The main reason for the thermocouple measurement error

Thermocouple is a tool which is used to measuring temperature. Anything according to the experimental results show that there is always error in measuring, then what caused the thermocouple measurements appear the error? Main factors influencing thermocouple measurement error exactly what?

a, depth,

1, the choice of the temperature measuring point

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.

2, insert depth

thermocouple insertion under test site, 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) 。 For engineering measurement, the insert depth is also related to such as the measured object is static or flowing, such as the flow of liquid or high-speed airflow temperature measurement, will not be restricted by the above, the insert depth is shallow, some concrete numerical value should be determined by experiment.

2, response time

the 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.

the temperature measured, the changing instantly change process, in particular, 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.

is error is normal, but we have to minimizing the error value. So how can we avoid the thermocouple in the error of the measurement? This needs our attention to the above two factors.