GB2306735A - Gas detecting safety device - Google Patents

Abstract

A gas detecting safety device comprises a detector (43) for sensing the presence of a toxic gas eg carbon monoxide produced by malfunction of a boiler or other appliance and a relay (25) for insertion into the electricity supply to the boiler or other appliance so as to shut off the appliance once the presence of the toxic gas has been detected.

Description

GAS DETECTING SAFETY DEVICE This invention relates to a gas detecting safety device.

Where central heating boilers and like apparatus are used, these have an outside flue to which the combustion products of the boiler are fed. Should this outside flue and its connections become blocked or leak, toxic fumes will find their way back into the room or location at which the boiler is situated. These fumes are mainly carbon monoxide.

The fumes may not be readily noticed with serious effects on the occupants of the room, which may, in the worse cases, prove to be fatal.

The present invention seeks to provide a safety device for dealing with this problem.

According to the invention, there is provided a gas detecting safety device and a relay for insertion into the electricity supply to the boiler or other appliance such as to shut off the appliance once the presence of the toxic gas has been detected.

Preferably, the device is provided with an audible and/or visual signal providing an indication of shut down of the appliance.

Suitably, the device may be a self-contained unit having means for connecting it to the electricity supply at the point fed by the boiler and is provided with a socket into which the plug which would normally be connected into the mains socket to operate the boiler or appliance is inserted.

The invention will now be described in greater detail, by way of example, with reference to the drawings FIG.1 is a schematic view of a gas detecting safety device in accordance with one embodiment of the invention, and; FIG.2 is a circuit diagram of the device shown in FIG.1.

Referring firstly to FIG.1, there is shown the safety device in accordance with the invention comprising a unit 1 having a mains input supply indicated by the lead 3 and an output supply for connection to a boiler or like appliance indicated by the three pin socket 5. The face of the unit is provided with a carbon monoxide sensor 7 test and reset buttons 9 and 11 and two L.E.D. indicator 13 and 15, the one 13 on the left showing white for normal operation and red once the toxic gas has been detected by the gas detector. The other L.E.D. 15 on the right hand side of the unit 1 will show green to indicate that the unit is on and this L.E.D. 15 will flash prior to the operation of the unit 1 on detection of the toxic gas.

The circuit of the unit will be described hereafter in relation to FIG.2.

As far as the operation of the unit 1 is concerned, the connection to the boiler or like appliances is unplugged and a plug (not shown) on the end of the unit input lead 3 will be plugged into the socket. The lead from the boiler or other appliance is then plugged into the three pin socket 5 provided on the unit. Once the unit 1 is connected into the main supply as just described, the power on indicator 13 will light up green and the operational L.E.D 15 will show white indicating that the device is in operation The device will remain in this state until the sensor 7 detects the presence of a particular level of toxic gas, particularly carbon monoxide, and as soon as the presence of this gas is detected, the power on indicator 13 will start to flash indicating that the gas has been sensed.Shortly thereafter, the electronics in the unit, responsive to the operation of the gas sensor 7 will cut off a relay positioned between the input and output of the unit, thus cutting off the electricity supply to the boiler or other appliance, and the operating L.E.D. 15 will change from white to red. At the same time an audible alarm will be sounded to alert people to the fact that the boiler or other appliance has been switched off.

Also seen on the front of the unit is a one amp fuse holder 17.

FIG.2 shows a suitable circuit arrangement for the above described unit.

Electricity supply is provided by means of the input lead indicated at 21 which feeds electric current from the input to the output three pin socket indicated at 23. Interposed between the input and output is a relay 25 which is provided with a pair of normally open contacts 27 and 29 which control the supply of electricity. The two pairs of contacts provide a double pole cut off arrangement for the live and neutral of the supply.

Suitably, a suppressor 31 may be connected across the output from the relay 25 to suppress the effects of arcing of relay contacts. From the main supply prior to the relay, there is taken off by means of lines 33 and 35 and passed to a power supply unit 37.

This power supply unit 37 provides a live output 39 which is connected to the relay coil 41 of the relay 25 and is also connected to the electronic circuitry for operating the unit.

The power supply unit 37 is suitably a small transformer, rectifier and smoothing circuits.

The voltage produced by the power supply unit 37 is typically 8 volts for the analogue sensor circuit and 4-5 volts for the digital drive etc.

A carbon monoxide detector is shown at 43 which is energised from the live output VCC of the power supply unit and, in the form shown, has an energised resistance 45 of which the resistance varies depending upon whether the presence of the gas CO is sensed. The output of the gas detector 43 is provided over a line to a comparator 47 where it is compared to a reference value generated by voltage divider 49. The comparator 47 is provided with a latch circuit 51. The output from the latched comparator 47 is fed to a signal processor and driver unit in the form of a micro-controller 53. This unit 53 drives the gas detector 43 with the required waveforms and amplifies and smooths the resultant signal from the comparator in a form suitable for the level detectors provided in the unit.

The circuit works by integrating a different signal from the detectors and, using the micro controller, the time for the gas to reach a known level is determined. As the concentration of the gas changes, so does the integration time and this is used to drive alarms comprising a buzzer 55 and the L.E.D. operating indicator 57 and to directly control the relay 25. The controller also cycles the detector resistance in order to keep it in optimum condition.

As shown in the drawing, a second gas detector 6 can be provided using similar circuitry to the C.O. detector 43, for example for detecting the leakage of the supply gas and this will also then operate to shut off the boiler or other appliance when a leak is detected.

It will be appreciated that various modifications and alterations may be made to the above described detector device without departing from the scope of the invention.

For example, the mechanical relay which has been shown in the circuit diagram could be replaced by a solid state relay, which in this case would only switch the live line of the electricity supply. This is particularly desirable where an inflammable gas is being detected since a range of mechanical contacts could set off an explosion if the appropriate concentration of gas is present.

While the operation of the device is controlled, as shown, by a micro controller, it would be equally possible to implement this controller by other methods for example it could be merely a simple comparator circuit which is used to drive the L.E.D's and control the relay when a preset level of gas is reached. While the particular advantage of the current embodiment of the invention is that the safety device can be connected up quite simply without requiring the need for installation by electrician because it merely plugs into the mains and the boiler is supplied from the unit. Other arrangements can be provided in which the relay is wired into the circuit of, for example, the gas control valve.

Claims (7)

CLAIMS:

1. A gas detecting safety device comprising a detector for sensing the presence of a toxic gas produced by malfunction of a boiler or other appliance and a relay for insertion into the electricity supply to the boiler or other appliance so as to shut off the appliance once the presence of the toxic gas has been detected.

2. A device as claimed in claim 1, wherein the device is provided with an audible and/or visual signal providing an indication of shut down of the boiler or other appliance.

3. A device as claimed in claim 1 or 2, wherein the device is a selfcontained unit having means for connecting it to the electricity supply at the point fed by the boiler or other appliance and is provided with a socket into which the plug which would normally be connected into the mains socket to operate the boiler or appliance is inserted.

4. A device as claimed in any preceding claim, wherein the relay is provided with a pair of make contacts so that the electricity supply to the boiler is shut off when the device is not in operation.

5. A device as claimed in any preceding claim, wherein the detector is a carbon monoxide detector.

6. A device as claimed in any preceding claim wherein a comparator is provided in which the output from the gas detector is compared with a reference value, the output from the comparator being fed to a microcontroller which controls the operation of the relay.

7. A gas detecting safety device substantially as described herein with reference to the drawings.