GB2204696A

GB2204696A - Temperature sensor

Info

Publication number: GB2204696A
Application number: GB08809092A
Authority: GB
Inventors: Martin Alexander Haley
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1987-05-12
Filing date: 1988-04-18
Publication date: 1988-11-16
Also published as: GB8809092D0; GB8711161D0; DE3812195A1; FR2617968A1

Description

1 TEMPERATURE SENSORS This invention relates to temperature sensors.

The invention is more particularly concerned with sensors for measuring the temperature of gases or other fluids.

Platinum resistance thermometers are used in many applications where a robust, accurate sensor with a wide temperature sensing range is required. One application where such thermometers are used, is in ensing the temperature of the airstream flowing along the outside of an ircraft in flight.

The platinum sensing element may take the form of a wire, either straight or spirally coiled, which is supported either by spaced insulating discs or by extending along bores in an insulating body. Alternatively, the wire may be wound spirally around the outer surface of an insulating body such as a glass rod.

In another construction, the sensing element takes the form of a printed platinum track on an insulating substrate which may be rectangular or in the form of a solid rod.

It is an object of the present invention to provide a temperature sensor with an improved response.

According to one aspect of the present invention there is provided a temperature sensor including a sensing element provided by a track of 2 electrically conductive material of having a resistance that varies with temperature such that temperature can be measured from the resistance across points on the track, the sensor having a tubular member with an electrically insulating surface, the track being formed on the insulating surface, and the tubular member being open to allow fluid flow along the inner and outer surfaces of the tubular member such that the sensing element is exposed to the temperature on both surfaces.

The track is preferably formed on the outer surface of the tubular member. The tubular member may be of a ceramic, such as alumina. The track is preferably coated on its outer surface with an electrically insulative layer, such as a vitreous glaze. The track may be of platinum and may be deposited on the tubular member by silk-screen printing.

The tubular member may have a metal region formed on its surface which is brazed to a mounting bracket. The tubular member may be located within an outer tubular casing such that fluid can flow along the casing around the outside of the tubular member.

Temperature sensor apparatus for measuring the outside air temperature of an aircraft, will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a cut-away side elevation view of the apparatus;.1 3 Figure 2 is a view of the apparatus from one end; and Figure 3 is a perspective view to an enlarged scale of a part of the apparatus.

4 With reference to Figures 1 and 2, the sensor apparatus has an outer protective casing 1 of tubular shape that is supported at a spaced position from the aircraft body 2 by an arm 3. The arm 3 locates the casing 1 at the desired position relative to airflow over the aircraft body and parallel to it. The casing 1 is open at both ends so that air can flow smoothly through the apparatus.

Within the casing 1 there is located a mounting bracket 5. The bracket comprises three radial limbs 6 which project inwardly from the casing and are linked at their inner end by an integral circular collar 7. The limbs 6 are separated from one another by air gaps 8 so that flow of air along the casing is not prevented.

The collar 7 supports the rear, downstream end of a sensor device 10 which is shown in greater detail in Figure 3. The device 10 comprises a tube 11 of a ceramic, such as alumina, which is 25.4mm long. The tube 11 has a circular section with an outer diameter of 4.6mm and an inner diameter of 3.6mm; both ends of the tube are open. At its rear, downstream end a mounting band 15 of pl atinum 2mm wide encircles the outer surface of the tube 11, the collar 7 of the bracket 5 embracing this band 15 and being brazed to it.

Towards the forward, upstream end of the tube 11, a'platinum resistance element 17 is coated on the outer surface of the tube in a region extending over a distance of 17mm from the forward end. The resistance element 17 is spaced from the mounting band 15, at the rear end, by a distance of 6.5mm, so that it is electrically insulated from the mounting band. The element 17 may be of any conventional shape, 1 i t such as a serpentine track of straight sections extending parallel to the axis of the tube 11, as shown in Figure 3. Alternatively, a spiral pattern track may be used. The track is about O.Olmm thick.

The platinum resistance element 17 and the mounting band 15 may be deposited by silk-screen printing on the tube 11 a paste of platinum powder in an organic carrier which is subsequently removed by firing.

A protective vitreous overglaze 18 is applied on top of the element 17 to protect it from wear and to insulate it, so that it is not affected by, for example, moisture condensing on tbe-element.

Opposite ends of the track are connected to respective platinum wires 20 and 21 which are each SOmm long. The diameter of the wires 20 and 21 is such that they do not add significantly to the resistance of the element 17. The wires, 20 and 21 are connected to respective copper leads 22 and 23 within the support arm 3, that is, outside the air flow path through the casing 1.

The leads 22 and 23 extend to a voltage measuring unit 30 inside the aircraft body 2 which provides output signals representative of temperature to an indicator 40 or other utilising means, via line 31.

In operation, air flows through the easing 1, so that some of the air flows axially through the tube 11, and some of the air flows along its outer surface through the annular passage between the sensor device 10 and the casing 1. Both the inner and outer surfaces of the tube 11 will thereby be exposed to the heating or cooling effect of the air. In 6 this way, rapid changes in temperature of the air are communicated rapidly to the platinum resistance element with little thermal lag caused by the ceramic substrate on which it is mounted.

The tubular shape of the ceramic support 11 gives it high strength, enabling a thinner wall to be used. The tube 11 also has a high stiffness against transverse flexing, thereby reducing the risk of vibration of the tube. Because the resistance element is a track deposited on the tube there is no movement of the element relative to its support on vibration.

It will be appreciated that materials other than platinum, such as nickel or copper could be used to form the resistance element. The electrical lyconductive material forming the resistance element could be deposited on the insulating support by other means, such as by vapour deposition. Materials other than ceramics could be used to form the tubular support providing there is an electrically insulative surface on the support for receiving the resistance element.

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Claims

A temperature sensor including a sensing element provided by a track of electrically conductive material having a resistance that varies with temperature such that temperature can be measured from the resistance across points on the track, wherein the sensor has a tubular member with an electrically insulating surface, wherein the track is formed on the insulating surface, and wherein the tubular member is open to allow fluid flow along the inner and outer surfaces of the tubular member such that the sensing element is exposed to the temperature on both surfaces.

2.

3.

5.

A temperature sensor according to Claim 1, wherein the track is formed on the outer surface of the tubular member.

A temperature sensor according to Claim 1 or 2, wherein the tubular member is of a ceramic.

A temperature sensor according to Claim 3, wherein the tubular member is of alumina.

A temperature sensor according to any one of the preceding claims, wherein the track is coated on its outer surface with an electrically insulative layer.

6. A temperature sensor according to Claim 5, wherein the electrically insulative layer is a vitreous glaze.

8 A temperature sensor according to any one of the preceding claims, wherein the track is of platinum.

8.

A temperature sensor according to any one of the preceding claims, wheren the track is deposited on the tubular member by silk-screen printing.

9. A temperature sensor according to any one of the preceding claims, wherein tubular member has a metal region formed on its surface which is brazed to a mounting bracket.

10. A temperature sensor according to any one of the preceding claims, wherein the tubular member is located within an outer tubular casing such that fluid can flow along the casing around the outside of the tubular member.

11. A temperature sensor substantially as hereinbefore described with reference to the accompanying drawings.

12. Any novel feature or combination of features as hereinbefore described.

Published 1955 at The Patent Office, State House, 66.171 High Holborn, London WC1R 4T?. Further copies may be obtained from The Patent office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Com 1/87.

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