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Precautions for the Selection of Temperature Sensors and Methods to Avoid Errors

Ⅰ. Precautions for selecting temperature sensors

1. Whether the environmental conditions of the measured object have any damage to the temperature measuring element.

2. Whether the temperature of the measured object needs to be recorded, alarmed and automatically controlled, and whether it needs to be measured and transmitted remotely. 

3. In the case where the temperature of the measured object changes with time, whether the lag of the temperature measuring element can meet the temperature measuring requirements.

4. The size and accuracy of the temperature measurement range.

5. Whether the size of the temperature measuring element is appropriate.

6. What is the price and whether it is convenient to use.

Ⅱ. How to avoid errors in temperature sensors?

When installing and using the temperature sensor, the following errors should be avoided to ensure the best measurement effect.

1. Errors caused by improper installation

For example, the installation position and insertion depth of the thermocouple cannot reflect the real temperature of the furnace. In other words, the thermocouple should not be installed too close to the door and heating, and the insertion depth should be at least 8 to 10 times the diameter of the protection tube.

2. Thermal resistance error

When the temperature is high, if there is a layer of coal ash on the protective tube and dust is attached to it, the thermal resistance will increase and hinder the conduction of heat. At this time, the temperature indication 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.

3. Errors caused by poor insulation

If the thermocouple is insulated, too much dirt or salt slag on the protection tube and the wire drawing board will lead to poor insulation between the thermocouple and the furnace wall, which is more serious at high temperature, which will not only cause the loss of thermoelectric potential but also introduce interference. The error caused by this can sometimes reach 100℃.

4. Errors introduced by thermal inertia

This effect is especially pronounced when making fast measurements because the thermal inertia of the thermocouple causes the meter's indicated value to lag behind the change in the temperature being measured. Therefore, a thermocouple with a thinner thermal electrode and a smaller diameter of the protection tube should be used as much as possible. When the temperature measurement environment permits, the protective tube can even be removed. Due to the measurement lag, the amplitude of the temperature fluctuation detected by the thermocouple is smaller than that of the furnace temperature fluctuation. The larger the measurement lag, the smaller the amplitude of the thermocouple fluctuations and the larger the difference from the actual furnace temperature.

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