4.3 micron band, the percentage of Planckian
blackbody energy is about 0.82% at a fire/flame temperature of 2500
degrees K (see FIGS. 13a and 13b). Thus, optical fire detectors
that use the 4.3 micron narrow band to sense fires can fail to
detect nonhydrocarbon fires, and do not present a proportional
measure of energy consumed during a fire, as they often can see
less than one percent of the fire's total radiated energy.
[0134] Besides observing radiant energy over a given spectral band,
a fire/flame detector can also observe the changes in radiant
energy over time to make a better determination of whether a fire
is occurring, as opposed to a non-fire event that may otherwise
result in a false alarm trigger. Further characteristics of a fire
can therefore be used to improve the detection ability of the
fire/flame detector.
[0135] For example, it has been observed by the inventors that the
wide, continuous band of blackbody radiant energy pulsates as the
fire's rising thermal energy causes the burning material(s) to
further outgas, consuming more oxygen in rapid, irregular,
exothermic chemical reactions. As the temperature of the fire
further rises, the radiant blackbody energy correspondingly
increases and the carbon particulates, if the fire is a hydrocarbon
type (i.e., a fire involving hydrogen and carbon), remain after the
other outgassing components are consumed. These hot carbon
particles also radiate blackbody emissions and their emissivity is
high.
[0136] A calm, controlled fire, such as a candle burning in still
air, radiates a constant blackbody radiant heat of the gaseous
flame and particulates that can be felt within about one foot of
the flame. In contrast, for an uncontrolled, unwanted fire,
especially a growing fire, the radiant heat that is felt by the
hand at a distance is pulsating and irregular. It has been observed
by the inventors that most threatening fires tend to pulsate at a
rate of approximately 2 to 100 Hertz. This flickering or pulsating
causes ripples to occur at a similar rate in the detected blackbody
energy.
[0137] The differences between uncontrolled, unwanted fires and
calm, controlled fires or non-fire energy sources can be
advantageously used by the fire/flame detector to discriminate
between fire situations which call for a response and situations
which call for no response or merely continued monitoring. For
example, the discriminator in the fire/flame detector may observe
the frequency and regularity at which the detected radiant energy
is pulsating, and thereby weed out potential false alarm
situations. For example, if the fire/flame detector observes that
the detected energy has a time-varying component between 2 and 100
Hertz, the discriminator may conclude that a potential unwanted
fire situation exists. If, on the other hand, the fire/flame
detector observes that the detected energy has no time-varying
component, or has one or more time-varying components outside of
the 2 to 10 Hertz frequency band, then the discriminator may
conclude that it is unlikely that a fire situation exists. The
discriminator may combine this information with other information
to arrive at a final conclusion of whether a potential unwanted
fire situation exists.
[0138] The ultimate criteria used to determine whether a fire
situation exists can largely depend upon the application in which
the fire/flame detector is employed. The fire/flame detector is
therefore advantageously configured with a programmable
microprocessor so that the discrimination mechanism can be tailored
to each particular environment.
[0139] The discriminator can also be programmed with "false alarm
profiles" to further assist in distinguishing between fire and
non-fire situations. To accomplish this type of programming, the
output of the fire/flame detector sensors is measured in response
to various non-fire or non-dangerous flame sources anticipated to
occur in the area where the fire/flame detector will be deployed.
For example, the response of the fire/flame detector sensors to an
oven, flashlight or a lit match may be measured and recorded. The
energy profile resulting from the oven, flashlight, lit match or
other non-dangerous fire source can be stored in a memory within
the fire/flame detector. After the detector is deployed, and when a
potential fire situation later occurs, the fire/flame detector can
compare the current energy profile with the stored "false alarm"
profiles and can prevent itself from declaring a fire situation if
a close match is found.
[0140] Referring now to FIGS. 3 and 5, sensor sensitivities and
sensor types that are used in a fire/flame detector 32 are
illustrated. It should be understood that a variety of different
sensors may be used in different configurations to accomplish the
same or equivalent purpose. In accordance with one illustrated
embodiment (FIG. 3), suitable silicon (Si) photodiode sensors are
used for detecting radiant energy within the visible band and near
band infrared spectrums. The wavelength (in nanometers) of the
radiant energy is indicated along the x-axis and the sensor
sensitivity in relative percentage is indicated on the y-axis. For
a wide infrared spectrum, a suitable lead sulfide (PbS) sensor can
be used. With reference specifically to FIG. 5, in accordance with
an alternative embodiment, a Germanium photodiode sensor may be
sandwiched on top of the lead sulfide (PbS) sensor.
[0141] In accordance with the embodiment illustrated in FIG. 11,
sensor digital data (once converted by the A/D converter) is
continuously transmitted to the controller 39. The controller 39
analyses the sensor digital data and determines if there is any
sign of sparks, flames, or fire (whether or not visible to the
human eye). The controller 39 therefore acts in this embodiment as
a discriminator so as to discriminate between an unwanted and/or
uncontrolled fire, and a non-fire or controlled fire source.
[0142] To this end, the controller 39 compares the radiant energy
sensed by the visible band and nearband IR sensors against the
radiant energy sensed by the wideband IR sensor. The radiant energy
sensed by the visible band and nearband IR sensors can be from
nonfire sources such as electrical lights, reflected and/or direct
sunlight modulated by such things as tree branches or leaves in a
breeze, reflected sunlight off water, steady-state IR sources such
as infrared curing ovens, and the like. The radiant energy sensed
by the wideband IR sensor is indicative of blackbody radiation. The
relative levels of visible/nearband IR energy versus wideband IR
energy, and the time relationship of those energy levels, can be
analyzed by the controller 39 in order to determine the presence or
lack of presence of a fire.
[0143] In a preferred embodiment, the radiant energy sensed by the
visible band and nearband IR sensors (i.e., the A/D sampled outputs
of the visible band and nearband IR sensors) is digitally
subtracted from the radiant energy sensed by a wide band IR sensor
(i.e., the A/D sampled output of the wideband IR sensor), resulting
in a "compensated" measured energy level. The compensated measured
energy level is compared against a predetermined threshold level.
If the predetermined threshold level is exceeded, a possible fire
situation is declared. The visible, nearband IR and wideband IR
sensor outputs are then compared against false alarm profiles to
verify that known false alarm sources have not caused the measured
energy level to exceed the threshold.
[0144] As described further hereinafter, multiple threshold levels
for comparison may be established, with each threshold level
resulting in a different response or action by the fire/flame
detector.
[0145] A preferred mechanism for discriminating between fires
potentially requiring a responsive action and other radiant energy
sources (including non-fires or certain types of controlled fire or
energy sources) may be described with reference to FIGS. 28 through
34. FIG. 28 is a functional diagram illustrating the basic steps of
the discrimination technique. While this technique is explained
with reference to an embodiment which takes advantage of
microprocessor processing speed and power, it will be understood
that some or all of the functions described can be implemented, if
desired, using analog circuitry or a combination of digital and
analog circuitry.
[0146] FIG. 34 shows a circuit for processing a sensor input signal
and, more particularly, a circuit for processing an output from a
wide band IR sensor 502 (such as a lead sulfide (PbS) sensor) and
generating a first signal 521 indicative of a DC level of the
sensor output and a second signal 522 indicative of a transient
level of the sensor output. The wide band IR sensor 502 acts
similar to a variable resistor, having a resistance that depends on
the amount of radiant energy detected in the wide band IR range.
The output of the wide band IR sensor 502 is provided to an
amplifier 505 which is biased using a 2.5 volt reference signal 512
and a 5 volt reference signal 511 with suitable resistance values
as shown in FIG. 3r. The amplifier 505 produces a first amplified
signal 508 that is low pass filtered by the collective action of
resistor R32 and capacitor C16, and then integrated and scaled
using amplifier 507 to arrive at a wide band IR DC output signal
521, designated MIR.sub.DC herein.
[0147] The first amplified signal 508 is also high pass filtered
using capacitor C14 and then amplified by amplifier 506, which
essentially acts as a buffer, to arrive at a wide band IR transient
output signal 522, designated MIR, herein. The circuit 501 of FIG.
34 thereby outputs both a wide band IR DC output signal 521 and a
wide band IR transient output signal 522. It will be understood
that the wide band sensor is sometimes referred to in the text and
the drawings as "WBIR" and at other times as "MIR", and likewise
with the output signal(s) from the wide band IR sensor; however,
the designations WEIR and MIR are used interchangeably herein and
are not intended to refer to different aspects of the described
embodiments.
[0148] A circuit similar to the circuit shown in FIG. 34 is
provided for processing the output of the near band IR detector and
producing two signals indicative of a DC level and transient level,
respectively, of the near band IR detector output, except the
component values of the elements of the circuit would be altered to
match the characteristics of the near band IR sensor as may be
readily accomplished by one skilled in the art. Likewise, a circuit
similar to the circuit shown in FIG. 34 is provided for processing
the output of the visible band detector and producing two signals
indicative of a DC level and transient level, respectively, of the
visible band detector output, except the component values of the
elements of the circuit would be altered to match the
characteristics of the visible band sensor.
[0149] FIG. 28 shows a wide band IR sensor 302 outputting a wide
band IR DC signal and a wide band IR transient signal, a near band
IR sensor 303 outputting an near band IR DC signal and a near band
IR transient signal, and a visible band sensor 304 outputting a
visible band DC signal and a visible band IR signal. Each of the DC
and transient signals for the wide band IR sensor 302, near band IR
sensor 303, and visible band sensor 304 is sampled and converted
into the digital domain by A/D converters 306, 307 and 308,
respectively. (In a preferred embodiment, a single A/D converter is
shared among all three sensors 302, 303 and 304.)
[0150] The A/D converters 306, 307 and 308 output digitally sampled
sensor signals 312, 313 and 314, which are designated in FIG. 28 as
MIR.sub.DC, NIR.sub.DC, and VIS.sub.DC, respectively, each
representing the "raw" DC component of the DC signal from the
corresponding sensor 302, 303 or 304. The A/D converters 306, 307
and 308 also output digitally sampled sensor signals 317 and 318,
which are designated in FIG. 28 as MIR.sub.T and VIS.sub.T,
respectively, each representing the "transient" component of the
transient signal from corresponding sensor 302 or 304.
[0151] The MIR.sub.DC signal 312 is provided to a "fast" digital
filter 321 and to a "slow" digital filter 322. Likewise, the
NIR.sub.DC signal 313 is provided to a "fast" digital filter 323
and to a "slow" digital filter 324, and the VIS.sub.DC signal 314
is provided to a "fast" digital filter 325 and to a "slow" digital
filter 326. In each case, the "fast" digital filter has a
relatively fast time constant, and the "slow" digital filter has a
relatively slow time constant. In each case, the slow digital
filter outputs a slow filtered signal that (with adjustment or
correction, in some cases) is used as a "baseline" for comparison
against a fast filtered signal that is output from the fast digital
filter. The "fast" digital filter and "slow" digital filter may
each comprise a low pass filter, with the low pass filter of the
"fast" digital filter having a higher cutoff frequency than that of
the "slow" digital filter.
[0152] Subtractors 332, 333 and 334 operate to generate comparison
signals between the fast filtered signal and the slow filtered
signal for each of the digitized sensor signals, with the
adjustments as noted below. FIG. 29 is a graph illustrating the
output of any one of the subtractors 332, 333 or 334. At
predetermined intervals of time (although it may be done
continuously as well), the slow filtered signal is subtracted from
the fast filtered signal to arrive at a difference signal
designated as .DELTA.MIR, .DELTA.NIR and .DELTA.VIS for subtractors
332, 333 and 334, respectively. In essence, the slow filtered
signal represents a steady state or DC baseline for comparison, and
the fast filtered signal represents a more rapidly occurring change
in the radiant energy detected by the particular sensor. The
difference signals .DELTA.MIR, .DELTA.NIR and .DELTA.VIS therefore
represent the change in radiant energy for each of the particular
energy bands with respect to a measured baseline that varies
gradually over time.
[0153] In two situations the output of a slow or fast digital
filter is adjusted prior to being applied to a substractor. First,
a compensation is made in compensation function block 328 to the
output of the slow digital filter 322 of the wide band IR sensor
input. In compensation function block 328, the output of the slow
digital filter 322 is forced to the same value as the output of the
fast digital filter 321 if the output of the fast digital filter
321 is less than the output of the slow digital filter 322. This
effect is illustrated in FIG. 30, which is a graph showing a plot
of a slow filter output signal 402 and a fast filter output signal
403. The dotted line portion 404 indicates what the output of the
slow filter would have been without the compensation provided by
the compensation function block 428, and is present where the
output of the fast digital filter 321 is less than the output of
the slow digital filter 322. The output of compensation function
block 428 is sent to the subtractor 332.
[0154] One purpose of compensation function block 428 is to ensure
the output of subtractor 332 will always be positive, which will
ensure proper monitoring where a fire suddenly loses energy (such
as where it is doused with fire suppressant) or else a source of
wide band IR radiant energy is removed from the view of the WBIR
(or MIR) sensor. Thus, the fire detector will be able to more
easily determine if a temporarily suppressed fire is going to
self-extinguish or is starting to regrow, in which case further
treatment may be required.
[0155] A second compensation is made in compensation function block
329. This second compensation function block 329 is connected to
the output of the fast digital filter 325 associated with the
visible band sensor input and can be used to reject false alarm
sources such as flashlights. Compensation function block 329
provides the equivalent of a peak detection function which holds
the output of the fast digital filter 325 at its peak and
thereafter allows it to steadily decline. The compensation function
block 329 may be realized as an asymmetrical digital filter with a
fast rise time and slow decay time.
[0156] FIG. 31 is a graph illustrating the effect of asymmetrical
digital filtering on the fast digital filter output of the visible
band sensor. In FIG. 31, a plot of the fast digital filter output
signal 411 is shown along with a plot of the slow digital filter
output signal 412. The dotted line portion 413 indicates the output
of the fast digital filter after asymmetrical filtering carried out
by the compensation function block 329. As can be seen in FIG. 31,
the signal after asymmetrical filtering decays more slowly than the
actual output of the fast digital filter. By such asymmetrical
filtering, the fire detector in essence creates an "artificial"
visible light that lingers when an actual visible light is shut
off. In this manner, false alarms caused by flashlights or other
man-made electrical or battery light sources can in many instances
be avoided. The output of the compensation function block 329
(referred to as the "flashlight rejection" algorithm) is provided
to subtractor 334.
[0157] The output of subtractor 332 (associated with the wide band
IR sensor input signal) is connected to a temperature coefficient
block 341 which adjusts the difference signal .DELTA.MIR by a
coefficient to compensate for ambient temperature fluctuations.
This compensation is made where, for example, a lead-sulfide (PbS)
based wide band IR sensor is used, because such sensors are
sensitive to temperature variations. The near band IR sensor and
visible band sensor may be constructed of silicon, and therefore,
on the other hand, would be largely temperature independent.
[0158] The temperature compensated difference signal M.DELTA..sub.T
is compared against the difference signal relating to the visible
band sensor. However, because the visible band sensor input signal
and wide band IR input signal are in terms of different units, a
unit conversion adjustment is made to the visible band difference
signal .DELTA.VIS in unit conversion function block 342. The
temperature compensated difference signal M.DELTA..sub.T is thus
compared by use of a subtractor 345 against the unit converted
visible band difference signal V.DELTA..sub.C, to arrive at a
compensated energy value M.DELTA..sub.T' which generally provides
an indication of wide band radiant energy less visible radiant
energy, with the adjustments for certain false alarm sources as
noted above.
[0159] The near band IR difference signal .DELTA.NIR output from
subtractor 333 is used to set a threshold for comparison against
the compensated energy value M.DELTA..sub.T'. The output of
subtractor 333 is applied to a threshold value lookup table 347
(which may be stored, for example, in non-volatile RAM) . The
threshold value output from the threshold lookup table 347
preferably changes as a step function of .DELTA.NIR, with a change
in .DELTA.NIR leading to a proportional change (usually a
fractional change) in the selected threshold value output from
threshold value lookup table 347.
[0160] The compensated energy value M.DELTA..sub.T' is compared
against the selected threshold value M.sub.TH by a subtractor (or
comparator) 350. A response function block 360 monitors the output
of the subtractor 350 and declares a suitable early warning, alert
or alarm condition in response to the compensated energy value
M.DELTA..sub.T' exceeding the selected threshold value M.sub.TH,
indicating that a certain "dangerous" or potentially dangerous
amount of radiant energy has been detected.
[0161] The response function block 360 preferably makes a response
decision based not only on the output of subtractor 350, but also
on certain false alarm rejectors that are built in to the system.
Two particular such false alarm rejectors are shown in FIG. 28.
First, a flicker pulse count detector 352 is utilized to provide an
indication that the radiant energy source is flickering or
pulsating in a "chaotic" manner typical of uncontrolled or growing
fire sources. FIG. 32 is a diagram illustrating operation of a
flicker detection algorithm in accordance with various aspects of
the present invention. According to a preferred flicker detection
algorithm, a "flicker" is detected by comparing positive
transitions in the digitized transient wide band IR signal (MIRT)
317 against positive transitions in the digitized transient visible
band signal (VIS.sub.T) 318. Each positive transition of the
digitized transient wide band IR signal 317 is counted as a
"flicker", unless the digitized transient visible band signal 318
also has a positive transition at about the same time.
[0162] If both of the digitized transient wide band IR signal 317
and the digitized transient visible band signal 318 have a positive
transition at about the same time (within a certain programmable
tolerance), then the event is not deemed a "flicker," regardless of
how wide the respective pulses turn out to be. Thus, in FIG. 32, a
first pulse (positive transition) 432 in the digitized transient
wide band IR signal 317 is not counted as a valid flicker event,
but a second pulse (positive transition) 433 and a third pulse
(positive transition) 434 are counted as valid flicker events.
[0163] According to the false alarm rejection technique embodied in
the flicker pulse count detector 352, a certain number (e.g., two)
of valid flicker pulses must be counted in each consecutive time
frame (e.g., two seconds) (which may, if desired, be a sliding time
frame) or else the flicker pulse count detector 352 outputs a value
of "FALSE" indicating that the detected energy pattern does not
appear to conform to an uncontrolled or growing fire situation. If,
on the other hand, the flicker pulse count detector 352 detects at
least two valid flicker pulses in each consecutive time frame, and
if it does so for a predetermined number of consecutive time frames
(spanning, e.g., ten seconds), then the flicker detection algorithm
is satisfied and the flicker pulse count detector 352 outputs a
value of "TRUE," indicating that the detected energy pattern could
be caused by an uncontrolled or growing fire.
[0164] The above process performed by the flicker pulse count
detector 352 is known as flicker pulse count aging because it
monitors the flickering nature of the detected radiant energy over
time. If the flickering is not maintained for a sufficient amount
of time (e.g., ten seconds), then the flicker pulse count detector
352 provides an indication that the energy source may not be an
actual fire for which a responsive action is advisable. In one
aspect, the flicker pulse count detector 352 may be viewed as
applying a digital bandpass filter that outputs a "TRUE" value when
valid flickers occur within a certain rate range.
[0165] In addition to the flicker pulse count detector 352, another
false alarm rejector is a wide band IR peak energy pulse detector
353 that serves to weed out false alarm sources producing wide band
IR energy of a steadily growing nature such as industrial ovens. As
shown in FIG. 28, the digitized transient wide band IR signal
(MIR,) is provided to a "fast" digital filter 319 and a "slow"
digital filter 320, in a manner analogous to the digitized DC wide
band IR signal (MIR.sub.DC). The output of the "fast" digital
filter 319 and the "slow" digital filter 320 are sent to the wide
band IR peak energy pulse detector 353, which qualifies a fire by
looking for a narrow peak in the transient wide band IR signal.
[0166] FIG. 33 is a diagram illustrating a wideband peak energy
pulse detection algorithm, and shows a wide band IR fast filter
output signal 461 (such as may be output from the "fast" digital
filter 319) plotted over time on a graph along with a wide band IR
slow filter output signal 462 (such as may be output from the
"slow" digital filter 320). FIG. 33 also shows a peak energy pulse
detection threshold level 463 that varies over time such that it
remains a preset amount above the slow filter output signal
462.
[0167] Each time the wide band IR fast filter output signal 461
exceeds the peak energy pulse detection threshold level 463, the
amount of time it spends above the peak energy pulse detection
threshold level 463 is measured to arrive at a peak pulse width
.DELTA.t. If the peak pulse width .DELTA.t is "narrow"--i.e., less
than a predefined narrowness criteria, then the peak is deemed a
"valid" narrow peak. If a valid narrow peak has occurred within a
predetermined amount of time (e.g., two seconds), then the wide
band IR peak energy pulse detection algorithm has been satisfied,
and the wide band IR peak energy pulse detector 353 outputs a
"TRUE" value indicating that the detected wide band IR energy may
conform to an uncontrolled or growing fire. Otherwise, the wide
band IR peak energy pulse detector 353 outputs a "FALSE" value.
[0168] The wide band IR peak energy pulse detector 353 operates
under the assumption that uncontrolled or growing fires tend to
have rapid or narrow spikes of broadband radiant energy, and that
such spikes of broadband radiant energy can be observed using the
wide band IR sensor. Thus, wide band IR energy profiles that fail
to display such characteristics are assumed to be related to
non-fire or controlled fire sources. The wide band IR peak energy
pulse detector 353 need not be used in all fire detection
applications and may, for example, be employed only when the fire
detector is placed in any environment having sources of wide band
IR radiant energy such as industrial ovens.
[0169] Referring again to FIG. 28, the response function block 360
makes a response decision based on the output of subtractor 350, as
well as the flicker pulse count detector 352 and the wide band IR
peak energy pulse detector 353 if those false alarm rejectors are
employed. If the subtractor 350 indicates that the compensated
energy value M.DELTA..sub.T' exceeds the selected threshold value
M.sub.TH, then a certain amount of dangerous or potentially
dangerous radiant energy has been detected. The response function
block 360 then, if desired, uses the outputs of the flicker pulse
count detector 352 and the wide band IR peak energy pulse detector
353 to weed out false alarms. For example, the response function
block 360 may require that both the outputs of the flicker pulse
count detector 352 and the wide band IR peak energy pulse detector
353 be "TRUE" in order to declare a certain status level, such as
an "ALARM" situation calling for an appropriate response.
[0170] In addition, the fire detector may be provided with a second
threshold level (M.sub.TH2) against which the compensated energy
value M.DELTA..sub.T' is compared, in order to support various
types of multi-stage responses. In this manner, the fire detector
can have a threshold value corresponding to different energy
levels, such as 3 kW and 13 kW, for example. The second threshold
level may be implemented by using a second threshold lookup table
(which can be integrated with the first threshold lookup table) and
a second subtractor connected to the second threshold level
M.sub.TH2 and to the compensated energy value M.DELTA..sub.T'.
[0171] The response function block 360 may or may not use the false
alarm rejectors for arriving at a fire detection decision. For
example, it may be desired to program the fire detector to respond
rapidly to a 3 kW fire. In such a case, the response function block
360 could issue an appropriate response by observing when the
compensated energy value M.DELTA..sub.T' exceeds the threshold
level of 3 kW, while disregarding the outputs provided by the
flicker pulse count detector 352 and the wide band IR peak energy
pulse detector 353. The response function block 360 may be
programmed to provide a different type of response to a 13 kW fire.
In such a case, the response function block 360 may be programmed
to observe not only when the compensated energy value
M.DELTA..sub.T' exceeds the second threshold level of 13 kW, but
also to issue a response only when the outputs provided by the
flicker pulse count detector 352 and the wide band IR peak energy
pulse detector 353 are also both TRUE.
[0172] In addition, the fire detector could be provided to
circuitry analogous to that shown in FIG. 28 for processsing the
digitized transient wide band IR signal 317 and comparing the
detected transient wide band IR energy to a threshold level (such
as 3 kW), after compensation for the transient visible band energy
in a manner similar to that shown for the DC wide band IR and
visible band signals in FIG. 28.
[0173] In an alternative embodiment, mathematical techniques such
as Fast Fourier Transforms (FFT's) are used to separate the
temporal radiant energy spectral response of the WBIR, NBIR, and VB
spectra into the individual Fourier components, thereby
transforming the spectral radiant energy received as a function of
time into a representation of radiant energy received as a function
of frequency. By subtracting the individual frequency components of
the nonfire sources from the individual frequency component of a
real fire, a compensated energy level can be obtained, which is
then used to eliminate potential false alarm sources as described
above.
[0174] In more detail, FFT's can be used to obtain individual
Fourier components for each of the WBIR, NBIR and VB sensors at
each a plurality of predetermined frequencies (such as 2, 5, 7 and
10 Hertz, for example). The magnitudes of WBIR frequency components
are compared for each of the predetermined frequencies against the
magnitudes of the VB frequency components, to arrive at a first set
of energy level comparison values. Similarly, the magnitudes of
WBIR frequency components are compared for each of the
predetermined frequencies against the magnitudes of the NIR
frequency components, to arrive at a second set of energy level
comparison values. The first set of energy level comparison values
and second set of energy comparison values may be applied to a
lookup table to determine whether the profile matches that of a
fire or potential fire situation.
[0175] Use of a wideband IR sensor as the primary sensor realizes
several benefits, particularly where use of a UV sensor is
eliminated. First, the fire/flame detector may be housed in a
self-contained, low-cost plastic, polypropylene, Teflon or
fiberglass housing, whereas UV-based sensors require relatively
expensive sapphire or quartz window lenses. Being able to use such
a housing also eliminates problems found in UV-based sensors
relating to sealing the UV sensor window. A similar advantage may
be experienced over narrow band IR sensors. Because impurities in
the housing material can have a significant impact on the quality
of detection of a narrow band IR sensor, materials such as
polypropylene, Teflon or plastic may be unacceptable for use as a
housing and/or window with such narrow band IR sensors, but will,
in contrast, have far less impact on a wide band IR sensor which
does not rely on one narrow IR band or a few narrow bands for fire
detection.
[0176] As another significant benefit, a WBIR-based fire/flame
detector according to the present invention can detect most any
type of hydrocarbon (propane, butane, gasoline, etc.) and
nonhydrocarbon-based fires (such as silane, hydrogen, sodium azide,
etc.). In contrast, narrow band IR detectors typically only look
for the CO.sub.2 spike emission line output centered at
approximately 4.3 microns, which is best generated by a
well-oxygenated, clean-burning, hydrocarbon fire (such as a propane
flame). UV-based sensors are subject to "blindness" caused by cold
CO.sub.2 suppressant gas and/or black smoke generated by a
polypropylene fire. Such detectors can also be blinded by
chemicals, acetones, vapors and gases in the atmospheres, or by
contaminants that foul the window lens such as oil, paint residue
(e.g., liquid and powder), dirt, etc. With WBIR as the primary
sensor, the fire/flame detector can "see through" most contaminants
because the longer infrared wavelengths of WBIR can penetrate them,
with the exception of certain contaminants such as thick black
paint, or thick layers of contaminants.
[0177] In addition, a wide band IR sensor can have a significantly
improved field of view over a narrow band IR sensor. Narrow band IR
sensors require relatively precise filtering (such as may be
carried out by a Fabry-Perot filter) tuned by the thickness of a
material used in the sensor. When an energy source (such as a fire)
is located at an angle to the narrow band IR sensor, the radiant
energy emitted by the source strikes the sensor material at an
angle and travels through a greater amount of the sensor material.
This results in a distortion that makes the radiant energy appear
to be located at a different wavelength than it actually is, and
can cause a narrow band IR sensor to fail to detect a fire.
Conventional narrow band IR sensors avoid this problem by
maintaining a relatively tight field of view, such as 90.degree.,
for the sensor. A wide band IR sensor, on the other hand, can
detect fires while having a 120.degree. or even greater field of
view.
[0178] Using wide band IR can reduce maintenance problems because
frequent, costly, manual window-lens cleaning of the UV lens can be
eliminated. The flame/fire detector can also be made more rugged,
reliable, and trouble-free without a UV sensor, which is typically
made of UV transmitting glass or quartz.
[0179] As an additional benefit to relying on wideband IR as the
primary sensory input, the need for UV "through the lens" testing
is eliminated. Each UV test source generally requires extra
circuitry, which is usually high-voltage circuitry that can be
susceptible to reliability problems. Such high-voltage circuitry is
unnecessary where no UV sensor is used.
[0180] It will be understood that while a preferred embodiment is
described with respect to use of three sensors (i.e., a visible
band sensor, a nearband IR sensor, and a wideband IR sensor), other
sensor arrangements can be used to obtain the same or equivalent
results. For example, a fire/flame detector may use a number of
sensors each operating over a distinct narrow energy band range,
and sum up the sensor outputs so as to obtain an indicia of total
blackbody energy. While such a design would be more complicated due
to the greater number of sensors, the same principles of fire/flame
detection as previously described would apply to such a
configuration.
[0181] In accordance with a particular embodiment as illustrated in
FIG. 11, sensor data is A/D converted and the resulting digital
data is transmitted to the controller 39. The controller 39
analyses the sensor digital data and determines if there is any
sign of sparks, flames, or fire. Upon detecting an "alert," a "fire
early warning," or an "alarm" condition, the controller 39
selectively triggers one or more of three individual relays within
an alarm unit 56 (one-, two-, or three-stage). In accordance with
one embodiment, a three-stage version of the multi-stage alarm unit
56 comprises an "alert" relay 58, a "fire early warning" relay 60,
and an "alarm" relay 62. Alternatively, in accordance with another
embodiment, a two-stage version of the multi-stage alarm unit 56
comprises only the "alert" relay 58 and the "alarm" relay 62. Each
of the relays may be coupled to distinctive LED indicators, audible
alarms, or the like.
[0182] In accordance with one approach, the controller 39 compares
the sensor digital data against programmed threshold values (of
characteristics of fire signatures or false alarm models), to
determine if the observed data indicates a cause for concern. The
controller 39, upon detecting characteristics that warrant an
"alert" condition, triggers the "alert" relay. Likewise, the
controller 39, upon detecting characteristics that warrant a "fire
early warning" condition (in the three-stage embodiment) or an
"alarm" condition, triggers either the "fire early warning" (in the
three-stage embodiment) relay 60 or the "alarm" relay 62. The
appropriate relay may in turn trigger an associated LED indicator
or audible alarm. A timer 64 is set in every instance to either
reject false alarm situations or allow the flame or fire sufficient
time to self-extinguish. Only upon detecting an "alarm" condition,
and that also after a predetermined time limit, are the suppression
agents activated.
[0183] In accordance with the general operation, the present system
typically observes a fire in as little as 16 milliseconds (but can
be less than one millisecond), then verifies the fire condition
multiple times to ensure its existence. Following this exercise,
the system (in the three-stage alarm embodiment) declares a "fire
early warning" condition. For example, if the fire is a spray gun
fire, the present system declares an "alert" condition to cause
shutdown of the spray gun paint flow, electrostatics, and conveyor
16. The present system continues to monitor the fire condition
during a predetermined limit of time to allow it to
self-extinguish. In the event the fire persists, the system
declares an "alarm" condition and activates release of suppression
agents to quell the fire.
[0184] Alternatively, the system (in the two-stage alarm
embodiment) looks for any sign of fire (small) and reports it so
that personnel on the monitored facility can immediately respond to
it. If the fire continues to grow, the system activates the "alarm"
condition to activate release of the suppression agents to quell
the fire.
[0185] The following discussion relates to a preferred embodiment,
in which multiple levels of responses are provided for different
responsive actions in the optical fire/flame detector based upon
both the type of fire and the radiant wide band continuous spectral
output of the fire. There are different types of fires, including
explosive fires; fast-burning, "fireball" fires; slow-burning,
flickering fires; large, growing fires; etc. Different kinds of
responsive actions may need to be taken depending upon the type of
fire.
[0186] In a particular embodiment, WBIR is used as the primary
sensor in a multispectral sensor array of an optical fire/flame
detector with digital signal processing in the electrostatic
finishing industry. In this industry, spray guns are used to apply
paint coatings in an electrostatic paint line or booth. Such spray
guns apply approximately 100,000 volts to the atomized paint (e.g.,
liquid or powder). Because of the possibility of a malfunctioning
spray gun or an improperly grounded part, arcing can occur, which
can quickly ignite the paint mist, resulting in a "fireball"-type
fire. The majority of the time, if the fireball is detected within
one-half second and the paint flow and electrostatics are
immediately shut down, the fire will self-extinguish. In a paint
line or booth, paint mist accumulates on the detector's window
lens, even with air shields. While this might blind a UV sensor,
the preferred WBIR-based fire/flame detector is far less affected
by accumulated paint.
[0187] In another preferred embodiment, WBIR is used as the primary
sensor in a multispectral array including NBIR and VB sensors and
digital signal processing in semiconductor clean-room applications
such as, e.g., chemical wet benches. An acid-proof, plastic housing
can be used because WBIR (and NBIR and VB) can see through the
plastic integral window, allowing all types and classes of
hydrocarbon and nonhydrocarbon fires to be detected.
[0188] By way of example, the following are different responsive
actions for different types of fires: For an explosive type fire,
the action taken could be to signal for the release of a high-speed
water jet in several milliseconds in order to suppress the
explosive fire. In a "fireball" fire, such as occurs, e.g., in a
paint-booth spray-gun fire, the action taken is usually to shut off
the paint flow and the electrostatic high-voltage supply to the
spray gun, which will usually self-extinguish the fireball. For a
slow-burning, flickering fire, such as a solvent rag burning in a
paint spray booth or a solvent fire in a polypropylene chemical wet
bench, the action may be to warn the operator with lights and/or
sound annunciators only, as a suppression release would be
premature and could damage costly product. For a large, growing
fire, the action may be to warn the operator with annunciators and
signal for a release of suppression agent. Also, different types of
suppression agent may be released depending upon the type of
fire.
[0189] Another type of multilevel response to a fire is illustrated
by the following example. Suppose a small, solvent rag ignites
spontaneously in an automatic paint spray booth. The preferred,
multilevel-response optical fire/flame detector detects the
slow-burning, small flickering fire and signals a first-stage-level
response (such as "Fire Early Warning" stage). The first-level
response signals strobe lights and audio annunciators to warn the
operator. No suppression agent would be released at the first
level, as the fire might self-extinguish or be extinguished
manually with a portable extinguisher, thereby averting a costly
cleanup and process shutdown. Also, as discussed below, the
preferred detector can record the spectral history of the
first-level fire to aid in diagnosing the cause of the fire,
especially if it should self-extinguish without being
discovered.
[0190] If the fire were to ignite the paint overspray and generate
a fireball fire, the second-stage level would be declared ("Alert"
stage), which could be to shut down the paint flow and
electrostatics to the spray guns. If the fireball did not
self-extinguish, and instead ignited the paint residue on the booth
floor and began growing into a larger, dangerous fire, the
preferred, multilevel optical fire detector would sense the radiant
output (using the WBIR sensors) of the fire, and when the fire
exceeded a certain energy criteria, would signal for release of
suppression agents ("Alarm" stage).
[0191] The following is another example of a multilevel response to
a fire that is possible in a preferred embodiment. Suppose a
solvent chemical leaks inside a semiconductor process wet bench and
is ignited by an electrical spark. The preferred, multilevel
optical fire detector detects the small, flickering fire, and when
it grows to certain criteria (such as, e.g., 3 kW) energy level, a
first-stage response level is advantageously declared. The
first-level response signals strobe lights and audio annunciators
to warn the operator that a hidden fire is occurring inside the wet
bench. Also, the detector preferably digitally records the spectral
history of the first-level fire, as discussed in greater detail
below, to aid in diagnosing the cause of the fire, especially if it
should self-extinguish without being discovered. This can assist
the operator in future fire prevention.
[0192] When a first-level response is declared, the operator has
the option of manually extinguishing the fire and/or completing the
process, or waiting to see if the fire will self-extinguish because
of the limited supply of solvent and/or the high air flow "blowing
out" the fire without a costly suppression release. In this regard,
it has been estimated that about 80% of wet-bench fires
self-extinguish. Allowing the fire a chance to self-extinguish can
therefore save many thousands of dollars by avoiding the release of
fire suppressants and the consequent negative effects on the
materials at the manufacturing site (such as computer chips
fabricated on large wet-benches).
[0193] If the fire continues to burn, consuming more solvent fuel,
and rises in temperature to ignite the polypropylene bench
material, the preferred multilevel detector will signal a
second-stage response when the fire's energy level reaches a preset
level (such as, e.g., a 13 kW energy level threshold), which will
cause activation of lights and/or sound to alert the operator, and
the second-stage response will signal for a suppression release.
The preferred WBIR detector is capable of "seeing through" the
suppression agent and continuing to signal for suppression until
the fire is extinguished. Should the fire "reflash" later, the WEIR
detector can again respond.
[0194] The fire detector may make response level declarations based
on radiant energy output and fire signal characteristics, in
addition to using temporal information such as the relative rate of
growth or periodic fluctuations of the energy level in each of the
observed spectral bands. Once the fire has been detected, spectral
data from the fire (including the time period just before the fire
detection) can be digitally recorded and analyzed at a later
time.
[0195] In accordance with another feature of the present invention,
the microcomputer (otherwise referred to as controller or
microprocessor) 36 and the controller verify proper operation of
each other, and upon detecting any sign of failure, trigger the
fault relay 66.
[0196] In a preferred embodiment, a real-time graphical display of
the digital sensor data detected by the flame detector 32 is
generated and viewed at a "SnapShot.TM." display 68. The digital
sensor data is represented in the form of relative spectral
intensities versus present time. The "Snapshot" display is
preferably viewed with an IBM compatible personal computer (with an
RS-232 interface port). An associated memory (RAM) 68a may store a
particular display.
[0197] A "FirePic.TM." generator 70 facilitates retrieval of sensor
spectral data stored prior to an occurrence of fire. A graphical
display of relative spectral intensities versus time preceding the
fire provides evidence to enable analysis and determine the true
cause of the fire. The "FirePic" data may be stored, for example,
in a non-volatile RAM 72. As indicated in FIG. 18, the "FirePic"
data may indicate a "FirePic" number and data such as the date, the
time, the temperature, the MIR.sub.(DC and T), NIR.sub.(DC and T),
and VIS.sub.(DC and T) readings of sensor signal data, the input
voltage, and the control switch settings. FIGS. 19, 20, and 21
indicate "alert," "fire early warning," and "alarm" events relating
to exemplary fire signatures. FIG. 19a represents an exemplary fire
signature that would trigger the "alert" relay 58. FIG. 20a
represents an exemplary fire signature that would trigger the "fire
early warning" relay 60. FIG. 21a represents an exemplary fire
signature that would trigger an "alarm" relay 62. A printout of a
graphical display (from the "FirePic" generator, or the "SnapShot"
display, or of fire signatures) may be obtained with a printer
76.
[0198] In more detail, the spectral data of the optical fire/flame
detector--i.e., the digitally converted output values from the
visible band (VIS), near band IR (NIR) and wideband IR (WBIR or
MIR) sensors--can be digitally recorded (with or without other
digital processing information such as parameter settings, etc.)
immediately prior to a fire and/or during a fire. The digitized
sensor data is maintained in a circular buffer, so that the most
recent sensor data over a predefined time period (e.g., eight
seconds) is held at any given time. When a detection event occurs,
the controller 39 determines that a recording will be made, at
which time the data stored in the circular buffer is transferred to
a location in a nonvolatile memory.
[0199] The type of nonvolatile memory may comprise, for example, a
CMOS RAM backed with a lithium battery and shutdown logic, or an
SRAM combined with a "shadow" EEPROM (electrically erasable
programmable read only memory). Such nonvolatile RAM memory can
offer years of storage life in the absence of external power. In
addition to storing sensor data in the nonvolatile memory,
detection events and parameters may also be recorded, including
warning status level. The stored data may then be used for
post-fire event analysis. Such data can be used to help determine
the cause of the fire and measures can be taken to ensure that the
fire does not recur in the future.
[0200] While an EEPROM-based system may be used, use of other types
of nonvolatile memory provides several advantages over an EEPROM
based system. While it is possible to continuously write to
volatile RAM during a fire event and, after the fire event is over,
store the data in the EEPROM, this is a relatively time consuming
process (taking several seconds). Should the fire event cause the
electrical power to be interrupted or reset, the stored sensor data
is likely to be lost before transfer to the EEPROM is complete.
Also, if after a fire event, an operator uses a match, butane
lighter, or handheld tester to make sure the detector is working
properly, the real fire data in volatile RAM can be overwritten
with useless test data.
[0201] Thus, in a preferred embodiment, spectral data of the
fire/flame detector is stored in nonvolatile, battery-backed RAM,
which records substantially faster (i.e., in a matter of
milliseconds) than an EEPROM. A large-capacity nonvolatile RAM is
preferably used, so that multiple fire events can be stored, each
with a predefined amount of data (e.g., eight seconds of data).
Moreover, the time and date of each event can be stored, thereby
enabling discrimination between real fire data and test data after
a fire event. Preferably, added to each data package is more signal
processing data including parameters such as, for example, and
indication of which warning, alert or alarm stages were declared in
the multilevel-response optical fire detector.
[0202] The controller 39 initially and routinely after preselected
periods of time, such as every ten minutes, performs diagnostic
evaluation or tests on select system components, such as checking
for continuity through the relay coils, checking to ensure that the
control settings are as desired, and so on. Upon detecting some
cause for concern, the diagnostic test relating to the area of
concern may be performed every thirty seconds or any such
preselected period of time. It should be understood that any or all
the parameters including reaction times, etc., may be programmed to
address particular requirements. A digital serial communication
circuit 69 (see FIGS. 11 and 12) controls serial connections of one
or more of a plurality of flame detectors 32 to the controller 39
to ensure clear communication through the otherwise noisy
environment.
[0203] Referring now to FIG. 12, in accordance with an alternative
embodiment of the present system, the microprocessor 36 located
within the flame detector 32 itself processes all the sensor
digital data to determine the nature of the prevailing condition
and triggers an appropriate one of the multistage (e.g., two- or
three-stage) alarm unit 56. In this embodiment only the "SnapShot"
display 68 and its associated memory 68a is located external to the
detector component 32. The digital communication serial circuit 68
controls serial connections of one or more of a plurality of flame
detectors 32 to any peripheral devices such as the printer 76,
"SnapShot" display 60, etc.
[0204] The system performs extensive diagnostic evaluations, the
logic of which will now be considered with reference to FIG. 22. A
start of the diagnostic evaluation operations is indicated by
reference numeral 80. To ensure that the "alarm" relays are
functioning properly, current is passed through each of the relay
coils, as illustrated by a block 82. Continuity of current through
the relay coils is determined as illustrated by a block 84.
[0205] The diagnostic evaluation proceeds to check the control
settings for the various system components. The step is illustrated
by a block 86. The control settings are compared against stored
data on control settings desired by a user, as indicated by a
decision block 88. If the control settings are as desired, the
diagnostic evaluation operation proceeds to the next step. If the
control settings are not as desired, they are initialized in
accordance with the stored data, as indicated by a block 90. The
next step in the diagnostic evaluation is a test to determine
communication between the detector unit and the controller unit.
This step is illustrated by a query block 92. In the event the
communications are satisfactory, operation proceeds to a step
illustrated by a block 94 that indicates that the system is ready
to commence its detection operations. In the event the
communications are not satisfactory, steps to correct any existing
problems may be taken, as indicated by a block 96. After the
communication problems are corrected or solved, operation returns
to the query block 92 until communications between the detector and
the controller are found to be satisfactory.
[0206] With reference to FIG. 23, a lens test may if desired be
performed by the system to ensure its optimum performance, in those
embodiments where the housing includes a lens (such as lens 100
shown in FIG. 4) as part of the viewing window 132b on the face of
the detector 32. Such a lens test, as noted previously, is not
ordinarily necessary in embodiments of the invention where no UV
sensor is utilized. However, should a lens test be desired, the
start of the lens test is indicated at 104 in FIG. 23. Light from
an infrared LED or any other infrared source (not shown) is
transmitted from within the detector 32 through the lens 100 of the
detector 32. This step is illustrated by a block 106. The intensity
of light reflected back by the detector grill 102 is measured to
determine the transmittance level of the detector lens 100. This
step is illustrated by a block 108. Preset threshold intensity
values (of transmittance) provided by the lens manufacturer are
stored as indicated by a block 110. As illustrated by a decision
block 112, the measured intensity values are compared against the
stored values to determine if there is any degradation in
transmittance characteristics or levels. In the event the measured
intensity values are greater than the stored values, the system
proceeds to the next step indicated by a block 114. At that point,
the overall system operation for detection can commence. In the
event the measured intensity values are less than the stored
values, indicating degraded transmittance characteristics,
operation proceeds to the next step indicated by a block 116.
[0207] The measured intensity values are registered in memory and a
number is assigned to each registered value. A decision block 118
determines if the number of intensity values registered exceeds the
number ten. If the answer is affirmative, the test proceeds to one
of two options. Under option one, in the event there are multiple
detectors, a fault condition is relayed to an external computer, as
illustrated by a block 120. Under option two a fault condition is
declared and an alarm is sounded, as illustrated by a block 122. If
the answer to decision block 118 is negative, as illustrated by a
block 124, the lens test is repeated every thirty seconds.
[0208] In addition to the above tests, an additional diagnostic
test could also consist of moisture detection to verify the seal
integrity of a housing. If a moisture detection test is desired, a
moisture detector is preferably located within the housing and
provides an output for use by the controller 39 in determining
whether the housing seal has been damaged or is leaking.
[0209] With reference to FIGS. 24, 25, and 26, the logic for the
overall system operation for detection is described. Once the
system is installed at a desired facility, prior to operation of
the system the control settings for the various system components
are programmed. Referring now to FIG. 24, a start is indicated at a
block 150. The system of the present invention runs diagnostic
evaluations, such as those described above, at the very outset and
repeatedly during system operation to ensure proper functioning of
all its system components. This step is illustrated by a block 152.
Following the diagnostic evaluations, the parameters for the system
components are adjusted in accordance with ambient conditions
(e.g., ambient temperature adjustments, ambient light adjustments).
A block 154 illustrates this step. Sensor signals from each of the
sensors MIR.sub.(DC and T), NIR.sub.(DC and T), and VIS.sub.(DC and
T) are received from the sensor array 38, as illustrated by a block
156. At this point operations split into two paths, indicated as a
path 1 (for detecting an "alert" condition) and a path 2 (for
detecting "fire early warning" and "alarm" conditions).
[0210] To determine an "alert" condition, transient sensor signals
MIRT, NIRT, and VIST are monitored, as illustrated by a block 158.
The MIRT signal value is compensated by subtracting from it the
VIST signal value, as illustrated by a block 159.
[0211] Referring now to FIG. 25, the compensated MIRT signal value
is compared against predetermined threshold values (one or more as
desired), as indicated by a decision block 160. If the compensated
MIRT signal value exceeds the predetermined threshold value, an
"alert" timer is set as indicated by a block 162. In the next step,
illustrated by a decision block 163, the system determines if a
predetermined time limit has passed. Once the predetermined time
limit is passed, an "alert" condition is declared, as illustrated
by a block 164. Following that step, another predetermined period
of time is enforced or allowed to pass, during which no action is
taken, in order to allow the fire to self-extinguish. This step is
illustrated by a block 165. After that point, operation loops back
to point A, whereby the system again receives sensor signals. Of
course, until the predetermined time limit actually expires,
operation loops back to the point before decision block 163.
[0212] Referring again to FIG. 24, to determine a "fire early
warning" condition or an "alarm" condition, sensor signals
MIR.sub.DC, NIR.sub.DC, and VIS.sub.DC are passed through long-term
and short-term averaging filters as illustrated by a block 166.
These signals are monitored to obtain values as illustrated by a
block 168. To eliminate false alarm rejection, in the event the
short-term filter output values are less than the long-term filter
output values, as illustrated by a decision block 170, the
long-term filter output values are jam set (forced) to adopt the
short-term filter output values, as illustrated by a block 172.
[0213] Referring now to FIG. 26, the sensor signal MIR.sub.DC
reading is compensated by the sensor signals NIR.sub.DC and
visible.sub.DC readings, as illustrated by a block 174. This step
is taken to distinguish a real fire from other sources more likely
to emit substantial visible light. Once the MIR.sub.DC signal is
compensated to eliminate declaring a false alarm, the MIR.sub.DC
signal value is compared against programmed parameters, as
indicated by a decision block 176. In the event the MIR.sub.DC
signal value is determined to be less than the programmed
parameters, operation loops back to point A, beginning the cycle of
receiving the sensor signals from the sensor array 38, and so
on.
[0214] In the event the MIR.sub.DC signal value is greater than the
programmed parameters, a decision block 178 determines if the
variations in the MIR.sub.DC signal values are significant. If it
is determined that the variations in the MIR.sub.DC signal values
are not significant, as illustrated by a block 180, the system
ensures that the "fire early warning" and "alarm" timers are set to
zero. Following that, operation once again loops back to point
A.
[0215] If it is determined that the variations in MIR.sub.DC signal
values are significant, the timers for the "fire early warning" and
the "alarm" are set to begin counting. This step is illustrated by
a block 182. If the "fire early warning" timer indicates that a
predetermined time limit has passed, as indicated by a decision
block 184, a "fire early warning" condition is declared, as
illustrated by a block 186. Once the "fire early warning" condition
is declared, the appropriate relay is activated as illustrated by a
block 188. At that point, operation may ultimately loop back to
point A. Of course, until the predetermined time limit has expired,
operation loops back to the point before decision block 184.
[0216] Once a "fire early warning" is declared, as illustrated by a
decision block 190, the system determines if the "alarm" timer
indicates that a predetermined time limit has passed. If not,
operation loops back to the point before decision block 190, to
ensure that the appropriate time limit has passed. If the "alarm"
timer indicates that a predetermined time limit has passed, as
indicated by a decision block 190, a "alarm" condition is declared,
as illustrated by a block 192. Once the "alarm" condition is
declared, the appropriate relay is activated, as illustrated by a
block 194. At that point, operation ultimately may loop back to
point A.
[0217] Referring now to FIG. 27, starting at point C, operation of
the system in accordance with its two-stage alarm embodiment
compares the MIR.sub.DC signal value against a first predetermined
threshold value, as indicated by decision block 198. The first
predetermined threshold value corresponds to a "small" fire of a
size considered to be a hazard. If the MIR.sub.DC signal value is
less than the first predetermined threshold value, operation loops
back to point A, where the system continues to read signal values.
If the MIR.sub.DC signal value exceeds the first predetermined
threshold value (stored in memory), the system declares a
"pre-alarm" (or "alert") condition as indicated by a block 200.
Subsequently or immediately, the system activates the appropriate
"alert" relay, as indicated by a block 201, enabling personnel at
the monitored facility to investigate the fire, and ceases all
ambient considerations. The system continues to monitor for a rise
in the fire, as indicated by a block 202. This may be done by
reading optical radiation amounts emitted by the fire. It should be
recognized that other ways of monitoring a rise in fire known to
those skilled in the art may alternatively be used. As indicated by
decision block 204, the system compares the optical radiation
amounts emitted by the fire against a second predetermined
threshold amount (stored in memory). If the optical radiation
amount emitted by the fire exceeds the second threshold amount, the
system declares an "alarm" condition as indicated by a block 206,
and activates the appropriate relay and suppression agents, as
indicated by a block 208.
[0218] It should be recognized that the system could compare
readings against more than two energy thresholds. The energy
thresholds can be empirically determined by performing fire tests
of the sizes and at distance desired by the monitored facility.
Also, the specific thresholds used may vary depending on the choice
of sensor, amplification of signals, etc. For example, in a clean
room environment with chemicals, an alcohol fire having a four-inch
diameter viewed at a distance of eight feet has an energy output of
3 kilowatts (kW) and may be predetermined as the first threshold.
Similarly, a fire having an eight-inch diameter viewed from a
distance of eight feet has an energy output of 13 kW and may be
predetermined as the second threshold.
[0219] While some embodiments (such as the fire detection system of
FIG. 11) have been described with a controller external to the
flame detector, it will be appreciated that the functionality of
the controller can be located within the flame detector. Having an
external controller can be efficient where multiple detectors are
deployed in the same locality, so that the multiple detectors can
share the same controller and therefore be implemented with reduced
cost. In some situations it may be preferable for each fire
detector to have its own controller, and to have all of the
controller electronics along with the sensor electronics enclosed
within a self-contained unit.
[0220] Certain alternative embodiments involve use of different
types of sensors for the primary wide band IR (WBIR) sensor. In a
preferred embodiment, the WBIR sensor is manufactured from lead
sulfide (PbS), which has a high sensitivity to wide band IR over
the necessary operational temperature ranges, in addition to having
relatively low cost, proven reliability, and ready availability.
Other sensors can also be used to sense wide band IR in certain
fire detection applications.
[0221] There are two main classes of practical sensors that can be
used for wide band IR fire detection. The first class includes
photon detectors, which have time constants typically in the
microsecond range, and the second class includes thermal detectors,
which have time constants typically in the millisecond range.
[0222] Photon detectors may include any of a number of quantum
photodetectors such as photoconductive (or photoresistive)
detectors or photovoltaic detectors. A photoconductive (or
photoresistive) sensor is one in which a change in the number of
incident photons causes a fluctuation in the number of free charge
carriers in the semiconductor material. The electrical conductivity
of the responsive element is inversely proportional the number of
photons. This change is conductivity is monitored and amplified
electrically. A photovoltaic sensor is one in which a change in the
number of photons incident on a p-n junction causes fluctuations in
the voltage generated by the junction. This change in voltage is
monitored and amplified electrically.
[0223] Photon detectors include sensors made from material(s) in
the lead salt family such as lead sulfide (PbS), lead telluride
(PbTe), lead selenide (PbSe), lead tin telluride (PbSnTe), the
doped germanium family (Ge:AuSb, Ge:Cu, Ge:Hg, Ge:Cd, Ge:Zn,
Ge-Si:Zn, Ge-Si:Au, etc.), indium antimonide (InSb), indium
arsenide (InAs), telluride (Te), mercury cadium telluride (HgCdTe),
and other such materials.
[0224] Thermal detectors and sensors that can be used for wide band
IR sensing include both pyroelectric sensor types and thermopile
sensor types. Pyroelectric sensor types include such sensors as
deuterated triglycine sulfate (DTGS or TGS), lithium tantalate
(LiTAO.sub.3), barium titanate (BaTiO.sub.3), and the like.
Pyroelectric sensors are thermal sensors and use a crystal which
develops a charge on opposite crystal faces (similar to a
capacitor) when incident radiation causes the crystal temperature
to change. Thermopile sensor types are those in which thermovoltaic
and generate a voltage when thermal radiation strikes their
surface. Usually thermopile sensors are manufactured as a small
matrix array. The way they operate is by sensing an output voltage
across a junction of dissimilar metals. When the temperature of the
junction fluctuates because of changes in the level of incident
radiation, the output voltage generated by the junction will
fluctuate. This voltage is monitored and amplified
electrically.
[0225] For any of the above wide band IR sensors, to set the
wavelength cutoffs for the desired wide band IR spectral range,
appropriate interference type or absorption type filters, or a
combination thereof, may be used.
[0226] Further information of interest may be found in U.S. Pat.
application Ser. No. 08/866,024 (attorney docket no. 226/036)
entitled "Fire Detector With Multi-Level Response," U.S. Pat.
application Ser. No. 08/865,695 (attorney docket no. 226/037)
entitled "Fire Detector With Event Recordation," U.S. Pat.
application Ser. No. 08/866,023 (attorney docket no. 226/038)
entitled "Fire Detector and Housing," and U.S. Pat. application
Ser. No. 08/866,028 (attorney docket no. 226/039) entitled "Fire
Detector With Replaceable Module," each of which applications is
filed concurrently herewith, and each of which is incorporated by
reference herein as if set forth fully herein.
[0227] While the present invention has been described in
conjunction with specific embodiments thereof, many alternatives,
modifications, and variations will be apparent to those skilled in
the art in view of the foregoing description. Accordingly, the
invention is intended to embrace all such alternatives,
modifications, and variations that fall within the spirit and scope
of any appended claims.
* * * * *