Why Use Compensation Wires?
Due to the need to maintain a constant temperature for the reference end of a thermocouple during temperature measurement, any introduced measurement error can be a significant variable, affecting the accuracy of the temperature reading. However, in field applications, the reference end of the thermocouple is often near a high-temperature heat source, making it unstable due to the influence of the heat source. Therefore, the reference end of the thermocouple must be moved to a location with more stable temperatures. Compensation wires are made of the same metal material as the thermocouple or of a low-cost, easily obtainable metal material with the same thermoelectric properties (thermoemf) within a specified temperature range (usually 0 to 100℃) as the connected thermocouple. These wires can extend the function of the thermocouple during measurement or serve as connecting wires between the thermocouple and instruments (such as electronic potentiometers). Therefore, compensation wires should be connected to the thermocouple during use. However, they do not eliminate the effect of a non-zero reference end temperature, so it is still necessary to adjust the reference end temperature to 0℃ during operation.
Please note the following points when using compensating conductors:
Compensating wires of various types are only compatible with their respective thermocouple models. In other words, the thermoelectric power of various thermocouples and their corresponding compensating wires must be consistent within the specified temperature range (e.g., 0-100℃).
2. When connecting compensation wires to a thermocouple meter, both pairs of connection points must be at the same temperature, and the positive and negative poles cannot be connected incorrectly. Compensation wires act as a thermocouple within a certain temperature range (0~100℃), so their current flows from the positive pole through the reference terminal to the negative pole. Therefore, when connecting to a thermocouple, the positive pole of the compensation wire should be connected to the positive pole of the thermocouple, and the negative pole should be connected to the negative pole of the thermocouple. If the polarity is reversed, not only will the function of the compensation wire be lost, but it will also counteract a portion of the thermocouple's thermal electromotive force, causing the meter's indicated temperature to be lower.
Compensation wires and thermocouple connection points must not exceed the specified temperature range for use.
4. Select the wire diameter of the compensation cable based on the specific requirements of the instrument connected. For instance, when connecting to a moving-coil instrument, a thicker wire diameter can be chosen to reduce its resistance, ensuring it does not affect the external resistance of the instrument.
5. For longer thermocouple lines, it is advisable to use multiple, thicker compensation wires for easier installation and laying.
Compensating wires should be divided into two types: extended and compensating, depending on the core wire alloy material.
Extended Compensation Wires: Available in NX (Nickel Chrome Silicon-Nickel Silicon Magnesium), KX (Nickel Chrome 10-Nickel Silicon 3), EX (Nickel Chrome 10-Copper Nickel 45), JX (Iron-Copper Nickel 45), and TX (Copper-Copper Nickel 45).
Compensating Compensation Wires: Available in SC and RC (Copper-Copper-Nickel 0.6), KC (Copper-Copper-Nickel 40), NC (Iron-Copper-Nickel), etc.
Opportunities for using extended or compensating compensation ground wires:
Extended-type: When the environment at the cold end of the compensation wire exceeds 100 degrees or falls below 0 degrees, only the extended-type compensation wire can be used for accuracy in measurement, although it is more expensive.
Compensatory: Economical, but requires a relatively stable cold-end temperature.
Characteristics of Compensation Wires:
Excellent thermal and electrical properties, good electrical insulation, and long service life.
2. Soft, with excellent bending properties, and easy to use.
The coating material is stable and reliable, offering certain temperature resistance and cold resistance.
