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Multi-point flameproof thermocouples are suitable for the production of flammable and explosive compounds at the site, and multiple measurements at multiple locations or locations must be measured simultaneously. Widely used in petrochemical distillation tower installations.
How multi-point flameproof thermocouple works:
The working principle is that the two ends of the conductors of different compositions are welded and form a loop, the direct temperature measuring end is called the measuring end, and the terminal end is called the reference end. When there is a temperature difference between the measuring end and the reference end, a thermal current is generated in the circuit, and the display meter is connected, and the corresponding temperature value of the thermoelectromotive force generated by the thermocouple is indicated on the meter.
The thermoelectromotive force of the multi-point flameproof thermocouple will increase with the temperature of the measuring end. The magnitude of the thermoelectromotive force is only related to the thermocouple conductor material and the temperature difference between the two ends, and has nothing to do with the length and diameter of the hot electrode.
The assembled multi-point flameproof thermocouple is mainly composed of a junction box, a protective tube, an insulating sleeve, a connecting terminal and a hot electrode, and is composed of various mounting fixtures.
The main technical indicators of multi-point flameproof thermocouple:
1. Thermal response time: When the temperature changes stepwise, the output of the thermocouple changes to 50% of the change. The time required is called the thermal response time and is expressed by T0.5.
2. Thermocouple nominal pressure: generally refers to the static external pressure that the protective tube can withstand at room temperature without breaking. In fact, the allowable working pressure is related not only to the material of the protective tube, the wall thickness of the diameter, but also to its structural form, installation method, depth of insertion, and flow rate and type of the medium to be measured.
3. The depth of the thermocouple is small: it should be no less than 8~10 times of the outer diameter of the protection tube.
4. Thermocouple insulation resistance: The test voltage of the insulation resistance at room temperature is DC 500V±50V. The atmospheric conditions for measuring the insulation resistance at room temperature are temperature 15~35°C, relative humidity 45%, atmospheric pressure 86~106kPa.
a. For thermocouples with a length > 1 m, the product of the insulation resistance value at room temperature and its length shall not be less than 100 MΩ·m.
Namely: Rr·L≥100MΩ·mL>1m (where: Rr-thermocouple's normal temperature insulation resistance value MΩL-thermocouple length.m)
b. For thermocouples with length ≤ 1 m, the insulation resistance value at room temperature should be not less than 100 MΩ.
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