GB2045921A

GB2045921A - Improvements relating to the measurement of temperature

Info

Publication number: GB2045921A
Application number: GB8004269A
Authority: GB
Original assignee: GE Healthcare UK Ltd
Current assignee: GE Healthcare UK Ltd
Priority date: 1979-02-15
Filing date: 1980-02-08
Publication date: 1980-11-05

Abstract

Temperature monitoring and/or measuring apparatus comprising radiation detector (9) and temperature probe 7 including at least one optical fibre 8 and radiation emitter 4 responsive to heat for the emission of radiation therefrom and located at the end of the optical fibre or fibres which convey the emitted radiation to the radiation detector. The fibre may be surrounded by cable 8 and the probe provided with a protective sheath. <IMAGE>

Description

SPECIFICATION Improvements relating to the measurement of temperature This invention relates to apparatus for monitoring and/or measuring relatively high temperatures.

Hitherto thermocouple pyrometers have been employed for measuring high temperatures, but these suffer from a number of disadvantages. For example, the wires of the thermocouple may be vul nerable to chemical attack when the pyrometers are used in corrosive or other deleterious environments and these wires, moreover, need to be electrically insulated from one another, such as by ceramic mat erial, which adds undesirably to the physical dimen sions of the pyrometer.

The present invention provides temperature monitoring and/or measuring apparatus comprising radiation detector means and temperature probe means including at least one optical fibre and radiation emitting means responsive to heat for the emission of radiation therefrom and located at the end of optical fibre or fibres, the optical fibre or fibres con veying the emitted radiation to the radiation detector means.

Since the temperature probe means of the apparatus simply comprises the heat-responsive member and at least one optical fibre (for example of glass or pure silica), the apparatus may be used in environments in which a thermocouple pyrometer discussed above may suffer from chemical attack.

Moreover, the probe means does not involve wires which need to be electrically insulated from one another thereby enabling the size of the probe means to be kept to an absolute minimum. Further, since the temperature probe is not electrically con ductive it may be used to measure gas temperatures in electrically heated plasmas or as points of high electrical potential. Still further, the probe means may have a lower thermal conductivity and capacity than the thermocouple probe so that apparatus according to the present invention will have an advantage when it is required to measure the temp eratu re at a discrete point without significantly decreasing the temperature at that point due to the conduction of heat away therefrom.

The radiation emitting means of the probe means may comprise an opaque end cap member which may be of very thin metal (e.g. evaporated) or other material (e.g. boron nitride) fitted to the end of an optical fibre, this opaque end cap acting as a near perfect black body for emitting radiation according to Plancks radiation law. This is to say, the body emits energy in the form of quanta of energy of amounts given by the product of the frequency of such energy and Planck's constant. The material of the opaque end cap may be chosen so that when its temperature exceeds 400"C say, the radiation emit ted therefrom and conveyed by the glass fibre to radiation detector means in the form of an optical detector is sufficient to enable quantitative measurements of the probe temperature to be made.It is contemplated that temperatures up to 1 000on may be monitored and!or measured where pure silica optical fibres are used.

The radiation detector means may, for the range of wavelength of the light emitted and transmitted through the fibre, advantageously comprise a lead sulphide photo-conductive detector in the case where the or each optical fibre has a pure silica core.

However, silicon or germanium junction diodes may also be used.

For the purpose of modulating the emitted energy beam and thereby enabling a.c. detection methods to be employed, a radiation bearn chopper may be introduced into the optical fibre or fibres between the temperature probe means and the radiation detector means, for example the optical detector.

The output from the radiation detector means may be amplified by amplifier means and then fed to temperature gauge means which will be calibrated prior to operation of the apparatus.

It may be advantageous in certain applications to arrange that the optical fibre or fibres including or excluding the temperature probe means may be encased within a protective sheath.

In one embodiment of the invention, the probe means including the radiation emitting means is positioned in a cavity in a solid structure for measuring and/or monitoring the temperature of said solid structure. The probe means may be fitted into a hole drilled or otherwise formed in the solid structure or it may be moulded into said structure so that it forms an integral part thereof.

The solid structure referred to may for example take the form of an engine block or a turbine blade to mention just two examples.

By way of example embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic longitudinal sectional view of temperature-responsive probe means of temperature monitoring and/or measuring apparatus according to the invention; Figure 2 is a diagrammatic longitudinal sectional view showing one end of an optical fibre connected at its other end to the probe means for Figure 1; and Figure 3 shows temperature measuring apparatus suitable for gas temperature measurement.

Referring to Figure 1 of the drawings, the probe means comprises an optical fibre 1 which may comprise a pure silica core 2 with glass cladding 3. Over the end of the optical fibre 1 is fitted an opaque end cap 4 which may, for example, comprise thin gauge metal. The material of the end cap is chosen so that it constitutes a near-perfect black body whereby the cap when subjected to a relatively high temperature (e.g. 400"C) emits radiation (i.e. quanta of energy given by the product of frequency and Plancks constant) which will be transmitted along the core 2 of the fibre 1. This end cap may be of metal, such as platinum or irridium, and may be evaporated on the end of the fibre or it may be fitted in the form of a sleeve.The cap may alternatively be composed of non-metallic material, such as boron nitride, and may be diffused into the fibre end to provide the radiation emitting means. The other end of the fibre 1 is shown in Figure 2 and the energy emitted by the temperature probe is applied to radiation detector means in the form of an optical detector 5 which may comprise a suitably-biased lead sulphide photoconductive detector, although other detectors could alternatively be used. The output from this detector 5 is then passed to a pre-amplifier stage of an amplifier before being fed to a temperature meter or gauge, which, as will be appreciated, will need to be calibrated before the apparatus is brought into operation.

In Figure 3 of the drawings there is shown an apparatus for measuring the temperature of gas within a chamber 6. Temperature-responsive probe means 7, which may be of the same form as that shown in Figure 1, extends in gas-tight manner through the wall chamber 6 so that the end cap 4 of the probe means is exposed to the gas within the chamber.

The probe means 7 may be provided with a protective sheath (not shown), for example of ceramic material, and the fibre is embodied in cable 8 extending to an optical receiver. The optical receiver comprises an optical detector 9 which may be of the form described with reference to Figure 2 and an amplifier 10. Again the output from the amplifier 10 will be applied to a temperature gauge suitably calibrated.

As will be appreciated from the foregoing description of various embodiments of the invention, it will be seen that the optical fibre of the apparatus is flex ible and energy emitted from the end cap may be readily guided to a remote measurement point without a direct line-of-sight path being necessary between the emitting surface and the optical receiver.

Moreover, the temperature probe may be made very small and of low thermal capacity which renders it particularly suitable for measuring temperatures at a point without significantly altering the temperature profile at the point of interest. Yet another advantage of the glass fibre temperature probe is that it is not electrically conductive and may therefore be used to measure gas temperatures in electrically-heated plasmas or, alternatively, it may be used to measure the temperature at a point with high electrical potential. If desired, more than one optical fibre may be employed.

Claims

1. Temperature monitoring and/or measuring apparatus comprising radiation detector means and temperature probe means including at least one optical fibre and radiation emitting means responsive to heat for the emission of radiation therefrom and located at the end of the optical fibre or fibres, the optical fibre or fibres conveying the emitted radiation to the radiation detector means.

2. Apparatus according to claim 1 in which the radiation emitting means of the probe means comprises an opaque end cap member.

3. Apparatus according to claim 2 in which the end cap member is made of metal.

4. Apparatus according to claim 2 in which the end cap member is made of boron nitride.

5. Apparatus according to any one of the preceding claims in which the radiation detector means is an optical detector.

6. Apparatus according to any one of the preceding claims including a radiation beam chopper in the optical fibre or fibres between the temperature probe means and the radiation detector means.

7. Apparatus according to any one of the preceding claims including amplifier means for amplifying the output of the radiation detector means, and temperature gauge means for receiving the amplified output from the amplifier means.

8. Apparatus according to any one of the preceding claims in which the optical fibre or fibres are encased within a protective sheath.

9. Apparatus according to any one of the preceding claims in which the probe means including the radiation emitting means is positioned in a cavity in a solid structure for measuring and/or monitoring the temperature of the said solid structure.

10. Apparatus substantially as herein described with reference to the accompanying drawings.