Thermocouple Compensation Wire KX-H-YVRP Multi-strand Soft Core Shielded Temperature Measuring Cable；

I. Principle of Compensation Wires

Compensating wires, which have thermoelectric properties similar to those of thermocouples within a certain temperature range, are called compensating wires for thermocouples. According to the intermediate temperature rule for thermocouples, the total electromotive force value of the thermocouple temperature measurement circuit is only related to the temperatures of the hot junction and the reference junction, and is not affected by changes in the intermediate temperature. Therefore, compensating wires that match the thermocouple material can be used to replace the expensive thermocouple material that needs to be extended, extending the reference junction from the thermocouple terminal box to the instrument terminal, and compensating for the original reference junction temperature with the compensating wire. In addition to reducing measurement errors, compensating wires offer the following advantages: they can improve the physical and mechanical properties of the thermocouple temperature measurement circuit, such as using multi-strand cores or small-diameter compensating wires can enhance the flexibility of the circuit, making connections easier and more shielded against external interference; they can also lower the cost of the measurement circuit.

II. Compensation Wire Classification

Extended and compensating types are differentiated in principle. The nominal chemical composition of the alloy wire in the extended type is the same as that of the thermocouple it is paired with, thus the electromotive force is also the same, indicated by "X" in the model. The compensating type has a different nominal chemical composition from the thermocouple it is paired with, but within its operating temperature range, the electromotive force is close to the nominal value of the electromotive force of the paired thermocouple, indicated by "C" in the model. In terms of compensation accuracy, there are general and precision grades. The error after compensation in the precision grade is generally half that of the general grade, commonly used in applications requiring high measurement accuracy. For example, for compensation wires with S and R scales, the precision grade has a tolerance of ±2.5℃, while the general grade has a tolerance of ±5.0℃; for compensation wires with K and N scales, the precision grade has a tolerance of ±1.5℃, and the general grade has a tolerance of ±2.5℃. In the model, the general grade is not marked, and the precision grade is indicated by adding an "S". In terms of operating temperature, there are general-purpose and heat-resistant types, with general-purpose operating temperatures of 0 ~ 100℃ (some are 0 ~ 70℃), and heat-resistant operating temperatures of 0 ~ 200℃. Additionally, compensation wires can be categorized by the number of cores (single-core or multicore, soft wire), by whether they have a shielding layer (general type or shielded type), and there are also compensation wires specifically for intrinsically safe circuits used in explosion-proof environments.

III. Several Issues in Application

1. Matching Compensation Wires with Thermocouples: Various compensation wires are only compatible with thermocouples of the same scale to avoid undercompensation or overcompensation. The compensating electromotive force (emf) values for commonly used thermocouples at 100℃ and 200℃ are listed in Table 1: Table 1 - Compensating emf values for commonly used thermocouples at 100℃ and 200℃.

Thermocouple Name Thermocouple Type Number Reference End Potential at 0℃ mV 100℃ 200℃

Platinum Rhodium 10—Platinum S 0.646 1.441 Platinum Rhodium 13—Platinum R 0.647 1.469 Platinum Rhodium 30—Platinum Rhodium 6 B 0.033 0.178 Nickel Chrome—Nickel Silicon K 4.096 8.138 Nickel Chrome Silicon—Nickel Silicon N 2.774 5.913

Nickel-Chromium — Copper-Nickel E 6.319 13.421 Iron — Copper-Nickel J 5.269 10.779 Copper — Copper-Nickel T 4.279 9.288

When using compensation wires with a K scale in conjunction with thermocouples of an N scale, over-compensation occurs, resulting in a displayed temperature that is too high; conversely, using N scale compensation wires with K scale thermocouples leads to under-compensation, showing a lower temperature.

Thermocouple Compensating Wire KX-H-YVRP multi-strand soft-core shielded temperature measuring cable