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Factors affecting the measurement of thermal resistance temperature sensor

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Factors affecting the measurement of thermal resistance temperature sensor

Date of release:2018-12-03 Author: Click:

Thermal resistance temperature sensor is a kind of measuring instrument for temperature change, the accuracy is the most basic requirements, in the process of using thermal resistance temperature sensor is the most important is to ensure the accuracy of measurement, reduce the error, reduce the external factors influence on the measurement to a minimum, the following China experts in sensor network to introduce you to the influencing factors of thermal resistance temperature sensor.

Insert depth

The choice of thermocouple temperature measuring point is the most important. The location of temperature measuring point must be typical and representative for the production process, otherwise it will lose the significance of measurement and control. When the ambient temperature is low, there is heat loss. The temperature measurement error is caused by the inconsistency between the thermocouple temperature sensor and the temperature of the object under test. In short, the error due to heat conduction is related to the insertion depth. The depth of insertion is related to the material of the protection tube. Metallic protection pipe is good because of its conduct heat performance, its insert depth should a few deeper, ceramic material is adiabatic performance is good, can insert a few shallower. For engineering temperature measurement, the insertion depth is also related to the static or flowing state of the measured object, and the specific value should be determined by experiments.

The response time

The basic principle of temperature measurement by contact method is that the temperature measuring element should reach the thermal balance with the measured object. Therefore, it is necessary to maintain a certain time during temperature measurement to achieve a thermal balance between the two. The length of holding time is related to the thermal response time of the temperature measuring element. The thermal response time mainly depends on the sensor structure and measurement conditions, which vary greatly. For gas medium, especially for stationary gas, the equilibrium should be maintained at least for more than 30min. For liquids, the fastest time is more than 5 minutes. The response time of the sensor is required to be in the millisecond level if the whole process is only 1 second, especially the instantaneous change process, in which the temperature is constantly changing. Therefore, the common temperature sensor not only can't keep up with the temperature change speed of the measured object, but also can't reach the thermal balance and produce measurement error. It is best to choose the sensor with fast response. In addition to the influence of the protective tube, the measuring end diameter of the thermocouple is also the main factor, that is, the finer the wire is, the smaller the measuring end diameter is, and the shorter the thermal response time is.

Thermal impedance increase

For the thermocouple temperature sensor used at high temperature, if the measured medium is gaseous, the dust deposited on the surface of the protection tube will be melted on the surface, thus increasing the thermal impedance of the protection tube. If the medium under test is a melt, slag will be deposited during use, which not only increases the response time of the thermocouple, but also makes the indicating temperature lower. Therefore, in addition to regular verification, in order to reduce the error, regular sampling inspection is also necessary.

Thermal radiation

The thermocouple temperature sensor inserted into the furnace for temperature measurement will be heated by the thermal radiation from the hot object. It is assumed that the gas in the furnace is transparent, and when the temperature difference between the thermocouple and the furnace wall is large, the temperature measurement error will be caused by energy exchange. In general, in order to reduce the thermal radiation error, should increase the heat conduction, and make the furnace wall temperature as close as possible to the temperature of the thermocouple. In addition, thermocouple installation location, should be from the solid as far as possible to avoid thermal radiation, so that it can not radiate to the surface of the thermocouple; It is better to have a thermocouple with thermal radiation shield.

The above four factors are the factors that affect the measurement of the linear displacement sensor. We must control the influence of these factors on the specific measurement process in the daily measurement process to ensure the accuracy of measurement.

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