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technical article
Several issues with multi-point thermocouples must be noted
2012-1-21 12:44:04

Main technical parameters of multi-point thermocouple

公称压力:一般是指在工作温度下保护管所能承受的静态外压而破裂。 Multi-point thermocouple nominal pressure: Generally refers to the static external pressure that the protection tube can withstand at operating temperature and rupture. The minimum insertion depth of the thermocouple: should not be less than 8-10 times the outer diameter of its protective sleeve (except for special products)

Edge resistance: When the ambient air temperature is 15-35 ° C and the relative humidity is <80%, the insulation resistance is ≥5 Megohm (voltage 100V). Thermocouple with splash-proof junction box, when the relative temperature is 93 ± 3 ℃, the insulation resistance is ≥0.5 Mohm

(Voltage 100V) Insulation resistance at high temperature: The insulation resistance (per meter) of the thermocouple (including double-branch type) and the protection tube and the double-branch hot electrode at the high temperature should be greater than that specified in the table below. value.


Multi-point thermocouple is a kind of temperature-sensing element, which converts the temperature signal into the thermo-electromotive force signal and the electrical instrument into the temperature of the measured medium. The basic principle of thermocouple temperature measurement is that two homogeneous conductors with different components are closed.

In the loop, when there is a temperature gradient at both ends, a current will flow through the loop. At this time, there is a Seebeck electromotive force-thermoelectromotive force between the two ends. This is the so-called Seebeck effect.

   适用于生产现场存在温度梯度不显著,须同时测量多个位置或单个位置的多处测量。 Multi-point thermocouples are suitable for production sites where the temperature gradient is not significant, and multiple locations or a single location must be measured simultaneously. Multi-point thermocouples are widely used in large fertilizer synthesis towers, storage tanks and other devices.


Several problems encountered with multipoint thermocouples:

1. The thermoelectric potential of a thermocouple is a function of the temperature difference between the two ends of the thermocouple's working end, not a function of the temperature difference between the cold end and the working end of the thermocouple;

2. The size of the thermoelectric potential generated by the thermocouple. When the thermocouple material is uniform, it has nothing to do with the length and diameter of the thermocouple, but only with the composition of the thermocouple material and the temperature difference between the two ends.

3. After the material composition of the two thermocouple wires of the thermocouple is determined, the magnitude of the thermoelectric potential of the thermocouple is only related to the temperature difference of the thermocouple; if the temperature of the cold end of the thermocouple is kept constant, the thermoelectric potential of the thermocouple is jobs

Single value function of terminal temperature.

的作用就是测量温度。 Multipoint thermocouples measure temperature. Some points must be paid attention to when using:

1. Cold junction constant temperature or cold junction temperature compensation of multi-point thermocouple.

2. The connecting wire of the multi-point thermocouple to the instrument must use the compensation lead with the same index number as the thermocouple.

3. The division number of the multi-point thermocouple and the measuring instrument must be the same.