GAS ALARMS

Technical Area

This invention relates to gas alarms and in particular to alarms which can be located in an area where a gas appliance is or may be used, or gas stored, to provide an alarm should there be any escaping gas detected and which, at the same time, is safe to have in such an area.

Background to the Invention

Whilst in Australia all buildings must have smoke detectors, many buildings use gas for cooking, hot water or heating and, in many cases, these gas appliances have pilot lights and, in most cases, have means whereby there are thermal cutouts. However, gas stoves, for example, do not normally have such things and cut-outs can fail in devices such as hot water services and heating systems, so there can be a release of gas into the atmosphere which can reach dangerous levels, either to the health of people breathing the air or from a fire safety point- of-view where an explosive, inflammable mixture can develop and there is normally no way of detecting this other than by smell.

In many cases persons' sense of smell are compromised and they would not

recognise the gas smell until the level is dangerous and, if a person is asleep, it is quite possible they would not be awoken.

Outline of the Invention

The object of the invention is to provide such a detector.

The invention includes a gas alarm comprising a unit adapted to be connected to an electrical power source which includes therein a sensor unit for the type of gas to be detected, power supply means to operate a heater coil in the sensor and the remaining circuitry, means whereby when the output of the sensor indicates the presence of the gas to be detected to cause operation of a warning device.

The alarm can be used in different circumstances, such as in enclosed building spaces and motor vehicles and can be adapted to ascertain the presence or various gasses,

Preferably the device includes test means whereby the operation of the device can be checked and it may also include a fan to ensure that air from the surround is fed into the sensor.

Description of an Embodiment of the Invention

In order that the invention may be more readily understood, one embodiment of this shall be described in relation to the accompanying drawings; in which:

Fig 1 Shows an external view of a first embodiment of the alarm connected to a standard power point;

Fig 2 Shows a plan view of the embodiment of Fig 1 ; and Fig 3 Shows the operating circuit of the sensor element.

The alarm can be used for sensing the presence of a gas and for domestic and industrial areas this would be natural gas or LPG although in some areas methane could be used as could coal gas. The operation of the alarm can be considered to be similar for each of these but the actual operating parameters of the detector, or even the type of detector itself, could be adapted to changed to suit the particular gas type to be monitored.

The alarm has a casing 10 of a moulded plastics material having associated therewith pins 11 for direct connection to a general purpose outlet 20. If required, there could be provided a flexible conductor connected into the alarm and having a plug on the end thereof for connection to an outlet.

The input power passes through a transformer to provide a required output voltage and there is then preferably a rectification and smoothing circuit to provide a constant voltage, and one particular example, a 9-volt regulated

voltage. If required the power supply may have two output voltages as will be described later herein.

The sensor device 15 may be a commercially-available device and in general terms such devices comprise a sintered-bulk semi-conductor which have a heating coil 16 located therein, the arrangement being such that if air containing a combustible gas is passed through the sensor element, the gas will be burnt by the heating element and the temperature in device will rise, causing a variation in resistance of the semi-conductor and effectively a change in an output voltage V _RL across a load R _L .

It was stated earlier that the power supply could provide more than one voltage and as can be seen from Rg 3 the heater 16 may use a voltage V _H and the operating circuit a voltage V _c .

The change in the voltage V _RL can be ascertained by a detector circuit and indicates an alarm condition, when the change reaches a pre-determined value. This, in turn, will initiate an operation of an alarm device which may be both audible and visible. In one particular form the alarm device can be a Piezo horn which has an operating frequency of 3.7 Khz but this of course is a preferment as such a horn can readily fit within a small casing and gives a substantial warning signal.

The casing can have thereon indicator lights 17,18, one of which 17 is a power indication light so there is a visible indication that the device is operating and the other 18 being an alarm device which can be, say, a flashing red light or whatever is desired which operates when an alarm condition is detected by the sensor.

In another embodiment of the invention there is, in the casing, a fan (not shown) which enables ambient air to be drawn through the sensor thereby providing a more sensitive indication of the presence of gas.

The alarm also has a testing circuit which has a manual operation button 19 which indicates the alarm is operating correctly.

The device of this embodiment is designed for use in enclosed spaces having a source of power, specifically domestic and commercial premises.

The invention also includes self-powered alarms which could be used in substantially enclosed barbeque areas and the like and alternatively powered alarms which could be used, for example, in gas powered vehicles and which are operated from the vehicle's power supply.

It is to be understood that many other variations and modifications can be made in the alarm of the invention without departing from the spirit and scope thereof.