How to connect the three wires of a thermocouple

1. Working principle and application of thermocouples
Thermocouples are sensors used to measure temperature, based on the principle of thermoelectric effect. The thermoelectric effect refers to the electromotive force generated by different metal conductors under the action of temperature difference, and thermocouples use this effect to measure temperature. A thermocouple is composed of two different metal wires, with their two ends connected to form a measuring point. One wire is called a positive wire, and the other is called a negative wire.
In a thermocouple, the junction of the positive and negative wires is called the measurement point of the thermocouple and is usually placed at the location where the temperature needs to be measured. When the temperature of the measurement point changes, the temperature difference between different metal wires leads to the generation of electromotive force, which has a certain relationship with temperature. By measuring the magnitude of the electromotive force, the temperature of the measurement point can be calculated.
Thermocouples are widely used in industrial, instrumentation and other fields, such as temperature measurement in gas furnaces, chemical equipment, power equipment, etc. It has the advantages of fast response speed, wide measurement range, and high reliability. The temperature measurement of thermocouples is influenced by many factors, including wire material, ambient temperature, connection method, etc.
For the connection method of the three wires of the thermocouple, according to international standards, two wires (positive wire and negative wire) are used to measure the electromotive force, and the other wire (compensating wire) is used to compensate for temperature errors in the electromotive force. The connection method of positive and negative wires is different from that of compensating wires.
2. Connection method of three wires
The positive and negative wires are connected to the two input ports of the measuring instrument, and the compensating wire is connected to the third input port of the measuring instrument with either wire.
This connection method is suitable for measuring situations where the temperature error of the compensating wire needs to be ignored. The function of the compensation wire is to compensate for the temperature error between the positive and negative wires. If this error does not need to be considered, the compensation wire can be connected to any wire to the third input port.
The positive wire is connected to one input port of the measuring instrument, the negative wire is connected to another input port of the measuring instrument, and the compensating wire is independently connected to one compensating instrument.
This connection method is suitable for situations where temperature errors of compensating wires need to be considered. Due to the independent connection of the compensating wire with the positive and negative wires to different instruments, the temperature error of the compensating wire can be eliminated and the measurement accuracy can be improved through the compensating instrument.
Thermocouples are a commonly used temperature sensor that can be quickly and widely applied in industrial and instrumentation fields. In the three wire connection method of thermocouples, different connection methods are selected based on whether the temperature error of the compensating wire needs to be considered. Connection 1 is suitable for situations where compensating wire errors are ignored, while connection 2 is suitable for situations where compensating wire errors need to be considered.