What is the error caused by thermal inertia of temperature sensor

The reason why the temperature sensor can measure temperature is mainly due to the external thermal resistor or thermocouple. Sometimes we hear that the thermal inertia of the temperature sensor causes the temperature sensor deviation. What is the thermal inertia of the temperature sensor? What can be done to deal with the deviation caused by thermal inertia?

The thermal inertia of the temperature sensor is actually the thermal inertia of the thermal resistor or thermocouple on the surface of the temperature sensor. Because of the thermal inertia of the thermal resistor or thermocouple, the indication value of the instrument lags behind the change of the measured temperature. This effect is particularly prominent when performing rapid measurements.

Therefore, thermal resistors or thermocouples with thinner thermocouples and smaller protective tube diameters should be used as much as possible. When the temperature measurement environment permits, the protective tube can even be removed. Due to the measurement lag, the amplitude of the temperature stability detected by the thermal resistor or thermocouple is smaller than the amplitude of the furnace temperature stability. The greater the measurement lag, the smaller the amplitude of the thermal resistor or thermocouple stability, and the greater the difference from the actual furnace temperature.

When using a thermocouple with a large time constant to measure or control temperature, the temperature displayed by the instrument is very unstable, but the actual furnace temperature may be very unstable. In order to accurately measure the temperature, a thermal resistor or thermocouple with a small time constant should be selected. The time constant is proportional to the heat transfer coefficient, and is proportional to the diameter of the thermal resistor or thermocouple heat end, the density of the material and the specific heat. If you want to reduce the time constant, in addition to increasing the heat transfer coefficient, the most effective measure is to reduce the size of the heat end as much as possible.

In application, materials with good thermal conductivity and protective sleeves with thin walls and small inner diameters are usually used. In more precise temperature measurements, bare wire thermal resistors or thermocouples without protective sleeves are used, but thermocouples are easily damaged and should be calibrated and replaced in time.

The deviation caused by the thermal inertia of the temperature sensor has a great influence on the measurement value during measurement, especially when making precise measurements, we must pay attention to the thermal inertia of the temperature sensor. We must try to avoid the deviation caused by the thermal inertia of the temperature sensor or use appropriate compensation to weaken this deviation.