GB2276970A

GB2276970A - Gas alarm

Info

Publication number: GB2276970A
Application number: GB9406506A
Authority: GB
Inventors: Clive Rowlands; Martin Sharp; Jim Robinson
Original assignee: DEE ELECTRONICS Ltd
Current assignee: DEE ELECTRONICS Ltd
Priority date: 1993-04-06
Filing date: 1994-03-31
Publication date: 1994-10-12
Also published as: GB9406506D0; GB9307187D0

Abstract

Gas alarm apparatus comprising a housing 1 accommodating a gas detector 15, an alarm B1 and associated circuitry. In order to avoid the need for a pump to circulate gas past the detector, the housing has a gas flow path between an inlet 11 and an outlet 13 and circulation of gas through the housing is by convection current generated by the heat of the apparatus. The gas detector provides part of the heat source. An additional heating element may be provided. Where the apparatus is mains powered, its transformer 8 provides a source of heat. The housing is in the form of a plug with projecting pins to mate with a mains socket, Figs. 1 - 5, not shown. <IMAGE>

Description

Title: Gas Alarm DESCRIPTION The present invention relates to a gas alarm for detecting and signalling the presence of an undesirable gas or gases.

Gas alarms are known which will detect the presence of a particular gas or types of gases, for example combustible gases. The fact that they have to detect a particular gas makes them expensive to produce and heretofore they have been large in size and installation has required permanent wiring into a main supply. Such known gas alarms have their sensors mounted externally or require a mechanical pump for drawing gas samples through the sensor. Positioning the sensor externally leaves it open to damage whilst provision of a mechanical pump increases the cost.

If a gas alarm could be made which is of a relatively compact nature, of economical construction and which could detect the presence of a large variety of undesirable gases it is believed that it would enjoy a ready market in the domestic sphere. The presence of combustible gases and suffocating gases including products of combustible gases presents a considerable hazard in the domestic environment.

Accordingly, it is an aim of the present invention to provide a smoke alarm which overcomes one or more of the above disadvantages and is rendered suitable for domestic uses.

Accordingly, a first aspect of the invention provides gas alarm apparatus comprising a housing accommodating a gas detector, an alarm and associated circuitry, characterised in that there is a gas flow path through the housing between an inlet and outlet which flow path passes the gas detector and in which circulation of gas through the housing is by convection current generated by the heat of the apparatus.

By positioning the detector within the housing it is safe from damage and by utilising convection current to generate a flow through the housing the need for a mechanical pump is avoided. A preferred gas detector also includes a heating element. For a mains powered alarm a transformer incorporated in the housing provides a heat source which will supplement the heat generated by the gas detector. Where the alarm is not mains powered then the power may be by way of a remote battery pack by way of a flying lead or suitable socket connection.

According to another aspect of the invention there is provided gas alarm apparatus comprising a housing accommodating a gas detector, an alarm and associated circuity and further comprising a mains plug by which the apparatus is plugged directly into a mains outlet socket This aspect of the invention renders it particularly convenient for use around the house in any desired location. Depending on the intended market the mains plug will be configured to suit the local socket configurations be they 3-pin 13 amp type, as in this country, Europlug type, or 2-pin types.

A preferred gas detector is capable of detecting combustible gases including solvents, CO, SO2 and even smoke.

By simplifying the circuitry the housing can be reduced in size to little more than twice the size of a conventional 3-pin 13 amp plug.

The present invention will now be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a front view of the apparatus, Figure 2 is a rear view, Figure 3 is a side view, Figure 4 is a plan view, Figure 5 is an inverted plan view, Figure 6 is a front view with housing cut away to show the convection path, and Figure 7 is a circuit diagram of the device.

Referring to the drawings, a gas alarm comprises a housing 1 of generally rectangular configuration as viewed from the front and side, having projecting from the rear face thereof three pins 3r 5 / 7 to mate, in use, with a 3-pin mains 13 amp socket outlet, not shown, providing power to the apparatus. Other pin configurations may be employed to suit the local requirements and the formation 9 from the rear of the housing from which the pins project is. designed to accept other pin configurations. A.C. mains power is to a transformer 8 of the device and associated power supply circuitry provides power for a gas detector 15 comprising a heating coil 17 and sensing material 19.

IC1 acts as a comparator to compare the output from the sensing material with a reference voltage and to power up the sounder B1 and light emitting diode LD2 when an undesirable gas is detected. Light -emitting diode LD1 is illuminated when the device is powered up.

It will be seen that the housing has an inlet port 11 disposed in its lowermost side and in the example to the left hand side of the housing as viewed from the front. The inlet is shown immediately below the gas detector 15. Above the gas detector in the top left hand portion of the housing is the transformer 8, whilst the housing has an outlet at 13 disposed in the upper wall of the housing towards the right hand side so that a flow path is generated between the inlet and outlet as designated by dotted lines 25 Heat from the various components within the device is exploited to set up a convection current with air being driven into inlet 11 passing across the sensor 15 and exiting at outlet 13. This continuous flow of air across the sensor provides efficient monitoring of the environment.

The size of the inlet and outlet orifice is carefully correlated with the heat evolution of the circuit components to produce adequate convection current through the housing.

It will be noted that the housing also has an orifice 17 positioned close to the sounder B1. In the illustrated embodiment the circuit derives it's power from the mains via the transformer allowing operation from 220 or 240 volts without modification. For operation from 110 or 120 volts a different transformer would be fitted. For operation from 12 or 24 volts (car, van, etc.) a regulator is fitted in place of the transformer and associated components. For 6 volt operation (battery pack) the transformer and rectifier are removed.

The smoothed and regulated supply is applied to the gas sensor heating element and also a bridge circuit which has the sensing element part of the gas sensor as one arm. The bridge circuit is connected to the comparator such that when the bridge is unbalanced, through the presence of a 'pollutant', an audible alarm is sounded and also a warning red LED (LD2) is illuminated.

The alarm will continue to sound until after the 'pollutant' has dispersed, the bridge will then return to it's normal state.

Claims

1. Gas alarm apparatus comprising a housing accommodating a gas detector, an alarm and associated circuitry, characterised in that there is a gas flow path through the housing between an inlet and outlet, which flow path passes the gas detector and in which circulation of gas through the housing is by convection current generated by the heat of the apparatus.

2. Apparatus as claimed in claim 1 further comprising a heating element.

3. Apparatus as claimed in claims 1 or 2 when mains powered, in which a transformer incorporated in the housing provides a heat source which will supplement the heat generated by the gas detector.

4. Apparatus as claimed in claim 1 or 2 in which power is by way of a remote battery pack by way of a flying lead or suitable socket connection.

5. Apparatus as claimed in any one of claims 1 to 3 in which a mains plug is formed integrally with the housing by which the apparatus is plugged directly onto a mains outlet socket for use.

6. Gas alarm apparatus comprising a housing accommodating a gas detector, an alarm and associated circuity and further comprising a main plug by which the apparats is plugged directly into a mains outlet socket.

7. Apparatus as claimed in claim 6 in which there is a gas flow path through the housing between an inlet and outlet, which flow path passes the gas detector and in which circulation of gas through the housing is by convection current generated by the heat of the apparatus

8. Apparatus as claimed in claims 6 or 7 in which a main transformer incorporated in the housing provides a heat source to supplement the heat of the gas detector.

9. Apparatus as claimed in claims 6, 7 ot 8 further comprising a heating element.

10. Apparatus as described in any one of the preceding claims when capable of detecting combustible gases including solvents, CO, CO2 and even smoke.

11. Apparatus constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.