Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question dated 2020-07-14

1. The ice bath method is commonly used in laboratories, where the temperature of the reference end is kept at 0 degrees, but it is costly and difficult to implement. 2. Cold-end temperature correction method: This is commonly used in applications where high precision is not required; that is, when the cold-end temperature cannot be kept at 0 degrees, it is necessary to adjust the reading indicated by the instrument. It’s easy to do, but the errors are large. 3. Compensation bridge method: It is rarely used alone; it utilizes the potential generated by an unbalanced bridge to compensate for the change in thermoelectric potential caused by variations in the cold junction temperature of the thermocouple. Compensation bridges are available as separate products, as well as built into instruments. 4. Compensation wire method: This is the most commonly used method. It involves extending the thermocouple so that its cold end is placed in a location with a more stable temperature (usually the control room). The cold-end temperature is then adjusted manually, by setting the instrument’s zero point to room temperature, or through automatic compensation by the circuit within the instrument. It is also impossible to extend precious metal thermocouples, as the high cost makes it unfeasible; instead, base metals with similar thermoelectric properties are used as extension wires. The intermediate temperature rule forms the theoretical basis for the use of compensation wires. Compensation wires cannot automatically compensate for changes in the temperature at the cold end of the thermocouple; they merely move the cold end of the thermocouple to a location with a more stable temperature. Compensation still needs to be carried out manually using instruments.

Ice bath method, cold junction temperature correction method, compensation bridge method, compensation wire method.

Cold junction temperature stabilization, Wheatstone bridge compensation, zero point adjustment

Cold junction constant temperature method/Cold junction temperature correction method/Compensating wire method/Compensating bridge method

Freezing point cell method, computational correction method, correction coefficient method, zero point shift method, compensator method, software processing method, etc

Freezing-point cell method, computational correction method, correction coefficient method, zero shift method, compensating device method, software processing method, etc.

Ice bath method, cold junction temperature correction method, compensation bridge method, compensation wire method.

Water bath, bridge, compensation wire, calculation correction

Compensation wire led into the constant temperature control room, freezing point compensation, numerical compensation, bridge compensation