working principle

1thermocoupleIt is a commonly used temperature measuring element in temperature measuring instruments. It directly measures temperature and converts the temperature signal into a thermoelectric signal, which is then converted into a 4-20mA signal through a temperature transmitter and introduced into the control system to display the temperature.

2. The basic principle of thermocouple temperature measurement is that two conductors A and B with different compositions form a closed loop. When there is a temperature gradient at both ends, current will flow through the loop, and there will be an electromotive force - thermoelectric potential - between the two ends, which is called the Seebeck effect.

cold junction compensation

1. The calibration table is obtained under the condition of a free end temperature of 0 ℃, and different thermocouples have different calibration tables. According to the principle of thermoelectric effect, its thermoelectric potential is related to the temperature at both ends, and the scale is given under the condition of a cold end temperature of 0 ℃. However, in practical use, the cold end is often close to the object being measured, and due to the influence of ambient temperature, its temperature cannot be maintained at 0 ℃, resulting in measurement errors.

2. So corresponding measures are taken for compensation or correction, commonly used methods include cold end constant temperature method, compensation wire method, compensation bridge method, calculation correction method, etc.