thermocouple vacuum gauge structure and principle
Thermocouple vacuum gauge is used to measure the temperature change of hot wire by thermocouple, and the thermoelectric potential produced by thermocouple is used to characterize the pressure in the gauge. The pressure measurement range of thermocouple gauge is 102-10-1 PA.
The structure principle diagram of thermocouple vacuum gauge is shown in the figure. It consists of thermocouple gauge and measuring circuit. The thermocouple gauge tube is mainly composed of hot wire and thermocouple. The hot end of the thermocouple is connected with the hot wire, and the other end is led out of the tube through the lead as the cold end, and connected to the millivolt meter for measuring the potential of thermocouple. The measuring circuit is relatively simple.
thermocouple vacuum gauge schematic diagram
During the measurement, the hot wire of the gauge tube is connected with a certain heating current. At a lower pressure (λ ≥ R2), the thermocouple potential E depends on the pressure P in the gauge tube, because the change of the hot wire temperature depends on the heat conduction of the gas. When the pressure decreases, the heat carried away by the gas molecules decreases, and the temperature of the hot wire increases, so the thermal couple potential E increases; conversely, the thermal couple potential E decreases.
When the heating current of the gauge changes, its sensitivity and measuring range are affected. If the heating current is increased, the gauge sensitivity will be improved, and the higher pressure can be measured, but the measurement range will be narrowed; otherwise, if the heating current is reduced, the gauge sensitivity will be reduced, and only lower pressure can be measured, but the measurement range will be wider.
When the heating current is constant, if the relationship between the thermocouple potential E and the pressure P has been measured in advance, the pressure of the measured system can be directly given according to the indication of the millivoltmeter.