When installing and using a temperature proximity sensor, the following considerations should be taken to ensure the best possible measurement results.
1. The installation error is inappropriate
If the installation position and insertion depth of the thermocouple do not reflect the actual temperature in the furnace, in other words, the thermocouple should be installed not too close to the door and heated, and the insertion depth should be at least 10 times the diameter of the protective tube8; The spacing between the casing and the thermocouple wall is filled with material to overflow or intrude of insulating cold air, so the thermocouple protection tube and refractory mud or asbestos insulation material are blocked to avoid the application of the gap between the wall holes of the convection furnace of cold and hot air and affect the accuracy of temperature measurement; The cold end of the thermocouple is too close to the furnace body and the temperature exceeds 100°C;
The installation of thermocouples should avoid strong magnetic fields and strong electric fields as much as possible, so thermocouples and power cable lines should not be in the same sequence to avoid interference caused by introduction errors; The thermocouple cannot be installed in the flow area of the medium to be measured, and when the temperature in the trachea is measured by the thermocouple, the thermocouple must be installed in the velocity direction of the flow rate, and the gas is in full contact with the gas.
2. Wrong introduction of insulation
For example, the thermoelectric dipole and furnace wall are not well insulated due to excessive dirt or salt slag of the thermocouple insulating protective tube and cable plate, which is more serious at high temperatures, which not only causes losses, but also introduces interference with the thermal potential, and the resulting error is sometimes as high as 100 degrees Celsius
3. Thermal inertia introduction error
Due to the thermal inertia of the thermocouple, the indicator value of the meter is particularly important for the rapid measurement of temperature changes. Thermoelectrodes with small thermocouple protection tubes should be used as much as possible. The temperature environment allows and even the pipes can be protected. Due to the measurement hysteresis, the temperature fluctuations of the amplitude detected by the thermocouple temperature fluctuation amplitude are small. The greater the measurement delay, the smaller the amplitude fluctuation of the thermocouple and the greater the actual temperature difference.
When thermocouples or temperature control time constants, temperature indicator gauges can fluctuate very little in the furnace where the actual temperature changes. In order to accurately measure temperature, the time constant of the thermocouple should be chosen. In addition to increasing the heat transfer coefficient, suitable and effective methods are to reduce the heat end time constant at the hot end and the heat transfer coefficient inversely proportional, proportional to the density and thermocouple diameter at the specific heat and heat end, material, such as reducing the time constant. In use, it is usually made of a good thermally conductive material, and the protective sleeve has a thin wall and a small diameter. In temperature measurement accuracy, unprotected bare wire thermocouple tubes are used, but thermocouples are easily damaged and should be corrected and replaced in time.
4. High temperature resistance and other errors, such as a layer of ash and dust attached to the protective pipe, will increase the thermal resistance and hinder the heat conduction, and the temperature value will be lower than the measured value. Therefore, thermocouple protection tubes should be kept clean outside to reduce errors