GB2130717A

GB2130717A - Radiation pyrometer

Info

Publication number: GB2130717A
Application number: GB08304479A
Authority: GB
Inventors: John Pointer
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1982-02-18
Filing date: 1983-02-17
Publication date: 1984-06-06
Also published as: GB2130717B; GB8304479D0

Abstract

A radiation pyrometer for indicating the temperature of the blades 5 of a gas-turbine engine 4 has four light guides in the form of heat- resistant sapphire rods 32 to 35 the forward ends of which are located close to one another in a row. A sapphire lens 21 focuses radiation emitted by the turbine blades onto the rods, the image plane 45 being tilted out of parallel with the lens so as to allow for the angle of the turbine blades. Each rod extends within a metal sheath 36 to 39, the forward ends of which are brazed into apertures in a metal plate 40 which lies in the image plane. At their rear ends, the sheaths are brazed into a metal plate 47, the sapphire rods being aligned and optically coupled with respective fibre-optic bundles 65 to 68. A small gap separates the forward end of each fibre-optic bundle from its respective rod, so as to allow for axial displacement of the rods relative to the fibre-optic bundles. The fibre-optic bundles are enclosed within a rubber sleeve 84 that extends within a cable 2 which is coupled at its rear end with a receiver unit. Within the receiver unit each fibre- optic bundle is connected to a respective photocell assembly that provides an electrical output in accordance with the radiation emitted by different regions 24 to 27 of the turbine blades. <IMAGE>

Description

SPECIFICATION Radiation sensor means This invention relates to radiation sensor means and, more particularly, to optical pyrometer means.

The invention is more especially, but not exclusively, concerned with optical pyrometers for gas-turbine engines.

Optical pyrometers are already used in gasturbine engines to view the turbine blades so as to enable an indication of their temperature to be derived from the radiation emitted from the blades. A fibre-optic cable may be included in the pyrometer so that its associated electrical radiation detector can be mounted remote from the hot region of the engine.

Various problems have been experienced in the provision and use of such pyrometers. One difficulty arises from the high temperature to which the pyrometers are subjected which can result in damage to or degradation of the fibreoptic bundles. Another disadvantage of optical pyrometers is that they only provide an indication of the temperature of a small part of the turbine blades whereas, in practice, it can be desirable to know how the temperature varies over the surface of the turbine blades.

It is an object of the present invention to provide an optical pyrometer that can be used to alleviate the above-mentioned difficulties and disadvantages.

According to one aspect of the present invention there is provided an optical pyrometer sensing unit including optical imaging means, a plurality of temperature-resistant optical radiation guides the forward ends of which are located substantially in the image plane of said imaging means, a plurality of fibre-optic bundles the forward ends of which are each coupled to the rear ends of respective ones of said optical radiation guides and the rear ends of which are each coupled to respective radiation-responsive means.

The rear end of said radiation guides may be separated from the forward ends of said fibreoptic bundles so as thereby to allow for axial displacement of said radiation guides relative to said fibre-optic bundles. The optical imaging means may be a lens and it may be substantially of sapphire. The optical radiation guides may be rods substantially of sapphire, the forward ends being arranged in a row. The image plane may be inclined relative to said optical imaging means.

The said plurality of fibre-optic bundles may extend within an individual cable.

An optical pyrometer, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates the pyrometer schematically; Figure 2 is a sectional side-elevation view of the forward end of the pyrometer; Figure 2a shows a part of Figure 2 in greater detail; Figure 3 is a cross-sectional view along the line Ill-Ill of Figure 2; Figure 4 is a cross-sectional view along the line IV--IV of Figure 2; Figure 5 is a cross-sectional view along the line V-V of Figure 2; and Figure 6 shows the rear of the pyrometer.

With reference to Figures 1, 2 and 6, the pyrometer includes a sensing head unit, indicated generally by the numeral 1 as the forward end of the pyrometer; a fibre-optic cable 2 that extends rearwardly of the head; and a receiver unit 3 to which the rear end of the cable 2 is coupled. The pyrometer head 1 projects through the housing of a gas-turbine engine 4 in the region of the highpressure blades. The pyrometer head 1 is positioned to view the blades 5 as they pass in front of it, and to supply radiation emitted from four spaced areas along the length of the blade to the receiver unit 3.

The pyrometer head 1 extends between inner and outer walls 10 and 11 of the engine housing 6, the forward end of the head projecting within a guide tube 12 mounted on the inner wall. The pyrometer head is secured within the guide tube 12 by means of a locking tube 1 3 that extends coaxially about the pyrometer. At its forward end, the locking tube 1 3 is screwed into the rear end of the guide tube 12 so as to bear on the external surface of the pyrometer head 1 and urge it forwardly. The rear end of the locking tube 1 3 projects through the outer wall 11 of the engine housing 6, for ready access.

The nose 14 of the head 1 is surrounded by a tubular sleeve 1 5 to which purging air is supplied via apertures 1 6. Purging air passes forwardly over the surface of the pyrometer head 1 and into the engine, to help cool the nose 14 and keep it free from soot and other contaminants.

The nose 14 of the pyrometer head 1 comprises an outer tubular shell 20 of a nimonic alloy in the forward end of which is mounted a plano-convex lens 21 of sapphire. Midway along its length there is positioned a circular plate 22 formed with a vertically-arranged rectangular aperture 23. The rear end of the shell 20 is welded to an intermediate outer sleeve 30 of nimonic alloy. Within the sleeve 30 are mounted four light guides in the form of straight sapphire rods 32, 33, 34 and 35. The rods 32 to 35 are each encased in metal sleeves 36 to 39 of a lowexpansion alloy (such as of iron, nickel and chromium) which are preferably a loose fit about the rods so as to accommodate relative expansion between the sapphire and metal. At their forward ends the sleeves 36 to 39 are brazed to a metal plate 40 that is sealed about its edge to the intermediate outer sleeve 30.The plate 40 has four apertures 41 to 44 within which extend the forward ends of the respective light guides 32 to 35. The apertures 41 to 44 are arranged in a vertical line ciosely spaced one above the other (as can be seen more clearly in Figure 3). The front surface 45 of the plate 40 defines an image plane of the lens 21 and is inclined away from the vertical, out of parallel with the lens. The rear ends of the sleeves 36 to 39 are brazed to a similar plate 47 that is welded into the rear end of the intermediate outer sleeve 30. The rear ends of the rods 32 to 35 are equally spaced about the axis of the pyrometer as shown in Figure 4.

The outer intermediate sleeve 30 is welded about its rear end to the casing 50 of the rear section 51 of the pyrometer head. The casing 50 is a composite structure formed of stainless steel and nimonic alloy and that is provided with external splines 52. The splines 52 slot into keyways 53 on the interior surface of the guide tube 12, thereby serving to maintain the correct orientation of the pyrometer head 1 within the guide tube.

The forward end of the rear section 51 is provided by a substantially cylindrical body 55 having four apertures 56 to 59 that are aligned with the rear ends of the sapphire rods 32 to 35.

Within the apertures 56 to 59 are secured the forward ends of fibre-optic assemblies 61 to 64 which are optically coupled with the rear ends of the sapphire rods 32 to 35. At its rear end, the body 55 has a tail portion 60 of frusto-conical shape that projects axially of the pyrometer.

The assemblies 61 to 64 each have a respective bundle 65 to 68 of approximately 1800 glass fibres of 50 micron diameter. The fibre bundles 65 to 68 are each enclosed along their entire length within a woven glass-fibre sleeve 69 to 72 that is removed from the first centimeter or so at the ends of the bundles. The forward end of each assembly 60 to 64 is terminated by fusing the end of each respective bundle together with a molten glass collar 77 within a metal cap 78 (Figure 2a). The rear end of the metal caps 78 are fitted over the forward end of short metal ferrules 79 that extend coaxially of each fibre bundle 65 to 68. The bore 80 through each ferrule 79 is of increased diameter at its rear end which also receives one end of the glass-fibre sleeves 69 to 72.A short silicone rubber sleeve 83 is fitted over the rear end of each ferrule 79 and embraces each fibre-optic assembly 61 to 64 where it emerges from the ferrule. The four fibre-optic assemblies 61 to 64 extend out of the rear end of the casing 50 within a single silicone rubber sleeve 84 that constricts the assemblies 61 to 64 about the tail 60. The assemblies 61 to 64 extend along the length of the cable 2 within the sleeve 84.

The fibre-optic cable 2 is joined to the rear end of the pyrometer head 1 and comprises an outer braided stainless steel sheath 90 enclosing a coaxial corrugated tube 91 also of stainless steel.

The forward end of the sheath 90 is sandwiched between a retaining collar 92 and the exterior of the rear section 51 of the pyrometer head casing 50, the corrugated tube 91 being welded to the casing 50 at its rear end.

The fibre-optic cable 2 extends rearwardly from the pyrometer head 1 to a remote cooler location where the cable is joined to the receiver unit 3 (Figure 6). The receiver unit 3 includes four photocell assemblies 101 to 104 to which respective ones of the four fibre-optic assemblies 61 to 64 are optically coupled. Each photocell assembly 101 to 104 is arranged to provide an electrical output along lines 105 to 108 respectively to a connector 109. The outputs of the photocell assemblies 101 to 104 are indicative of temperature. More particularly, these rely on the fact that the radiation emission characteristic of a hot body changes with temperature, the shorter wavelength radiation predominating as the temperature of the body increases.The photocell assemblies 101 to 104 may, for example, include a single detector that is responsive to radiation within a narrow band, such as, by use of a suitable optical filter or by the inherent spectral response of the detector itself.

Alternatively, the photocell assemblies 101 to 104 may each include two detectors that are responsive to radiation within different narrow bands, the emitted radiation illuminating both detectors so that by comparing the outputs of the two detectors the ratio of radiation at different wavelengths can be determined, and hence the temperature.

The connector 109 on the receiver unit 3 is coupled via line 110 to a display or other utilisation unit 200 where a display of temperature is provided. The receiver unit 3 and display unit 200 can be mounted at a remote, cooler location.

In operation, the lens 21 focuses an image of a part of one turbine blade 5 onto the image plane 45, the area of the blade viewed being defined by the aperture 23 in the plate 22. The positioning of the ends of the light guides 32 to 35 defines more precisely four regions 24 to 27 of the blade 5 from which emitted radiation is received. The angle of inclination of the image plane 45 is selected according to the orientation of the blade 5 so that radiation is sharply focused on the ends of the light guides 32 to 35. The sapphire rod light guides 32 to 35 are capable of withstanding the high temperatures that can be experienced at the pyrometer nose 14. The use of separate rods has the advantage of enabling the ends of the light guides to be mounted.closer together than would be possible with a bundle of optical fibres because of their outer sleeving.

Preferably a small gap 46 separates the rear end of the sapphire rods 32 to 35 and the fibreoptic assemblies 61 to 64, the gap being sufficient to allow the sapphire rods and the fibre-optic assemblies to expand when they are heated, without physical contact between them. In this way, abrasion of the ends of the rods 32 to 35 and the fibre-optic assemblies 61 to 64 is avoided so that there is no reduction of transmission from the rods to the fibre bundles 65 to 68.

Although the amount of radiation transmitted from the rods 32 to 35 to the fibre bundles 65 to 68 would normally be greater if they were close together, the provision of the gap 46 has the advantage of reducing variations in transmission between the rods and the fibre bundles caused by changes in alignment of the rods with the fibre bundles. It will be appreciated that if a rod was displaced laterally (such as caused by vibration or thermal effects) by, for example, half its width, this would lead to far greater reduction in the radiation transmitted to its fibre bundle if it was close to the fibre bundle, than if it was separated axially from it by some distance. The sapphire rod light guides 32 to 35 also have the advantage of enabling the glass fibre-optic bundles 65 to 68 to be spaced rearwardly from the nose 14 of the pyrometer head 1, away from the region exposed to greatest heating.

As an alternative to sapphire rods, various other light guides could be used, such as, step index rods or fused fibre-optic bundles.

Claims

1. An optical pyrometer sensing unit including optical imaging means, a plurality of temperatureresistant optical radiation guides the forward ends of which are located substantially in the image plane of said imaging means, a plurality of fibreoptic bundles the forward ends of which are each coupled to the rear ends of respective ones of said optical radiation guides and the rear ends of which are each coupled to respective radiationresponsive means.

2. An optical pyrometer sensing unit according to Claim 1 , wherein the rear end of said radiation guides are separated from the forward ends of said fibre-optic bundles so as thereby to allow for axial displacement of said radiation guides relative to said fibre-optic bundles.

3. An optical pyrometer sensing unit according to Claim 1 or 2, wherein said optical imaging means is a lens.

4. An optical pyrometer sensing unit according to Claim 3, wherein said lens is substantially of sapphire.

5. An optical pyrometer sensing unit according to any one of the preceding claims, wherein the said optical radiation guides are rods substantially of sapphire.

6. An optical pyrometer sensing unit according to any one of the preceding claims, wherein said image plane is inclined relative to said optical imaging means.

7. An optical pyrometer sensing unit according to any one of the preceding claims, wherein the forward ends of said optical radiation guides are arranged in a row.

8. An optical pyrometer sensing unit according to any one of the preceding claims, wherein said optical radiation guides each extend within a respective metal sheath.

9. An optical pyrometer sensing unit according to Claim 8, wherein each said optical radiation guide is a loose fit within said metal sheath so as thereby to allow for relative thermal expansion of said radiation guide and said sheath.

10. An optical pyrometer sensing unit according to Claim 8 or 9, wherein the forward end of each said sheath is joined to an aperture in a metal plate.

11. An optical pyrometer sensing unit according to any one of Claims 8 to 10, wherein the rear end of each said sheath is joined to an aperture in a metal plate.

1 2. An optical pyrometer sensing unit according to any one of the preceding claims, wherein the forward ends of the fibres in each said fibre-optic bundle are fused together.

13. An optical pyrometer sensing unit according to any one of the preceding claims, wherein the said plurality of fibre-optic bundles extend within an individual cable.

14. An optical pyrometer sensing unit according to any one of the preceding claims, wherein the said plurality of fibre-optic bundles extend within an individual resilient sleeve that constricts the bundles together.

1 5. An optical pyrometer sensing unit substantially as hereinbefore described with reference to the accompanying drawings.