Effective way to reduce the measurement error of thermocouple

How can we reduce the measurement error caused by the use of thermocouples? First of all, if we want to solve the error, we need to understand the cause of the error, so as to effectively solve the problem! Let's analyze several reasons for the error: First, determine whether the thermocouple is installed correctly. If the installation is improper, errors will occur. Here are four points for the installation of the thermocouple: 　　1, the insertion depth should be at least The diameter of the protective tube is 8-10 times; the space between the protective tube of the thermocouple and the wall is not filled with insulating material, which causes heat overflow or cold air intrusion in the furnace. Therefore, the gap between the thermocouple protective tube and the furnace wall hole should be made of refractory mud or Asbestos rope and other insulation materials are blocked to prevent the convection of hot and cold air from affecting the accuracy of temperature measurement; 　　2, the cold end of the thermocouple is too close to the furnace body to make the temperature of the measured place too high; 　　3, the installation of the thermocouple should avoid strong magnetic fields as much as possible And strong electric field, so thermocouple and power cable should not be installed in the same conduit to avoid introducing interference and causing errors; 　　4. Thermocouple cannot be installed in an area where the measured medium seldom flows. When using a thermocouple to measure the gas temperature in the tube At this time, the thermocouple must be installed against the direction of the flow rate and fully in contact with the gas. Secondly, in the use of thermocouples, the deterioration of the thermocouple insulation is also one of the reasons for the error: 　　 protection tube, pull wire plate dirt, excessive salt slag will lead to poor insulation between the thermocouple electrodes and the furnace wall, which is more serious at high temperatures. , This will not only cause the loss of thermoelectric potential but also interference, and the error caused by this may even reach hundreds of degrees Celsius. In addition, the error caused by the thermal resistance of the thermocouple: Dust or coal dust on the thermocouple protection tube 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. So keep the thermocouple protection tube clean. The latter is the error caused by the thermal inertia of the thermocouple: the inertia of the thermocouple makes the indicator value of the instrument lag behind the change of the measured temperature, so you should try to use a thermocouple with a thinner thermoelectrode and a smaller protective tube diameter. Due to the hysteresis, the amplitude of the temperature fluctuation detected by the thermocouple is smaller than the amplitude of the furnace temperature fluctuation. Therefore, in order to accurately measure the temperature, you should choose a material with good thermal conductivity, a protective sleeve with a thin tube wall and a small inner diameter. In temperature measurement with relatively high accuracy requirements, bare-wire thermocouples without protective sleeves are often used. In summary, we can reduce the measurement error of the thermocouple by checking in four aspects. The first step is to check whether the thermocouple is installed correctly. The second step is to check whether the insulation of the thermocouple has deteriorated. The third step is to check whether the thermocouple protection tube is clean. Four steps to check whether the error is caused by the thermal inertia of the thermocouple!

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