Regarding the issue of thermocouple compensation wires

There is already some error at a distance of half a meter; at such a distance, it’s even more necessary to use compensation wires for connection

Isn’t it better to use the transmitter that’s already in the junction box?

If the temperature at the cold end of the thermocouple is the same as that at the transmitter terminals, a compensation wire is not necessary. A compensation wire of over ten meters is no problem

I think the wire must be compensated~!

1. For S-type and R-type thermocouples, their compensation wires are SC and RC; both belong to the category of compensation wires, and they have relatively low accuracy among all types of compensation wires. The error is very small within the range of 0–60°C, but there is a significant negative error in the range of 100–150°C. If the measurement accuracy is high, it is necessary to keep the temperature of the compensation contact below 100°C. 2. The compensation wires for K-type thermocouples are of the KC and KX types. KX is an extended compensation wire; its characteristic curve remains linear over a wide temperature range with very low error, but it is expensive and has high resistance. Therefore, in situations where the operating temperature is not too high and the accuracy requirements for temperature measurement are not very strict, it is best to use the inexpensive compensated wire KC. Compensation wires: yunrun.com.cn/product/242.html. When using compensation wires, the following points should be noted: 1. Various compensation wires can only be paired with thermocouples of corresponding models. Models that do not match cannot be used. 2. Compensation wires have positive and negative poles. When in use, the positive and negative poles of the compensation wire must not be connected incorrectly; otherwise, it will not only fail to provide compensation but also cause greater measurement errors. Theoretically proven, the error caused by reversing the polarity of the compensation wire is approximately twice that of not using a compensation wire. 3. The temperature at the connection point of the thermocouple and the compensation wire must not exceed the specified operating temperature. Because it exceeds the specified operating temperature range, the thermoelectric properties of the compensation wire differ significantly from those of the thermocouple, resulting in measurement errors. 4. Since the thermoelectric properties of the compensation wire are not exactly the same as those of the thermocouple, it is necessary for the temperatures at the two contacts at the connection point to be equal; otherwise, measurement errors will occur. 5. The diameter of the compensation wire should be selected according to the specific requirements of the display instruments being used. For example, for the compensation wires connected to dynamic meters, it is advisable to use wires with a larger diameter so as to reduce their resistance, thereby preventing it from exceeding the external resistance value specified by the meter. 6. For easier installation, multi-strand compensation wires can be used; additionally, waterproof, corrosion-resistant, or fire-resistant compensation wires can be selected as needed.

Actually, when it comes to the use of thermocouples, one approach is to use thermocouples along with compensation wires connected directly to the DCS system, while another approach involves using integrated temperature sensors together with signal cables to connect to the DCS system. Since the cost of integrated temperature sensors is relatively low, it is more reasonable to use these in most cases; after all, compensation wires are quite expensive. I’m a bit confused by the idea of using separate temperature sensors – why would they need to be installed in places where they can be seen?