Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR TESTING
FUEL GAS CONTROL SYSTEMS FOR
GAS FIRED APPLIANCES
BACKGROUND OF THE INVENTION
Brief description of the Invention
The present invention relates to methods and apparatus for testing and
analyzing
operability of fuel gas control systems for appliances such as water heaters,
furnaces,
cooking ranges and ovens, decorative fireplace inserts, pool heaters and
similar gas
fired appliances. More particularly, the present invention relates to methods
and
apparatus for testing operability of a thermocouple device of a fuel gas
control system
and for testing operability of a safety valve solenoid-high temperature
electricity cut off
fuse, (ECO fuse) circuit of a fuel gas control system under simulated load
conditions.
Background of the Invention
Gas control systems for appliances are commercially available and widely used.
A gas
control system supplies fuel gas to an appliance under conditions such that
the fuel gas
may be safely ignited in the appliance firing chamber. In situations where
safe
ignition of the fuel gas cannot be ensured, the gas control system will
prevent fuel gas
from entering the appliance firing chamber. Such gas control systems are
available for
both natural gas and liquefied petroleum gas, (LPG), fuels.
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Such gas control systems are well known and understood and only such
description will
be given here as is required to describe the method and apparatus of the
present
invention. An illustrated description of a typical gas control system may be
found in
"Service Manual For Residential Gas Water Heater Control"., published in 1997
by
White Rogers division of Emerson Electric Company.
A gas control system for an appliance comprises several elements acting
cooperatively
to achieve the functions of safely controlling flow of fuel gas to the
appliance firing
chamber and ensuring ignition of the fuel gas. Typically, a gas control system
comprises a fuel gas control valve having a safety valve solenoid, an ECO
fuse, a pilot
flame device, an appliance burner and a heat sensing thermocouple device. The
safety
valve solenoid, ECO fuse and thermocouple device are connected in a series
electrical
circuit. In one type of gas control system, a pilot flame from the pilot flame
device is
maintained continuously for activating the thermocouple device and for
igniting the fuel
gas at the appliance burner. In another type of gas control system, fuel gas
is ignited
at the appliance burner by a spark gap igniter and the gas burner flame
activates the
thermocouple device. The ECO fuse senses temperature in the medium heated,
(water, or air), in an appliance and the ECO fuse breaks upon sensing high
temperature
in the heated medium, for stopping flow of fuel gas to the appliance burner
and the
pilot flame device.
A gas control valve in a typical fuel gas control system comprises a solenoid
activated
safety valve and a manual shunt valve. The solenoid activated safety valve is
opened,
for flow of fuel gas through the gas control valve, upon the solenoid being
activated by
a millivolt DC current generated by the thermocouple device upon sensing a
pilot flame
at the pilot flame device in the appliance firing chamber. The manual shunt
has three
positions: "off", which prevents flow of fuel gas through the gas control
valve;
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"pilot", which allows flow of fuel gas to the pilot device when the solenoid
safety valve
is open; and "on", which allows flow of fuel gas to the pilot device and the
appliance
burner when the solenoid safety valve is open. The gas control valve also
comprises
a manual override which, upon manual activation, opens the safety valve when
the
manual shunt is in "pilot" position, for allowing ignition of a pilot flame at
the pilot
flame device before the thermocouple device senses temperature sufficiently
high to
generate a millivolt DC current sufficient to activate the solenoid and open
the safety
valve.
The thermocouple device comprises a bimetallic thermocouple, a first
electrical
conductor connected to one leg of the bimetallic thermocouple, and a second
electrical
conductor connected to the other leg of the bimetallic thermocouple. The first
electrical conductor is commonly a copper tube which runs from the first leg,
of the
thermocouple to the body of the gas control valve. The second electrical
conductor is
an electrically insulated wire which runs from the second leg of the
thermocouple,
through the copper tube, for electrical connection to the safety valve
solenoid. The
copper tube of the first electrical conductor: connects the first leg of the
thermocouple
to the body of the gas control valve; supports the second electrical conductor
from the
second leg of the thermocouple to the gas control valve for connection to the
safety
valve solenoid; and provides support for the thermocouple in the appliance
firing
chamber. A thermocouple, as used in gas control systems, generally has a DC
out put
voltage in the range of about 7 to 30 millivolts, depending on the bimetallic
elements
and the temperature to which the thermocouple is exposed. 'the thermocouple
and
safety valve solenoid are matched to ensure that the thermocouple will
generate
sufficient DC voltage to operate the solenoid under normal operating
conditions.
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The thermocouple, ECO fuse and safety valve solenoid are in a closed loop,
series
electrical array such that a millivolt DC current flows from the thermocouple
second
leg, through the second electrical conductor, through the ECO fuse into the
input of the
safety valve solenoid. From the safety valve solenoid output, the millivolt DC
current
flows through the body of the gas control valve, through the first electrical
conductor
to the thermocouple first leg, thus completing the closed loop electrical
circuit.
The ECO fuse is a thermal fuse located in the medium being heated by the
appliance.
For example, in the water tank or the air outlet plenum of a water heater or
an air
heater. In the event the medium becomes overheated, the ECO fuse will melt and
break the electrical connection between the thermocouple and the safety valve
solenoid, thus shutting off fuel gas to the main burner and the pilot burner
of the
appliance.
Description of Pertinent Art
It is well known that appliance gas control systems often fail in operation.
Such
failures may be caused by a variety of causes, such as failure of the safety
valve
solenoid, failure, or melting, of the ECO fuse, or failure of the
thermocouple. Often,
the causes of such failures are difficult to determine. The gas control valve
and ECO
fuse are supplied as a unit and the thermocouple device is supplied as a
separate unit.
Neither unit is subject to repair and must be replaced when the unit fails. As
each unit
is relatively expensive, it is desirable to determine which unit has failed
and to replace
only the failed unit.
A thermocouple device may be easily checked by disconnecting it from the gas
control
valve and connecting the first and second electrical conductor to a millivolt
meter. A
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pilot flame is then applied to the thermocouple and the DC voltage generated
is
registered by the millivoltmeter. In such a test, if the millivolt output from
the
thermocouple device is at least about 7 millivolts, the thermocouple device is
considered operational. This test is referred as an "unloaded test" of the
thermocouple
device. This test of the thermocouple does not test the safety valve solenoid
and ECO
fuse portion of the fuel gas control system.
A second test method, employing a special adaptor and a millivolt meter, for
testing
the entire electrical circuit of a fuel gas control system, (safety valve
solenoid, ECO
fuse, thermocouple device), under loaded conditions is disclosed in "Service
Manual
For Residential Gas Water Heater Control",published 1997, White Rogers
division of
Emmerson Electric Company. For this method, the thermocouple device is
disconnected from the gas control valve and a special adaptor is connected
between the
gas control valve and the thermocouple device. The special adaptor reconnects
the
thermocouple device, safety valve solenoid and ECO fuse and also allows a
millivolt
meter to be connected to both leads from the thermocouple. According to this
method, after the adaptor is installed and the millivolt meter is connected to
each of the
thermocouple leads, the gas control valve is set to "pilot" position and the
manual
override of the safety valve is engaged. The pilot flame is then ignited and
is allowed
to heat the thermocouple for about 3 minutes. The millivolt meter is observed
during
this heating period. A 7 millivolt output from the thermocouple device should
be
sufficient to energize the safety valve solenoid and hold the safety valve
open such that
flow of gas to the pilot device will continue when the safety valve manual
override is
released. According to this method, if the thermocouple device output measured
by
the millivolt meter does not rise to at least 7 millivolts at the end of the 3
minute test
period, (after ensuring that the pilot flame is properly directed onto the
thermocouple),
then the thermocouple device is judged faulty and should be replaced. On the
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hand, if the thermocouple output rises to at least 7 millivolts but the pilot
flame will not
remain lit when the safety valve manual override is released, the gas control
valve is
judged faulty and should be replaced.
The test method described in the paragraph above tests the thermocouple under
load
conditions and tests the gas control system electrical circuit as a whole, but
does not
test the safety valve solenoid and ECO fuse portion of the electrical circuit.
That is, a
condition may exist where the ECO fuse is intact and the safety valve solenoid
is
operational, but the thermocouple device does not generate a millivolt current
sufficient
to energize the safety valve solenoid. In such case, according to the above
test
method, the recommendation is to replace the gas control valve when, in fact,
the
thermocouple device should be replaced with one having a higher millivolt
output.
SUM1VIARY OF THE INVENTION
Now, according to the present invention, I have invented apparatus and a
methods for
testing operability of a safety valve solenoid and an ECO fuse of a fuel gas
control
system under electrical load conditions to determine whether the safety valve
solenoid
and ECO fuse, are functionally operable and for separately testing the
millivolt output
of a thermocouple device in the fuel gas control system.
The advantages of the apparatus and test methods of the present invention
include the
ability to determine whether the safety valve solenoid and EC:O fuse are
operable
separately from the thermocouple device and whether the safety valve solenoid
and
thermocouple device are compatible for operating together as elements of a
fuel gas
control system. These and other advantages of the methods and apparatus of the
present invention will be described in the Detailed description of the
invention which
follows.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 of the drawings is a sectional view of the adaptor of the present
invention,
showing the adaptor connected to the thermocouple port of a gas control valve.
(shown
in ghost view);
Fig 2 of the drawings is a preferred electrical schematic of the test
instrument of the
present invention;
Fig. 3 of the drawings is a plan view of the test instrument of the present
invention,
showing external electrical connectors, manual adjustment means and a
millivolt
voltage visual display.
DETAILED DESCRIPTION OF THE INVENTION
The detailed description of the invention which follows is made with reference
to the
drawings and in terms of a preferred embodiment of the invention. The detailed
description is not intended to limit the scope of the present invention, and
the only
limitations intended are those embodied in the claims hereto.
According to the method of the present invention, the apparatus of the
invention is used
to: determine operability of a safety valve solenoid and an ECO fuse in an
appliance
fuel gas control system; determine operability of a thermocouple device in the
fuel gas
control system; and from these two determinations determine whether the safety
valve
solenoid and the thermocouple device are compatible for operation together in
the fuel
gas control system;
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In Fig 1, an adaptor 100 is shown in sectional view. Adaptor 100 is designed
for
connection to the thermocouple connection port of a gas control valve, as
shown in
ghost view in Fig 1. Adaptor 10 comprises an electrically conductive, hollow
tubular
member 101 having threads 102 at a first end for threadingly engaging the
thermocouple port of a gas control valve, and having a flange 103 at a second
end for
assisting in the manual engagement of the threads 12 in the gas control valve
thermocouple port and for providing a connection for a ground wire of the test
instrument, as will be described below. An electrically conductive cylindrical
member
104 passes axially through tubular member 101 and is held in place and is
electrically
insulated from tubular member 101 by hollow cylindrical insulating member 105.
A
first end 106 of cylindrical member 104 extends axially to a position about
even with
the first end 107 of tubular member 101 for contacting an electrical input
connection
109 for a safety valve solenoid and an ECO fuse, not shown. A second end 108
of
cylindrical member 104 extends axially beyond flange 103 of tubular member
101.
For performing the tests of the safety valve solenoid and ECO fuse, according
to the
method of the present invention, a thermocouple device, not shown, is
disengaged
from the thermocouple port of the gas control valve and adaptor 100 is
threadingly
engaged in the gas control valve thermocouple port. Upon such engagement,
cylindrical member 104 first end 106 contacts the voltage input side 109 of a
safety
valve solenoid-ECO fuse electrical circuit of the fuel gas control system and
the
threaded tubular member 101 contacts the ground side of the safety valve
solenoid-
ECO fuse electrical circuit. The protruding end 108 of cylindrical member 104
and
the flange 103 of tubular member 101 provide means for connecting the test
instrument
of the present invention to the safety valve solenoid-ECO fuse circuit, as
will be
described below.
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The test instrument of the present invention is an electronic instrument
which, working
in cooperation with adaptor 100, is employed in the method of the present
invention for
testing operability of the safety valve solenoid and ECO fuse of a fuel gas
control
system and is employed for testing operability of a thermocouple device of the
fuel gas
control system.
In Fig 2, an electrical schematic of a preferred embodiment of the test
instrument 200
is shown. Test instrument 200 comprises a voltage regulated power source 201,
an
adjustable DC millivolt current source 202, switching means 203 and millivolt
display
204.
Test instrument 200 has first and second test modes. The first test mode is
for testing
millivolt output of a heated thermocouple device of an appliance fuel gas
control
system. The second test mode is for testing operability of a safety valve
solenoid-
ECO fuse circuit of an appliance fuel gas control system. Test instrument 200
is
switched from first test mode to second test mode by closing switching means
203.
In Fig 2, all electrical grounds 205 and external ground 206 are connected to
provide a
common electrical ground for test instrument 200.
In fig 2, Power source 201 provides a source of voltage regulated DC current
via line
207 for operating other electronic components of test instrument 200. and
provides
unregulated DC current as required for operation of transistor 208 in
adjustable
millivolt DC current source 202. In a preferred embodiment, as shown in Fig 2,
power source 201 comprises a battery 209, preferably of 9 volts, having a
positive pole
electrically connected via switch 210 to voltage regulator 212. The negative
pole 213
of battery 301 is connected to test instrument ground system 205. Unregulated
DC
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current from battery 209 is converted to a voltage regulated DC current,
preferably of
volts, at voltage regulated DC current line 207.
In Fig 2, voltage regulated DC current is supplied, via line 207, to a voltage
divider
comprising resistor 213 and variable potentiometer 214. DC current is fed via
line
215 into amplifier 216 wherein DC current is converted to a millivolt DC
current at
amplifier 216 output 217. The voltage range of the rnillivolt DC current at
output 217
is varied by adjusting variable potentiometer 214. Amplifier 216 is an op-amp
in an
inverting configuration having a gain equal to 1 plus the ratio of the
resistances of
resistor 218 and resistor 219, (1+ R218/R219j. Preferably the gain of
Amplifier 216
is 2. The millivolt DC current from amplifier 216 flows via line 217 into
transistor
208. Transistor 208 is a switching transistor which limits the flow of the
millivolt DC
current to a safety valve solenoid- ECO fuse circuit to be tested according to
the
method of this invention. As the resistance of the safety valve solenoid is
low, in the
mini ohm range, it is desirable that the millivolt DC current have a rather
high
amperage, in the range of about 1 amp. The millivolt DC current flows from
transistor 208 via line 219. A first portion of the millivolt DC current from
line 219
flows via line 220 as feed back current to amplifier 216 and a second portion
of
millivolt current from line 219 flows, via line 221 for testing operability of
a safety
valve solenoid-ECO fuse circuit according to the second testing mode of the
present
invention .
In the second testing mode of the present invention, switch 203 is closed and
millivolt
DC current flows via line 221, through switch 203 and via line 222 to external
connector 223. From external connector 223, millivolt DC current flows into a
safety
valve solenoid-ECO fuse circuit, as will be described below.
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In Fig 2, millivolt display means 204 is electrically connected to line 222
for providing
a visual display of the voltage of a millivolt DC current carried by line 222.
In the
first test mode, with switch 203 open, line 222 carries a millivolt DC current
from a
heated thermocouple device, as will be described below. In the second test
mode,
with switch 203 closed, line 222 cazries a millivolt DC current supplied from
variable
millivolt source 202.
Millivolt visual display 204 may comprise any convenient device which will
accurately
display the voltage of a millivolt DC current generated in the first test mode
or the
second test mode of test instrument 200 operation. Commonly, the millivolt DC
currents generated will have voltages in the range of about 0 to 30
millivolts, and a
visual display in the range of about 4 to 20 millivolts is adequate for
millivolt visual
display 204. Millivolt display 204 may comprise a digital millivolt meter, an
analog
millivolt meter, or, in a preferred embodiment, a light emitting diode (LED)
display.
In Fig 2, the preferred millivolt visual display 204 is an LED display.
millivolt DC
current from line 222 is fed via line 224 into a first stage amplifier 225.
First stage
amplifier 225 is an op-amp in differential, (inverting), configuration.
Reference
current from line 207 is fed to fixst stage amplifier 225 via line 228.
resistance values
of resistors 226 and 227 are selected to bias the first stage amplifier out
put, at line
229, to 2.5 volts. First amplifier stage out put current from line 229 is fed
into second
stage amplifier 230. Second stage amplifier is also an op-amp amplifier in
differential,
(inverting ), configuration. A reference current is fed to second stage
amplifier 230
via line 231. Voltage of the second stage reference current is established by
selecting
the resistance values of resistors 232 and 233. Preferably, the second stage
reference
current is 2 volts. With the output current of first stage amplifier at 2.5
volts and
second stage reference current at 2 volts, the difference is 0.5 volts. Upon
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amplification of this difference by the second stage amplifier, the second
stage
amplifier output is at 1 volt, (2-0.5 x 2 = 1 volt).
In Fig 2, output current from second stage amplifier 230 is fed into an
electrical ladder
comprising amplifiers 234, 235, 236, 237,and 238. These amplifiers are op-amps
used as comparators to drive display LEDs 239, 240, 241, 242, and 243.
Resistors
244, 245, 246, 247, 248 and 249 form a series of voltage dividers which
provide the
various voltage thresholds required by each comparator. When no voltage is
applied
from second stage amplifier 230, all the comparator amplifiers are at the
ground power
supply rail. Preferably, resistors 244, 245, 246, 247, 248, and 249 are
selected such
that amplifier comparators 238, 237, 236, 235, and 234 are serially activated
to the
regulated voltage rail 250 upon 4 millivolt increases in millivolt DC current
fed into the
first stage amplifier 225. 'That is, with base out put current of first stage
amplifier 225
at 2.5 volts, and reference current to second stage amplifier 230 at 2 volts,
the overall
gain of the two amplifiers is set at 80 by selecting resistance values of
resistors 251 and
252 for first stage amplifier 225 and of resistors 253 and 254 for second
stage amplifier
230. At an overall gain of 80, the output of second stage amplifier 230
increases 80
millivolts for each millivolt of input into first stage amplifier 225. For
example, when
input current to first stage amplifier 225 is 4 millivolts, out put current
from second
stage amplifier 230 is 1.32 volts, (1 + 4x 80). With amplifier comparators
238, 237,
236, 235, and 234 circuits set to serially activate the amplifiers upon each 4
millivolt
increase in current input into first stage amplifier 225, the 1.32 volt output
from second
stage amplifier 230 will cause output of amplifier comparator to change from
the
ground rail to the regulated voltage rail 250. As amplifier comparator 237
remains at
the ground rail, current flows from the output of amplifier 238 through LED
243,
causing LED 243 to light. As the voltage from second stage amplifier 230
increases,
each comparator amplifier 237, 236, 235, and 234 will switch to the regulated
voltage
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Doer oo-oos
rail upon each increase of 320 millivolts, causing each LED 242, 241, 240, and
239 to
light in succession, turning off the LED behind it.
In Fig 3, the exterior of test instrument 200, with manual instrument controls
and
millivolt visual display elements, is shown. The electrical circuitry of test
instrument
200 is shown if Fig 2, and is described above. Test instrument 200 has two
modes of
operation, In the first mode of operation, test instrument 200 is employed to
test
operability of a thermocouple device employed in a fuel gas control system for
a gas
fired appliance. In a second mode of operation, test instrument 20 is employed
for
testing operability of a safety valve solenoid~ECO fuse circuit of a fuel gas
control
system for a gas fired appliance. Test instrument 200, in this embodiment, is
battery
powered. Battery power is switched on or off by power switch 210. Operation of
test instrument 200 will be given with reference to Fig. 1, 2 and 3 of the
drawings.
In the first mode of operation, test instrument 200 is employed to test
operation of an
appliance fuel gas control system thermocouple device. In this first mode of
operation, the millivolt output from adjustable millivolt source 202 is not
required.
However, electrical power from constant voltage source 201 is required for
operation
of the LED visual millivolt display. Switch 210 is closed for generating a
constant
voltage current for operation of the LED displays of millivolt display 204.
Switch 203
is placed in the open position to prevent the millivolt current from
adjustable millivolt
source 202 from interfering with the first mode test of a thermocouple device.
For the first mode test, a thermocouple device is disconnected from the
thermocouple
port of a fuel gas valve in a fuel gas control system. Test instrument
external
connector 206 is connected to the copper tube first electrical conductor of
the
thermocouple device and external connector 204 is connected to the
thermocouple
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second electrical conductor. The gas control valve manual shunt is placed in
"pilot"
position and the manual override is depressed for allowing fuel gas to enter
the pilot
flame device. A pilot flame is ignited and the manual override is held in the
depressed
position for maintaining the pilot flame. millivolt visual display 204 is
observed for a
period of about 3 minutes. If LED 241 lights, representing 12 millivolts
output from
the thermocouple device, the thermocouple device is judged operational and the
test
may be discontinued. If LEI) 243 or 242 light, but LED 241 does not light, the
thermocouple device is judged questionable and may need to be replaced. If
none of
the LEDs light, the thermocouple device is defective and must be replaced. In
all
cases, care must be taken to ensure that good electrical contact is maintained
between
the connectors 223 and 206 and the thermocouple device. Also, care should be
taken
to see that the thermocouple device is properly placed in relation to the
pilot flame to
ensure that the thermocouple is properly heated.
In the second test mode, adaptor 100 and test instrument 200 are employed to
test the
safety solenoid valve-ECO fuse circuit of a fuel gas supply system. For the
second
mode test, a thermocouple device is disconnected from a thermocouple port of a
gas
control valve in a fuel gas control system. Adaptor 100 is connected to the
gas control
valve at the thermocouple port. External connector 223 of test instrument 200
is
connected to cylindrical member 104 of adaptor 100, and external connector 206
is
connected to flange 103 of adaptor 100. Test instrument variable potentiometer
is
turned counter clockwise to its lowest setting, power switch 210 is closed and
switch
203 is closed. The gas control valve manual shunt is placed in "pilot"
position, the
manual overnde is depressed and the pilot flame is lit. the manual overnde is
kept
depressed to maintain the pilot flame. Variable potentiometer 214 is turned
clockwise
until LED 241 lights, representing 12 millivolts DC' current applied to the
safety valve
solenoid-ECO fuse circuit of the fuel gas control system. Then, the manual
override
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is released and an observation whether the pilot flame remains lit is made. If
the pilot
flame remains lit, the safety valve solenoid-ECO fuse circuit is judged to be
operable.
The test may be continued by turning the variable potentiometer counter clock
wise
until LED 241 goes out and LED 242 is lit. Observation is made to determine
whether the pilot flame remains lit. If the pilot flame remains lit when LED
242 is lit,
the safety valve solenoid is judged in good condition and should be operable
with a
thermocouple device which is in good condition. If the pilot flame does not
remain lit
when LED 241 is lit, the test is repeated with the variable potentiometer
being rotated
clockwise until LED 240 lights, representing 16 millivolt DC: current applied
to the
safety valve-ECO fuse circuit. If the pilot flame remains lit when LED 240 is
lit but
does not remain lit when L,ED 241. is lit, the safety valve solenoid- ECO fuse
circuit is
judged operable, but care must be taken to select a thermocouple device having
sufficient millivolt out put to activate the safety valve solenoid. If the
pilot flame does
not remain lit when LED 240 or L,ED 239 are lit, the safety valve solenoid-ECO
fuse
circuit is judged faulty and the gas control valve must be replaced.
While the present invention has been described with reference to preferred
embodiment, the same are to be considered illustrative only and not limiting
in
character, and that many modifications to the methods and apparatus of the
present
invention will occur to those skilled in the art without departing from the
spirit and
scope of the invention, which is defined only by the appended claims.
l~
