When installing and using a temperature sensor, pay attention to the following items:
1. Improper installation errors such as the location of the thermocouple and the depth of insertion do not reflect the true temperature of the furnace, in other words, the thermocouple should not be installed too close to the door and heating place, the depth of insertion should be at least for the protection tube 8 to 10 times of the diameter; the gap between the protective sleeve of the thermocouple and the wall is not filled with heat insulating material, so that the heat in the furnace overflows or cold air invades. Therefore, the gap between the thermocouple protection tube and the wall hole hole is made of refractory mud or asbestos rope The insulation material is blocked to avoid the convection of hot and cold air and affect the accuracy of temperature measurement; the thermocouple cold end is too close to the furnace body to make the temperature exceed 100°C; the thermocouple installation should avoid the strong magnetic field and strong electric field as much as possible, so it should not be The thermocouple and the power cable are installed in the same conduit to avoid introducing interference to cause errors; the thermocouple cannot be installed in the area where the measured medium rarely flows. When measuring the temperature of the gas inside the tube with a thermocouple, the thermocouple must be directed against the flow velocity. Installed and fully in contact with the gas.
2. Insulation becomes poor and the introduced error is such as thermocouple insulation. Excessive dirt or salt residue of the protection tube and wire-pulling board causes poor insulation between the thermocouple pole and the furnace wall, which is more serious at high temperatures. This will not only cause thermoelectricity. The loss of potential and will also introduce interference, and the resulting errors can sometimes reach Baidu.
3. Inaccuracy introduced by thermal inertia Due to the thermal inertia of the thermocouple, the indicator value of the meter lags behind the change in the measured temperature, and this effect is particularly pronounced during rapid measurements. Therefore, thermocouples with thinner thermocouples and smaller diameters should be used as much as possible. When the temperature measurement environment permits, the protection tube can even be removed. Due to the measurement hysteresis, the amplitude of the temperature fluctuation detected by the thermocouple is smaller than the amplitude of the fluctuation of the furnace temperature. The larger the measurement lag, the smaller the amplitude of the fluctuation of the thermocouple and the greater the difference from the actual furnace temperature. When using thermocouples with large time constants for temperature measurement or temperature control, although the temperature displayed by the instrument fluctuates little, the actual furnace temperature may fluctuate greatly. In order to accurately measure the temperature, a thermocouple with a small time constant should be selected. The time constant is inversely proportional to the heat transfer coefficient and is proportional to the diameter of the hot end of the thermocouple, the density of the material, and the specific heat. To reduce the time constant, in addition to increasing the heat transfer coefficient, the most effective method is to minimize the size of the hot end. . In use, a protective sleeve with a thin wall and a small internal diameter is generally used with good thermal conductivity. In the more precise temperature measurement, a bare wire thermocouple without a protective sleeve is used, but the thermocouple is easily damaged and should be promptly corrected and replaced.
4, thermal resistance error at high temperatures, such as a protective layer of coal ash, dust attached to the above, the increase in thermal resistance, hinder the conduction of heat, then the temperature of the measured value 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.
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