Factors of thermocouple measurement error

Main factors of thermocouple measurement error

1. Errors caused by unstable thermoelectric characteristics of thermocouples

After using a thermocouple thermometer for a period of time, due to the influence of the environment in which it is used, its own thermoelectric performance will change to a certain extent, and the temperature measured by the thermocouple thermometer will deviate from the true temperature to a certain extent. The main factors affecting the stability of thermocouples are:

(1) Pollution and corrosion of the thermocouple electrode by the measured object;

(2) Deformation stress caused by the deformation of the hot electrode by external force;

(3) The microstructure of the temperature-sensing electrode changes under high temperature;

(4) The hot electrode is oxidized when exposed to the air.

2. The influence of thermocouple inhomogeneity

The uniformity of the thermocouple refers to the uniformity of the thermoelectrode material of the thermocouple. If the two thermoelectrode materials in the thermocouple are uniform, the thermoelectric potential generated by the thermocouple loop is positively correlated with the temperature difference between the two ends, and has nothing to do with the temperature gradient along the length of the thermoelectrode.

3. Selection of measuring temperature point

Choosing a suitable temperature measurement point is a very important consideration when installing a thermocouple. Choosing a representative temperature measurement point is of special significance to the entire production environment. Improper location selection, control and measurement will be meaningless. At the measuring point, the insertion depth of the thermocouple also affects the temperature measurement. When there is a temperature difference between the external environment and the temperature of the measured object, the temperature measured on the thermocouple will exchange heat with the external environment as the sensor extends, and then Bring measurement errors. Due to the ever-changing ambient temperature, this temperature error is immeasurable. In addition to errors introduced by heat conduction due to the depth of insertion, the material of the external protection tube of the thermocouple will also introduce measurement errors. For example, a metal protection tube has better thermal conductivity, so it needs to be inserted deeper during the measurement process to avoid heat loss. For the protective tube made of ceramic material, it needs to be inserted shallower.