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Vacuum gauge principle knowledge
Low-temperature gas molecules hitting high-temperature solids, will take heat from the solid. The vacuum gauge that calculates the pressure by the heat captured by the gas molecules becomes a heat conduction vacuum gauge. Heat conduction vacuum gauge is mainly used in the field of low-vacuum. Representative thermal conductivity gauges include Pirani gauges and thermocouple gauges. Gauge vacuum gauge metal cylinder with a platinum thin wire inside, both ends connected to the electrode. Platinum thin wires heat when the platinum thin wires are supplied with current through the electrodes, and the heat of the platinum wires will be taken away by gas molecules colliding with fine gold wires or heat radiation or by solid heat conduction. Qb = Qg + Qr + Qs (1) Q is the heat released by the thin line per unit time, and R is Thin wire resistance, I is thin wire current. Qg is expressed as Qg = αΔπda (T-T0) p (2) where T and T0 are the temperatures of the thin wire and the metal cylinder, respectively, P For gas pressure, a is the length of the thin wire. The remaining Qs and Qr can be expressed as Qs = Sκ (T-T0) / L (4) Qr = πdaσε (T4-T04) , κ is the solid conductivity, and L is the length of the electrode. (4) represents heat radiation, and σ and ε are called constant and solid emissivity, respectively. If we keep T and T0 constant, then (3) and (4) are constants. Equation (1) can be expressed as I2R = Ap + I02R (5) A = αΛπda (T-T0) if I02R represents a certain amount of solid heat conduction and heat radiation. I0 is the current of the thin wire when the pressure is 0, Heat loss due to solid heat conduction and heat radiation. A type is not dependent on the pressure of a fixed number If you know the fine wire resistance R, current I0 and the fixed number A, you can get the pressure (5) P