Device for measuring the temperature of a substrate

A device for measuring the temperature of a substrate comprising a thermocouple comprising electric wires joined to each other at least one junction; a fixing element suitable for fixing said junction to said substrate in order to measure its temperature; characterized in that the fixing element comprises a thermally conductive element suitable for bearing a portion of electric wires adjacent to said junction; said thermally conductive element being capable of thermally coupling said portion of electric wires to said substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under the Paris Convention to the French Patent Application No. 10 56451, filed on Aug. 5, 2010.

FIELD OF THE DISCLOSURE

The invention relates to a device for measuring the temperature of a substrate, and in particular a device for measuring the temperature of a substrate which radiates in the infrared spectrum towards an external radiative environment when there is a great difference in temperature between the external radiative environment and said substrate.

BACKGROUND OF THE DISCLOSURE

One of the problems of the electronic-type payloads on board satellites in the space environment is dissipating the heat produced by the payload.

In the case, for example, of a telecommunications satellite, the payload frequently comprises travelling-wave tubes (“TWT”), intended to amplify the signal to be transmitted with very low background noise. Now, these travelling-wave tubes release a large quantity of heat which has to be dissipated in order to avoid a rise in temperature of the payload and of the TWT itself jeopardizing its correct operation. In the case of radiative TWTs, the collector is cooled down by means of an external radiator which radiates in the infrared spectrum directly towards a colder external radiative environment. The collector of these radiative travelling wave tubes can reach a temperature of the order of 200° C. depending on its operating mode, whereas the tube itself has a temperature of a few tens of ° C.

The heat dissipation ability of a travelling-wave tube is then an element determining the power of the payload.

Before launching the satellite, ground tests are carried out on the heat dissipation of the useful payload, in a test chamber in an environment simulating the conditions encountered in space, and in particular, with simulations of a very cold or very hot environment.

During these tests, the radiative travelling wave tubes are equipped with several temperature sensors and in particular thermocouple-type temperature sensors on the radiator. These sensors are fixed onto a metal plate with glue.

However, these sensors measure the surface temperature of the radiator with significant errors, typically 45° C. when the collectors of the travelling-wave tubes have a temperature of 150° C. in a test chamber at −50° C.: these errors result from the fact that the thermocouple measures its own temperature and that the temperature of the junction (or weld) of the thermocouple reaches equilibrium between the temperature of the substrate measured and the external radiative environment. The conductive leak in the thermocouple wires is the main contributor to the measuring error.

SUMMARY OF THE DISCLOSURE

The purpose of the present invention is to propose a device capable of accurately measuring the temperature of a substrate, and in particular of accurately measuring the temperature of a substrate which radiates in the infrared spectrum towards an external radiative environment when there is a great difference in temperature between the radiative environment and said substrate.

To this end, a subject of the invention is a device for measuring the temperature of a substrate comprising:a thermocouple comprising electric wires joined to each other at least one junction;a fixing element suitable for fixing said junction to said substrate in order to measure its temperature;

characterized in that the fixing element comprises a thermally conductive element suitable for bearing a portion of electric wires adjacent to said junction; said thermally conductive element being capable of bringing said portion of electric wires into thermal contact with said substrate, and in that said fixing element comprises a thermally conductive support suitable for bearing said junction, and in which the thermally conductive element comprises a flexible lug fixed to said support; said flexible lug being suitable for exerting a pressure on said junction,

Advantageously, this measuring device makes it possible to keep a predefined length of the electric wires of the thermocouple situated close to the junction of the thermocouple produced by the weld, at a temperature close to the temperature of the substrate; the surface temperature of which is to be measured with the aim of limiting the conductive leak between the junction and the thermocouple wires.

Advantageously, this measuring device can be easily withdrawn from the radiator of the radiative travelling wave tubes, after the satellite's qualification ground tests.

Advantageously, this measuring device does not damage the collector of the radiative travelling wave tubes and, in particular, leaves no trace of glue on the latter.

Advantageously, this measuring device makes it possible to keep the fixing of the junction of the thermocouple against the radiator in an external radiative environment the temperature of which varies over a wide range of values.

Advantageously, this measuring device is compact, and it is moreover simple to utilize and to remove. In particular, it is capable of being fixed on a weak surface of the radiator of the radiative travelling wave tubes for the ground tests. Thus, it does not block, or only slightly blocks, the radiation of the radiator towards the external radiative environment allowing the cooling down of the collector of the tube. Consequently, this measuring device does not modify the environment of the radiator nor the thermal behaviour of the latter and thus makes it possible to measure a temperature which accurately reflects the temperature of the radiator for the ground tests with an error of less than approximately 3° C. When the satellite is sent into space, the radiative tubes will no longer include a thermocouple-type measuring device and their mechanical integrity will not be modified.

Advantageously, this measuring device can be used immediately after it is fixed to the substrate. The glue for fixing the junction to the measuring device need not be expected to polymerise, as the time for polymerization of the glue occurs during the manufacture of the measuring device.

Depending on the particular embodiments, the measuring device comprises one or more of the following characteristics:said portion of electric wires has a length comprised between approximately 30 mm and approximately 70 mm,the measuring device comprises a protective element capable of insulating said portion of electric wires from the external radiative environment,said protective element is capable of fixing said portion of electric wires to said thermally conductive element,said protective element is made of a thermally conductive material in order to produce the conductive bridge between said portion of electric wires and said thermally conductive element,said protective element comprises an adhesive strip,said thermally conductive element is made of a material capable of insulating it from radiative exchanges with the external environment, in which at least a part of said thermally conductive element covers at least a part of said portion of electric wires in order to insulate them against said radiative exchanges with the external environment,said thermally conductive element comprises a projecting support element, said support element being suitable for bearing at least a part of said portion of electric wires,said thermally conductive material is made of a material chosen from aluminium, aluminium alloys, copper and copper alloys,the support is thermally coupled to the junction and the substrate, said support being electrically insulated from said junction by a glue,said flexible lug is bent at least twice,said flexible lug comprises a first lug part detachably fixed to the support and to the substrate, and a second lug part forming the support element, andthe second lug part is surrounded by a flattened loop of electric wires and by said protective element in order to form a sheath having a homogeneous temperature.

DETAILED DESCRIPTION OF THE DISCLOSURE

With reference toFIGS. 1 and 2, the measuring device2according to the first embodiment of the invention comprises a thermocouple4suitable for measuring the temperature of a substrate6and an element8for fixing part of the thermocouple4to said substrate6.

The thermocouple4, only partially shown, comprises two electric wires10the ends of which are connected to each other by two junctions. These electric wires10are made of different metals or metal alloys such as, for example, the pair of materials Copper and Constantan or the pair of materials Chromel and Alumel. The thermocouple4generates, by the Seebeck effect, a difference in potential which depends on the difference in temperature between the two junctions. In order to measure an unknown surface temperature, one of the two junctions is maintained at a known temperature, the other junction12produced by the weld being in contact with the surface of the substrate6the surface temperature of which is to be measured.

The substrate6is, for example, an element for cooling down electronic components, such as a radiative travelling-wave tube mounted on a satellite. The substrate6can be arranged in an external radiative environment the temperature of which varies within a very wide temperature range, typically between −173° C. up to approximately 130° C. such as, for example, in a test chamber.

The fixing element8is suitable for fixing the junction12to said substrate6. To this end, the fixing element8comprises a support14suitable for bearing the junction12, and a flexible lug16capable of bearing a portion of electric wires10adjacent to the junction.

The support14is, for example, constituted by a plate. The junction12is glued to the support14with electrically insulating and thermally conductive glue17.

The support14is made of a thermally conductive material so that the junction12measures a temperature as close as possible to the temperature of the substrate6. This material is, for example, aluminium, aluminium alloys, copper or copper alloys.

The flexible lug16is also made of a thermally conductive material. It therefore forms a thermally conductive element. It is in thermal contact with the substrate6in order to maintain the temperature of the portion of electric wires10as close as possible to the temperature of the substrate6and thus ensure an accurate measurement of the temperature of the substrate by limiting the conductive leak between the junction12and the portion of electric wires10adjacent to the junction12.

According to the embodiment shown, the flexible lug16is in contact with the support14which is, itself, in contact with the substrate6.

As a variant, the flexible lug16can be in direct contact with the substrate6(seeFIG. 3). What is important here is to create a thermal link between the substrate6and the portion of electric wires10adjacent to the junction12.

The support14and the flexible lug16are each passed through by an opening18and20respectively, passed through by a screw22capable of being screwed into the substrate6in order to fix the measuring device2to the substrate6.

The flexible lug16is made of a material capable of protecting the portion of electric wires10situated between the substrate6and the flexible lug16from the radiative exchanges with the external environment. These radiative exchanges are diagrammatically represented, inFIG. 1, by an arrow24.

The flexible lug16is bent twice so as to constitute a step below which the junction12is glued. Thus, the flexible lug16exerts a slight pressure on the junction12which helps to hold the latter against the support14and increases the conductive coupling between junction12and the support14.

The flexible lug16comprises a support element26which projects beyond the support14. This support element26is suitable for bearing the portion of electric wires10.

More precisely, the flexible lug16comprises a first lug part16A detachably fixed to the support14and to the substrate6, two bends, and a second lug part16B forming the support element26.

Thus, advantageously, the surface of the substrate6facing the support element26remains a surface suitable for radiating towards the external radiative environment in order to cool down the substrate.

The portion of electric wires10is fixed around the support element26using an adhesive strip28wound around a flattened loop of electric wires surrounding the support element26.

The adhesive strip28is smoothed using a tool, over the electric wires10in order to create a sleeve or a sheath suitable for resisting detachment in an extreme temperature environment. This smoothing makes it possible to remove air bubbles and avoid detachment of the adhesive strip28when the surrounding temperature is very high.

The adhesive strip28is made of a thermally conductive material, allowing radiative insulation with respect to the external environment and exhibiting low infrared emissivity, such as aluminium or an aluminium alloy. The smoothing also makes it possible to make the surface of the adhesive strip28reflective and reduce its infrared emissivity.

The portion of electric wires10borne by the flexible lug16has a length comprised between approximately 30 mm and approximately 70 mm.