DE8708316U1 - Thermocouple reference point - Google Patents

Description

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Reference number: G 87 08 316.7 Industrieanlagen-Betriebsgesellschaft mbH

Thermoelement reference point

The subject of the innovation is a highly accurate electronic multi-channel reference point for thermocouples.

Many applications in civil, military or space projects require precise temperature measurements for laboratory tests and in operation, and the number of measuring points can be high (e.g. 100 per engine, per satellite). Thermocouples are usually used for the measurement, which require a reference temperature, a reference point. The accuracy of the measurements depends, among other things, on how precisely the temperature of the reference point can be set and kept constant. In addition, to avoid systematic measurement errors, it is desirable to connect all measuring points to the same reference point. This creates the requirement for a highly accurate thermocouple reference point to which a large number of measuring points can be connected. For the aerospace application, there are additional requirements such as very compact construction and the ability to be replaced in high vacuum (10" ⁶ Torr). In addition, general requirements apply, such as high reliability, calibration capability and low-cost production through the use of commercially available components and materials.

These requirements are not met by comparable, commercially available thermal reference points, which usually only offer up to 25 channels.

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. The innovation is based on the task of developing a thermal element reference point that allows a much higher number of connections in a much smaller construction volume and that also works very reliably and with high precision. The special choice of materials also ensures that it can be used in high vacuum (space).

According to the innovation, this task is solved as follows:

The thermocouple reference point (Fig. 1) is located in a cube-shaped housing with external dimensions of approximately 85 x 85 x 85 mm; it consists of a solid copper block that is split in two to enable the assembly of the internal elements. The copper block 1 is connected to the housing at only a few points using thermally well-insulated supports 9.

&bull; housing base 11. Below the copper block 1 there is a circuit board 8 with the control circuit, the supply and removal of the cables takes place via multi-pin connectors 12 on the housing walls 10.

The size of the copper block depends, among other things, on the number of thermocouple reference points. For 100 reference points, it is approximately 50 x 50 x 50 mm. The cross-section of the copper block is sufficiently large to keep the thermal resistance so low that the zone Z, in which the reference thermocouples are glued in, can be described as an isothermal area. The sensors 7 for the electronic control circuit and a temperature sensor 6 as an additional means of controlling the reference temperature are also located in this area. Heating to the desired temperature is provided by transistors 5 and heating resistors 4*.

are installed in the copper block in the edge zone of the isothermal area. Each of these elements is located in a cavity milled or drilled to measure. There is one hole in the copper block for each reference thermocouple.

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j The reference thermocouples 2 are conveniently glued half into the upper and half into the lower copper block in an electrically insulated manner, their push-in ends 3 lead to the connector plugs 12.

For highly precise setting and constant maintenance of the reference temperature, a control circuit was designed (Fig. 2) that keeps the reference temperature in the copper block constant over a wide operating range. Example of implementation:

Reference temperature: 15O ⁰ F - 65,56 ⁰ C with a tolerance in air 4T _Ref ^0,1 ⁰ C and in vacuum WT^ = 0,15°C, these values apply to an operating range Ty _mqebuncj from + 5 ⁰ C to + 55 ⁰ C.

Control of the reference temperature is also possible, as explained in more detail below.

The control circuit works as follows:

It is a mixed analog-digital control (Fig. 2). The IC1 works as a comparator. At the non-inverting input, it is given a very stable voltage that can be set with Pl, which is compared with the voltage at the inverting input. The latter consists of a voltage that depends on the block temperature and is generated via MTCl and NTC2 (7 Fig. 1), plus a small triangular voltage from IC2. When the electronics are started up and the actual temperature is significantly lower than the desired target temperature, the IC1 switches its output to zero and causes the transistors T^ to T^ to

the resistors Rl to R4 draw current. These heat up the block - until 20

near the target temperature, the voltages at the inputs of ICl begin to overlap and the constant heating current becomes a pulse-shaped one with a triangular frequency. In the steady state, just enough heating power is applied to compensate for the heat losses and thus keep the block temperature constant.

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File number: G 87 08 316.7 Industrial Company Ltd. . 4 _

The temperature sensor PtSOO (6, Fig. 1), installed as an additional control option in the second round of the block, is connected in the bridge BR. After the reference furnace has been calibrated (with a thermocouple calibrated according to DKD), the bridge can be calibrated to the required value using P2. Its /Low voltage range is then 0.1 V in the event of a deviation from the target temperature.

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The control circuit contains only commercially available components; the circuits used are known in principle; what is new is their application in the form shown in Fig. 2 for the purpose of highly accurate temperature control for thermocouple reference points.

The requirement for the thermocouple reference point to be replaceable in high vacuum or in space is met by the fact that all components were specifically selected for their outgassing resistance, including the special adhesives used.

The thermocouple sensors are connected to the thermocouple reference point via multi-pin connectors 12, the contacts of which are also made of appropriate thermocouple material to avoid parasitic thermoelectric voltages.

Claims (6)

Ref.: G 87 08 316.7 Industneanlagen-Betriebsgesellschaft mbH Protection claims 1. Thermoelectrothermal reference point, characterized in that thermocouples (2) with outwardly leading lines (3) as well as heating resistors (4), power transistors (5), a platinum resistance thermometer (6) and two NTC resistors (7) are accommodated inside a cube-shaped, two-part copper block (1). 2. Thermocouple reference point according to claim 1, characterized in that the copper block is surrounded by a housing (10), the housing base (11) and the housing cover (13). 3. Thermocouple reference parts according to claim 1, characterized in that a control board (8) is accommodated below the copper block (1), within the housing (10, 11, 13). 4. Thermocouple reference point according to claim 1, characterized in that up to 100 and more thermocouple reference points are simultaneously in the can be accommodated inside the copper block. 5. Thermocouple reference point according to claim 1, characterized in that the copper block and the control board are attached to the housing base (11) by means of thermally insulating stands (9). 6. Thermocouple reference point according to claim 1, characterized in that the thermocouple wire ends are led to multi-pole plugs (12). &igr; MU &idigr; i &igr; i MIi &igr; &igr; f iii t in I í ii i III fill«* i » ti III**· · I I M * t 14 · · &diams;