U.S. patent number RE28,915 [Application Number 05/378,997] was granted by the patent office on 1976-07-20 for detection of products of combustion.
This patent grant is currently assigned to BRK Shareholders' Committee. Invention is credited to Clarence Glenn Henderson, Wilbur L. Ogden.
United States Patent |
RE28,915 |
Ogden , et al. |
July 20, 1976 |
Detection of products of combustion
Abstract
A self-contained, self-powered, early warning fire detector and
alarm of small size and attractive appearance especially adapted
for use in residences; the detector including readily accessible
sensitivity control and operability test means, and having a
standby power source which additionally serves to monitor the
primary power source and inform occupants of malfunction of the
primary power source.
Inventors: |
Ogden; Wilbur L. (Aurora,
IL), Henderson; Clarence Glenn (Ottawa, IL) |
Assignee: |
BRK Shareholders' Committee
(N/A)
|
Family
ID: |
27008429 |
Appl.
No.: |
05/378,997 |
Filed: |
July 13, 1973 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
709415 |
Feb 29, 1968 |
03594751 |
Jul 20, 1971 |
|
|
Current U.S.
Class: |
340/507; 340/514;
340/634 |
Current CPC
Class: |
G08B
17/06 (20130101); G08B 17/11 (20130101); G08B
17/117 (20130101); G08B 29/12 (20130101); G08B
29/181 (20130101); G08B 29/183 (20130101); G08B
29/24 (20130101) |
Current International
Class: |
G08B
17/117 (20060101); G08B 29/00 (20060101); G08B
29/18 (20060101); G08B 17/11 (20060101); G08B
17/10 (20060101); G08B 29/12 (20060101); G08B
17/06 (20060101); G08B 017/10 () |
Field of
Search: |
;340/228,237S,213R,333,249 ;307/64-68,23,28,18 ;250/381
;315/86,87 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Myer; Daniel
Attorney, Agent or Firm: Mason, Kolehmainen, Rathburn &
Wyss
Claims
We claim:
1. In a warning device having a primary power source, an alarm unit
connected to said source and a load unit connected to said source;
a supervisory circuit comprising a secondary power source, a
capacitor in series with said secondary source, means coupling said
capacitor to one side and said secondary source to the other side
of said load unit to sense the voltage drop thereacross, trigger
means responsive upon charging of said capacitor for connecting
said alarm unit with said secondary source, said capacitor being
charged by said second source when the voltage drop across said
load unit falls below a predetermined value and when charged
triggering said trigger means, said trigger means during discharge
of said capacitor causing said secondary source to energize said
alarm unit .[.whereby the alarm unit,.]. whereby the alarm unit
emits periodic alarms of short duration when the output of the
primary source falls below a predetermined value.
2. In a device as set forth in claim 1, said primary source
comprising a battery and said secondary source comprising a standby
battery for the primary source battery.
3. In a warning device having a power source, means for detecting a
predetermined condition and thereupon emitting a signal, an
amplifier having a power input connected to said source and a
signal input connected to said detecting means for amplifying the
signal, a trigger device connected to the amplifier to be triggered
upon reception of the predetermined amplified signal, and an alarm
unit connected to said trigger device to be energized when the
latter is triggered, the improvement comprising, in combination
with rate of change detecting means, a plurality of capacitor banks
adapted to be connected selectively to the amplifier power input,
and switch means for selectively adding said capacitor banks to the
amplifier power input to vary the time constants and thus the
detecting sensitivity of the device.
4. In a device as set forth in claim 3, said switch means
comprising a plural position switch including a plurality of
positions for selectively adding capacitor banks to the amplifier
input and a further position for bypassing said trigger device and
directly connecting said alarm unit to the power source, said
switch means in its said further position in the absence of an
alarm serving to test the operability of the alarm, and following
an alarm serving to trip said trigger device and thereby reset the
same.
5. In a device as set forth in claim 4, wherein the device includes
a load unit connected to the primary source; a supervisory circuit
comprising a secondary power source, a capacitor in series with
said secondary source, means coupling said capacitor to one side
and said secondary source to the other side of said load unit to
sense the voltage drop thereacross, second trigger means responsive
upon charging of said capacitor for connecting said alarm unit in
series with said secondary source, said capacitor being charged by
said secondary source when the voltage drop across said load unit
falls below a predetermined value and when charged triggering said
second trigger means, said second trigger means during discharge of
said capacitor causing said secondary source to energize said alarm
unit, whereby the alarm unit emits periodic alarms of short
duration when the output of the primary source falls below a
predetermined value. .Iadd. 6. A warning device comprising a power
source, said power source comprising a battery,
means energized by said power source for providing first and second
audible warnings, said first audible warning being sensually
discernably different than said second audible warning, said
providing means having an operative state in which either said
first warning or said second warning is provided and an inactive
state in which neither said first warning nor said second warning
is provided,
means for detecting the presence of combustion,
first means responsive to said detecting means upon the detection
of the presence of combustion for placing said providing means in
its operative state and for causing said providing means to provide
said first warning,
means for establishing a first voltage representative of the output
voltage of said battery,
means for monitoring said first voltage, said monitoring means
including means for establishing a reference voltage and means for
comparing said first voltage to said reference voltage, said
establishing means comprising a diode, and
second means responsive to said comparing means for placing said
providing means in its operative state and for causing said
providing means to provide said second warning when said first
voltage differs from said
reference voltage by a predetermined amount. .Iaddend. .Iadd.7. A
warning device as defined in claim 6 further comprising means for
interrupting said first warning..Iaddend..Iadd.8. A warning device
as defined in claim 7 wherein said interrupting means comprises
manually manipulative means for resetting said first means to
interrupt the placing of said providing means in its operative
state by said first means..Iaddend. .Iadd. 9. A warning device as
defined in claim 6 wherein said battery comprises a 10.7 volt
battery. .Iaddend..Iadd. 10. A warning device as defined in claim 6
wherein said first warning comprises a substantially constant
signal. .Iaddend. .Iadd. 11. A warning device comprising a power
source, said power source comprising a battery,
means energized by said power source for providing first and second
audible warnings, said first audible warning comprising a
substantially constant signal and said second audible warning
comprising a periodic signal, said providing means having an
operative state in which either said first warning or said second
warning is provided and an inactive state in which neither said
first warning nor said second warning is provided,
means for detecting the presence of combustion,
first means responsive to said detecting means upon the detection
of the presence of combustion for placing said providing means in
its operative state and for causing said providing means to provide
said first warning,
means for monitoring the output voltage of said battery, said
monitoring means including means for establishing a reference
voltage and means for comparing at least a portion of said output
voltage to said reference voltage, and
second means responsive to said comparing means for placing said
providing means in its operative state and for causing said
providing means to provide said second warning when said portion of
said output voltage differs from said reference voltage by a
predetermined amount. .Iaddend. .Iadd. 12. A warning device as
defined in claim 11 wherein said periodic signal comprises a signal
that is alternately audible for a first time period and
substantially inaudible for a second time period, said first time
period being substantially less than said second time period.
.Iaddend..Iadd. 13. A warning device as defined in claim 12 wherein
said providing means comprises a single audible horn for providing
both said first and second audible warnings. .Iaddend. .Iadd. 14. A
warning device comprising a power source, said power source
comprising a battery,
means energized by said power source for providing first and second
audible warnings, said providing means having an operative state in
which either said first warning or said second warning is provided
and an inactive state in which neither said first warning nor said
second warning is provided,
means for detecting the presence of combustion,
first means responsive to said detecting means upon the detection
of the presence of combustion for placing said providing means in
its operative state and for causing said providing means to provide
said first warning,
means for monitoring the output voltage of said battery, said
monitoring means including means for establishing a reference
voltage and means for comparing at least a portion of said output
voltage to said reference voltage, said establishing means
comprising a zener diode, and
second means responsive to said comparing means for placing said
providing means in its operative state and for causing said
providing means to provide said second warning when said portion of
said output voltage differs from said reference voltage by a
predetermined amount. .Iaddend.
.Iadd. 15. A warning device as defined in claim 14 wherein said
comparing means comprises a unijunction transistor for comparing
said portion of said output voltage to said reference voltage.
.Iaddend..Iadd. 16. A warning device as defined in claim 15 wherein
said unijunction transistor includes a first terminal electrically
connected through first series resistive means to the anode of said
zener diode, the cathode of said zener diode being directly
electrically connected to a first output terminal of said power
source. .Iaddend..Iadd. 17. A warning device as defined in claim 16
wherein said unijunction transistor includes a second terminal
electrically connected through a path including second series
resistive means to a second output terminal of said power source.
.Iaddend. .Iadd. 18. A warning device comprising
means for detecting the presence of combustion,
means for emitting an audible signal, said emitting means having an
active state in which said audible signal is emitted and an
inactive state in which said audible signal is not emitted,
first means responsive to said detecting means upon the detection
of the presence of combustion for placing said emitting means in
said active state and for maintaining said emitting means in said
active state and
second means for placing said emitting means in said active state
and for maintaining said emitting means in said active state and
for simultaneously resetting said first means to interrupt the
placing and the maintaining of said emitting means in said active
state by said first means. .Iaddend..Iadd. 19. A warning device as
defined in claim 18 wherein said second means comprises a manually
manipulative means. .Iaddend..Iadd. 20. A warning device as defined
in claim 18 further comprising a power source for energizing said
emitting means, said power source comprising a battery, and means
for monitoring the output voltage of said battery and third means
responsive to said monitoring means for placing said emitting means
in said active state when said output voltage equals a nonzero,
reference value. .Iaddend. .Iadd. 21. A warning device as defined
in claim 20 wherein said monitoring means comprises means for
establishing a reference voltage and means for comparing at least a
portion of said output voltage to said reference voltage, said
nonzero reference value being a voltage having a predetermined
voltage difference between said portion of said output voltage and
said reference voltage. .Iaddend..Iadd. 22. A warning device as
defined in claim 21 wherein said power source comprises a 10.7 volt
battery. .Iaddend..Iadd. 23. A warning device as defined in claim
21 wherein said third means comprises means for conditioning said
emitting means to emit a periodic signal. .Iaddend..Iadd. 24. A
warning device as defined in claim 23 wherein said periodic signal
comprises a signal that is alternately audible for a first time
period and substantially inaudible for a second time period, said
first time period being substantially less than said second time
period. .Iaddend..Iadd. 25. A warning device as defined in claim 21
wherein said establishing means comprises a zener diode.
.Iaddend..Iadd. 26. A warning device as defined in claim 25 wherein
said comparing means comprises a unijunction transistor for
comparing at least said portion of said output voltage to said
reference voltage. .Iaddend. .Iadd. 27. A warning device as defined
in claim 26 wherein said unijunction transistor includes a first
terminal electrically connected through first series resistive
means to the anode of said zener diode, the cathode of said zener
diode being directly electrically connected to a first output
terminal of said power source. .Iaddend..Iadd. 28. A warning device
as defined in claim 27 wherein said unijunction transistor includes
a second terminal electrically connected through a path including
second series resistive means to a second output terminal of said
power source. .Iaddend..Iadd. 29. A warning device as defined in
claim 28 wherein said battery includes two output terminals and
wherein said first output terminal comprises the more electrically
positive one of said two output terminals of said battery and
wherein said second output terminal comprises the more electrically
negative one of said two output terminals of said battery.
.Iaddend..Iadd. 30. A warning device comprising
a power source, said power source comprising a battery,
means for emitting an audible signal, said emitting means having an
active state in which said audible signal is emitted and an
inactive state in which said audible signal is not emitted,
means for detecting the presence of combustion,
first means responsive to said detecting means for placing said
emitting means in said active state and for maintaining said
emitting means in said active state,
means for monitoring the output voltage of said battery and
second means responsive to said monitoring means for placing said
emitting means in said active state when said output voltage equals
a nonzero, reference value, said second means including means for
conditioning said
emitting means to emit a periodic signal. .Iaddend..Iadd. 31. A
warning device as defined in claim 30 further comprising means for
resetting said first means to interrupt the placing and the
maintaining of said emitting means in said active state by said
first means. .Iaddend..Iadd. 32. A warning device as defined in
claim 31 wherein said resetting means comprises manually
manipulative means. .Iaddend..Iadd. 33. A warning device as defined
in claim 30 wherein said monitoring means comprises means for
establishing a reference voltage. .Iaddend..Iadd. 34. A warning
device as defined in claim 33 wherein said monitoring means further
comprises means for comparing said output voltage to said reference
voltage. .Iaddend. .Iadd. 35. A warning device as defined in claim
34 wherein said battery comprises a 10.7 volt battery.
.Iaddend..Iadd. 36. A warning device as defined in claim 34 wherein
said periodic signal comprises a signal that is alternately audible
for a first time period and substantially inaudible for a second
time period, said first time period being substantially less than
said second time period. .Iaddend..Iadd. 37. A warning device as
defined in claim 34 wherein said establishing means comprises a
zener diode. .Iaddend..Iadd. 38. A warning device as defined in
claim 37 wherein said comparing means comprises a unijunction
transistor for comparing said output voltage to said reference
voltage. .Iaddend..Iadd. 39. A warning device as defined in claim
37 wherein said unijunction transistor includes a first terminal
electrically connected through series resistive means to the anode
of said zener diode, the cathode of said zener diode being directly
electrically connected to a first output terminal of said power
source. .Iaddend. .Iadd. 40. A warning device as defined in claim
39 wherein said unijunction transistor includes a second terminal
electrically connected through a path including second series
resistive means to a second output terminal of said power source.
.Iaddend.
Description
BACKGROUND OF INVENTION
This invention is closely related to and constitutes an improvement
upon U.S. Pat. No. 3,245,067, which describes and claims an early
warning fire detector characterized by a pair of impedance means or
resistance grids sensitive to the increase in electrical
conductivity of the air upon initiation of a fire, the grids being
connected in a bridge circuit and comprising a first grid freely
exposed to the atmosphere and a second grid accommodating only slow
or delayed access thereto of the atmosphere, whereby to provide a
rate-of-change device that senses the fast change in the electrical
conductivity of the atmosphere that occurs even in the incipient
stages of fire, as well as in the smoke, flame and heat stages of
fire. The second grid compensates the first or detector grid
against slowly occurring changes, such as atmospheric changes and
those due to one or more people smoking in the room, but does not
respond with sufficient rapidity to the fast change caused by a
fire, with the result that the bridge becomes unbalanced and a
signal is transmitted via an suitable to suiable alarm means.
The grids each comprise a substrate of known surface resistivity
and an electrode configuration in the form of two opposing and
interfitting comblike electrodes on the substrate, one comprising
the positive plate and the other the negative. Power is supplied to
the positive plate of one grid and the negative of the other; the
negative of the one grid and the positive of the other being
connected and the junction constituting the output of a bridge
which is coupled to the amplifier and the alarm or other suitable
control devices.
SUMMARY OF IMPROVEMENTS
This invention utilizes the same basic structure and mode of
operation as that of said patent, and attains the same results but
in a more efficient, economical and facile manner.
In the first instance, this invention provides an entirely
self-contained, self-powered and self-alarming device requiring no
external wiring, no control panels, no alarm panels, and no human
supervision.
Secondly, it is housed in an extremely compact and attractive
package especially designed for use in homes, apartments and small
proprietorships which heretofore have not had available to them
early warning fire detection and alarm, except at exorbitant
cost.
Third, the unit is constructed in such manner that the same can
readily be installed and serviced by any individual homeowner, the
unit being installed by screwing two screws into the ceiling and
being serviced essentially solely by timely replacement of
batteries.
Fourth, the physical construction of the device and its housing are
such as to afford extremely prompt and efficient response to the
presence of products of combustion.
Fifth, the unit embodies a primary battery and a standby or
replacement battery, and circuit means causing the standby battery
to continually monitor the strength or the primary battery and to
give a supervisory warning to the homeowner when the strength of
the primary battery falls below a predetermined but safe value,
whereby the homeowner is warned to replace the primary battery with
the standby battery and to secure in reasonable time a fresh
replacement for the standby battery.
Sixth, the circuitry of the detector includes means for varying the
sensitivity of the device, thereby to adjust the device from a
highly sensitive setting when the family is home alone to a
relatively reduced sensitivity preventing false alarming when the
family is entertaining and the house is filled with guests who may
be smoking.
The circuitry also includes means facilitating resetting of the
detector following an alarm, and for testing the reliability of the
detector and its primary battery whenever desired.
Preferably, the sensitivity control and the test-reset circuits are
connected to a single multiple position switch readily accessible
to the homeowner to facilitate performance by him of the described
functions.
Other improvements reside in various electrical and structural
details which will become obvious in the following detailed
description.
THE DRAWINGS
FIG. 1 is a perspective view of our detector as it would appear
mounted on the ceiling of a room;
FIG. 2 is an enlarged bottom plan view of the detector, with the
cover thereof broken away to reveal the physical components and
their assembly;
FIG. 3 is a vertical section taken substantially on line 3--3 of
FIG. 2;
FIG. 4 is a top plan view of the detector grid assembly, the view
being taken substantially on line 4--4 of FIG. 3;
FIG. 5 is an enlarged cross-sectional view of the detector grids
and grid mounting provided by this invention, the view being taken
substantially on line 5--5 of FIG. 2; and
FIG. 6 is a schematic diagram of the electrical circuit of the
detector.
DETAILED DESCRIPTION
Referring first to the electrical circuitry, FIG. 6, the device is
comprised of sensing means, an amplifier, an alarm circuit, a
primary power supply, a supervisory circuit including a secondary
power supply, a sensitivity adjustment, and a reset-test
circuit.
Sensor
The sensing means of the detector comprises an impedance bridge
made up of two impedance or resistance grids R1 and R2 mounted in
such manner that one grid R1 (called the detector) is open to the
atmosphere, and the other grid R2 (called the compensator) is
relatively closed to the atmosphere--resulting in a rate-of-change
device that senses fast changes caused by combustion, but ignores
relatively slow changes such as atmospheric variations or changes
due to an individual smoking in the room.
When the detector senses the occurrence of combustion, in the form
of invisible and/or visible combustion gases, its resistance is
lowered by the combustion products impinging on the surface of grid
R1. This unbalances the bridge, causing a signal to be passed
through coupling capacitor C1 to the amplifier A.
Amplifier
The amplifier A is made up of a single stage metal oxide silicon
enhancement mode field effect transistor or MOSFET. This transistor
matches the high impedance of the sensor bridge to the low
impedance of the trigger circuit.
The MOSFET is adjustably biased by potentiometer R4 through
resistor R3, until the drain current through resistor R6 reaches a
desired sensitivity setting. When the detector resistance decreases
due to combustion products, current through R6 increases until the
voltage drop developed across resistor R5 is sufficient to turn on
a trigger device T, which is preferably a silicon controlled
rectifier. Resistor R7 in the MOSFET source normally limits the
bias current to a value less than that required to trigger the
SCR.
Alarm Circuit
When the SCR triggers into the "on" condition, current flows
through the horn H from battery B1, thereby sounding an alarm.
Power Supply
Power is supplied by a 10.7 volt mercury battery B1, which provides
the small bias current to operate the sensors and the amplifier,
and also provides the current necessary to drive the horn in the
event of an alarm.
Supervisory Circuit
When the current of battery B1 begins to fall off at the end of
battery life, the voltage drop across R7 is decreased. When this
voltage drop reaches a predetermined level, at which the bucking
voltage of battery B1 is overcome by battery B2, capacitor C7
charges through resistor R8 to the point where a PUT or
programmable unijunction transistor Q3 switches on, in turn
triggering an SCR Q4. When Q4 is triggered on, it connects the
battery B2 to the horn H and thereby sounds an alarm. SCR Q4 can
only remain switched on as long as gate current is supplied from
the PUT Q3. Q3 remains on until capacitor C7 discharges through the
PUT anode, whereupon Q3 shuts off, causing Q4 to shut off, and the
horn to stop sounding. At this point, C7 again begins to charge
through resistor R8 from battery B2, and after an elapsed time of
approximately 5 minutes, the cycle is repeated. The duration of
each horn blast is 1 to 2 seconds. Because very little current is
drawn from the supervisory battery B2 (except during the short horn
blasts), this circuit will continue to sound the described trouble
alarm for approximately 600 hours.
During normal operation, there is no drain on the supervisory
battery, therefore, this battery will last its shelf life, which at
present time is 2 years. The small current drawn from the primary
supply during normal operations results in a battery life of at
least one year--providing the unit is not in alarm condition for
any great period of time during this year. At the end of one year,
or sooner if the primary battery has been alarmed often, the
primary battery B1 should be removed and the supervisory battery B2
put into the primary battery position. A new battery should be
installed as promptly as reasonably possible into the supervisory
position, or supervision will be lost.
In any event, the supervisory circuit R8, C7, Q3, Q4 and B2
(assuming a battery is in position in the supervisory circuit) will
always inform the homeowner or proprietor of the fact that the
primary battery is due to be replaced whenever its output falls
below that required to produce the predetermined voltage drop
across R7. Under normal conditions, one battery is replaced per
year and practically no other maintenance is required of the
homeowner.
Sensitivity Control
The potentiometer R4 provides a basic sensitivity adjustment for
the detector from the standpoint of factory and/or
factory-authorized adjustment, but it is generally not advisable to
recommend setting of the potentiometer by an unskilled individual.
However, it is desirable to provide the homeowner with some degree
of control over the sensitivity of the detector due to the wide
divergence of atmospheric conditions existing in the home when
occupied solely by members of the family and the conditions that
exist when a number of guests are present in the home. A setting of
optimum sensitivity for the family could result in vexatious
false-alarming of the detector when a number of guests are
present.
To accommodate sensitivity adjustment, the circuit is provided with
two banks of capacitors, i.e., a first bank comprised of capacitors
C3 and C4 and a second bank comprised of capacitors C5 and C6, both
having center taps adapted to be coupled to the source of the
amplifier A, and switch means SW including contacts 1 and 2
accommodating connection of the first bank only to the amplifier to
afford a relatively low sensitivity and connection of both banks to
the amplifier to afford a relatively high sensitivity (the switch
position shown in FIG. 6). The switch is made conveniently
accessible to the homeowner to facilitate selection of high
sensitivity or low sensitivity as desired.
Test-Reset Circuit
The trigger device T and its connections in the circuit are such
that once triggered it will remain triggered until reset. To
accomplish resetting, switch SW is provided with contacts 5 and 6
which when closed will cause the trigger device to be bypassed, the
load thereon relieved and the device thereby to be reset to
nonconducting or "off" condition, whereupon the alarm is turned off
until the rate-of-change of ambient conditions is again such (or
remains such) that the device is again triggered.
By connecting the bypass through switch contacts 5 and 6 in such
manner that the primary power source B1 becomes directly closed
upon the horn H, the switch will simultaneously provide the
homeowner a convenient means for manually checking the operability
of the device and the condition of the battery, that is, he may
manually sound the alarm and check the detector without having to
trigger the device by starting a fire, burning a match or blowing
smoke on the unit, although all of these others are further
alternatives for testing the operability of the detector.
Structure
The components of the detector are transistorized and miniaturized
to the extends presently feasible, physically and economically, and
all are arranged compactly on a circuit board 20 as shown in FIGS.
2 and 3. The upper surface of the board comprises a printed circuit
providing the electrical connections between the components, and
the components themselves are mounted on the lower surface of the
board; the horn H, the potentiometer R4, the switch SW and the
batteries B1 and B2 being identified for sake of reference.
The grids R1 and R2 of FIG. 6 are formed on glass substrates 22 and
24, respectively, each being mounted in a ceramic holder 26, 28 of
generally triangular form. Each holder has three holes
therethrough, adjacent its corners, two of which are provided with
conductive grommets 30 and washers 32 which serve to secure the
substrates in the holders and to effect electrical connection with
the "comblike" grid pattern on the substrate.
The substrates are preferably thin square pieces of high purity
modified boro-silicate glass and the grid patterns are preferably
tin oxide applied to the substrates in accord with known tin oxide
technology, the two washers 32 of each assembly physically and
electrically contacting the respective portions of the grid
pattern.
Depending from the circuit board 20 are three shouldered pins 34a,
34b and 34c, one of which (the pin 34c at the right in FIG. 5)
comprises the center junction of the impedance bridge, and the
other two of which comprise the power leads to the bridge. Pin 34b
includes a second shoulder or boss 36 whereby the upper grid can be
mounted on the pins solely with its free or ungrommeted hole
aligned with the boss 36, whereby the two grommeted holes are
properly connected with the respective electric circuit elements,
the two grommets firmly engaging the respective pins 34a and 34c to
establish the necessary electrical connection. The bottom grid may
then readily be slipped on the pins with one grommet on the center
junction pin 34c and the other grommet on the pin 34b having the
second shoulder 36.
The lower substrate 22 carries the detector R1 and the same is
mounted with the grid bearing surface thereof facing downwardly and
freely exposed. The upper substrate 24 carries the compensator grid
R2 and it is mounted with the grid bearing surface thereof facing
upwardly and having access to the atmosphere solely through a hole
38 in the circuit board 20, whereby the grid R2 is shielded and
effectively responsive only to slowly occurring ambient change and
not to rapid ambient change. The shoulders on the pin 34 serve to
space the grid R2 from the circuit board and in order to form an
enclosed compensating chamber about the grid (except for the
opening 38) a sheet or tube 40 of flexible tape is slipped over the
peripheral surfaces of the holders 26, 28 and into engagement with
the lower surface of the circuit board.
The tape 40 and the two grids may conveniently be slipped off to
facilitate cleaning of the grids, which should be done periodically
to insure the proper balance of the bridge.
The switch SW may take a variety of forms, and could in fact
constitute several switches However, we have found it convenient to
utilize a double pole, triple throw switch having a central
position (which we employ for high sensitivity), a first settable
end position (which we use for low sensitivity) and an opposite end
position having automatic spring return (which we utilize for the
test-reset position--the switch thereby automatically returning to
the high sensitivity position after reset or test). This switch is
preferably equipped with a relatively long handle 42 for a purpose
to be described.
Housing
The components of the detector are all assembled on the circuit
board in a single layer (except for the stacking of the two grids)
and the same are selected of the minimum practical and feasible
height whereby to provide a working assembly of extremely low
profile.
The entire assembly is then mounted in a shallow inverted
rectangular or square sheet metal pan 44 having short depending
sidewalls 46. The mounting is preferably effected by passing three
or four sheet metal screws 48 through the circuit board and some
suitable spacers 50 and threading the same into the pan, whereby to
mount the board in the pan but in spaced relation to the surfaces
thereof. For the sake of rigidity of mounting, it is also
preferable to bolt or otherwise secure the switch SW to one
sidewall 46 of the pan.
The pan in turn is adapted to be mounted on the ceiling of a room,
or the top wall of an enclosure or duct, by a pair of screws
extending through appropriate holes 52 in the top wall of the pan.
Preferably, the holes are of keyhole shape to facilitate detachable
mounting of the pan in the ceiling.
Depending downwardly from opposite sidewalls 46 of the pan, to a
level below all of the detector components, are a pair of brackets
54 which are adapted for the detachable reception of a pair of pins
56 extending upwardly from the inner surface of a cover 58 for the
detector. The cover is an integral member formed of metal or a
suitable plastic and having an attractive configuration and
exterior surface (i.e., lower and outer side surfaces). The cover
is essentially of pan shape and larger than the pan 44 so that its
upstanding sidewalls are spaced outwardly from the depending
sidewalls 46 of the pan. The sidewalls of the cover extend upwardly
to a level somewhat below the level of the upper surface of the pan
so that they are spaced from the ceiling when the device is
installed, and preferably terminate slightly above the lower edge
of the sidewalls 46 so as to conceal the components of the
detector. Centrally of the lower wall thereof, the cover 58 is
provided with a plurality of small, closely spaced perforations 60
aligned generally with the grid R1 of the lower substrate 22.
Products of combustion inherently rise to the ceiling and then
spread horizontally along the ceiling. According to the present
invention, the spacing of the sidewalls of the cover from the
ceiling and the pan and the perforation 60 together provide a path
for highly effective and efficient circulation through the housing
and over the detector grid of the products of combustion
irrespective of the direction of circulation of such products.
Products of combustion from a fire occurring below the detector
will rise upwardly through the perforations 60 and spread laterally
outward through the spaces between the pan and the cover and the
ceiling, whereby to assure prompt and thorough exposure of the
detector grid to such products. In the event of a fire remotely of
the detector, the products will rise to the ceiling and spread
horizontally along the ceiling, whereupon the spaces between the
cover and ceiling, coupled with the low profile of the detector
components, will act to more or less "scoop" the products slightly
downwardly and over the detector grid, whereby again to assure
prompt and thorough exposure of the grid to such products.
In a practical commercial embodiment, the detector with all of its
advantages and special features is only 7 inches square and 13/4
inches deep. In this model, the handle 42 of the switch protrudes
slightly outwardly beyond the sidewalls of the cover to facilitate
operation by a broom handle or the like so that the householder
need not climb on a ladder or a chair to set the sensitivity or
test the operability of the unit.
Thus, the invention provides a totally self-contained and early
warning fire detector of low profile and attractive appearance that
may be mounted on the ceiling in a private home and which, when so
installed, provides for extremely fast and efficient exposure of
the detector grid to the products of combustion and immediate
warning of the presence of fire.
While we have shown and described what we regard to be the
preferred embodiment of our invention, it is to be appreciated that
various changes, rearrangements and modifications may be made
therein without departing from the scope of the invention as
defined by the appended claims.
* * * * *