Note: Descriptions are shown in the official language in which they were submitted.
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Carbon Monoxide Activated Safety Shut-Off System for Gas
Appliances
Field of the Invention
This invention relates to the field of gas appliances, and
more particularly, to propane powered internally vented
appliances, such as refrigerators.
Background of the Invention
Gas powered appliances that vent the products of combustion
internally into the dwelling in which the appliance is located
can result in the accumulation of unacceptable levels of
carbon monoxide (CO). For example, propane powered
refrigerators that are not vented to the outdoors by a chimney
or flue, which are commonly being used in homes, cottages and
trailers etc., can emit harmful levels of CO into the
dwelling.
Under normal operating conditions the level of CO emissions
will be below acceptable limits of approximately 100 parts per
million (ppm). However, if there is an imbalance during
combustion, such as a decrease in the available oxygen, the
level of CO can increase beyond the acceptable limit. High
levels of CO can cause severe physical damage to the occupants
of the dwelling, if the level of CO remains undetected for an
unacceptable period of time. Consequently, there is a need
for automatically controlling the operation of this type of
appliance based on the level of CO emissions.
There are currently passive CO sensors available that can be
mounted near the exhaust flue of an internally vented
appliance to monitor the level of CO being emitted. However,
these sensors merely sound an alarm when the level of CO
exceeds a predetermined maximum. Someone must then physically
turn off the flow of gas to stop the combustion thereby
eliminating the CO emissions. This is an unacceptable method
of monitoring and controlling CO emissions because it requires
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human intervention to (a) hear the alarm from the sensor and
(b) turn off the flow of gas to stop combustion.
As a result, there is a need for a safety shut-off system that
is capable of (a) monitoring the level of CO emitting from the
flue of an internal vented gas powered appliance and (b)
capable of automatically turning off the flow of gas to stop
combustion when the level of C0 exceeds a predetermined
maxlmum .
Summary of the Invention
An object of the preferred embodiment of the present invention
is to provide a gas shut-off system that is capable of
terminating the flow of gas to a burner of an appliance when
the level of Co emissions exceeds a predetermined amount.
In accordance with one aspect of the invention there is
provided an apparatus for terminating a supply of gas to a gas
powered internally vented appliance having a burner, a valve
control means and a thermocouple, said apparatus comprising:
sensing means for monitoring carbon monoxide levels being
emitted from the burner; signal generating means connected to
the sensing means for providing a electrical signal when the
level of carbon monoxide emissions is above a predetermined
level; and switching means, connected between the signal
generating means and the valve control means, responsive to
the electrical signal, for operating the valve control means
to terminate the supply of gas to the burner.
In accordance with another aspect of the invention there is
provided in a gas powered appliance having a burner, a valve
control means and a thermocouple; an apparatus for terminating
the supply of gas to the burner comprising: means for
providing an electrical signal responsive to the level of
carbon monoxide being emitted from the appliance, and means
responsive to the electrical signal for terminating the supply
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of gas to the burner when the level of carbon monoxide exceeds
a predetermined level.
In accordance with another aspect of the invention there is
provided an apparatus for terminating a supply of gas to a gas
burner having an exhaust flue comprising: a thermocouple
adapted to produce an electrical signal in the presence of a
flame from the gas burner; valve means for controlling the
supply of gas to the gas burner, the valve means being
maintained in an open position when subjected to the
electrical signal; sensing means for detecting the presence of
carbon monoxide in an area adjacent the exhaust flue, and
adapted to produce an electrical control signal when the level
of carbon monoxide is detected above a predetermined level;
and switch means controlled by the electrical control signal,
the switch means being connected between the thermocouple and
the valve means, whereby in the presence of carbon monoxide
above the predetermined level the electrical signal is removed
from the valve means closing the valve means and terminating
the supply of gas to the gas burner.
Brief Description of the Drawings
An embodiment of the invention will be described by way of
example in conjunction with the drawings in which:
Fig. 1 illustrates a perspective view of a refrigerator
showing mainly the back with the gas shut-off system of the
present invention mounted thereon;
Fig. 2 illustrates a schematic representation of a
typical gas control valve;
Fig. 3A illustrates a perspective exploded view of the
gas control valve of Fig. 2 interconnected with the gas shut-
off system of the present invention;
Fig. 3B illustrates a cross sectional view of a split
adapter interconnecting various components of the gas shut-off
system of the present invention;
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Fig. 4 illustrates a block diagram of the main components
of a CO sensor interconnected with the gas shut-off system of
the present invention; and
Fig. 5 illustrates the switching circuit of the present
invention.
Detailed Description of An Embodiment of the Invention
Fig. 1 illustrates the back of a refrigerator 10 with a gas
shut-off system 12 mounted to the refrigerator 10 and
interconnected with a gas control valve 18. The shut-off
system 12 includes a carbon monoxide (C0) sensor 14 and a
split adapter 16. The sensor 14 has a pair of wires 22
extending therefrom to the adapter 16 for providing a gas
shut-off signal to the gas control valve 18 in the event that
excessive levels of CO are discharged into the dwelling. The
details of this operation will be discussed in conjunction
with Figs. 4 and 5.
In general, when the refrigerator is operating under normal
conditions, a burner assembly 31 supports a flame 46 and
combustion of propane occurs in a combustion chamber 24 of the
refrigerator 10 with the products of combustion being
exhausted through a flue 26 into a room (not shown) in which
the refrigerator 10 is located.
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When there is a requirement to cool down the refrigerator 10,
flame 46 is fed with a relatively large gas supply which
provides the necessary energy to cool the refrigerator 10.
When the refrigerator 10 is at the required temperature, the
intensity of the flame 46 is dramatically reduced by reducing
the supply of gas to the burner 31.
A schematic representation of a typical gas control valve 18
commonly used in propane powered refrigerators is detailed in
Fig. 2. The gas control valve 18 includes a chamber 34 having
a pair of baffles 36 for directing the flow of gas through the
chamber 34; a reset button 32; a valve plate 38 connected to a
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electromagnetic valve assembly 44 which is biased by a spring
40. A gas inlet pipe 28 provides the supply of propane and a
gas outlet pipe 30 supplies the propane to the burner assembly
31.
The operation of the control valve 18 will be discussed with
reference to Fig. 2 without the interconnection of the shut-
off system 12 of the present invention.
When the thermocouple 20 is heated by the flame 46, the
thermocouple 20 generates a small electrical charge
(approximately 27 mV) which energizes the electromagnetic
valve assembly 44 which in turn holds the valve plate 38 in a
gas flow position. Specifically, the valve plate 38 is
oriented to allow the flow of propane from the inlet pipe 28
to the outlet pipe 30 by passing between the space in the
baffles 36.
If the flame 46 becomes extinguished the electromagnetic valve
assembly 44 is no longer energized, since the thermocouple 20
no longer generates the required voltage. Consequently, the
electromagnetic valve assembly 44 drops the valve plate 38 on
portions of the baffles 36. As a result, the flow of propane
from the inlet pipe 28 to the outlet pipe 30 is terminated.
To restart the flow of propane, the reset button 32 is
depressed, which pushes the valve plate 38 against the bias of
spring 40 of the electromagnetic valve assembly 44 and lifts
the valve plate 38 above the baffles 36. This allows the flow
of propane to reach burner 31. The flame 46 is then lit to
heat the thermocouple 20 which eventually will generate enough
electricity to charge the electromagnetic valve assembly 44 to
maintain the valve plate 38 in a gas flow position. At this
stage the reset button 32 is released and propane will
continue to flow from the inlet pipe 28 to the outlet pipe 30
by passing between the space in the baffles 36.
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Fig. 3A illustrates the interconnection of the shut-off system
12 of the present invention with the control valve 18 and the
thermocouple 20.
The adapter 16 (detailed in Fig. 3B) includes an external
threaded protrusion 54 at one end and an internally threaded
portion 55 at the other end. A conducting element 56 extends
outwardly from the protrusion 54 and inwardly to a cavity 59
in the adapter 16. The conducting element 56 is insulated
from the body of the adapter 16 by an insulating sheath 58.
The body of the adapter 16 is provided with an aperture 60
that extends through the sides of the adapter to expose a
portion of the conducting element 56.
The protrusion 54 of adapter 16 is threaded into an interface
50 of the control valve 18. The wires 22 from the sensor 14
have a bi-polar connector 48 located at its end. The
connector 48 has two electrically separated metal strips 49.
The connector 48 is inserted into the aperture 60 of the
adapter 16 such that one of the metal strips 49 makes
electrical contact with the portion of the conducting element
56 that extends into the cavity 59 of the adapter 16. The
thermocouple 20 having a threaded end 52 is threaded into the
internally threaded portion 55 of the adapter 16. A portion
of the threaded end 52 of the thermocouple 20 makes electrical
contact with one of the metal strips 49, i.e. the metal strip
opposite the strip contacting the conducting element 56.
Fig. 4 illustrates the CO sensor 14 having a CO analyzer 62, a
sensor processor 64 and a speaker 66. These are all known
elements and will not be discussed in detail since they are
commonly available items. A switching circuit 70 in the form
of a MOSFET (metal-oxide-semiconductor field-effect
transistor) is added to the CO sensor 14 to provide the
necessary signals to the electromagnetic valve assembly 44 in
the control valve 18 to terminate the flow of propane to the
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outlet pipe 30 in the event that excessive amounts of CO
emissions are detected.
The precise acceptable limits of carbon monoxide vary
depending on the specific safety regulations in force in the
district of interest. For example, the Ontario Fuel Safety
Branch, in Canada, has established that 100 ppm of CO is the
upper acceptable limit before the occupant may become at risk.
The switching circuit 70 is electrically connected to the
processor of the sensor 14 such that when a predetermined
level of CO is detected the circuit 70 will effectively drop
the voltage across the electromagnetic valve assembly 44 to 0
volts, which in turn will close the valve 38 to terminate flow
of propane to the outlet pipe 30.
More specifically, Fig. 5 illustrates a typical MOSFET circuit
connected at the drain (D) to the thermocouple 20 and at the
source (S) to the electromagnetic valve assembly 44. The gate
(G) is attached to a DC voltage source supplied by the sensor
14. The following three operating conditions will be
encountered and accommodated by the shut-off system 12:
1. Normal APPliance Operation
CO Below Limit & Flame On
In this situation VGS is greater than the threshold
voltage of the MOSFET, or approximately +5 Volts. This
situation will induce a current iD that is greater than 0
amperes resulting in a "short" circuit which in turn
causes the voltage induced in the thermocouple
(approximately 27 mV) to be applied to the
electromagnetic valve assembly 44. When the
electromagnetic valve assembly 44 is energized the valve
38 is maintained in a gas flow position (i.e. above
baffles 36) to continue the flow of propane to the outlet
pipe 30 to provide fuel to the burner assembly 31.
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2. Carbon Monoxide Hazard
Excessive Levels of CO Detected & Flame On
In this situation the sensor processor 64 will reduce the
VGS voltage from +5 volts to approximately 0 volts. This
situation will in turn reduce the current iD to 0 amperes
resulting in an "open" circuit such that the voltage
induced in the thermocouple 20 is not applied to the
electromagnetic valve assembly 44 so that the valve 38
drops into a position in which the flow of propane is
terminated (i.e. the valve 38 rests on the baffles 36).
The flame 46 will be extinguished and eventually the
thermocouple 20 will cool down such that no voltage is
generated by the thermocouple 20.
3. ProPane Leak Hazard
Co Below Limit and Flame is Extinguished
In this situation VGS remains at +5 volts and the MOSFET
is "short" circuited. However, the voltage generated by
the thermocouple 20 drops to zero since it cools down
with no flame 46. This voltage, or more particularly the
lack of voltage, is applied across the electromagnetic
valve assembly 44 such that the valve 38 drops into a
position in which the flow of propane is terminated (i.e.
the valve 38 rests on the baffles 36).
In summary, the shut-off system 12 does not affect the normal
operation of the thermocouple 20, but includes the additional
feature of safely terminating the flow of propane to the
outlet pipe 30 in the event that the CO emissions exceed a
predetermined level.
The present invention provides a simple gas safety shut-off
system that can be easily retrofitted to many existing
refrigerators by merely unscrewing the thermocouple, inserting
the adapter and the connector from the CO sensor and then
screwing the thermocouple into the adaptor. The resulting
arrangement provides an added measure of safety in the event
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of excess levels of CO being emitted from the flue of the
refrigerator.
