Thermocouple insertion depth on the influence of the temperature measurement

In industrial temperature measurement in the 0 ~ 400 ℃ above all thermocouples as a general instrument temperature measuring tool, the installation position of thermocouple, the choice of the temperature measuring points is the most important. The location of the temperature measurement points, for the production process, must be typical and representative, otherwise you will lose the meaning of measurement and control.

insert depth of thermocouple insertion under test sites, along the length direction of the sensor will produce heat. When the environment temperature low heat loss. The thermocouple do not agree with the temperature of the measured object and produce temperature measurement error. In a word, the error induced by heat conduction, related to the insertion depth. And insert depth related to the protection tube material. Metal protection tube because of its thermal performance is good, the insert depth should be a little bit deep ( About the diameter of 15 - 20 times) , ceramic material thermal insulation performance is good, can be inserted into the shallow some ( About the diameter of 10 - 15 times) 。

the effects of response time contact method of temperature measurement is the basic principle of temperature measuring element to reach thermal equilibrium with the object being measured. When measuring temperature, therefore, need to keep a certain time and to make both reach thermal equilibrium. While keeping the length of time, with temperature measuring elements related to the thermal response time. And thermal response time depends on the structure of the sensor and measurement conditions, the difference is great. For the gas medium, especially the static gas, at least should be a balance of more than 30 min to reach; For liquid, the fastest also want to in more than 5 min. To temperature changing were places, especially in an instant change process, the whole process of only 1 second, insist on the sensor response time in milliseconds. Ordinary temperature sensor, therefore, not only to keep pace with the speed of change in the temperature of the object appear lags behind, and the measurement error due to reach thermal equilibrium. Had better choose fast response of the sensor. Except for thermocouple protection tube, diameter of the measuring junction of the thermocouple, and the main factors that accidentally silk the thinner, measuring the diameter is smaller, the shorter its thermal response time. In order to improve the verification efficiency of many enterprises adopt automatic calibration device, the incoming thermocouple calibration, however, the device is not very perfect.

the influence of thermal radiation in furnace used for temperature measurement of the thermocouple, thermal radiation emitted by objects will be a very high heat. Assumed in furnace gas is transparent, and thermocouple and furnace wall temperature difference is bigger, the temperature measurement error due to energy exchange. Therefore, in order to reduce the thermal error, should increase the heat transfer, the temperature of the thermocouple as close as possible. In addition, when installation should be paid attention to: (1) thermocouple installation position, should as far as possible to avoid thermal radiation from solid, make its can't radiation to the thermocouple surface; (2) the thermocouple with best thermal radiation shielding.

the influence of thermal impedance increase at high temperatures using thermocouple, if the medium to be measured for the gas, so protecting tube surface deposition of dust will burn melt on the surface of the thermal impedance in the protecting tube increase; If the medium to be measured is melt, slag deposition in use process, not only increase the response time of the thermocouple, and also indicate the temperature is low. In addition to the regular verification, in order to reduce the error of sampling is often necessary.