U.S. patent application number 13/013519 was filed with the patent office on 2011-05-26 for temperature and low water monitoring for boiler systems.
This patent application is currently assigned to C. COWLES & COMPANY. Invention is credited to Christopher L. Murray.
Application Number | 20110122918 13/013519 |
Document ID | / |
Family ID | 43597028 |
Filed Date | 2011-05-26 |
United States Patent
Application |
20110122918 |
Kind Code |
A1 |
Murray; Christopher L. |
May 26, 2011 |
TEMPERATURE AND LOW WATER MONITORING FOR BOILER SYSTEMS
Abstract
A dual functionality temperature control measurement and low
water cut-off measurement system is taught within a single tapping
to a boiler. This dual functionality combines a low water cut-off
and temperature sensor into one control utilizing a sensing element
suitable for use in a single existing tapping for a boiler.
Independent of low water functionality, the temperature sensor is
also capable of monitoring temperature as a replacement probe in an
existing temperature sensor-only well. A conductive member provides
a compression fit inside the probe well for thermistors, while
simultaneously providing conduction with the well interior for a
low water cutoff signal in a two-conductor well.
Inventors: |
Murray; Christopher L.;
(West Haven, CT) |
Assignee: |
C. COWLES & COMPANY
New Haven
CT
|
Family ID: |
43597028 |
Appl. No.: |
13/013519 |
Filed: |
January 25, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11697063 |
Apr 5, 2007 |
7891572 |
|
|
13013519 |
|
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Current U.S.
Class: |
374/208 ;
374/E1.001 |
Current CPC
Class: |
G01F 23/00 20130101;
F24H 9/2007 20130101; G01K 13/00 20130101; B23P 19/00 20130101;
F22B 37/46 20130101; G06K 13/00 20130101; F22B 37/47 20130101; F24D
19/1009 20130101; Y10T 29/4973 20150115 |
Class at
Publication: |
374/208 ;
374/E01.001 |
International
Class: |
G01K 1/00 20060101
G01K001/00 |
Claims
1-5. (canceled)
6. An immersion thermowell adapted for mounting to the wall of a
vessel, adapted to isolate a sensor from contact with liquid in
said vessel, said sensor remaining in a thermal and electrical
communicating relationship with said liquid, further adapted to
allow a probe to measure thermal and electrical properties of said
liquid, comprising: an electrically conductive housing shell
coaxially joined to an electrically insulating collar coaxially
joined to an electrically and thermally conductive sensor tube,
forming a generally cylindrical chamber extending coaxially within,
and having first and second ends, the first end being open and the
second end being sealed, said sensor tube having a generally smooth
exterior surface and said sensor tube being electrically isolated
from said housing shell by said collar.
7. An immersion thermowell set forth in claim 6 comprising a
mounting means integrally formed on the surface of said housing
shell, in a circumferential portion thereof of limited axial extent
intermediate the first and second ends.
8. An immersion thermowell with mounting means set forth in claim 7
comprising an annular pipe thread integrally formed in said
circumferential portion of said housing shell.
9. An immersion thermowell set forth in claim 6 wherein the
junction of said housing shell and said collar are sufficiently
sealed to prevent liquid ingress when exposed to fluid pressures
typical of boiler vessels.
10. An immersion thermowell set forth in claim 6 wherein the
junction of said collar and said sensor tube are sufficiently
sealed to prevent liquid ingress when exposed to fluid pressures
typical of boiler vessels.
11. An immersion thermowell set forth in claim 6 wherein said
collar is coaxially joined to said housing shell so that said
collar extends axially beyond said housing shell to a point
intermediate said housing shell and said second end.
12. An immersion thermowell set forth in claim 6 wherein said
sensor tube is coaxially joined to said collar so that said sensor
tube extends axially beyond said collar to said second end.
Description
[0001] This application is a Continuation application of patent
application Ser. No. 11/697,063 filed Apr. 5, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to safety devices that
automatically cut-off the burner operation of a hot water boiler.
More specifically, the present invention relates to the type of
boiler used in residential and light commercial heating
applications that include a control system for monitoring both the
temperature and level of the water in the boiler. The system allows
these attributes to be measured through a single probe inserted
into the boiler through a single tapping.
[0004] 2. Description of Related Art
[0005] In conventional boilers of the type used in residential and
light commercial heating the water level is monitored with a low
water cutoff (LWCO) sensor. When the water level in the boiler
drops below the level of the low water cutoff sensor, the burner is
turned off until the water level is brought back up to a safe
level. These controls are well known in the art.
[0006] One example is U.S. Pat. No. 6,390,027, issued to Lyons and
Murray, entitled, "CYCLE CONTROL SYSTEM FOR BOILER AND ASSOCIATED
BURNER," which is incorporated by reference. In the '027 design, a
cycle control system is used with a boiler to determine the
presence of an adequate level of fluid within the boiler.
[0007] In operation, an LWCO has a probe that extends into the
boiler through a single tapping. Generally, the probe has two
electrically conductive surfaces that are isolated from each other.
An electrical signal is provided to one of these conductive
surfaces. When the water level is above the level of the probe, the
circuit between the conductive surfaces is closed by virtue of the
conductivity of the water surrounding the probe. When the water
level falls below the probe, there is no conductivity between the
metal conductive surfaces. Thus, the circuit is open, and the
control detects a low water condition.
[0008] Another component of monitoring boiler systems is
information concerning the temperature of the water in the boiler.
There are many temperature control systems in the art currently
used to monitor water temperature in a boiler. Commercially
available temperature controllers include, for example, the
Honeywell L7224U Aquastat Relay. In these devices, a temperature
sensing thermistor is inserted into a hollow well. The hollow well
is then inserted within a tapping in the boiler and the boiler is
filled with water. The thermistor is connected to a central control
unit. The central control unit monitors the temperature gradient,
and is typically programmed to shut down the burner to prevent the
water in the boiler from exceeding a preset limit. The central
control unit may also be programmed to turn the burner ON to
maintain a minimum boiler temperature.
[0009] In U.S. Pat. No. 5,340,019, issued to Bohan, Jr., et al.,
entitled, "ELECTRONIC AQUASTAT IN IMMERSIBLE CAPSULE," a liquid
immersible electronic aquastat is taught in which a temperature
responsive element and substantially all associated electronic
circuitry are arranged on a circuit board within a tubular capsule
of liquid impervious material. The capsule or well houses a
thermocouple, while conducting heat energy from the surface of the
well to the temperature sensor.
[0010] A need exists to combine the two safety functions of
monitoring for low water cutoff and temperature measurement in a
single probe with supporting control circuitry to allow it to
perform in existing boiler tappings, thus eliminating the need to
drain the boiler to insert a new tapping.
[0011] In U.S. Pat. No. 5,111,691, issued to John, et al.,
entitled, "CONDUCTANCE/THERMAL LIMIT CONTROL APPARATUS AND METHOD,"
a temperature probe is taught which mounts in a liquid container.
The probe has a conductance electrode coupled to a conductance
control circuit. A temperature sensor is combined with this low
water cutoff probe. This control, however, does not allow for the
ability to replace the sensor of an existing aquastat such as the
Honeywell devices described above without draining the boiler and
possibly the entire heating system. Furthermore, this design only
provides high temperature limit with no provision to turn the
burner on to maintain a minimum boiler temperature, or to control
the circulator pump on a call for heat.
[0012] One problem in the industry has been the reluctance to
accommodate multiple tappings for water cutoff probes and
temperature sensor probes. This requires expensive redesigns of
boiler castings to accommodate a second hole in the boiler wall for
the additional probe. It is desirable to combine the two
measurement functions in a single probe, which can be inserted into
a single well. It is further desirable to construct a probe/well
design that can accomplish the multiple measurements in a single
device that is interchangeable with existing well designs currently
available in the industry. In this manner, it is not necessary to
provide a new tapping or to drain existing boilers currently in
operation in order to incorporate the present invention. In
addition, it is desirable for the present invention to maintain a
minimum boiler temperature.
[0013] Another problem that occurs is when the control circuitry is
set to maintain a minimum water temperature and the temperature
sensor is not in the boiler. In the prior art, the control
circuitry would incorrectly determine that the water temperature is
too low, and try to run the boiler, causing an unsafe, high
temperature condition. This is generally referred to as a "run-away
boiler" condition. In the present invention, if the dual probe
sensor is connected to the control circuitry but not inserted into
the well, the control circuitry will sense a low water condition,
and not allow the burner to fire.
SUMMARY OF THE INVENTION
[0014] Bearing in mind the problems and deficiencies of the prior
art, it is therefore an object of the present invention to provide
a probe for sensing water level (low water cutoff) and temperature
in a single unit.
[0015] It is another object of the present invention to provide a
probe for sensing water level and temperature in a single unit that
allows for integration into an existing tapping.
[0016] It is another object of the present invention to provide a
probe in a well that may accommodate both sensing functions of low
water cutoff and temperature measurement within the integration of
an existing tapping, or may accommodate temperature measurement
alone.
[0017] It is yet another object of the present invention to provide
a control unit that allows a user to set the limits for temperature
and monitor low water conditions.
[0018] It is another object of the present invention to provide
visual signals to the user to indicate which functions, temperature
and low water, are currently active.
[0019] A further object of the present invention is to provide a
safe condition when the dual probe sensor is connected to the
control circuitry but not properly inserted within the well, which
would otherwise cause a run-away boiler condition.
[0020] Still other objects and advantages of the invention will in
part be obvious and will in part be apparent from the
specification.
[0021] The above and other objects, which will be apparent to those
skilled in the art, are achieved in the present invention, which is
directed to a probe having a dual measurement function within a
well inserted within a boiler taping comprising: a temperature
sensor including at least one thermistor in a housing; thermistor
conductors connecting to the at least one thermistor and protruding
from the housing; and a low water cutoff sensor including a
conductive member connecting to a low water cutoff conductive wire,
forming a compression fit against the well interior, the conductive
member and the low water cutoff conductive wire in electrical
communication with the well, such that the conductive member and
the low water cutoff conductive wire are at approximately the same
voltage potential as the well. The probe may also include a sheath
surrounding the thermistor conductors, the sheath providing
rigidity for the thermistor conductors to allow for manual
installation within the well without having the thermistor
conductors collapse upon insertion.
[0022] The well further includes a conductive nut threaded for
threadedly securing into the boiler tapping and in electrical
communication with the boiler interior wall; and a dielectric
spacer electrically separating the well, the low water cutoff
conductive member, and the low water cutoff conductive wire from
the conductive nut, such that a conductive path between the boiler
interior wall and the well is formed when water within the boiler
interior surrounds and contacts the well, and the conductive path
is open when the water within the boiler interior does not surround
or contact the well.
[0023] The housing may comprise a temperature sensitive
thermoplastic (TPE) over-mould. The low water cutoff conductive
member preferably includes beryllium copper (BeCu), and is seated
in an exterior channel or groove with the member. The thermistor is
preferably encapsulated in a resin that may include blue hysol. The
probe outputs may be integrated with an outdoor temperature sensor,
a return temperature sensor, an ambient temperature sensor, and the
like, and these boiler system and environmental temperature
measurements may be collectively utilized to control boiler
function.
[0024] In a second aspect, the present invention is directed to a
system for monitoring low water cutoff and temperature in a boiler
comprising: a temperature sensor within a housing, in which the
housing may have an external channel or groove; conductors
connecting to the temperature sensor and protruding from the
housing; a semi-rigid sheath surrounding the conductors; a low
water cutoff sensor including: a conductive member connecting to a
low water cutoff conductive wire, where a first portion of the
conductive member may be within the housing, and a second portion
of the conductive member may be seated external to the housing and
may also be within the external channel or groove, and forming a
compression fit against the well interior, the conductive member
and the low water cutoff conductive wire in electrical
communication with the well, such that the conductive member and
the low water cutoff conductive wire are at approximately the same
voltage potential as the well; a conductive nut threaded for
connection to the boiler interior wall and in electrical
communication with the boiler interior wall; a dielectric spacer
electrically separating the well, the low water cutoff conductive
member, and the low water cutoff conductive wire from the
conductive nut, such that a conductive path between the boiler
interior wall and the well is formed when water within the boiler
interior surrounds and contacts the well, and the conductive path
is open when the water within the boiler interior does not surround
or contact the well; and a controller comprising: a microprocessor:
a unity buffer receiving input signals from the probe and providing
a high impedance input for the microprocessor; and software for
filtering the temperature sensor and the low water cutoff sensor
inputs.
[0025] In a third aspect, the present invention is directed to a
method for replacing an existing temperature sensor in a single
tapping well within a boiler with a dual functioning low water
cutoff sensor and temperature sensor probe, the method comprising:
removing the existing temperature sensor from the single tapping
well; inserting a dual functioning probe within the well
comprising: the temperature sensor probe having a housing and
conductors protruding from the housing, peripherally protected by a
semi-rigid sheath, the housing having an external channel or
groove; the low water cutoff sensor probe including a conductive
member connecting to a low water cutoff conductive wire, having a
first portion of the conductive member within the housing, and a
second portion of the conductive member seated external to the
housing and within the external channel or groove, and forming a
compression fit against the well interior, the conductive member
and the low water cutoff conductive wire in electrical
communication with the well, such that the conductive member and
the low water cutoff conductive wire are at approximately the same
voltage potential as the well; and connecting the probe to a
microcontroller circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The features of the invention believed to be novel and the
elements characteristic of the invention are set forth with
particularity in the appended claims. The figures are for
illustration purposes only and are not drawn to scale. The
invention itself, however, both as to organization and method of
operation, may best be understood by reference to the detailed
description which follows taken in conjunction with the
accompanying drawings in which:
[0027] FIG. 1 depicts an assembly drawing of a sensor well.
[0028] FIG. 2 depicts an assembly drawing of the well of FIG. 1
with an elongated brass nut.
[0029] FIGS. 3A & 3B depict a combined low water cutoff and
aquastat thermistor insert for installation into the proposed
embodiments of FIGS. 1 and 2.
[0030] FIG. 4 is a wiring diagram for a control system.
[0031] FIG. 5 depicts the control system of the instant
invention.
[0032] FIG. 6 depicts flow chart of one embodiment of the control
system of the present invention.
[0033] FIG. 7 is an assembly drawing of a gas boiler control
housing of the present invention having high/low temperature and
low water cutoff indicators.
[0034] FIG. 8 depicts the temperature sensor assembly of the
present invention.
[0035] FIG. 9 depicts the program flow for utilizing the dual probe
design of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0036] In describing the preferred embodiment of the present
invention, reference will be made herein to FIGS. 1-9 of the
drawings in which like numerals refer to like features of the
invention.
[0037] The present invention teaches a dual functionality of
temperature control measurement and low water cut-off measurement
within a single tapping in a boiler. This dual functionality
combines a low water cut-off and temperature sensor into one
control utilizing a sensing element suitable for use in an existing
3/4'' tapping for typical boilers. The tappings generally comprise
a threaded brass nut for insertion in a boiler housing wall, a
hollow, cylindrical temperature/low water cut-off well for
protecting and securing the sensors, and an insulator (dielectric),
which electrically separates the brass nut from the cylindrical
well. The sensor well allows a user to insert the temperature
sensor and low water cutoff sensor without draining the system.
Importantly, the sensor well may be used for both temperature and
low-water cutoff measurements. In this manner, the dual function
capability may be employed in boilers where only a single tapping
is available.
[0038] FIG. 1 depicts an assembly drawing of a well 10 of the
present invention. A brass well nut 1 is securely and
circumferentially attached to the temperature/low water cutoff well
or tube 3. Insulator 4 extends circumferentially around a portion
of well 3, electrically isolating brass nut 1 from well 3. In this
manner, electrical connection between the well 3 and brass nut 1 is
communicated only by the conductivity of surrounding water. If the
water level is below well 3, the electrical connection is broken,
and a low water cutoff condition is realized. Typically, well 3 is
made of copper, although other conductive metal combinations may be
used with equal success. Importantly, well 3 extends through, but
makes no contact with, brass nut 1. Any contact would result in the
electrical shorting of the low water cutoff circuitry. Brass well
nut 1 may be any other suitable, non-brass material, provided it
can survive the exposure requirements in adverse boiler
environments, and lend suitable conductivity for the proper
operation of the low water cutoff control circuitry. The electrical
isolation between well 3 and brass nut 1 is controlled by insulator
4. Insulator 4 is preferably made of a material that substantially
resists electrical connection, such as a modified polyphenylene
oxide resin (PPO), or the like. One such example is NORYL.RTM.
N300X, which is a blend of polyphenylene ether (PPE) and
polystyrene (PS).
[0039] Brass nut 1 includes a threaded portion, or some other
appropriate means for connecting the probe assembly to the boiler.
Importantly, brass nut 1 allows well 10 to be inserted within the
wall of a boiler above the minimum water line, and remain there
indefinitely by creating a watertight seal upon installation. The
connection of brass nut 1 to the wall of the boiler also allows
well 10 to be in electrical communication with the boiler interior
wall. Generally, in operation, portions of well 3 and insulator 4
are exposed within the boiler interior to the water.
Simultaneously, brass nut 1, which is in electrical communication
with the boiler interior wall, is also exposed to the water. When
an electrical signal is applied to well 3, it remains isolated from
brass nut 1 as well as the boiler interior wall. In this manner, no
electrical communication is established between well 3 and brass
nut 1. This is because insulator 4 prohibits electrical
conductivity. Under normal operating conditions, the water level is
high enough in the boiler to surround and encompass exposed
portions of well 3 and brass nut 1. The conductivity of the water
effectively bypasses the operation of insulator 4 and completes the
low water cutoff circuit, connecting well 3 to the boiler interior
wall at brass nut 1. When electrical connection is detected, the
control circuitry connected to the probe determines that adequate
water is in the boiler. When the water level is below well 10, well
3 is no longer in electrical communication with the boiler interior
wall at brass nut 1. The absence of an electrical signal to
complete the circuit, i.e., an open circuit, allows the system to
determine that the water level is sufficiently low, and
subsequently shuts down the burner.
[0040] FIG. 2 depicts an assembly drawing of a well 10a of the
present invention with an elongated brass nut 11. Electrically, the
well 10a configuration of FIG. 2 is the same as the well 10
configuration of FIG. 1.
[0041] FIGS. 3A and 3B depict a combined low water cutoff and
thermistor insert for installation into the proposed embodiments of
FIGS. 1 and 2. The probe 20 contains preferably two thermistors per
assembly (not shown), encased within a temperature sensitive
thermoplastic (TPE) over-mould 23. As illustrated in FIGS. 3A and
3B, probe 20 is secured in well 3 by a resilient, compression-fit
conductive member 24, such as a wire having a spring constant, a
shaped wire clip (shown), a peripheral or semi-peripheral resilient
conductive band, or a solid-shaped conductive material capable of
fitting within the well to ensure good electrical contact with the
well interior wall, and which may provide a compressive force that
simultaneously holds or pushes an adjacent temperature sensor
against the well interior wall. If conductive member 24 is in the
form of a resilient wire, it is preferably constructed of beryllium
copper (BeCu). Conductive member 24 is configured to extend upward
from the surface of probe 20. Conductive member 24 terminates on a
conductor within the assembly. In doing so, conductive member 24
makes electrical connection with well 3, which is exposed to the
boiler water environment. This connection allows a low water cutoff
signal to propagate from the controller circuitry, making a circuit
with well 3 and the electrically isolated brass nut 1 when
conductive water is present. Conductive member 24 forms part of the
contact path for the low water cutoff circuit. The water provides
the connection from well 3 to brass nut 1, thereby bypassing
insulator 4. When water is no longer present, the low water cutoff
circuit is open, i.e., insulator 4 does not allow the signal to
propagate, and a low water level is detected. The conductive member
24 secures the thermistor assembly within a well by forming a
compression fit, while simultaneously providing a secure fitting
for electrical contact for the low water cutoff signal. This design
readily accommodates existing wells that were not otherwise
constructed for this purpose. The probe of the present invention
may be placed in a temperature sensor well design that is unable to
accommodate a low water cutoff application. The supporting control
circuitry will measure temperature, while the low water cutoff
electrical signal monitors resistance. If the probe is in a
temperature-sensor only well, the conductive member will sense zero
ohms of resistance and temperature sensing will remain active while
the low water cutoff function is inactive. This allows the present
invention to replace an existing, non-dual function probe, and
provide at least the same functionality as the probe it
replaced.
[0042] The conductive member ensures that the probe of the present
invention is inserted in the well. In contrast, if a probe is not
inserted in the well, the temperature measurement cannot be sensing
boiler temperature. This would cause a controller connected to a
prior art probe to initiate a continuous firing of the boiler,
otherwise known as a run-away boiler condition. However, in the
present invention, a signal from the conductive member will ensure
that the probe is inserted. Ensuring that the probe is installed in
the well addresses this run-away boiler condition in a manner that
is unique to the present invention.
[0043] In the preferred embodiment, the encapsulated thermistor 20
has a 30 K-ohm resistance at 25.degree. C. with an operating
temperature range on the order of -40.degree. C. to +125.degree. C.
Clearly, these specifications are boiler dependent, and may be
adjusted for specific applications. In operation, probe 20 is
placed in well 3. When inserted, conductor 24 is forced down into
channel 26. This ensures that conductive member 24 will remain in
pressure contact with the interior wall of well 3. The wires 28
connected to, and extending from, probe 20, arc covered by a
heat-shrink wrap 30. This heat-shrink wrap serves the dual function
of insulating the wiring system from the environment, and also
providing rigidity to the wire structure. For the preferred
two-thermistor design, four conductors are used, such as 26 AWG
7/34 T.C., or the like, with insulation and an overall TPE cable
jacket. The rigidity provided by the wrapping allows the thermistor
assembly, including the compression-fit conductive member 24, to be
push-inserted within an existing well without collapsing onto
itself. In contrast, the thermistor disclosed in U.S. Pat. No.
5,111,691 issued to John, teaches wires without any means for
rigidity, mainly because the John disclosure does not suggest or
teach using the thermistor assembly for replacement in wells that
were not specifically designed for it. The '691 patent also does
not include a wire member assembly necessary to engage with the
well simultaneously for a low water cutoff signal and temperature
sensing signal.
[0044] Thus, the present invention allows for a dual probe
combining temperature measurement and low water cutoff to be
inserted within an existing well of a boiler without requiring a
new tapping. The probe can be inserted within an existing well
because of the rigidity of the wire system that allows the
thermistor to be friction fit while providing for electrical
connection for the low water cutoff signal. The control circuitry
may then monitor safe operation of the boiler. However, dual
sensing may be accommodated only if the existing well includes a
dielectric spacer for the low water cutoff signal conductivity
measurement.
[0045] FIG. 4 is a wiring diagram 40 for a control system. The
wiring diagram depicts how a thermostat 42, circulating pump 44,
burner 46, and multi-zone controller 48 are connected in a
preferred embodiment.
[0046] FIG. 5 depicts the control system 50 of the instant
invention. Control system 50 has controls that allow for adjusting
the low temperature setting 52, high temperature setting 54, and
the temperature differential 56. A display 58 is used for
indicating the water temperature to the user or technician.
Diagnostic lights 51, 53, 55, and 57 indicated active temperature,
high temperature, active low water cutoff, and low water,
respectively.
[0047] In operation, a temperature control circuit is used in
conjunction with the temperature sensor. The temperature sensor
inputs a temperature signal for sensing a high temperature range
with adjustable differential. The measured temperature is used to
determine the operation of the burner through comparator circuitry
and relays for the safety functioning of the burner, e.g., a high
temperature condition may require burner shut-off and a low
temperature condition may require the burner to be turned on. A
thermostat signal is also used as an input to allow for a "demand
heat" condition.
[0048] A conductance sensor is used for measuring the variable
conductivity of the water in the boiler. The sensor receives an AC
source signal and provides a variable resistance to the signal
based on the conductivity of the water. The variable resistance
forms a resistor divider network with a predetermined series
resistance. The AC source signal (rail voltage) is preferably a 5
volt signal operating at approximately 400-500 Hz. The probe input
is on the order of 100 mV of the rail. Specifically, the source
signal is preferably sinusoidal with an amplitude span of
approximately +2.5 volts to -2.5 volts (peak-to-peak). Generally,
there are no active electronics within the sensor, although the
present design does not preclude the addition of such devices. The
resistance divider formed by a series resistor and a variable
resistance, which represents the measured water conductance, acts
to attenuate the source signal in an amount proportional to the
water conductivity.
[0049] Referring to FIG. 6, the probe input 61 is then directed to
a unity buffer 62, which provides a high impedance for interfacing
with the analog input of the microprocessor 63. The signal is
biased at +2.5 volts through a high impedance resistor. This shifts
the signal from +2.5 volts (p-p) to 0-5 volts (p-p), which enables
it to be received properly at the analog input of microprocessor
63. No amplification is performed during this biasing. The probe
input port is voltage surge protected by a diode.
[0050] Microprocessor 63 receives the buffered probe signal at an
analog input 64 to microprocessor 63. The analog input signal is
normally sampled in sequence with a drive signal (AC source
signal). Microprocessor 63 performs a sample-and-hold function for
a high output drive signal and a low output drive signal,
respectively. The signal's peak-to-peak voltage is then measured.
Internal to the microprocessor is an analog-to-digital (A/D)
converter that converts the bias signal returned from the probe
into a digital value with 8-bit resolution (0-255).
[0051] Software filtering is performed by the microprocessor at a
preferred rate of approximately 1/10 Hz. Sixteen samples are
measured and averaged in order to eliminate or account for
externally induced noise. A second average (long-term average) is
performed with the sixteen-sample averaged value. The resultant
averaging function filters out adverse effects due to air bubbles
and probe-induced or probe-coupled transients. The measured,
averaged value is then compared via software to threshold
conditions such as: a) shorting; b) good/poor conductivity
threshold; and c) an empty boiler condition. As the measurement
software loop progresses, the resultant determination (short, good
conductor, etc.) must be shown to persist for a predetermined
number of cycles before a declaration may be made and action taken.
If the measurement condition is removed before the predetermined
number of cycles is accumulated, a counter is reset and the
measurement cycle is repeated. Once an actionable condition is
determined, the user is notified by a series of LED indicators 65
and appropriate action is taken, e.g., the boiler may be shut down
for a "no water" condition.
[0052] The action taken by the controller includes toggling a
burner relay 66. Relay 66 is turned on or driven by a relay driver
circuit 67 which requires redundant burner signals to ensure that
any action affecting burner operation is not based on faulty
circuitry.
[0053] Preferably, four settings are available for the temperature
display 68 of the present invention: high temperature 69; low
temperature 70; high temperature plus differential 71; and low
temperature plus differential 72. The high temperature settings 69
and 71 limit the boiler water temperature to a safe operating
temperature. The low temperature settings 70 and 72 maintain a
minimum temperature in the boiler. In a cold start condition, the
burner does not fire unless there is a call for heat from the
system thermostat 73. In the low temperature sensor limit of the
present invention, turning the temperature control setting to off,
turns the controller into a cold start apparatus.
[0054] FIG. 7 is an assembly drawing of a gas control housing 74 of
the present invention having high/low temperature and low water
cutoff indicators 75. Probe well 76 is shown drawn to approximate
scale. Housing 74 comprises a lower module 77, a printed circuit
board assembly 78, and a housing cover 79. Circuit board assembly
78 includes electronics, the high temperature and low water
indicators, a temperature probe check (HT active), a water probe
check (LW active), high temperature settings, high temperature
differential, and burner firing signals.
[0055] FIGS. 8A and 8B depict the temperature sensor assembly 80 of
the present invention. The conductors 82 from each of two
thermistors 84 are wrapped in semi-rigid heat shrink tubing 86 and
terminated with connectors 88, preferably using terminals such as
AMP P/N 770666, or the like, and a corresponding connector, such as
AMP P/N 770602-4, or the like. The heat shrink tubing is preferably
a polyolifine heat shrink sleeve or equivalent. The thermistors are
housed in a plastic or metal housing 81. In one embodiment the
thermistors are first encapsulated in a resin, such as blue hysol
or the like. Conductors 82 are soldered to each thermistor lead.
The solder joints are protected by an adhesive lined polyolifine
sleeve, preferably a sleeve with a temperature rating on the order
of 135.degree. C. Sharing the same housing is beryllium copper
conductor clip 83, which connects to its own dedicated conductor
85. Clip 83 extends outside of housing 81 in order to make contact
with the metal interior wall of the well. Clip 83 may be formed
from 22 AWG wire or other resilient material. Clip 83 helps
position the thermistors 84, which are opposite the clip, against
the well.
[0056] Many different versions of temperature probes are suitable
for use in the present invention. In one embodiment, a preferred
probe includes epoxy coated point matched disc thermistors with
nickel PTFE insulated lead wires. One such probe may be comprised
of NTC thermistors from GE. These probes have a solid-state sensor,
strong mechanical strength, and a wide operating temperature range
of about -50.degree. C. to 150.degree. C. Another such sensor is a
Betatherm Corporation sensor, which is also a ceramic chip NTC
thermistor design with nickel plated CP wire, and glass
encapsulating material. These probes are representative of the
types of probes which may be used in the present invention;
however, the present invention may accommodate other probe designs,
and is not limited to the probes identified above, provided each
probe meets the physical restraints of the well design, and the
environmental restrictions on boiler operation.
[0057] FIG. 9 depicts the program flow 90 for utilizing the dual
probe design of the present invention. Upon initiating the power up
sequence 91, the burner 92 and circulator 94 are off. The water
sensor is first initiated 96. For a low water condition, the low
water LED is activated 98 and burner 92 and circulator 94 are
turned off or kept off. For a high water condition, the low water
LED is either switched off or kept off 100. A temperature
measurement is made 102. If the temperature is low, the circulator
is turned off or kept off 104. The high temperature LED is turned
off or kept off 106, as the case may be, and the burner is
activated or turned on 108. If the temperature measurement 102 is
not low, the thermostat input is monitored for a call for heat 110.
If there is no call for heat, the maximum temperature limit is
checked 112. If the maximum temperature is reached, the high
temperature LED is turned on 114 and the burner 92 and circulator
94 are turned off. If the maximum temperature limit 112 is not
attained, the high temperature LED 116 remains off, and again the
burner 92 and circulator 94 also remain off. If the thermostat
input 110 calls for heat, the circulator is turned on 118. The
maximum temperature limit is monitored 120. When the maximum
temperature is reached, the high temperature LED is turned on 122,
and the burner is turned off 124. The water sensor is then
monitored 96. If Maximum temperature is not reached, the high
temperature LED 106 is turned off or kept off and the burner 108 is
turned on or kept on. The water sensor 96 is then monitored.
[0058] Importantly, the present invention's controller allows for
external temperature inputs as well as various boiler system
temperature inputs. This would include outdoor temperature, boiler
return temperature, boiler supply temperature, indoor temperature,
and the like. This allows for efficient burner operation under
various environmental and system conditions. For example, in this
manner, an outside temperature or call for heat is monitored, and
the boiler is limited to the outdoor reset controller conditions.
Thus, the dual function sensors are integrated with a controller
that monitors external environmental temperature. If the controller
system monitors a high outside temperature, it would regulate its
temperature accordingly. Otherwise, the system would not
distinguish between a moderate fifty-degree day and a cold
ten-degree day, insomuch as it will work all the time as if it is
in an environment of a cold day all year long. It will consistently
heat the water to a maximum temperature without regard for the
outside temperature. By incorporating boiler system and
environmental temperature measurements, the system can provide
significant energy efficiency.
[0059] One feature of the present invention is the ability to
replace sensors from existing controllers without replacing the
wells, that is, it has the unique ability to be interchangeable
with current systems. In some systems, it is possible that the
interchange of the present sensor system into an existing system
will not allow the dual function of the present invention to be
completely activated. In these circumstances, only temperature
function may be employed. Indicator lights will signal which
functions are active.
[0060] While the present invention has been particularly described,
in conjunction with a specific preferred embodiment, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art in light of the foregoing
description. It is therefore contemplated that the appended claims
will embrace any such alternatives, modifications and variations as
falling within the true scope and spirit of the present
invention.
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