On 2018-08-08 14:48:54
How to deal with inaccurate thermocouple and thermal resistance measurement
In the process of industrial production, temperature needs to be monitored. Thermocouple and thermal resistance are the most commonly used temperature monitoring sensors.
Generally, when the temperature range is - 200 ~ 500 ℃, platinum resistance PT100 and copper resistance cu50 are mainly used. Platinum thermistor is widely used because of its high temperature coefficient, high resistivity and good reproducibility.
The resistivity of copper resistance is small, its volume is large, and it is easy to oxidize at high temperature. When the temperature range is 500-1800 ℃, thermocouple is mainly used.
K-type thermocouple has good linearity, stable chemical performance, large thermoelectric potential and relatively cheap price. It is the best choice for measuring oxidizing gas.
In the process of field temperature measurement, the phenomenon of inaccuracy or fluctuation of temperature measurement often occurs, which needs to be analyzed and dealt with specifically.
Improper joint handling usually, in order to facilitate operation, the wiring between the temperature sensor and other devices is only wrapped with insulating tape. This connection mode will increase the contact resistance, which will lead to high measurement value for the thermal resistance temperature measurement; for the thermocouple, if the connector is before the voltage is converted into the current (V / I) signal, it is equivalent to the increase of the cold end circuit resistance and the increase of the line voltage drop, which will make the temperature measurement value low. Whether it's multi wire thermal resistance or two wire thermocouple, the joint should be welded.
Tin welding is not only simple and convenient, but also firmly connected, with small contact resistance, and can prevent oxidation. Generally, the thermal resistance outgoing line is usually thin and easy to break or pull off after welding, so special treatment shall be made for the welding position.