Weak current College】 【thermocouple fault analysis】.

Proper use of the thermocouple can accurately be temperature value, to ensure product conformity, but also can save the material consumption for thermocouple, save money and ensure product quality. Not installed correctly, thermal conductivity and time lag and other errors, they are a thermocouple in use by major errors.

1. improper installation error
If the location of the thermocouple installation and insertion depth does not reflect the real temperature of the furnace and so on, in other words, the TC should not be packed in too close to the door and heating, the insertion depth should be at least as protective tube diameter 8-10 times; thermocouple protective casing and the interval between wall does not fill insulation material cause furnace heat overflow or cold air intrusion, thermocouple protection tubes and furnace wall application hole gap between refractory mortar or insulating materials such as asbestos rope to avoid blockage of hot and cold air convection and the impact of temperature measurement accuracy; thermocouple cold end too close to the furnace to temperatures above 100 degrees centigrade; thermocouple installation should, as far as possible, avoid the magnetic and electric field, it should not be the thermocouple and the power cable mounted on the same root Intraductal so as not to introduce interference causing error; thermocouple will not install on little medium flow range, when using thermocouples measure tube gas temperature, you must make the thermocouple upstream along the flow velocity, direction and fully installed and gas exposure.

2 insulated variation introduced by errors
E.g. thermocouple insulation, protection tube and La Board dirt or salt slag too much cause thermocouple interelectrode and wall insulation bad, in more severe under high temperature, not only cause the loss of thermoelectric power and the introduction of interference, the resulting error sometimes up to Baidu.

3 error thermal inertia
Due to the inertia of the thermocouple meter indicates the value behind the measured temperature changes, rapid measuring this effect is particularly pronounced. It should be fine using thermal-electrode, protection tube diameter smaller thermocouple. Temperature measuring environmental permit, can even take away the protective tube. Due to the presence of measuring latency, thermocouple detection of temperature fluctuation of temperature fluctuation amplitude relatively small amplitude. Measuring latency, the greater the amplitude of the thermocouple fluctuation, the smaller, and the actual temperature variations. When using the time constant of thermocouple or temperature, and meter display of temperature while volatility is very small, but the actual temperature fluctuations can be quite large. In order to accurately measure the temperature, should choose the time constant of the thermocouple. Time constant is inversely with the heat transfer coefficient, and the diameter of the thermocouple hot end, material density and heat proportional, if you want to decrease the time constant, apart from increasing the heat transfer coefficient, the most effective approach is to minimize the size of the hot end. Use, usually with good thermal conductivity of materials, the inner diameter of the tube wall thin, small protective casing. In the more precise temperature measurement, use no protection casing of raw silk thermocouple, thermocouple easily damaged, it should be timely correction and replacement.

4 thermal resistance errors
High temperatures, such as protecting tube with a layer of ash and dust in the above, the thermal resistance increase, hamper the transmission of heat, the temperature indication than the measured temperature value of true. Therefore, you should keep the thermocouple protective tube external cleansing to reduce error.