The correct use of thermocouple can not only get a temperature value accurately, qualified products, but also can save thermocouple materials consumption, save money and can guarantee the quality of the product.
Installation is not correct, thermal conductivity and time lag error, they are main error of the thermocouple is in use.
1, improperly installed into the error, such as the location of the thermocouples installed and insertion depth cannot reflect the reality of the furnace temperature, etc. , in other words, the thermocouple should not be in too close to the door and heating, the depth of the insert should be at least 8 ~ 10 times the diameter of the protection tube;
Thermocouple protection tube and the wall between the interval of missing adiabatic material overflow or cold air invading the furnace heating, so the space between the thermocouple protection tube and furnace wall hole used refractory mortar or insulating material such as asbestos rope jam to avoid cold and hot air convection and affect the accuracy of temperature measurement;
Thermocouple cold end is too close to the furnace temperature over 100 ℃;
The installation of thermocouples should as far as possible to avoid the strong magnetic field and strong electric field, so should not be thermocouple and the power cable line in order to avoid interference caused by errors within the same catheter;
Thermocouple cannot be installed in a few measured medium flowing area, when measured with thermocouple tube gas temperature, thermocouple must be made against the flow direction of installation, and fully contact with the gas.
2, the error of the insulation deterioration and introduce such as thermocouple insulation, protection tube and anchor plate too much dirt or salt slag between the thermocouple interelectrode and wall insulation fault, at high temperatures is more serious, which not only causes the thermoelectric potential loss but also can introduce interference, the resulting error sometimes can reach on baidu.
3, the introduction of thermal inertia error due to thermal inertia of thermocouple instrument behind the change of the measured temperature, indicating value this influence is particularly acute in rapid measurement.
So should be used as thermal electrode is small, small thermocouple protection tube diameter.
Temperature measuring environmental permits, even protecting tube can be taken.
Due to measurement values, using thermocouples detect temperature fluctuations of the amplitude of the furnace temperature fluctuation amplitude of the small.
After measured value, the greater the thermocouple is the smaller the amplitude of the fluctuations, and the actual temperature difference.
When using the time constant of thermocouple temperature or temperature control, digital display table shows the temperature fluctuation is small, but the actual furnace temperature fluctuations can be quite large.
In order to accurately measure temperature, should choose small thermocouple time constant.
With thermocouple time constant is inversely proportional to the heat transfer coefficient, heat the density and specific heat is proportional to the diameter, material, such as to reduce the time constant, in addition to the increased heat transfer coefficient, effective way is to try to decrease the size of the hot end.
Use, usually USES the material with good thermal conductivity, thin, small diameter of the tube wall to protect casing.
In the precision of temperature measurement, using unprotected casing bare wire thermocouple, thermocouple easy damaged, should be timely correction and replacement.
4 error at high temperature, thermal resistance, such as protecting tube with a layer of ash, dust attached to the above, the thermal resistance increase, hinder the heat conduction, when the temperature is lower than the true value of measured temperature value.
Therefore, we should maintain the cleanness of thermocouple protection tube outside, to reduce the error.