The selection of compensation wire has a great influence on the accuracy of thermocouple temperature measurement, and the instrument operator must be familiar with the performance and indicators of various compensation wires. The following is a brief introduction to the precautions for the use of the compensation wire.
1. For S-type thermocouples and R-type thermocouples, there are two types of compensation wires: SC and RC, both of which belong to compensation type compensation wires, and the accuracy is low among various types of compensation wires. The error is small in the range of 0-60°C, but there is a larger error in the range of 100-150°C. If the measurement accuracy is high, the temperature of the compensation contact must be kept below 100°C.
2. Compensation wires of K-type thermocouple have KC type and KX type. KX is an extended compensation wire. The characteristic curve is linear in a wide temperature range, with small errors, but high cost and large resistance. Therefore, when the operating temperature is not high and the temperature measurement accuracy requirements are not too strict, the cheaper compensation type KC type compensation wire should be used.
Issues that need to be paid attention to when using compensation wires:
1. Various compensating wires can only be paired with corresponding types of thermocouples. Different types cannot be used.
2. Compensation wires are divided into positive and negative poles. When in use, the positive and negative poles of the compensation wire must not be connected incorrectly, otherwise it will not only fail to compensate, but will also cause a large measurement error. Facts have proved that the error caused by the wrong polarity of the compensation wire is about twice that of no compensation wire.
3. The temperature at the connection point of the thermocouple and the compensation wire shall not exceed the specified operating temperature. Because it exceeds the specified operating temperature, the thermoelectric characteristics of the compensation wire and the thermocouple are quite different, which causes measurement errors.
4. Since the thermoelectric characteristics of the compensation wire and the thermocouple are not exactly the same, it is required that the temperature of the two junctions at the connection be the same, otherwise it will cause measurement errors.
5. The wire diameter of the compensation wire should be selected according to the different requirements of the equipped display instrument. For example, for the compensation wire connected to the moving coil instrument, you can choose a thicker wire to make its resistance smaller, so that it will not exceed the external resistance value specified by the instrument.
6. In order to facilitate installation, multi-strand compensation wires can be selected, or waterproof, anti-corrosion, and fire-proof compensation wires can be selected as required.
