Several issues that are easily overlooked when verifying thermocouple temperature sensors

During the process of testing thermocouple temperature sensors, some calibration personnel can easily handle rare situations such as weak wiring terminals, short circuits, or deviations from the core of the thermocouple temperature sensor, resulting in inaccurate measured data. However, they may forget some results that affect the testing results but are easily overlooked.

Length of thermocouple temperature sensor

The calibration routine of JJG351-1996 "Low cost Metal Thermocouple Temperature Sensor for Tasks" clearly stipulates that the length of the thermocouple temperature sensor should not be less than 750mm. Therefore, the length of the thermocouple temperature sensor is determined based on the consideration that the thermocouple temperature sensor should have a sufficiently wide temperature gradient zone after separating the temperature measurement zone. The thermoelectric potential of the thermocouple temperature sensor also occurs in this area. To effectively prevent the heat transfer from the hot end (measuring end) of the thermocouple temperature sensor to the cold end (connecting end), the fundamental solution is to have sufficient spacing between the cold end of the thermocouple temperature sensor and the hot end. Individually speaking, the deviation caused by insufficient length of the thermocouple temperature sensor is negative, while the modified value is positive. The shorter the length, the greater the deviation, therefore, it is necessary to determine the length of the thermocouple temperature sensor before furnace calibration.

2. Twisted thermocouple temperature sensor wire

The thermocouple temperature sensor wire is thin and soft, and is prone to deformation. When the wire undergoes plastic deformation such as folding or twisting, which causes stress on the wire of the hot electrode, the thermoelectric characteristics of the thermocouple temperature sensor are transformed, thereby affecting the measurement results of the deformed thermocouple temperature sensor. Therefore, before calibration, it is necessary to straighten the thermocouple temperature sensor wire.

3 thermocouple temperature sensor wires are infected

If the thermocouple temperature sensor wire is infected or even oxidized, it will make the thermocouple wire not only bright but also dark and black. At this time, the thermoelectric characteristics of the thermocouple are extremely unstable, and the measurement data is poor. Therefore, it is necessary to clean the infected electrodes and eliminate the infectious layer.

4. Echoing the influence of time

The fundamental principle of temperature measurement in warfare is that the temperature measuring element must reach thermal equilibrium with the measured tool. Therefore, it is necessary to persist for a certain amount of time when measuring temperature in order to achieve thermal equilibrium between the two. Persisting in the right and wrong of time is related to the thermal response of temperature measuring components to time. The thermal response time depends heavily on the structure and measurement conditions of the sensor, with significant differences. Therefore, in the ordinary verification process, it is necessary to choose the appropriate heating rate and time for thermal equilibrium based on the differential example of thermocouple temperature sensors.

5 Effects of Insulation Resistance

At low temperatures, the insulation resistance of thermocouple temperature sensors drops sharply with decreasing temperature, resulting in leakage current. This current flows into the instrument through the previously reduced insulation resistance, causing instability or measurement deviation. Therefore, before installing the thermocouple temperature sensor into the furnace, do not neglect the testing of its insulation resistance. Only when satisfied with the calibration routine request can the temperature tolerance calibration be stopped.