The compensation wire is a pair of wires with an insulating layer that has the same nominal value as the thermoelectromotive force of the matched thermocouple in a certain temperature range (0~100°C). Errors due to temperature changes at the junction. The following editor will introduce to you what material the thermocouple compensation wire is, what the function of the thermocouple compensation wire is, and the classification of the thermocouple compensation wire.
1. What material is the thermocouple compensation wire?
The general compensation wire requires the positive and negative electrodes to be the same as the positive and negative materials of the thermocouple. K-type thermocouples are nickel-cadmium (positive) and nickel-silicon (negative), so according to the standard, nickel-cadmium-nickel-silicon compensation wires should be selected.
2. What is the function of the thermocouple compensation wire
It is to extend the hot electrode, that is, the cold end of the mobile thermocouple, and connect with the display instrument to form a temperature measurement system. Equivalently adopt the national standard of IEC 584-3 “Thermocouple Part 3 – Compensation Wire”. The products are mainly used in various temperature measuring devices, and have been widely used in nuclear power, petroleum, chemical, metallurgy, electric power and other departments.
3. Classification of thermocouple compensation wires
In principle, it is divided into extension type and compensation type. The nominal chemical composition of the alloy wire of the extension type is the same as that of the matched thermocouple, so the thermoelectric potential is also the same. It is represented by “X” in the model, and the nominal chemical composition of the alloy wire of the compensation type is the same. It is different from the matched thermocouple, but in its working temperature range, the thermoelectric potential is close to the nominal value of the thermoelectric potential of the matched thermocouple, which is represented by “C” in the model.
Compensation accuracy is divided into ordinary grade and precision grade. The error after compensation of precision grade is generally only half of that of ordinary grade, which is usually used in places with high measurement accuracy requirements. For example, for the compensation wires of S and R graduation numbers, the tolerance of the precision grade is ±2.5°C, and the tolerance of the ordinary grade is ±5.0°C; for the compensation wires of the K and N graduation numbers, the tolerance of the precision grade is ±1.5°C , the tolerance of ordinary grade is ±2.5℃. In the model, the ordinary grade is not marked, and the precision grade is added with “S”.
From the working temperature, it is divided into general use and heat-resistant use. The working temperature of general use is 0 ~ 100 °C (a few are 0 ~ 70 °C);
In addition, the wire core can be divided into single-strand and multi-core (soft wire) compensation wires, and can be divided into ordinary and shielded compensation wires according to whether they have a shielding layer, and there are also compensation wires for intrinsically safe circuits dedicated to explosion-proof occasions.