Conditions and precautions for using compensating cables for thermocouples

Compensation cable for thermocouple ● Installation and use:

Due to the lack of understanding of the compensation wire function by the operators of thermocouple equipment, they believe that ordinary wires are sufficient as long as they serve as a connection. When installing thermocouples, equipment manufacturers use ordinary wires as connecting wires, but from the user's perspective, they always assume that the equipment installation personnel are professionals and the methods are always correct, which did not arouse the necessary suspicion. In industrial production, although thermocouples have been widely used as temperature sensors for temperature measurement and control, and people are familiar with them, if the correct usage method is not paid attention to, it can cause significant deviation in temperature measurement and control, and in severe cases, directly cause economic losses. Therefore, it should be taken seriously.

Compensation cable for thermocouple ● Introduction to temperature measurement principle

In practical applications, there is always a distance between measuring and controlling instruments and thermocouples, as shown in Figure 2. C. D is also two homogeneous materials. According to the law of the intermediate conductor of thermocouples, the expression for the measured total potential E Z can be derived as follows: the material that satisfies equation (5) is called the compensating wire of the thermocouple. Because there are many types of thermocouples, there are also many types of thermocouple compensation wires. 2 . Correct use of compensating wires in industrial temperature measurement and control. In industrial temperature measurement and control, the position of the thermocouple is always at a certain distance from the measuring and control table (hereinafter referred to as the instrument). Therefore, a compensating wire connection is required from the output end of the thermocouple to the input end of the measuring and control table. Due to the fact that both thermocouples and compensation wires have positive and negative poles, the positive pole should be connected to the positive pole, and the negative pole should be connected to the negative pole when wiring. As shown in Figure 3, the temperature difference between T3 and T2 can cause measurement errors. The function of the compensation wire is to compensate for T3 and T2. Different types of thermocouples require corresponding types of compensation wires, and different types of compensation wires cannot be mixed.

Selection of compensation cables for thermocouples:

The compensation wire must be selected correctly according to the type of thermocouple used and the occasion in which it is used. For example, K-type thermocouple should choose the compensation wire of K-type thermocouple, and select the working temperature range according to the usage scenario. The typical working temperature for K X is -20 to 100 ℃, with a wide range of -25 to 200 ℃. The ordinary level error is ± 2.5 ℃, and the precision level is ± 1.5 ℃.

Compensation cable for thermocouple ● Contact connection:

Try to keep the two contact points as close as possible to the thermocouple terminal and maintain the same temperature as possible. The temperature at the connection point with the instrument terminal should be as consistent as possible. Where there is a fan in the instrument cabinet, the contact point should be protected from the fan blowing directly to the contact point.

Compensation cable for thermocouple ● Length of use

Because the signal of the thermocouple is very low, at the microvolt level, if used over a long distance, signal attenuation and strong electrical interference in the environment can cause distortion of the thermocouple signal, resulting in inaccurate temperature measurement and control. In severe cases, temperature fluctuations may occur during control. Based on our experience, it is usually better to control the length of the thermocouple compensation wire within 15 meters. If it exceeds 15 meters, it is recommended to use a temperature transmitter to transmit the signal. A temperature transmitter is used to measure the potential value corresponding to the temperature

Converted into direct current for transmission, with strong anti-interference ability.

Compensation cable for thermocouple ● Installation and wiring

The wiring of compensation wires must be kept away from power lines and interference sources. In places where crossing is unavoidable, try to use crossing methods as much as possible and avoid parallelism.

Compensation cable for thermocouple ● Precautions

Shielding compensation wire

To improve the anti-interference performance of thermocouple connection wires, shielded compensation wires can be used. For situations where there are many sources of interference on site, the effect is better. But it must be grounded for use.