Common fault handling methods for temperature detection instruments

Temperature measuring instruments commonly used in the industry are divided into two categories: non-contact temperature measuring instruments (eg, radiant, infrared). Contact temperature measuring instruments (such as: expansion, pressure, thermocouple, thermal resistance).
Since industrial thermal resistance and industrial thermocouples are widely used, they are mostly used in automatic interlock control systems. Here, the common fault handling methods for temperature detection instruments in use are introduced below.
I. Industrial Thermal Resistance Industrial thermal resistance is based on the fact that the resistance value of metal increases with increasing temperature to measure temperature. Zui is commonly made of metal platinum and copper, with index numbers Pt100, Pt10, Pt50 (temperature range -200 ~ 850 Â°C), Cu50, Cu100 (temperature range -50 ~ 150 Â°C).

Industrial RTD temperature measurement systems are generally composed of industrial thermal resistance, connecting wires and display instruments. The industrial thermal resistance and the display instrument must have the same index number. In order to eliminate the influence of the change of the resistance of the connecting wire on the temperature measurement, the three-wire connection method must be adopted.

Common causes of failure of industrial thermal resistance and treatment methods:

A common fault in industrial RTDs is industrial RTD disconnection and short circuit. Generally, the open circuit is more common because the thermal resistance wire is thinner. Open circuit and short circuit are easy to judge. You can use the â€œÃ—1Î©â€ file of the multimeter. If the measured resistance is less than R0, there may be a short circuit. If the multimeter indicates infinity, you can judge that the resistor is open. The short circuit of the resistor body is generally easier to handle, as long as it does not affect the length and thickness of the resistance wire, find the short circuit to blow dry, and strengthen the insulation. Resistor body breaking repair must change the length of the resistance wire and affect the resistance value. For this reason, it is better to replace the new resistor body. If welding repair is used, it must be verified after welding to be used. The common faults and treatment methods of the RTD temperature measurement system are as follows:

Fault phenomenon

possible reason

Approach

The display indicator indicates that the value is lower than the actual value or the indication is unstable.

There are metal chips and dust in the protection tube, dirt between the terminals and short circuit of the thermal resistance (water accumulation, etc.)

Remove metal chips, clean dust, water droplets, etc., find short-circuit points, strengthen insulation, etc.

Display meter indicates infinity

Industrial thermal resistance or lead wire disconnection and loose terminals

Replace the resistor body, or solder and tighten the terminal block screws, etc.

Display meter indicates negative value

The display instrument and the thermal resistance wiring are wrong, or the thermal resistance has a short circuit.

Correct the wiring, or find the short circuit, strengthen the insulation

Resistance and temperature have changed

Thermal resistance wire material is corroded and deteriorated

Replace the resistor body (thermal resistance)

I. Industrial thermocouple

Industrial thermocouples weld two conductors or semiconductors A and B of different materials to form a closed loop. When there is a temperature difference between the two solder joints 1 and 2 of conductors A and B, a thermoelectric potential is generated between the two. Therefore, a certain amount of current is formed in the loop, which is called a thermoelectric effect. Industrial thermocouples work on this principle.
Industrial thermocouple common faults and treatment methods

Fault phenomenon

possible reason

Approach

The thermoelectric potential is smaller than the actual value (the display meter indicates a low value)

Thermal electrode short circuit

Find out the cause of the short circuit. If it is caused by moisture, it needs to be dried. If the insulator is damaged, replace the insulator; clean the dust;
Compensating for short-circuit between wires: finding the short-circuit point, strengthening the insulation or replacing the compensation wire

The thermoelectric potential is smaller than the actual value (the display meter indicates a low value)

Industrial thermocouple thermal electrode deterioration

If the length allows, cut the metamorphic section and re-weld, or replace the new thermocouple

The thermoelectric potential is smaller than the actual value (the display meter indicates a low value)

Compensation wire is reversed with industrial thermocouple polarity

Reconnect correctly

The thermoelectric potential is smaller than the actual value (the display meter indicates a low value)

Compensation wires are not compatible with industrial thermocouples

Replace the matching compensation wire

The thermoelectric potential is smaller than the actual value (the display meter indicates a low value)

Industrial thermocouples are not properly installed or the insertion depth does not meet the requirements

Reinstall as required

The thermoelectric potential is smaller than the actual value (the display meter indicates a low value)

Industrial thermocouple cold junction temperature compensation does not meet the requirements

Adjusting the cold end compensator