Ensure the correct selection of compensating cables based on the type of thermocouple used and the application. For instance, use K-type thermocouple compensating cables for K-type thermocouples, and choose the operating temperature range according to the application. Position the two terminals of the thermocouple lead as close together as possible, then maintain similar temperatures between the two terminals. Ensure the connection at the instrument terminal has as consistent a temperature as possible. In areas with fans in the instrument cabinet, protect the terminals from direct blast of the fan.
Due to the low signal level of thermocouples, which is microvolt-scale, signals can degrade and couple with environmental electromagnetic interference as the distance increases. This degree of degradation can cause signal distortion in thermocouples, leading to inaccurate temperature measurement and control. In severe cases, it can result in temperature fluctuations during control.
Based on our experience, it's generally advisable to keep the length of thermocouple compensating cables within 15 meters. If the length exceeds 15 meters, it's recommended to use a temperature transmitter for signal transmission. A temperature transmitter converts the corresponding electrical potential of temperature into a DC current for transmission, offering strong anti-interference capabilities.
Compensating wire routing must be kept away from power lines and interference sources. Where crossing is unavoidable, opt for a crossover method rather than parallel routing. To enhance the anti-interference capability of thermocouple connection wires, shielded compensating wires can be employed, which is particularly effective in environments with numerous interference sources. However, it is crucial to properly ground the shielding layer; otherwise, the shielding layer will not only fail to shield interference but may even amplify it.
This is a widely-used temperature sensor in industrial field applications. The thermocouple temperature measurement system is composed of thermocouples, supplementary display control instruments, PLC systems, or DCS systems. After the use of compensating cables in the thermocouple circuit, the electromotive force value of the thermocouple is only related to the temperature at the measuring end and the temperature at the connection point of the compensating cable and the instrument.
Compensating Wire: Utilized when standard materials are excessively costly, this material offers performance close to that of standard materials for temperature compensation.
Extended Wire: Wire with the same characteristics as standard even materials
Necessity of Use: During high-temperature measurements, non-resistive measurements typically employ noble metals (due to their good temperature linearity and high precision). However, when the measuring unit and the temperature source are not in the same location, compensating wires are used for temperature compensation to enhance the circuit's physical and mechanical properties.
The principle of operation: According to the middle temperature rule for thermocouples, the total electromotive force value of the thermocouple temperature measurement circuit is only related to the temperatures at the hot junction and the reference junction, and is not affected by the change in intermediate temperature. Therefore, a compensating cable that matches the thermocouple material can be used to replace the expensive thermocouple material that needs to be extended. The reference junction is extended from the thermocouple terminal box to the instrument terminal, with the compensating cable compensating for the original reference junction temperature.
