U.S. patent application number 12/991283 was filed with the patent office on 2011-06-23 for ignition control with safeguard function.
This patent application is currently assigned to Kidde-Fenwal, Inc.. Invention is credited to Walter Robert Greene, Juan Antonio Martinez.
Application Number | 20110151387 12/991283 |
Document ID | / |
Family ID | 41264842 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110151387 |
Kind Code |
A1 |
Greene; Walter Robert ; et
al. |
June 23, 2011 |
IGNITION CONTROL WITH SAFEGUARD FUNCTION
Abstract
An ignition control and method are provided for overseeing an
ignition process on a fuel-fired appliance having a fuel burner, a
fuel flow control valve, an ignition source, and a flame detection
device. A primary processor initiates the ignition process,
monitors the flame status signal and terminates the ignition
process in the presence of a flame status signal indicating no
flame after a specified period of time following the initiation of
the ignition process. A secondary processor monitors the flame
status signal independently of the primary processor and terminates
the ignition process in the event that the primary processor fails
to terminate the ignition process in the presence of a flame status
signal indicating no flame after a specified period of time
following the initiation of the ignition process. The primary and
secondary processors may each have the functional capability to
monitor the operation of the other.
Inventors: |
Greene; Walter Robert;
(Bellingham, MA) ; Martinez; Juan Antonio;
(Watertown, MA) |
Assignee: |
Kidde-Fenwal, Inc.
Ashland
MA
|
Family ID: |
41264842 |
Appl. No.: |
12/991283 |
Filed: |
May 9, 2008 |
PCT Filed: |
May 9, 2008 |
PCT NO: |
PCT/US08/63171 |
371 Date: |
January 25, 2011 |
Current U.S.
Class: |
431/66 |
Current CPC
Class: |
F23N 2227/36 20200101;
F23N 5/203 20130101; F23N 5/242 20130101; F23N 2223/08 20200101;
F23N 2231/12 20200101; F23N 2227/02 20200101; F24H 9/2085 20130101;
F23N 5/12 20130101 |
Class at
Publication: |
431/66 |
International
Class: |
F23N 5/00 20060101
F23N005/00 |
Claims
1. An ignition control for controlling an ignition process on a
fuel-fired appliance, the appliance having a fuel burner, said
ignition control comprising: a fuel control valve having an open
position in which fuel flows to said burner and a closed position
in which fuel flow to said burner is stopped; an ignition source
operatively associated with said burner, a flame detection device
for detecting the presence of a flame at said burner and
transmitting a flame status signal indicating flame or no flame; a
controller for overseeing the ignition process of igniting the fuel
supplied to said burner, said controller including a primary
processor and a secondary processor: said primary processor having
functional capability to operate the ignition device, to monitor
the flame status signal from the flame detection device and to
terminate the ignition process in the presence of a flame status
signal indicating no flame after a specified period of time
following an initiation of the ignition process; and said secondary
processor having functional capability to monitor the flame status
signal from the flame detection device and to terminate the
ignition process in the event that the primary processor does not
close the fuel control valve in the presence of a flame status
signal indicating no flame after a specified period of time
following an initiation of the ignition process.
2. The ignition control as recited in claim 1 further comprising
said secondary processor having functional capability to monitor
the operation of said primary processor.
3. The ignition control as recited in claim 1 further comprising
said primary processor having functional capability to monitor the
operation of said secondary processor.
4. The ignition control as recited in claim 3 wherein said
secondary processor continuously transmits a status signal to the
primary processor.
5. The ignition control as recited in claim 1 where each of said
primary processor and said secondary processor comprises a
microprocessor.
6. The ignition control as recited in claim 1 where each of said
primary processor and said secondary processor comprises a
microcontroller.
7. The ignition control as recited in claim 1 wherein each of said
primary processor and said secondary processor has functional
capability to position the fuel control valve in its closed
position to independently terminate the ignition process.
8. An ignition control for controlling an ignition process on a
direct spark ignition gas appliance, the gas appliance having a
burner, said ignition control comprising: a gas valve having an
open position in which gas flows to the burner of the gas appliance
and a closed position in which gas flow to the burner of the gas
appliance is stopped; an ignition source operatively associated
with the burner of the gas appliance, a flame detection device
operatively associated with the gas appliance for detecting the
presence of a flame at the burner and transmitting a flame status
signal indicating flame or no flame; a controller for overseeing
the ignition process of igniting the gas supplied to the burner of
the gas appliance, said controller including a primary processor
and a secondary processor: said primary processor having functional
capability to operate the ignition device, to monitor the flame
status signal from the flame detection device and to terminate the
ignition process in the presence of a flame status signal
indicating no flame after a specified period of time following an
initiation of the ignition process; and said secondary processor
having functional capability to monitor the flame status signal
from the flame detection device and to terminate the ignition
process in the event that the primary processor does not close the
gas valve in the presence of a flame status signal indicating no
flame after a specified period of time following an initiation of
the ignition process.
9. The ignition control as recited in claim 8 further comprising
said secondary processor having functional capability to monitor
the operation of said primary processor.
10. The ignition control as recited in claim 8 further comprising
said primary processor having functional capability to monitor the
operation of said secondary processor.
11. The ignition control as recited in claim 10 wherein said
secondary processor continuously transmits a status signal to the
primary processor.
12. The ignition control as recited in claim 8 where each of said
primary processor and said secondary processor comprises a
microprocessor.
13. The ignition control as recited in claim 8 where each of said
primary processor and said secondary processor comprises a
microcontroller.
14. The ignition control as recited in claim 8 wherein each of said
primary processor and said secondary processor has functional
capability to position the gas valve in its closed position to
independently terminate the ignition process.
15. The ignition control as recited in claim 8 wherein the gas
appliance comprises a gas furnace.
16. The ignition control as recited in claim 8 wherein the gas
appliance comprises a gas water heater.
17. The ignition control as recited in claim 8 wherein the gas
appliance comprises a commercial gas cooking apparatus.
18. A method for overseeing an ignition process on a fuel-fired
appliance, the appliance having a fuel burner, a fuel flow control
valve, an ignition source operatively associated with the burner, a
flame detection device operatively associated with the burner for
detecting the presence of a flame at the burner and transmitting a
flame status signal indicating flame or no flame; said method
comprising the steps of: providing a primary processor for
initiating the ignition process, for monitoring the flame status
signal and for terminating the ignition process in the presence of
a flame status signal indicating no flame after a specified period
of time following the initiation of the ignition process; providing
a secondary processor for monitoring the flame status signal
independently of said primary processor and for terminating the
ignition process in the event that said primary processor fails to
terminate the ignition process in the presence of a flame status
signal indicating no flame after a specified period of time
following the initiation of the ignition process.
19. The method as recited in claim 18 wherein said secondary
processor terminates the ignition process by closing the fuel flow
control valve to stop the delivery of fuel to the burner in the
event that said primary processor does not close the fuel flow
control valve in the presence of a flame status signal indicating
no flame after a specified period of time following an initiation
of the ignition process.
20. A method for overseeing an ignition process on a direct spark
ignition gas appliance, the gas appliance having a burner, a gas
valve, an ignition source operatively associated with the burner of
the gas appliance, a flame detection device operatively associated
with the gas appliance for detecting the presence of a flame at the
burner and transmitting a flame status signal indicating flame or
no flame; said method comprising the steps of: providing a primary
processor for initiating the ignition process, for monitoring the
flame status signal and for terminating the ignition process in the
presence of a flame status signal indicating no flame after a
specified period of time following the initiation of the ignition
process; providing a secondary processor for monitoring the flame
status signal independently of said primary processor and for
terminating the ignition process in the event that said primary
processor fails to terminate the ignition process in the presence
of a flame status signal indicating no flame after a specified
period of time following the initiation of the ignition
process.
21. The method as recited in claim 20 wherein said secondary
processor terminates the ignition process by closing the gas valve
to stop the delivery of gas to the burner in the event that said
primary processor does not close the gas valve in the presence of a
flame status signal indicating no flame after a specified period of
time following an initiation of the ignition process.
22. The method as recited in claim 20 wherein the steps of
providing a primary processor and of providing a secondary
processor comprise providing a primary microprocessor and a
secondary microprocessor.
23. The method as recited in claim 20 further comprising the step
of said secondary processor monitoring the operation of said
primary processor.
24. The method as recited in claim 20 further comprising the step
of said primary processor monitoring the operation of said
secondary processor.
25. The method as recited in claim 24 further comprising the step
of said secondary processor transmitting a status signal to said
primary processor whenever said secondary processor is in an active
state.
26. The method as recited in claim 20 further comprising the step
of said secondary processor cycling in sequence through a primary
detect mode, an idle mode and a monitor mode.
27. The method as recited in claim 26 further characterized in that
the secondary processor may move from any of the primary detect
mode, the idle mode and the monitor mode directly into a lockout
mode.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to ignition control on gas
or other fuel-fired appliances and, more particularly, to an
ignition control including a microprocessor safeguard for an
ignition system.
BACKGROUND OF THE INVENTION
[0002] Ignition controls are customarily used in connection with
gas appliances, such as, for example, residential gas furnaces,
boilers, water heaters and commercial cooking equipment, equipped
with direct spark ignition systems. On gas appliances with direct
spark ignition, the stream of gas supplied to the burner of the
appliance is directly ignited by a spark. In conventional practice,
the ignition spark is provided by an electronic device, such as for
example an electronic spark generator. While such direct spark
ignition systems generally function properly to quickly ignite the
gas flowing to the burner, it is critical that the supply of gas to
the burner to be promptly terminated in the event that ignition has
not occurred or has failed to sustain a stable flame.
[0003] Conventional ignition control systems used in connection
with direct spark ignition gas appliances include a gas valve
having an open position and a closed position, an air blower, an
ignition source, a flame sensing device and a microprocessor
controller. The flame sensing device is operative to detect the
presence of a flame within the combustion chamber of the gas
appliance and generate a signal indicative of the flame status,
i.e. a flame present signal or a no flame present signal. The
microprocessor controller oversees the ignition process, as well as
controlling the operation of the air blower and positioning of the
gas valve.
[0004] In response to the receipt of a demand signal indicating
that operation of the burner of the gas appliance is desired, the
microprocessor controller will initiate the ignition process. To
initiate ignition, the microprocessor controller activates the air
blower to initiate the supply of combustion air to the burner of
the gas appliance, and then transmits an activation command signal
to the ignition device, and then opens the gas valve to initiate
the supply of gas into the burner. In response to the activation
command, the ignition device begins to generate a series of sparks
to attempt to ignite the air-gas mixture forming as the gas flows
into the burner. If ignition is successful, a flame is
established.
[0005] The microprocessor controller monitors the flame sensing
device to ensure that a flame has indeed been established and
maintained within the combustion chamber. The flame sensing device
is operative to detect whether or not a flame is present in the
combustion chamber. If the flame sensing method does detect the
presence of a flame, it emits a "flame present" signal. However, if
the flame sensing method does not detect the presence of a flame,
it emits a "no flame present" signal.
[0006] In conventional practice, the controller triggers a timer
circuit upon entry into the ignition process. If within a preset
time interval following entry into the ignition process, the
controller receives a "flame present" signal, the controller
maintains the gas valve in its open position, resets the timer
circuit, and goes into a combustion monitoring mode during which
the controller will at periodic time intervals, check the signal
received from the flame sensing device to verify that the signal
received from the flame sensing device is still a "flame present"
signal. However, if at the lapse of the preset ignition
verification time period, the signal received by the microprocessor
controller from the flame sensing device is a "no flame present"
signal, the controller will close the gas valve, lockout the gas
valve and the ignition device for a preselected lockout time
period, and operate the air blower for a preset period of time to
purge the gas appliance of any gas remaining in the combustion
chamber. The controller will not again initiate an ignition attempt
until the lockout time period has expired.
[0007] Thus, the timer circuit acts as a watchdog to prevent
uncontrolled release of gas into the combustion chamber when
ignition has not occurred within the preset time period following
entry into the ignition process. It is critical that the ignition
control and oversight function be made as reliable as possible.
Failure to terminate gas flow in the event of an ignition failure
or a subsequent flame failure, would lead to an undesirable build
up of gas within the combustion chamber. For example, U.S. Pat. No.
4,695,246 discloses an ignition control system for a gas appliance
that includes a single microprocessor having redundant
circuitry.
SUMMARY OF THE INVENTION
[0008] In an aspect of the invention, an ignition control is
provided for controlling an ignition process on a fuel-fired
appliance, the appliance having a burner. The ignition control
includes a fuel flow control valve having an open position in which
fuel flows to the burner and a closed position in which fuel flow
to the burner is prohibited, an ignition source operatively
associated with the burner, a flame detection device for detecting
the presence of a flame at the burner and transmitting a flame
status signal indicating flame or no flame, and a controller for
overseeing the ignition process of igniting the fuel supplied to
the burner, the controller including a primary processor and a
secondary processor. The primary processor has functional
capability to operate the ignition device, to monitor the flame
status signal from the flame detection device and to terminate the
ignition process in the presence of a flame status signal
indicating no flame after a specified period of time following an
initiation of the ignition process. The secondary processor has
functional capability to monitor the flame status signal from the
flame detection device and to terminate the ignition process in the
event that the primary processor does not close the fuel flow
control valve in the presence of a flame status signal indicating
no flame after a specified period of time following an initiation
of the ignition process. Each of the primary processor and the
secondary processor has functional capability to position the fuel
flow control valve in its closed position to independently
terminate the ignition process.
[0009] In an aspect of the invention, an ignition control is
provided for controlling an ignition process on a direct spark
ignition gas appliance, the gas appliance having a burner. The
ignition control includes a gas valve having an open position in
which gas flows to the burner of the gas appliance and a closed
position in which gas flow to the burner of the gas appliance is
prohibited, an ignition source operatively associated with the
burner of the gas appliance, a flame detection device operatively
associated with the gas appliance for detecting the presence of a
flame at the burner and transmitting a flame status signal
indicating flame or no flame, and a controller for overseeing the
ignition process of igniting the gas supplied to the burner of the
gas appliance, the controller including a primary processor and a
secondary processor. The primary processor has functional
capability to operate the ignition device, to monitor the flame
status signal from the flame detection device and to terminate the
ignition process in the presence of a flame status signal
indicating no flame after a specified period of time following an
initiation of the ignition process. The secondary processor has
functional capability to monitor the flame status signal from the
flame detection device and to terminate the ignition process in the
event that the primary processor does not close the gas valve in
the presence of a flame status signal indicating no flame after a
specified period of time following an initiation of the ignition
process. Each of the primary processor and the secondary processor
has functional capability to position the gas valve in its closed
position to independently terminate the ignition process.
[0010] In an embodiment, the primary processor has functional
capability to monitor the operation of the secondary processor. In
an embodiment, the secondary processor may continuously transmit a
status signal to the primary processor. In an embodiment, the
secondary processor has functional capability to monitor the
operation of the primary processor. Each of the primary processor
and the secondary processor may comprise a microprocessor.
[0011] In an aspect of the invention, a method is provided for
overseeing an ignition process on a fuel-fired appliance. The
appliance has a fuel burner, a fuel flow control valve, an ignition
source operatively associated with the burner, and a flame
detection device for detecting the presence of a flame at the
burner and transmitting a flame status signal indicating flame or
no flame. The method includes the steps of: providing a primary
processor for initiating the ignition process, for monitoring the
flame status signal and for terminating the ignition process in the
presence of a flame status signal indicating no flame after a
specified period of time following the initiation of the ignition
process, and providing a secondary processor for monitoring the
flame status signal independently of the primary processor and for
terminating the ignition process in the event that the primary
processor fails to terminate the ignition process in the presence
of a flame status signal indicating no flame after a specified
period of time following the initiation of the ignition process.
The secondary processor may independently of the primary processor
terminate the ignition process by closing the fuel flow control
valve to preclude the delivery of fuel to the burner in the event
that the primary processor does not close the fuel control valve in
the presence of a flame status signal indicating no flame after a
specified period of time following an initiation of the ignition
process.
[0012] In an aspect of the invention, a method is provided for
overseeing an ignition process on a gas appliance. The gas
appliance has a burner, a gas valve, an ignition source operatively
associated with the burner of the gas appliance, and a flame
detection device operatively associated with the gas appliance for
detecting the presence of a flame at the burner and transmitting a
flame status signal indicating flame or no flame. The method
includes the steps of: providing a primary processor for initiating
the ignition process, for monitoring the flame status signal and
for terminating the ignition process in the presence of a flame
status signal indicating no flame after a specified period of time
following the initiation of the ignition process, and providing a
secondary processor for monitoring the flame status signal
independently of the primary processor and for terminating the
ignition process in the event that the primary processor fails to
terminate in the presence of a flame status signal indicating no
flame after a specified period of time following the initiation of
the ignition process. The secondary processor may independently of
the primary processor terminate the ignition process by closing the
gas valve to preclude the delivery of gas to the burner in the
event that the primary processor does not close the gas valve in
the presence of a flame status signal indicating no flame after a
specified period of time following an initiation of the ignition
process.
[0013] In an embodiment, the method also includes the step of the
primary processor monitoring the operation of the secondary
processor. In an embodiment, the method also includes the step of
the secondary processor monitoring the operation of the primary
processor. In an embodiment, the method includes the step of the
secondary processor transmitting a status signal to the primary
processor whenever the secondary processor is in an active
state.
[0014] In an embodiment, the method includes the step of the
secondary processor cycling in sequence through a primary detect
mode, an idle mode and a monitor mode. In an embodiment, the
secondary processor may move from any of the primary detect mode,
the idle mode and the monitor mode directly into a lockout
mode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a further understanding of the invention, reference will
be made to the following detailed description of the invention
which is to be read in connection with the accompanying drawing,
where:
[0016] FIG. 1 is a schematic block diagram of the ignition control
system of the invention;
[0017] FIG. 2 is a flow chart of an ignition oversight sequence as
performed by the secondary processor of the ignition control system
of the invention;
[0018] FIG. 3 is a flow chart of the primary detect mode of the
test sequence of FIG. 2;
[0019] FIG. 4 is a flow chart of the idle mode of the test sequence
of FIG. 2; and
[0020] FIG. 5 is a flow chart of the monitor mode of the test
sequence of FIG. 2;
DETAILED DESCRIPTION OF THE INVENTION
[0021] Referring initially to FIG. 1, there is depicted, in block
diagram, an ignition control 10 for controlling an ignition process
on a gas appliance 2 having a burner 4. Although the ignition
control 10 will be described herein with reference to application a
gas furnace, such as a residential or commercial gas furnace, it is
to be understood that the ignition control 10 may be used in
connection with a wide variety of gas appliances, including but not
limited to, gas fired boilers, gas fired water heaters, and gas
fired commercial cooking equipment. The ignition control 10
includes a gas valve 20, an ignition source 30, a flame detection
device 40 and a controller 50. In the ignition control 10 of the
invention, the controller 50 includes a primary processor 150 and a
secondary processor 250.
[0022] The gas valve 20 has an open position and a closed position
and may be selectively positioned in either its open or closed
position through the controller 50. The gas valve 20 is disposed a
gas supply line 6 connected in gas flow communication with an
external gas source (not shown), such as for example a utility
natural gas line or a storage tank of liquid natural gas (LNG) or
propane. When the gas valve 20 is positioned in its open position,
gas flows from the external source through the gas supply line 6 to
the burner 4 of the gas appliance 2. When the gas valve 20 is
positioned in its closed position, gas flow through the gas supply
line 6 to the burner 4 of the gas appliance 2 is prohibited.
[0023] The ignition source 30 is operatively associated in a
conventional manner with the burner 4 of the gas appliance 2 so as
to ignite either the main gas flow to the burner 4 or a pilot gas
flow to the burner 4. Although the ignition control 10 will
described herein with reference to ignition of the main gas flow,
but it is to be understood that the ignition control may be readily
applied to direct spark ignition of a pilot gas flow. The ignition
source 30 may be an electronic spark generator, such as for example
a high-energy capacitive discharge spark across a 1/8 inch
electrode gap 32, although any variety of spark generating igniter,
or a hot surface igniter, or other type of ignition device, may be
employed as the ignition source, as desired.
[0024] The flame detection device 40 is operatively associated with
the gas appliance 2 for detecting the presence of a flame at the
burner 4 and for generating a flame status signal 45 indicating
flame or no flame. The flame detection device 40 may be any of a
variety of conventional device having functional capability to
sense the presence of flame at the burner 4. For example, by way of
illustration, but not limitation, the flame detection device may be
a flame electrode with rectification circuit. In an embodiment of
the ignition control 10, the flame detection device 40 and the
ignition source 30 may be coupled into a single device having
functional capability to both ignite the gas flow in response to a
command signal from the controller 50 and also to detect whether a
flame has resulted and generate the appropriate flame signal 45. In
an embodiment, the flame detection device 40 may be a flame rod
electrode not associated with the ignition source 30.
[0025] The controller 50 controls and oversees the process of
igniting the gas supplied to the burner 4 of the gas appliance 2.
As noted before, the controller 50 of the invention includes a
primary processor 150 and a secondary processor 250. Each of the
primary processor 150 and the secondary processor 250 may be a
microprocessor. For example, by way of illustration, but not
limitation, in an exemplary embodiment of the controller 50, the
primary processor 150 may comprise the PIC16C622A microcontroller
from Microchip Technologies and the secondary processor 250 may
comprise the PIC12F629 microcontroller from Microchip Technologies.
The primary microprocessor and the secondary microprocessor may be
mounted on a single pc board.
[0026] The primary processor 150 has functional capability to
operate of the ignition device 30, to drive the flame detection
device 40 and monitor the flame status signal 45 generated by the
flame detection device 40, and to terminate the ignition process in
the presence of a flame status signal 45 indicating no flame after
a specified period of time following an initiation of the ignition
process. The secondary processor 250 has functional capability to
monitor the flame status signal 45 from the flame detection device
40 and to terminate the ignition process in the event that the
primary processor 150 does not terminate the ignition process in
the presence of a flame status signal 45 indicating no flame after
a specified period of time following an initiation of the ignition
process. Each of the primary processor 150 and the secondary
processor 250 have functional capability to independently terminate
the ignition process by disabling the gas valve relay 22 thereby
forcing the gas valve 20 into its closed positioned in the presence
of a flame status signal 45 indicating no flame after a specified
period of time following an initiation of the ignition process.
[0027] The secondary processor 250 may also have functional
capability to monitor the operation of the primary processor 150.
In an embodiment, the secondary processor 250 has functional
capability to monitor the drive signal from the primary processor
150 to the flame detection device 40 and the drive signal from the
primary processor 150 to the gas valve relay 22 as a means of
monitoring the operation of the primary processor 150. For example,
if the flame detection device is active and generating a flame
present flame detection signal 45, but the signal from the primary
processor 150 to the gas valve relay is a disable signal, the
secondary processor 250 will conclude that some form of hardware
malfunction has occurred and will go into lockout, thereby shutting
the system down as a safety precaution.
[0028] The primary processor 150 may also have functional
capability to monitor the operation of the secondary processor 250.
For example, the secondary processor 250 may continuously transmit
an "I'm alive" status signal 55 to the primary processor 150. The
"I'm alive" status signal 55 may, for purposes of illustration, but
not limitation, comprise a digital signal having a repeating
sequence of four high beats followed by four low beats.
[0029] The primary processor 150 will monitor the thermostat 8,
which is mounted in the space to be heated by the gas furnace 2,
for a heat demand signal. In response to the heat demand signal,
the primary processor 150 will enable the gas valve relay 22 to
open the gas valve 20 and start an ignition time out clock. The
primary processor 150 may also have the functional capability to
control the operation of the air blower 60 for supplying combustion
air and purge air to the burner 4 of the furnace 2. If so equipped,
the primary processor 150 also starts the air blower 60 to supply
air to the burner to support ignition and combustion of the gas.
The ignition time out clock defines a preprogrammed time period for
ignition to occur such as, for example, but without limitation, in
the range of 1 to 25 seconds.
[0030] As an example, for an appliance having direct spark
ignition, before the gas valve 20 has been opened, the primary
processor 150 enables the ignition source 30 to produce a series of
high voltage sparks at a programmed interval of about 16
milliseconds. During the ignition time out clock period, the
primary processor 150 monitors the flame signal 45 generated by the
flame detection device 40 at preprogrammed intervals of at least
every 16 milliseconds. If a valid "flame present" flame signal 45
is detected within the time period of the ignition time out clock,
thus indicating successful ignition and a stable flame, the primary
processor 150 cuts power to the ignition source, thereby
terminating sparking, and leaves the gas valve 20 open and the air
blower 60 operating. Unless the flame is subsequently lost, the
primary processor 150 does not change the status of the gas valve
20 or the air blower 60 until the primary processor detects a loss
of the heat demand signal from the thermostat 8. Upon completion of
the heating cycle, indicated by loss of the demand for heat signal,
the primary processor 150 immediately closes the gas valve 20 and,
after a preprogrammed purge out period, disables, i.e. cuts power
to, the air blower 60 to terminate air flow to the burner 4 and
goes into an idle mode until a demand for heat signal is next
detected.
[0031] If the flame signal 45 indicates that no flame is present at
the expiration of the ignition time out clock, the primary
processor 150 immediately disables the gas valve relay 22 to close
the gas valve 20. If also designed to control the blower 60, the
primary processor 150 will, after a preprogrammed purge out period,
disable the air blower 60 to terminate air flow to the furnace 2.
The primary processor 150 will reinitiate the ignition process for
a preselected number of retries until either a successful ignition
has occurred or the maximum number of permitted retries has been
reached. If a stable flame is not present after the last permitted
trial for ignition, the primary processor 150 goes into a lockout
mode during which no further attempts to ignite are permitted. The
lockout period will last until the current demand for heat signal
expires and a new demand for heat signal is detected.
[0032] As noted previously, the controller 50 includes a secondary
processor 250 in addition to the primary processor 150. The
secondary processor 250 functions as a safeguard monitor of the
ignition process. The secondary processor 250 has the functional
capability to monitor the flame status signal 45 from the flame
detection device 40 and also has the functional capability to
monitor the operation of the primary processor 150 by monitoring
the flame sensor drive signal and the gas valve relay drive signal
generated by the primary processor 150. The secondary processor 250
also has the functional capability to terminate the ignition
process independently of the primary processor 150 in the event
that the primary processor 150 does not close the gas valve 20 in
the presence of a flame status signal 45 indicating no flame after
a specified period of time following an initiation of the ignition
process.
[0033] Referring now to FIGS. 2-5, the various modes in which the
secondary processor 250 operates in carrying out in its safeguard
oversight role with respect to the ignition process are illustrated
in the flow charts shown. Referring now to FIGS. 2 and 3, when
powered up, the secondary processor 250 operates in one of the
following modes: primary detect mode 220, idle mode 230, monitor
mode 240 and lockout mode 260. At 210, the secondary processor 250
determines whether it is undergoing a power up or a reset. When the
controller 90 is first powered up, the secondary processor 250
enters the primary detect mode. In this mode, the secondary
processor 250 verifies whether the primary processor 150 is active
by checking for signal levels on a designated two of its output
pins. The secondary processor 250 checks for high on the flame
drive pin at 222 and for low on the gas valve drive pin at 224. If
this signal pattern is not present, the primary processor 150 is
not active or malfunctioning and the secondary processor 250 will
set a FindPrimary counter. The secondary processor 250 will
continue to monitor these I/O pins and at 226 will decrement the
primary detect counter each time a specified time interval has
elapsed. If the primary FindPrimary counter reaches zero, at 228,
the secondary processor 250 will enter the lockout mode 260. If the
signal pattern is present on the designated I/O pins, the primary
processor 150 is verified active and the secondary processor 250
will transition into the idle mode 230. If the signal pattern is
found, the secondary processor 250 will also set a static flag to
prevent noise induced resets from executing the primary detect mode
220 again. The secondary processor 250 will also transition to the
idle mode 230 after a hardware reset. The transition into the idle
mode 230 may include a time delay.
[0034] In the idle mode 230, the secondary processor 250
continuously monitors the gas valve 20 to determine whether the gas
valve 20 is in an open state or a closed state. In this mode 230,
the secondary processor 250 also continuously monitors the flame
detection signal 45 to establish whether a flame is present or not.
Referring now to FIG. 4, at 232, if the detected state of the gas
valve 20 is open, the secondary processor transitions to the
monitor mode 240. If, however, the detected state of the gas valve
20 is closed, the secondary processor 250 at 234 checks the state
of the flame detection signal. If the flame detection signal
indicates that a flame is present, the secondary processor 250
immediately enters the lockout mode 260. The indication that a
flame is present even though the state of the gas valve 20 is
detected as closed is an indication that some form of hardware
failure has occurred, thereby necessitate a system shut down as a
safety precaution.
[0035] In the monitor mode 240, the secondary processor 250 will
continuously monitor the flame detection signals 45 from the flame
detection device 40 generated in response to periodic command
signals from the primary processor 150. Referring now to FIG. 5, at
242, the secondary processor 250 checks the state of the gas valve
20. If the gas valve 20 is detected to be in its closed state, the
secondary processor 250 transitions back into the idle mode 230. If
the gas valve 20 is detected to be in its open state, the secondary
processor 250 proceeds at 244 to check the flame detection signal
45. If the flame detection signal indicates that no flame is
present, the secondary processor 250 sets a FaultTimer at 246. The
secondary processor then loops back through steps 242 and 244 and
at 248 decrements the FaultTimer at the completion of each cycle,
which represents a time interval of about 400 microseconds.
[0036] If at 244 the flame detection signal indicates that flame is
present, the secondary processor 250 resets the FaultTimer at 249.
However, if the FaultTimer expires, that is reaches zero, the
secondary processor 250 immediately enters the lockout mode 260.
The FaultTimer is preset to a time period beyond which the gas
valve 20 is not to remain open in the event that a stable flame is
not established in the gas appliance 2. Since the primary processor
150 continuously tests for the presence of flame, the secondary
processor 250 will reset the FaultTimer to this maximum permissible
time period each time a successful flame detection is verified at
244. Thus, the gas valve 20 is never allowed to remain open beyond
the maximum permissible safe time limit without a positive flame
detection signal being detected by the second processor 250.
[0037] Upon entering the lockout mode, the secondary processor 250
immediately disables the gas valve relay 22 thereby forcing the
ignition control into a safe state and also stops transmitting the
"I'm alive" signal 55 to the primary processor 150. Upon loss of
the "I'm alive" signal 55, the primary processor 150 forces the gas
valve 20 closed and goes into a failure mode. The primary processor
150 will not reset until the controller 50 undergoes a power
down-power up cycle. The secondary processor 250 will not reset
until it again detects that the primary processor 150 is active as
it cycles through the primary detect mode 210. Additionally, upon
entering the failure mode, the primary processor 150 may signal the
existence of a fatal fault, for example by activating an indicator
light, such as a light emitting diode (LED) 52 on a control panel
54. For redundancy, the secondary processor 250 may also be
provided with the functional capability to activate the indicator
light 52.
[0038] While the present invention has been particularly shown and
described with reference to the exemplary embodiments as
illustrated in the drawing, it will be recognized by those skilled
in the art that various modifications may be made without departing
from the spirit and scope of the invention. For example, the
ignition control and the method of the invention may be used in
connection with combinations of fuel and ignition sources, other
than the exemplary gas and spark igniter embodiment described
hereinbefore, such as for example fuel oil and a high temperature
igniter. Further, those skilled in the art will recognize that
various types of flame detection devices, other than of the flame
electrode with rectification circuit type, may be employed in the
ignition control of the invention and in practicing the method of
the invention.
[0039] The terminology used herein is for the purpose of
description, not limitation. Specific structural and functional
details disclosed herein are not to be interpreted as limiting, but
merely as basis for teaching one skilled in the art to use the
present invention. Those skilled in the art will also recognize the
equivalents that may be substituted for elements described with
reference to the exemplary embodiments disclosed herein without
departing from the scope of the present invention.
[0040] Therefore, it is intended that the present disclosure not be
limited to the particular embodiment(s) disclosed, but that the
disclosure will include all embodiments falling within the scope of
the appended claims.
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