Requirements for Instrument Workers to Use Compensation Wires

Compensation wires are a pair of insulated wires with the same nominal value as the thermoelectric potential of the matched thermocouple within a certain temperature range (0~100 ℃). They are used to connect the thermocouple and the measuring device to compensate for the errors caused by temperature changes at the connection point between them and the thermocouple. In addition to reducing measurement errors, it can also improve the physical and mechanical properties of thermocouple temperature measurement circuits. For example, using multi core wires or small diameter compensating wires can enhance the flexibility of the circuit, making it easy to connect and shield from external interference; It can reduce the cost of measurement lines.

① Compensation wires with various division marks can only be used with thermocouples with the same division mark, otherwise they may be undercompensated or overcompensated

When we use compensating wires with K division marks and thermocouples with N division marks, it will cause overcompensation and display a higher temperature; On the contrary, using compensation wires with N division marks and thermocouples with K division marks will result in undercompensation and lower display temperatures

② Thermocouples and thermocouple compensation wires are divided into positive and negative poles, and the polarity cannot be reversed

Prove that the error caused by reversing the polarity of the thermocouple compensation wire during use is approximately twice that of not using the compensation wire. After replacing the on-site thermocouple in a certain chemical plant, there was a significant deviation between the temperature measurement value and the actual temperature, sometimes high and sometimes low. After careful inspection, it was found that the polarity of the thermocouple and the compensation wire was reversed. After adjusting the compensation wire according to the polarity, the fault was eliminated.

③ Thermocouples and thermocouple compensation wires have positive and negative poles, and when the polarity of the compensation wire is reversed, the instrument display value changes greatly:

a. After reversing the polarity of the compensation wire, when the temperature at the connection between the thermocouple and the compensation wire is higher than the temperature in the control room, the instrument displays a temperature lower than the actual measured temperature.

b. After reversing the polarity of the compensation wire, when the temperature at the connection between the thermocouple and the compensation wire is lower than the temperature in the control room, the instrument displays a temperature higher than the actual measured temperature.

c. After reversing the polarity of the compensation wire, when the temperature at the connection between the thermocouple and the compensation wire is the same as the temperature in the control room, the instrument displays the same temperature as the actual temperature.