GB2158229A

GB2158229A - Temperature-sensitive arrangement

Info

Publication number: GB2158229A
Application number: GB08411606A
Authority: GB
Inventors: Brian David Powell
Original assignee: Graviner Ltd
Current assignee: Graviner Ltd
Priority date: 1984-05-05
Filing date: 1984-05-05
Publication date: 1985-11-06
Also published as: GB8411606D0

Abstract

The arrangement has conductors 12 and 14 separated by concentric glass layers 16 and 18. The glass insulates the conductors 12 and 14 at normal temperatures. As the temperature increases, the electrical resistance of the glass decreases and its capability of accepting electrical charge increases. These effects are monitored by a detecting unit 20 which produces a warning output in the event of temperature increase. In addition the glass layers 16, 18 act as a fibre-optic which produces radiation in response to temperature increase and transmits this radiation along the fibre-optic to a radiation detector 22 which thus produces a second output indication of temperature increase. In an alternative arrangement, Fig. 3 not shown, a separate optical fibre (26), which produces radiation in response to temperature increase, is arranged inside the hollow, cylindrical centre conductor (14). <IMAGE>

Description

SPECIFICATION Temperature-sensitive elements The invention relates to temperature-sensitive elements and more specifically to such elements which are of elongate form so as, for example, to be capable of being mounted around an area within which temperature is to be monitored.

According to the invention, there is provided a temperature-sensitive element comprising a fibre-optic which produces radiation in response to temperature increase which it transmits to radiation detecting means to produce a temperature indicating output, and electrical means running alongside the fibre optic and electrically responsive to temperature increase to produce a further temperature indicating output.

The electrical mean may comprise means responsive to a change in the electrical resistance of material forming part of it. The said material may be or be part of material constituting the fibre-optic.

According to the invention, there is also provided a temperature-sensitive element comprising two of side-by-side electrical conducting means separated by material having an electrical parameter which changes in response to temperature change, radiation transmitting means arranged side-by-side with the electrically conducting means and being of a type which produces radiation dependent on its temperature, first detecting means connected to measure any changes in the said electrical parameter to provide a first indication of temperature, and second detecting means arranged to receive radiation transmitted by the radiation transmitting means to provide a second indication of temperature.

Advantageously, the electrical conducting means and the radiation transmitting means are elongate and colinear. For example, they may be in the form of a wire or cable.

In one particular arrangement, the said material comprises material constituting the radiation transmitting means.

In such an arrangement, for example, one of the said conducting means may comprise an electrically conductive tube and the other conducting means may comprise a conductor running along and within the tube but separated from it by the radiation transmitting means.

In another arrangement, the two conducting means comprise respective hollow tubes one arranged substantially concentrically with the other and separated from it by the said material, the radiation transmitting means being arranged substantially concentrically within the said one tube.

Advantageously, the radiation transmitting means comprises a fibre-optic element.

Advantageously, the second detecting means comprises means responsive to the intensity of the radiation received thereby so as to assess the magnitude of the temperature or the temperature change.

In the case where the radiation transmitting means is elongate, the second detecting means may comprise respective detecting means positioned at the opposite ends of the radiation transmitting means so as to receive radiation from each end thereof and adapted to compare the radiation intensities respectively received whereby to assess the position of temperature change.

The radiation detecting means may comprise means operative to detect the intensity of radiation in two predetermined and relatively narrow wavelength bands whereby to produce respective signals and means for measuring the ratio of the said signals, the two wavelength bands being selected so that the said ratio is a measure of the colour temperature corresponding to the radiation received.

According to the invention, there is further provided a temperature-sensitive element comprising a first conductor of hollow tubular form, a second conductor running substantially co-extensively within the first conductor and separated from the first conductor by material which responds to an increase in temperature by decreased electrical resistance and increased capacity to accept electrical charge, light transmitting means running substantially co-extensively within the first conductor and operative when subjected to temperature increase to produce radiation which travels along the radiation transmitting means, electrical circuit means connected to the first and second conductors and operative to measure the decreased resistance and increased capacity to accept electrical charge in response to temperature rise and to produce a first temperature indicating signal accordingly, and radiation detecting means so mounted in relation to an end of the radiation transmitting means as to receive radiation produced within and transmitted along the radiation transmitting means in response to temperature increase and to produce a second temperature indicating signal in response thereto.

Advantageously, output means is provided and connected to receive both said signals whereby to produce a temperature-increasing warning signal only when both said signals exist simultaneously.

In one particular form, the said substance comprises inner and outer substantially concentric layers of glass both running substantially co-extensively within the first conductor and between that conductor and the second conductor and having respectively different refractive indices so as to constitute the radiation transmitting means.

Instead, however, the second conductor may also be of hollow tubular form and the radiation transmitting means may in that case comprise a fibre-optic running substantially co-extensively within the second conductor.

Temperature-sensitive elements embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a diagrammatic cross-section through one of the elements; Figure 2 is a cross-section on the line Il-Il of Fig. 1; Figure 3 is a diagrammatic section through another of the elements; Figure 4 is a block circuit diagram of a detecting unit connected to the elements; and Figure 5 shows waveforms occurring in the detecting unit of Fig. 4.

As shown in Fig. 1, the temperature sensitive element comprises a hollow tubular conductive sheath 12 of circular cross-section having an inner coaxial conductor 14. The outer and inner conductors 1 2 and 14 are separated by outer and inner contiguous and concentric glass layers 1 6 and 18 (see also Fig. 2), which have respectively different refractive indices.

At one end of the element, an electrical detecting unit 20 is shown which is electrically connected to the conductors 1 2 and 14.

At the other end of the element, a radiation detector 22 is mounted and positioned so as to receive electromagnetic radiation issuing from that end of the element and specifically from the corresponding ends of the glass layer 18.

The glass layers 1 6 and 18 perform two functions.

First, they together constitute insulating material which separates the two conductors 1 2 and 14. However, the glass material is such that the electrical resistance between the two conductors 1 2 and 14 decreases with increasing temperature. Preferably, the glass material is also such that the capability of the arrangement to accept an electrical charge, applied between the two conductors also increases with increasing temperature. Therefore, by monitoring the conductors 1 2 and 14 and measuring the resistance between them and the charge-acceptance capability, an output signal may be produced which is dependent on the temperature of the element; the element will thus respond to a general increase in temperature and to a local increase in temperature.The detecting unit 20 carries out this monitoring function. As will be described in more detail below, the unit 20 may comprise means for holding the conductor 14 at fixed potential and subjecting the conductor 1 2 to a rectangular waveform which renders it alternately positive and negative (swinging for example between plus 5 and minus 5 volts), the positive and negative voltages being applied to the conductor 1 2 through respective fixed resistors, the one through which the positive voltage is applied being of higher value than the other.Thus, when the element is at normal ambient temperature, the resistance of the material between the conductors is high and the voltage between them swings between plus 5 and minus 5 volts in correspondence with the applied waveform. -However, as the temperature increases, the electrical resistance between the conductors 1 2 and 14 decreases and the capability of accepting charge increases. The result will be that the voltage between the conductors during the positive half cycles will be reduced as compared with that between them during the negative half cycles because the positive half cycles of the drive waveform are applied to the conductors through a higher value resistor than are the negative half cycles.The greater reduction in voltage between the conductors during the positive half cycles is partly due to the potential dividing effect of the higher value resistor but is also due to the increased current which flows because of the enhanced charge-accepting capabilities. The asymmetry between the voltages across the conductors during the positive and negative half cycles provides a means of detecting enhanced temperature.

In the event of a fault condition which causes the electrical resistance between the conductors 1 2 and 14 to decrease, there will be a corresponding decrease in voltage between the conductors but the inequality between the voltages applicable during the positive and negative half cycles will not be so great because the capability of accepting charge is not increased and therefore the increased volt drop effect of the charging current is not present. In this way, the unit 20 can distinguish between temperature increase on the one hand and a fault on the other.

The second function carried out by the glass layers 1 6 and 1 8 is to provide a fibreoptic and the refractive index of layer 1 8 is chosen to be greater than that of layer 1 6 so as to constrain electromagnetic radiation to travel longitudinally along the layer 1 8. The fibre-optic has the characteristic that, provided it is made of suitable glass material, it will respond to temperature increase by emitting radiation of corresponding intensity and transmitting that the radiation along itself so as to be received by the radiation detector 22.

It will thus respond both the general temperature increase and to local temperature increase. However, the total power radiated at all wavelengths increases very considerably with temperature and therefore the radiation emitted at the end of the fibre optic and received by the radiation detector 22 will be essentially determined by the highest temperature spot along the length of the fibre optic and will be largely independent of the length of the hot region.

The radiation detector 22 may take any suitable form, dependent on the temperatures to be detected. For example, the detector 22 may take the form of a germanium photodiode which responds to radiation at wavelengths between 0.5 and 1.8 microns and may therefore be used to measure temperatures down to about 200"C. Instead, it could be in the form of a silicon photo-diode which is responsive to radiation at wavelengths between 0.4 and 1.1 microns and can therefore be used to respond to temperatures down to about 250"C. If it is desired to respond to temperatures lower than these values, a pyroelectric or thermopile-type detector may be used.

The output of the actual radiation detector may be processed in suitable circuitry which compares its intensity with one or more predetermined values so as to produce a warning signal if it is considered to correspond to an excess temperature.

A suitable form of coincidence gate may be connected to receive the warning signals from the detectors 20 and 22 so as to produce an output signal only when both warning signals exist simultaneously. In this way, the risk of a false warning of temperature increase can be minimised.

In a modification, a radiation detecting unit corresponding to the detecting unit 22 may be positioned at the opposite end of the element (in addition to the element 22 at the first end thereof). Each such detecting unit will therefore receive radiation emitted by the fibre optic in response to temperature increase. The intensities of the radiation respectively received will depend on the transmission loss along the fibre optic and on the position therealong of the point of temperature increase. In this way, therefore, by taking into account the transmission loss effect, the position of the local overheat can be determined. In such an arrangement, the detecting unit 20 would also be provided.

Fig. 3, in which parts corresponding to those in Figs. 1 and 2 are similarly referenced, shows a modified form of the element.

Here, the inner conductor 14 is in the form of a conductive tube which runs concentrically with the outer tubular conductor 1 2. The conductors 1 2 and 1 4 are separated by material 24 made of glass and alumina.

A separate fibre-optic 26 runs along and within the tubular conductor 1 4.

The material 24 electrically insulates the conductors 1 2 and 14 but has the same type of electrical characteristics in relation to the conductors 1 2 and 1 4 as does the glass material 16, 1 8 in the element of Figs. 1 and 2. In other words, it acts as an electrical insulator at normal temperatures but decreases its electrical resistance and increases its electrical charge-acceptance capability as the temperature increases. In the manner described in connection with Figs. 1 and 2, therefore, the unit 20 monitors the conductors 1 2 and 14 so as to detect temperature increase.

The fibre optic 26 has the same fibre-optic characteristics as are provided by the glass 16, 18 in the element of Figs. 1 and 2. In other words, in response to temperature increase, either general or local, electromagnetic radiation is produced within the fibre-optic 26 and transmitted therealong to the radiation detector 22.

The arrangement of Fig. 3 has the advantage that the electrically insulating and temperature-sensitive material between the electrical conductors is separate from the material providing the fibre-optic and the radiationtransmitting capability. Therefore the material 24 on the one hand and the fibre-optic 26 on the other can perform their respective function optimally. In the element of Figs. 1 and 2, this may not be so.

Fig. 4 shows one form which the detector 20 of Figs. 1 and 3 may take.

As shown, a stabilised power supply 30 provides a stabilised plus 5 volt output on a positive rail 32, a stabilised minus 5 volt output on a negative rail 34, and a stabilised 0 volt output on a line 36 which is connected to the outer conductor 1 2 of the element.

Transistors 40 and 42 have their collectors connected to feed the inner conductor 14 of the temperature-sensitive element via respective resistors 44 and 46 and a line 47; resistors 44 and 46 are the unequal resistors referred to above and they have resistances of 2,700 and 430 ohms for example. The transistors are rendered conductive alternatively, thus applying a rectangular waveform, swinging between plus 5 volts and minus 5 volts, to the conductor 14. Transistors 40 and 42 are rendered conductive alternatively at a fixed frequency by means of a driver unit 48.

Line 50 is an output line connected to a monitoring unit 52.

Fig. 5A shows the output waveform produced on line 47. When the temperaturesensitive element is at ambient temperature so as efficiently to have no charge storage capability, the electrical resistance between the conductors 1 2 and 1 4 is such that waveform 5A is also, therefore, the output waveform on the output line 50 in these conditions.

However, if the temperature of the element increases, the waveform on line 47 will change to the form shown in Fig. 5B. This is because the increased temperature increases the charge acceptance capability between the conductors 1 2 and 1 4. The result will be to cause a significant reduction in the level of the waveform on line 47 during each positive half cycle, because the increased charging current flows through the relatively high resistance 44, while making relatively insignificant change in the level during each negative half cycle. Waveform 5B is thus the waveform produced on the output line 50.

By way of comparison, waveform 5C shows the waveform which is produced on line 47, and thus on line 50, when there is a fault causing a short-circuit between the conductors 1 2 and 14. Here, there is no increase in charge acceptance capability and, although the level of the output during the positive half cycles will be depressed relative to that during the negative half cycles, the amount of such depression will not be so marked.

The output line 50 is therefore connected to a suitable monitoring unit 52 which monitors the shape of the waveform on line 50. If the waveform is of the form shown in Fig. 5A no warning output is produced. If it has the form shown in Fig. 5B, a temperature warning output is produced. If it has the form shown in Fig. 5C, a fault warning is produced.

The unit 52 may take any suitable form. It may for example be of a type which digitally compares the shape of the waveform on line 50 with predetermined fixed reference levels so as to produce appropriate warning output signals. Such an arrangement is shown in our co-pending U.K. Patent Application No.

8329473 (Serial No.

Claims

1. A temperature-sensitive element, comprising a fibre-optic which produces radiation in response to temperature increase which it transmits to radiation detecting means to produce a temperature indicating output, and electrical means running alongside the fibre optic and electrically responsive to temperature increase to produce a further temperature indicating output.

2. An element according to claim 1, in which the electrical means comprises means responsive to a change in the electrical resistance of material forming part of it.

3. An element according to claim 2, in which the said material is or is part of material constituting the fibre-optic.

4. A temperature-sensitive element, comprising two side-by-side electrical conducting means separated by material having an electrical parameter which changes in response to temperature change, radiation transmitting means arranged side-by-side with the electrically conducting means and being of a type which produces radiation dependent on its temperature, first detecting means connected to measure any changes in the said electrical parameter to provide a first indication of temperature, and second detecting means arranged to receive radiation transmitted by the radiation transmitting means to provide a second indication of temperature.

5. An element according to claim 4, in which the electrical conducting means and the radiation transmitting means are elongate and co-linear.

6. An element according to claim 5, in which the electrical conducting means and the radiation transmitting means are each in the form of a wire or cable.

7. An element according to any one of claims 4 to 6, in which the said material comprises material constituting the radiation transmitting means.

8. An element according to claim 7, in which one of the said conducting means comprises an electrically conductive tube and the other conducting means comprises a conductor running along and within the tube but separated from it by the radiation transmitting means.

9. An element according to claim 7, in which the two conducting means comprise respective hollow tubes one arranged substantially concentrically with the other and separated from it by the said material, the radiation transmitting means being arranged substantially concentrically within the said one tube.

1 0. An element according to any one of claims 4 to 9, in which the radiation transmitting means comprises a fibre-optic element.

11. An element according to any one of claims 4 to 10, in which the second detecting means comprises means responsive to the intensity of the radiation received thereby so as to assess the magnitude of the temperature or the temperature change.

1 2. An element according to any one of claims 4 to 11, in which the radiation transmitting means is elongate, the second detecting means comprises respective detecting means positioned at the opposite ends of the radiation transmitting means so as to receive radiation from each end thereof and adapted to compare the radiation intensities respectively received whereby to assess the position of temperature change.

1 3. An element according to any one of claims 4 to 12, in which the second detecting means comprises means operative to detect the intensity of radiation in two predetermined and relatively narrow wavelength bands whereby to produce respective signals and means for measuring the ratio of the said signals, the two wavelength bands being selected so that the said ratio is a measure of the colour temperature corresponding to the radiation received.

14. A temperature-sensitive element, comprising a first conductor of hollow tubular form, a second conductor running substantially co-extensively within the first conductor and separated from the first conductor by material which responds to an increase in temperature by decreased electrical resistance and increased capacity to accept electrical charge, light transmitting means running substantially co-extensively within the first conductor and operative when subjected to tem perature increase to produce radiation which travels along the radiation transmitting means, electrical circuit means connected to the first and second conductors and operative to measure the decreased resistance and increased capacity to accept electrical charge in response to temperature rise and to produce a first temperature indicating signal accordingly, and radiation detecting means so mounted in relation to an end of the radiation transmitting means as to receive radiation produced within and transmitted along the radiation transmitting means in response to temperature increase and to produce a second temperature indicating signal in response thereto.

1 5. An element according to claim 14, including output means connected to receive both said signals whereby to produce a temperature-increase warning signal only when both said signals exist simultaneously.

16. An element according to claim 14 or 15, in which the material comprises inner and outer substantially concentric layers of glass both running substantially co-extensively within the first conductor and between that conductor and the second conductor and having respectively different refractive indices so as to constitute the radiation transmitting means.

17. An element according to claim 14 or 15, in which the second conductor is also of hollow tubular form and the radiation transmitting means comprises a fibre-optic running substantially co-extensively within the second conductor.

1 8. A temperature-sensitive element substantially as described with reference to Figs.

1 and 2 of the accompanying drawings.

1 9. A temperature-sensitive element, substantially as described with reference to Figs.

1, 2, 4 and 4 of the accompanying drawings.

20. A temperature-sensitive element, substantially as described with reference to Fig. 3 of the accompanying drawings.

21. A temperature-sensitive element, substantially as described with reference to Figs.

3 to 5 of the accompanying drawings.