Factors Affecting Measuring Error of Thermocouple of Temperature Instrument
1. Errors introduced by insulation deterioration
For example, too much dirt or salt slag on the thermocouple insulation protection tube and pull-wire plate leads to poor insulation between the thermocouple JI and the furnace wall, which will not only cause the loss of thermoelectric potential but also introduce interference, the resulting error can sometimes reach Baidu .
2, thermal resistance error
At high temperature, if there is a layer of coal ash and dust attached to the protective tube, it will increase the thermal resistance and hinder the heat conduction. At this time, the temperature indication is lower than the true value of the measured temperature. Therefore, the outside of the thermocouple protection tube should be kept clean to reduce errors.
3. Errors caused by improper installation
The gap between the thermocouple protection tube and the wall is not filled with insulation material, which will cause heat overflow in the furnace or cold air intrusion. Therefore, the gap between the thermocouple protection tube and the furnace wall hole should be blocked by refractory mud or asbestos rope and other insulation materials to prevent cold Convection of hot air affects the accuracy of temperature measurement;
The cold junction of the thermocouple should not be too close to the furnace body so that the temperature exceeds 100°C.
4, the error introduced by thermal inertia
Due to the thermal inertia of the thermocouple, the indicator value of the meter lags behind the change of the measured temperature. This effect is particularly prominent during rapid measurement. Therefore, a thermocouple with a thinner thermoelectric JI and a smaller protective tube diameter should be used as much as possible.
The protective tube can even be removed when the temperature measurement environment permits. Due to the measurement lag, the amplitude of the temperature fluctuation detected by the thermocouple is smaller
