Difference of temperature sensor

Temperature sensor: composed of thermocouple and thermal resistance

Thermocouple: simple understanding: connect one end of two metals (or alloys) of different materials

Thermocouple characteristics: when there is a temperature difference between the two ends of the thermocouple, the cold end of the thermocouple will have a voltage output. The output voltage is only related to the temperature difference between the two ends and the material of the thermocouple, and has nothing to do with the geometric size of the thermocouple, which means that the thermocouple can measure remotely without affecting the accuracy of temperature measurement.

Thermocouple temperature sensor: E, K, S, B

Thermal resistance

Simple understanding: the thermal resistance is formed by winding metal wires on various skeletons

Characteristics of thermal resistance:

When the temperature of the thermal resistance is different, its resistance value will change.

The thermal resistance uses the temperature characteristics of different metal materials. Because the lead resistance will be superimposed with the thermal resistance itself, the thermal resistance is not suitable for remote measurement (except when the error can be corrected on site)

common problem

The sensor graduation number is inconsistent with the instrument input graduation number, and the temperature measurement cannot be conducted or is inaccurate.

Improper selection of measuring range and inaccurate temperature measurement.

Thermocouple wiring error, unable to measure temperature.

The thermocouple is not connected with compensation wire, which causes large temperature error. If ordinary wires are used for connection, the temperature of the connector may be inconsistent with the ambient temperature of the instrument, and the difference will be directly added into the instrument error.

The instrument of time proportional control mode has not corrected the control deviation, and the control deviation is large.

Due to the defects of the time proportional adjustment method, the instrument adopting the time proportional adjustment method cannot automatically eliminate the static error, and the deviation correction potentiometer must be manually adjusted for correction. The instrument is set at the factory, and the set value is equal to the measured value, so the stabilized temperature is inevitably inconsistent with the set value, which has nothing to do with the instrument. It is only related to the thermal insulation characteristics and heating power of the system.

The self-tuning function is not used, and the temperature control effect is not ideal

Due to the inconsistency of the system working conditions, the PID parameter value of the instrument may not be the best, so it is necessary to start the self-tuning function to let the instrument automatically find the PID parameter value suitable for the system. Generally, the operation with self-tuning parameters can achieve satisfactory results