In industrial automation instruments, the thermocouple is a common temperature measuring element. It can convert temperature signals into electromotive force signals, so its application in industry is very extensive. Let's take a detailed look at the technical characteristics of thermocouples.

1. Temperature measurement range and allowable error

The temperature measurement range and allowable error of the thermocouple are closely related to its division number. Generally speaking, the temperature measurement range of the thermocouple is between -200℃ and 1800℃, and the allowable error is between ±0.5℃ and ±10℃.

2. Thermal response time

When the temperature of the thermocouple undergoes a step change, the time required for the output signal to change to 50% of the step change is called the thermal response time, which is represented by τ5. The thermal response time of the thermocouple is generally less than 1 second.

3. Nominal pressure

The nominal pressure of the thermocouple refers to the static external pressure that the protective tube can withstand without breaking at the operating temperature. In fact, the allowable working pressure of the thermocouple is not only related to the material, diameter, and wall thickness of the protective tube, but also to its structural form, installation method, insertion depth, and the flow rate and type of the measured medium.

4. Minimum insertion depth

The minimum insertion depth of the thermocouple should not be less than 8-10 times the outer diameter of its protective tube (except for special products). This is to ensure the measurement accuracy and stability of the thermocouple.

5. Insulation resistance (room temperature)

The insulation resistance of the thermocouple refers to the insulation resistance at room temperature. The test voltage for room temperature insulation resistance is DC 500±50V. The atmospheric conditions for measuring room temperature insulation resistance are temperature 15-35℃, relative humidity 80%, and atmospheric pressure 86-106KPa. The insulation resistance of the thermocouple should be greater than 100MΩ.