GB2514344A

GB2514344A - Temperature detection system

Info

Publication number: GB2514344A
Application number: GB1309016.2A
Authority: GB
Inventors: Paul David Smith; Paul Alan Rennie
Original assignee: Kidde Technologies Inc
Current assignee: Kidde Technologies Inc
Priority date: 2013-05-20
Filing date: 2013-05-20
Publication date: 2014-11-26
Anticipated expiration: 2033-05-20
Also published as: GB201309016D0; GB2527216B; GB2527216A; GB201514985D0; GB2514344B

Abstract

A temperature detector 10 comprises a first tube 21 defining a first chamber 24, and a second tube 22 defining a second chamber 23. The second chamber 23 contains a solid material 14 that evolves gas upon heating, while the first chamber 24 contains a lesser amount of, or no, such material. The first and second tubes 21, 22 may be in fluid communication with a single pressure switch (40,Fig.4a). The first and second tubes 21,22 may extend parallel to one another, or the second tube 22, may be located within the first tube 21 (see Fig.3a). The second tube 22 may contain a gas at a lower pressure than the first tube 21. The pressure switch (40,Fig.4a) may be configured to provide a first alarm indicative of a first pressure increase in the first tube 21 at a first temperature, and a second alarm indicative of a second pressure increase in the second tube 22 at a second higher temperature. The first alarm may indicate an overheat condition whilst the second alarm may indicate a fire condition. An integrity sensor may be provided in fluid communication with the first chamber to detect a drop in pressure of the pressurized gas.

Description

Temperature detection system

TECHNICAL FIELD

The present disclosure relates to a temperature detection system, and a temperature detector and pressure switch for use in a temperature detection system. The temperature detection system may be an overheat or fire alarm system. Overheat or fire alarm systems can be used to monitor a number of different environments including various parts of aircraft and in other aerospace applications.

BACKGROUND

A known overheat or fire alarm system comprises a temperature detector tube in fluid communication with a pressure sensor. The detector tube commonly comprises a metallic sensor tube containing a metal hydride core, typically titanium hydride, and an inert gas fill, such as helium. Such a system is shown in US- 3122728 (Lindberg).

Exposure of a portion of the detector tube to a high temperature (such as due to a localised fire) causes the metal hydride core to evolve hydrogen. The associated pressure rise in the detector tube causes a normally open pressure switch in the sensor to close. This generates a discrete fire alarm. The pneumatic pressure sensor is also configured to generate an averaging overheat alarm, at a lower temperature experienced over a longer portion of the tube. The temperature increase causes a pressure rise due to the thermal expansion of the inert gas fill, which also causes a normally open pressure switch in the sensor to close. A prior art detector tube is shown in Figs. 1(a) and 1(b).

In prior art systems, the discrete fire alarm and the averaging overheat alarm can be provided by first and second diaphragms in a single pressure sensor.

The first diaphragm is configured to be deformed at a first pressure corresponding to the increased pressure of the infill gas at the overheat condition, while the second diaphragm will not be deformed until the pressure is further increased to that corresponding to the lire condition. Such an arrangement can be difficult to manufacture and may be unable to distinguish between an overheat condition occurring over a large portion of the tube and a fire condition occurring over a very small portion of the tube (i.e. a cross-over of alarm conditions may occur).

The present disclosure seeks to address at least some of these issues.

SUMMARY

There is disclosed herein a temperature detection system comprising a first tube defining a first chamber, the first chamber containing a pressurised gas and a second tube defining a second chamber, the second chamber containing a material that evolves gas upon heating. The first and second chambers are in fluid communication with one or more pressure sensors. Heating at least a portion of each of the first and second tubes to a first temperature causes a higher pressure in the first chamber than the second chamber, and heating at least a portion of the first and second tubes to a second, higher temperature causes the material to evolve gas and results in a higher pressure in the second chamber than the first chamber.

The first tube containing a pressurised gas can be used to provide an overheat alarm. The second tube having the gas-evolving material can be used to provide a fire alarm. Using separate tubes for the overheat and fire alarms allows a less complex, lighter pressure sensor to be used. The pressure set-points of the tubes may also be able to be more finely controlled.

The first and second chambers and the first and second tubes may be elongated, i.e. their length may be much larger than their width or diameter. For example, the length of the tubes may be at least 100 or 1000 times their diameter.

The first and second chambers are hermetically sealed from one another.

The first and second tubes each have an opening (for example at one end thereof) for connection to a pressure sensor, so that the chambers are in fluid communication with the pressure sensor. The first and second tubes may each also have an additional opening for connection to another pressure sensor, for example an integrity sensor used to detect any leakage from the tubes.

The first and second tubes may define first and second open-ended chambers. The first and second chambers may have the same length. The first and second tubes may have the same length.

The gas may be an inert gas, such as argon or helium. The gas is usually known in the art as an "infill gas".

The term pressurised' is used to indicate that the gas is at a pressure above atmospheric pressure. For example, the gas may be pressurised to a pressure of 1.5 bar or more, or at least 2.0 bar.

The material that evolves gas upon heating comprises a material that when heated to a sufficiently high temperature will evolve a substantial amount of gas.

When located in a fixed volume, sealed container, heating such a material will evolve sufficient gas to cause a large increase in pressure within the container.

Some examples of such materials are listed in US-3122728, as referred to above.

The material may be a solid, such as a metal hydride. For example, a titanium hydride core may be used.

The one or more pressure sensors may be any sensor that can detect the pressure in the first and second chambers. A single sensor may be connected to both tubes, thus providing a lighter system having fewer parts. Alternatively, a first sensor may be connected to the first chamber and a second sensor may be connected to the second chamber.

The one or more pressure sensors may comprise one or more pressure switches that give a digital output, such as a switch comprising a deformable diaphragm and at least one electrical terminal, or one or more pressure transducers that give a continuous (analog) output, such as a piezoresistive transducer.

The step of heating at least a portion of each of the first and second tubes may involve placing the first and second tubes in an environment which subsequently undergoes an increase in temperature. In a fire condition, it is likely, that at least initially, a smaller portion of the tubes will be heated, compared to an overheat condition, where the majority of the length of the tubes in that environment will experience an increase in temperature.

The first chamber may contain a lesser amount of material that evolves gas upon heating. The term lesser amount' is intended to mean that there is less material by weight. The first chamber may contain no such material, i.e. a zero amount.

The first tube can be used to provide an overheat alarm without needing any gas-evolving material.

Under normal conditions, before the first and second tubes are exposed to elevated temperatures due to an overheat of fire condition (e.g. at room temperature), the second tube may contain a gas at a lower pressure than the first tube. The lower pressure gas may be an inert gas or may be air. The lower pressure gas may be at ambient or atmospheric pressure (at room temperature).

The one or more pressure sensors may be configured to provide a first alarm indicative of a first pre-defined pressure increase in the first tube at the first temperature and a second alarm indicative of a second pre-defined pressure increase in the second tube at the second, higher temperature Alternatively, the one or more pressure sensors may be configured to provide a first alarm indicative of the higher pressure in the first tube at the first temperature and a second alarm indicative of the higher pressure in the second tube at the second temperature activates a second alarm.

The first alarm may provide an indication of an overheat condition, while the second alarm may provide an indication of a tire condition. Using two separate tubes allows these two conditions to be more easily distinguished.

The first and second tubes may have a substantially or wholly circular cross-section, but other shapes would also be suitable. The first and second tubes may be cylindrical, but other shapes would also be suitable.

The first and second tubes may be secured to each other along at east a portion of their length. The securement may be direct or indirect, i.e. there may or may not be any intervening parts or layers forming the securement between the first and second tubes. For example, the first and second tubes could be tack welded together at a number of points along their length. Alternatively, the first and second tubes could be secured along their full lengths, for example by integrally forming the two tubes via extrusion or moulding.

Alternatively, the first and second may not be secured to each other at all.

The first and second tubes may be arranged such that the first and second chambers are in thermal contact. In other words, heating one of these chambers will cause a heat rise in the other chamber, or put another way, when installed in an environment to be monitored, both chambers will experience similar heat increases when subjected to a rise in temperature.

The first and second chambers may share a common wall. In other words, one of the walls, or a portion of a wall, of the first chamber may be one of the walls, or a portion of a wall, of the second chamber.

The common wall may be a wall of one of the tubes, or a wall that is common to both tubes.

The first and second tubes may extend parallel to each other along at least a portion (or all) of their lengths.

The first and second chambers may be spaced apart in a direction transverse to the longitudinal direction in which the first and second tubes extend.

In other words, the first and second chambers may run alongside each other, separated by walls of the first and second tubes (or a single common wall). In such an arrangement, the first and second tubes may be secured to each other, either by being integrally formed orty securing distinct first and second tubes together. In cross-section through the diameter of the tubes, the two tubes may form a figure-of-eight' shape, with the first and second chambers forming the two holes in the eight. In this arrangement, the first and second tubes may have a similar diameter, although this is not necessary.

In an alternative arrangement, the second tube may be located within the first tube. The first chamber may be defined between the (outer) first tube and the (inner) second tube. In otherwords, the gap between the outer surface of the second tube and the inner surface of the first tube may provide the first chamber.

The first chamber may therefore have at least a substantially annular cross-section.

The second chamber may be defined within the second tube. In such an arrangement, the first tube has a greater diameter than the second tube, and in particular the inner diameter of the first tube is larger than the outer diameter of the second tube. The first and second tubes may be arranged such that they share a central axis, ie. they may be arranged concentrically. In such an arrangement, the first and second tubes may not need to be secured directly to each other. Instead, the second tube may just sit inside the first chamber. The connection of each tube to one or more pressure sensors may hold the tubes in place. There may be intervening layers between the first and second tubes, for example to limit the relative movement therebetween.

The system may further comprise an integrity sensor in fluid communication with the first chamber to detect a drop in pressure of the pressurised gas, for example due to a leak in the first tube. In the arrangement where the first and second chambers are spaced apart side-by-side, an integrity sensor may also be connected to the second chamber. In the arrangement where the second tube is located within the first tube, it will only be necessary to connect the second tube to an integrity sensor, as the second tube will only be exposed to ambient pressure when the first tube has leaked (which will be detected by the integrity sensor connected thereto).

The first and second tubes may be formed of any suitable, heat-conducting materials. The tubes may be formed of a metal or a metal alloy, such as an Inconel alloy.

There is also disclosed herein a temperature detector comprising a first tube defining a first chamber and a second tube defining a second chamber, wherein the second chamber contains a material that evolves gas upon heating and the first chamber contains a lesser amount of, or no, material that evoives gas upon heating.

The first and second tubes may have any of the features previously described in relation to the first and second tubes of the temperature detection system.

The temperature detector may be used in a temperature detection system, such as that described above, with the first and second chambers in fluid communication with one or more pressure sensors.. The temperature detector may be used to detect (and distinguish between) overheat and fire conditions.

The temperature detection system may have any of the features described above, for example, the first chamber may contain a pressurised gas and/or the first and second tubes may be connected to a single (i.e. common) pressure switch.

There is also disclosed herein a pressure switch for use in a temperature detection system. The switch comprises a housing, a deformable diaphragm and first and second terminals. The diaphragm separates the interior of the housing into first and second switch chambers, wherein the first and second switch chambers each have an opening for fluidic connection to a pneumatic temperature detector tube. Increasing the pressure in the first switch chamber causes at least a portion of the diaphragm to deform and the second terminal to be closed.

Increasing the pressure in the second switch chamber causes at least a portion of the diaphragm to deform and the first terminal to be closed.

The pressure switch is a pneumatic sensor that can be connected to two separate detector tubes (as described above) at the same time. The switch behaves differently depending on whether the pressure in the first switch chamber is higher or lower than that in the second switch chamber. When the switch is connected to first and second detector tubes (via the openings), the pressure in the first switch chamber will correspond to the pressure in the first tube (i.e. the first chamber) and the pressure in the second switch chamber will correspond to the pressure in the second tube (i.e. the second chamber). The pressure switch thus provides an apparatus for comparing the pressures in the first and second tubes.

Knowing the relative pressures in the two tubes allows the temperature of the environment in which the tubes are located to be monitored.

The diaphragm may be secured to an inner surface or surfaces of the housing. The housing may be cylindrical, but other shapes are possible. The diaphragm may be circular, but other shapes will be suitable.

The diaphragm creates a hermetic seal between the first and second switch chambers.

The diaphragm may be arranged so that it will only deform when there is a sufficient pressure difference between the first and second switch chambers.

When there is a sufficient pressure difference, at least a portion of the diaphragm will deform towards the switch chamber having the lower pressure. The effect of this is that the volume of the higher pressure switch chamber is increased and the pressure in that chamber drops by a small amount (but not enough to reverse the action of the diaphragm).

The first and second terminals may be electrical contacts which are closed via electrical contact with the diaphragm, which may comprise or be formed of an electrically conductive material.

Alternatively, the diaphragm may contact the terminals indirectly. For example, the diaphragm could contact actuators (e.g. push-rods) that when contacted cause the first and second terminals respectively to close.

The first terminal may be located in the first switch chamber and the second terminal may be located in the second terminal. The first and second terminals may be secured to a wall or walls of the housing and extend into their respective switch chamber.

When the pressure in the first switch chamber is sufficiently higher than that in the second switch chamber, at least a portion of the diaphragm deforms in the direction of the second switch chamber. This causes the second terminal to be closed. In this position of the diaphragm, the first terminal is open.

If the pressure increases in the second switch chamber to a sufficient level, the diaphragm deforms in an opposition direction towards the first switch chamber.

This causes the second terminal to be opened and the first terminal to be closed.

The switch may be designed such that when the pressures in the first and second switch chambers are the same or similar, the diaphragm remains in an at-rest position where it is not deformed and both first and second terminals are open.

Closing the first and the second terminals may complete an electrical circuit and activate a first and a second alarm respectively.

The pressure switch may be used in conjunction with the temperature detector described above and may be the pressure sensor in the temperature detection system described above.

The present disclosure also extends to a temperature detection system comprising the pressure switch described above, a first pneumatic temperature detector tube connected to and in fluid communication with the first switch chamber and a second pneumatic temperature detector tube connected to and in fluid communication with the second switch chamber.

The system and first and second tubes may have any of the features described above. For example, the first tube may have a pressurised gas and/or the second tube may have a material that evolves gas upon heating.

In this system, the first terminal may be part of a circuit providing an overheat alarm and the second terminal may be part of a circuit providing a fire alarm.

The first and second tubes may be connected to the openings in any way, as long as a hermetically sealed fluidic connection is made between each tube and each switch chamber. For example, a capillary may be brazed to the tube and the switch chamber.

The system may further comprise a further pressure sensor connected to the first and/or second tube to provide an integrity alarm.

BRIEF DESCRIPTION OF THE DRAWINGS

Some exemplary embodiments of the present disclosure will now be described by way of example only and with reference to Figures 1 to 4, of which: Figures 1(a) and 1(b) show radial and axial cross-sectional views of a

portion of a prior art temperature detector;

Figures 2(a) and 2(b) show radial and axial cross-sectional views of a portion of a temperature detector according to an exemplary embodiment of the

present disclosure;

Figures 3(a) and 3(b) show radial and axial cross-sectional views of a portion of an alternative temperature detector according to another exemplary

embodiment of the present disclosure; and

Figures 4(a) to 4(c) show schematic axial cross-sectional views of a pressure sensor according to an exemplary embodiment of the present disclosure under three different pressure conditions.

DETAILED DESCRIPTION

Figs 1(a) and 1(b) show a portion of a prior art temperature detector 10 having a tube 12 and a gas-evolving material core 14 located in a hollow chamber 16. Only a portion of a length of the detector 10 is shown. At one end of the detector 10, the tube 12 is closed (not shown), while at the other end it is open so that it can be connected to a pressure sensor. The tube 12 may be formed from an Inconel alloy. The core 14 may be made of a metal hydride, such as titanium hydride. The core 14 has a ribbon-like material 18 wrapped around itto preserve its shape so that the core cannot disintegrate and cause a blockage in the tube.

The material 18 may be a molybdenum ribbon. Fig. 1(b) is a cross-sectional view taken in the radial direction along line X-X in Fig. 1(a) and shows portions 18b of the wrap material 18 along the length of the core 14. Gaps 1 8a are provided between the portions 18b to allow gas to escape from the core 14.

Figs 2(a) and 2(b) show a temperature detector 20 according to an exemplary embodiment of the present disclosure. Only a portion of a length of the detector 20 is shown. The detector 20 comprises a first tube 21 and a second tube 22. At one end of the detector 20, the tubes 21, 22 are closed (not shown), while at the other end they are open so that they can be connected to one or more pressure sensors. The tubes 21, 22 may be formed from an Inconel alloy. The tubes 21, 22 are integrally formed such that the radial cross-section of the detector 20 has a figure-of-eight shape. The first and second tubes 21, 22 share a common wall 25.

In alternative embodiments, the first and second tubes 21, 22 may be separately formed and secured to each other, for example, via tack welding.

The second tube 22 has a gas-evolving material core 14 covered in a wrap material (e.g. molybdenum) 18, as is used in the detector 10 of Fig. la. The core 14 may be made of a metal hydride, such as titanium hydride. A gap 23 is provided between the core 14 and the inner surface of tube 22.

The first tube 21 has a hollow chamber 24 that, in use, will be filled with a pressurised gas. The pressure in chamber 24 in the first tube 21 is used to detect a overheat condition due to a first temperature, while the pressure within the gap 23 inside the second tube 22 is used to detect a fire condition due to a second, higher temperature.

Fig. 2(b) is a cross-sectional view of the second tube 22 taken in the radial direction along line Y-Y in Fig. 2(a).

The outer diameter D of the second tube 22 may be between 1 mm and 5 mm, for example 1.6 mm, although other sizes will be suitable. The outer diameter D2 may be less than 1.0 mm, such as 0.6 mm. The length of the detector 20 may be up to 10 metres.

Figs 3(a) and 3(b) show an alternative temperature detector 30 according to another exemplary embodiment of the present disclosure. Only a portion of a length of the detector 30 is shown. The detector 30 comprises a first tube 31 and a second tube 32. The second tube 32 is located within the first tube 31. The tubes 31, 32 may be cylindrical and arranged coaxially. At one end of the detector 30, the tubes 31, 32 are closed (not shown), while at the other end they are open so that they can be connected to one or more pressure sensors. The tubes 31, 32 may be formed from an Inconel alloy.

The second tube 32 contains a core of gas-evolving material 14 and a gap 33. The core 14 may be made of a metal hydride, such as titanium hydride. The core 14 has a first wrap 19a (e.g. a molybdenum ribbon). The outer surface of the second tube 32 has a second wrap 19b (e.g. another molybdenum wrap). A gap 34 is provided between the first and second tubes 31, 32. In use, this gap 34 is pressurised with gas and used to detect an overheat condition. The pressure in the gap 33 within the second tube 31 is used to detect a fire condition.

Fig. 3(b) is a cross-sectional view of the detector 30 taken in the radial direction along line Z-Z in Fig. 3(a).

The outer diameter D of the first tube 31 may be between 1 mm and 5 mm, for example 2.6 mm, although other sizes will be suitable. The second tube 32 may be of a similar size to the second tube 22 in Fig. 2b. The length of the detector 30 may again be up to 10 metres.

The second tube 32 may be secured to the first tube 31 or may be free to move relative to the first tube 31.

In use, the first and second tubes 21, 22 or 31, 32 are connected to one or more pressure sensors so that the chambers/gaps 23, 24 or 33, 34 are in fluid communication with the pressure sensor(s). One example of a suitable solitary pressure sensor 40 is shown in Figs. 4(a) to 4(c).

In use, exposing the detector 20 or 30 to elevated temperatures will first cause the pressurised gas in the chamber/gap 24, 34 to expand. This will cause an increase in pressure. The gap 23, 33 within second tube 22, 32 may also contain a gas, which may be at a lesser pressure than the gas in the chamber/gap 24, 34.

Increasing the temperatures of the detectors 20, 30 further causes the core 14 to evolve gas. This causes a large increase in pressure of the gas within the gap 23, 33 within the second tube 22, 32 so that the pressure surpasses that in the chamber/gap 24, 34 in the first tube 21, 31. This flip of pressures provides a means for determining when the temperature has increased beyond an overheat condition.

Figures 4(a) to 4(c) show schematic crosssectional views of a pressure sensor 40 according to an exemplary embodiment of the present disclosure under three different pressure conditions.

Pressure sensor 40 is in the form of a switch comprising a cylindrical housing 41, a deformable diaphragm 42 and first and second terminals 44 and 45.

The diaphragm 42 is secured to an inner surface of housing 41 via an annular seal 43. The diaphragm 42 may be circular, although other shapes will be suitable. The diaphragm 42 separates the interior of housing 41 into first and second switch chambers 46, 48, which respectively contain the first and second terminals 44, 45.

The first switch chamber 46 has an open end forming opening 47 for connection to a first tube of a detector (e.g. tube 21 or 31 of Figs 2 and 3). The second switch chamber 48 has an open end forming an opening 49 for connection to a second tube of a detector (e.g. tube 22 or 32 of Figs 2 and 3). The first and second terminals 44, 45 are connected via any suitable circuitry (which will be apparent to the skilled person) to first and second alarms.

Fig. 4(a) shows the situation where the pressure P1 in the first switch chamber 46 is equal to, or not substantially different to, that of the pressure P2 in the second switch chamber 48. In this situation, there is not sufficient pressure difference acting on the diaphragm 42 and it therefore does not deform. This situation may be experienced at normal operating conditions of detector 20 or 30.

The pressure in the first chambers or gaps 24, 34 in normal operating conditions may be higher than that in the second tube 22, 32 (i.e. in gaps 23, 33), due to the presence of a higher pressurised gas in the former, but not high enough to deform the diaphragm. In this situation, the first and second terminals 44 and 45 are both open.

Fig. 4(b) shows the situation where the pressure P1 in the first switch chamber 46 is significantly higher than that of the pressure P2 in the second switch chamber 48. This situation may occur where the pressure in a first tube (21, 31) connected to the first switch chamber 46 is significantly higher than that in a second tube (22, 32) connected to a second switch chamber 48 due to an increase in temperature sufficient to increase the pressure of the gas in the first tube, but not sufficient to cause gas to be evolved from the core 14 in the second lube. Such an increase in temperature may be experienced at an overheat temperature (i.e. at a lower temperature than that caused by a fire).

The pressure difference causes the diaphragm 42 to deform towards the second switch chamber 48 and contact the second terminal 45. Closing the second terminal 45 will cause the activation of an overheat alarm. The first terminal 44 remains open.

Fig. 4(c) shows the situation where the pressure F'1 in the first switch chamber 46 is significantly lower than that of the pressure P2 in the second switch chamber 48. This situation may occur where the pressure in a second tube (22, 32) connected to the second switch chamber 48 is significantly higher than that in a first tube (21, 31) due to an increase in temperature sufficient to cause gas to be evolved from the core 14 in the second tube. Such an increase in temperature would be experienced during a fire condition (i.e. at a higher temperature than an overheat temperature).

The pressure difference causes the diaphragm 42 to deform towards the first switch chamber 46 and contact the first terminal 44. Closing the first terminal 44 will cause the activation of a fire alarm. The second terminal 45 remains open.

The foregoing description is only exemplary of the principles of the invention. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than using the example embodiments which have been specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.

Claims

CLAIMS1. A temperature detector comprising: a first tube defining a first chamber; and a second tube defining a second chamber, wherein said second chamber contains a material that evolves gas upon heating and said first chamber contains a iesser amount of, or no, material that evolves gas upon heating.
2. A temperature detection system comprising: a first tube defining a first chamber, said first chamber containing a pressurised gas; and a second tube defining a second chamber, said second chamber containing a material that evolves gas upon heating, wherein said first and second chambers are in fluid communication with one or more pressure sensors and wherein heating at least a portion of each of said first and second tubes to a first temperature causes a higher pressure in said first chamber than said second chamber, and heating at least a portion of said first and second tubes to a second, higher temperature causes said material to evolve gas and results in a higher pressure in said second chamber than said first chamber.
3. The system or detector of claim 1 or 2, wherein said first and second tubes are secured to each other along at least a portion of their length.
4. The system or detector of any preceding claim, wherein said material that evolves gas upon heating comprises a solid material.
5. The system or detector of any preceding claim, wherein said first and second tubes extend parallel to each other along at least a portion of their lengths,
6. The system or detector of claim 5, wherein said first and second chambers are spaced apart in a direction transverse to the longitudinal detection in which said first and second tubes extend.
7. The system or detector of any of claims ito 5, wherein said second tube is located within said first tube, said first chamber is defined between said first tube and said second tube and said second chamber is within said second tube.
8. A temperature detection system comprising: the detector of any of claims i or 3 to 6; and one or more pressure sensors, wherein said first and second chambers are in fluid communication with said one or more pressure sensors.
9. The system of any of claims 2 to 8, wherein said first chamber contains a lesser amount of, or no, material that evolves gas upon heating.
10. The system of any of claims 2 to 9, wherein said second tube contains a gas at a lower pressure than said first tube.
ii. The system of any of claims 2 to 10, wherein said one or more pressure sensors is configured to provide a first alarm indicative of a first pre-defined pressure increase in said first tube at a or said first temperature and a second alarm indicative of a second pre-defined pressure increase in said second tube at a or said second, higher temperature.
12. The system of any of claims 2 to ii, further comprising an integrity sensor in fluid communication with said first chamber to detect a drop in pressure of said pressurised gas.
13. A pressure switch for use in a temperature detection system, said switch comprising: a housing; a deformable diaphragm separating the interior of said housing into first and second switch chambers, wherein said first and second switch chambers each have an opening for fluidic connection to a pneumatic temperature detector tube; a first terminal; and a second terminal, wherein increasing the pressure in said first switch chamber causes at least a portion of said diaphragm to deform and said second terminal to be closed and increasing the pressure in said second switch chamber causes at least a portion of said diaphragm to deform and said first terminal to be closed.
14. The switch of claim 13, wherein said first terminal is located in said first switch chamber and said second terminal is located in said second switch chamber.
15. A temperature detection system comprising: the pressure switch of claim 13 or 14; a first pneumatic temperature detector tube connected to and in fluid communication with said first switch chamber; and a second pneumatic temperature detector tube connected to and in fluid communication with said second switch chamber.
16. A temperature detection system according to any of claims 2 to 12, wherein said one or more pressure sensors consists of the pressure switch of claim 13 or 14, said first chamber is in fluid communication with said first switch chamber and said second chamber is in fluid communication with said second switch chamber.