The resistance vacuum gauge, also known as the Pirani gauge, reflects the pressure changes based on the changes of hot filament resistance. It is mainly composed of gauge and measurement circuits. The measurement range of it is 104 to 10-1 Pa.
The structure of the resistance gauge is shown in Figure1. A cylindrical spiral hot wire wound with a high temperature coefficient resistance wire is encapsulated in the regulator casing. Both ends of the hot wire are led out the gauge tube and connect the measuring line. The gauge shell can be made of metal or glass. The metal shell has the advantages of durability, convenient removal of hot filaments, etc. The disadvantages are poor sealing performance and high price. The glass shell has the advantages of good sealing performance and low price, and the disadvantage is that it is easily damaged.
The resistance temperature coefficient and the resistivity of some resistance wires that wound heating wire are shown in Table 4-1, among which tungsten, platinum and nickel are commonly used. In order to ensure the working stability of the hot wire, in addition to cleaning the surface of the hot wire, sometimes a thin layer of glass, quartz or tantalum is applied on the surface of the hot wire to avoid oxidation or contamination of the hot wire when it is used under high pressure. But it is believed that this method will increase its thermal inertia.
Metal: Tungsten Platinum Nickel Chromium Iridium Molybdenum Iron Copper Silver
Coefficient in 0 ℃ 4.82 3.9 6.0 2.5 4.1 4.71 6.0 4.3 4.29
Resistivity in 0 ℃ 5.1 9.2-9.6 6.84 12.9 4.85 5.71 9.7 1.67 1.59
Table 4-1 Resistance Temperature Coefficient and Resistivity of Some Metals