GB2156154A

GB2156154A - Temperature sensors

Info

Publication number: GB2156154A
Application number: GB08407118A
Authority: GB
Inventors: Edward George Henry Read
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-03-19
Filing date: 1984-03-19
Publication date: 1985-10-02
Also published as: GB8407118D0

Abstract

A temperature sensor includes a fusible material 5 which softens at a predetermined ambient temperature to close an electrical circuit. The fusible material 5, for example paraffin wax, is kept in compression between a spring 4 and an electrode 3 such that when the fusible material softens the spring expands and makes electrical contact with the electrode. <IMAGE>

Description

SPECIFICATION Temperature sensor and its use in a fire alarm system This invention relates to a novel electrical temperature sensor or heat detector and to its use, especially in domestic fire alarm systems.

My invention provides a temperature sensor comprising a body of fusible insulating material so resiliently compressed between two conductors that when the fusible material is softened by heat the conductors are brought into electrical contact with each other.

In this specification the words "conductor" and "insulating" refer to the electrical properties of the material in question.

The expression "fusible material" used herein means any material that is a dimensionally stable solid below a given temperature but above that temperature starts to soften, thus enabling the conductors to make contact. The choice of the fusible material will of course depend upon the temperature at which the sensor is intended to operate.

When intended for use in a domestic fire alarm system for example the sensor will contain a fusible material that is dimensionally stable at room temperature, or say up to 50 C and begins to soften at a temperature that justifies the giving of an alarm, typically, say, 60"C to 80"C or above. It has been found that candle-wax and other grades of paraffin wax are admirably suited for temperature sensors for use in normally habitable environments such as homes, shops and offices, but other types of natural or synthetic fusible materials may equally well be used. I envisage for example sensors for use in mechanical or industrial environments where a cheap and instant alarm system to warn of overheating is required, and the fusible material will then have a much higher softening range.The invention is not therefore limited to the use of fusible materials softening at any particular temperature or over any particular temperature range as it is within the capacity of those skilled in the art to select appropriate fusible materials with regard to the intended application of the sensor.

In a preferred form of my invention two electrically conducting stops are disposed at either end of a helical compression spring one end of which is braced against one stop and the other end of which is held in compression away from the other stop by the fusible material in the form of a plug.When the fusible material softens or melts under the action of heat the compression spring expands and bridges the gap between the stops.

In a preferred embodiment of my invention to be hereinafter more particularly described the sensor consists of a tube containing the stops spaced axially apart. In between them is a helical spring and a plug of paraffin wax or other fusible material which holds the spring in compression.

The sensor according to my invention is particularly suitable for use in a low-voltage domestic fire alarm system. It may be connected into a circuit with a low-voltage power source (e.g. 3 to 1 2 volts) and a buzzer. The sensors in such a system may be disposed anywhere around the house, but are particularly suitable for embedding in a wall or ceiling. Such a low voltage domestic fire alarm system is easy for the home handyman to install and, because of its low voltage, much safer than generally similar systems operated by mains voltage. The sensor according to the invention cannot be triggered by smoke or fumes, as can sensors that rely on conductivity or the interruption of a beam of light.

A further advantage is that the sensors are cheap and disposable; that is, once one has gone off it has no further use and must be discarded and replaced with a new one. This is easily done and by regularly checking and (where necessary) replacing sensors, the householder can keep his alarm system in working order.

A preferred embodiment of my invention will now be described with reference to the drawings, in which: Figure 1 is a general isometric view of a temperature sensor according to my invention Figure 2 is a longitudinal cross section of the temperature sensor shown in Fig. 1 Figure 3 shows in cross section a temperature sensor according to the invention installed in a panel Figure 4 is a circuit diagram showing a domestic fire alarm system using sensors according to my invention.

Referring first to Figs. 1 and 2, a temperature sensor according to the invention comprises an open ended tube 1 mounted in which are two parallel metal stops 2, 3 spaced apart. Between the stops is a compression spring 4 which is, when uncompressed, sufficiently long to press against both stops and make electrical contact therebetween, but is normally held in a state of compression and out of contact with stop 3, by a plug of fusible non-conducting material 5. When the ambient temperature rises above the softening point of the fusible material the spring is allowed to expand and make contact between the stops 2 and 3.

Fig. 3 shows a temperature sensor as described with reference to Figs. 1 and 2 embedded in building material, for example insulating board.

Fig. 4 shows schematically a ground floor plan of a bungalow with a circuit diagram for a fire alarm system incorporating sensors according to the invention.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Temperature sensor and its use in a fire alarm system This invention relates to a novel electrical temperature sensor or heat detector and to its use, especially in domestic fire alarm systems. My invention provides a temperature sensor comprising a body of fusible insulating material so resiliently compressed between two conductors that when the fusible material is softened by heat the conductors are brought into electrical contact with each other. In this specification the words "conductor" and "insulating" refer to the electrical properties of the material in question. The expression "fusible material" used herein means any material that is a dimensionally stable solid below a given temperature but above that temperature starts to soften, thus enabling the conductors to make contact. The choice of the fusible material will of course depend upon the temperature at which the sensor is intended to operate. When intended for use in a domestic fire alarm system for example the sensor will contain a fusible material that is dimensionally stable at room temperature, or say up to 50 C and begins to soften at a temperature that justifies the giving of an alarm, typically, say, 60"C to 80"C or above. It has been found that candle-wax and other grades of paraffin wax are admirably suited for temperature sensors for use in normally habitable environments such as homes, shops and offices, but other types of natural or synthetic fusible materials may equally well be used. I envisage for example sensors for use in mechanical or industrial environments where a cheap and instant alarm system to warn of overheating is required, and the fusible material will then have a much higher softening range.The invention is not therefore limited to the use of fusible materials softening at any particular temperature or over any particular temperature range as it is within the capacity of those skilled in the art to select appropriate fusible materials with regard to the intended application of the sensor. In a preferred form of my invention two electrically conducting stops are disposed at either end of a helical compression spring one end of which is braced against one stop and the other end of which is held in compression away from the other stop by the fusible material in the form of a plug.When the fusible material softens or melts under the action of heat the compression spring expands and bridges the gap between the stops. In a preferred embodiment of my invention to be hereinafter more particularly described the sensor consists of a tube containing the stops spaced axially apart. In between them is a helical spring and a plug of paraffin wax or other fusible material which holds the spring in compression. The sensor according to my invention is particularly suitable for use in a low-voltage domestic fire alarm system. It may be connected into a circuit with a low-voltage power source (e.g. 3 to 1 2 volts) and a buzzer. The sensors in such a system may be disposed anywhere around the house, but are particularly suitable for embedding in a wall or ceiling. Such a low voltage domestic fire alarm system is easy for the home handyman to install and, because of its low voltage, much safer than generally similar systems operated by mains voltage. The sensor according to the invention cannot be triggered by smoke or fumes, as can sensors that rely on conductivity or the interruption of a beam of light. A further advantage is that the sensors are cheap and disposable; that is, once one has gone off it has no further use and must be discarded and replaced with a new one. This is easily done and by regularly checking and (where necessary) replacing sensors, the householder can keep his alarm system in working order. A preferred embodiment of my invention will now be described with reference to the drawings, in which: Figure 1 is a general isometric view of a temperature sensor according to my invention Figure 2 is a longitudinal cross section of the temperature sensor shown in Fig. 1 Figure 3 shows in cross section a temperature sensor according to the invention installed in a panel Figure 4 is a circuit diagram showing a domestic fire alarm system using sensors according to my invention. Referring first to Figs. 1 and 2, a temperature sensor according to the invention comprises an open ended tube 1 mounted in which are two parallel metal stops 2, 3 spaced apart. Between the stops is a compression spring 4 which is, when uncompressed, sufficiently long to press against both stops and make electrical contact therebetween, but is normally held in a state of compression and out of contact with stop 3, by a plug of fusible non-conducting material 5. When the ambient temperature rises above the softening point of the fusible material the spring is allowed to expand and make contact between the stops 2 and 3. Fig. 3 shows a temperature sensor as described with reference to Figs. 1 and 2 embedded in building material, for example insulating board. Fig. 4 shows schematically a ground floor plan of a bungalow with a circuit diagram for a fire alarm system incorporating sensors according to the invention. CLAIMS

1. A temperature sensor comprising a body of isulating fusible material so resiliently compressed between two conductors that when the fusible material is softened by heat the conductors are brought into electrical contact with each other.

2. A sensor according to claim 1 comprising a spring held in compression by the fusible material at normal ambient temperatures and disposed to defor the fusible material when the same is softened under the influence of heat.

3. A sensor according to claim 2 in which the spring is a helical spring held in compression at ambient temperature by a plug of the fusible material.

4. A sensor according to any preceding claim in which the fusible material is paraffin wax.

5. A sensor accordng to claim 1 substantially as hereinbefore described with reference to the drawings.

6. A fire alarm system comprising at least one sensor according to any preceding claim conected in an electrical circuit with a power source and an alarm device sich that when the conductors are brought into electrical contact the alarm device operates.

7. An alarm system according to claim 6 substantially as hereinbefore described with reference to Fig. 3.

8. A fire alarm kit for domestic istalllation comprising in a package, at least one sensor accordig to any or claims 1 to 5, a power souce adapted to receive at least one dry cell, and an alarm device.