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A special form of the Pirani gauge is the pulsed Pirani vacuum gauge where the sensor wire is not operated at a constant temperature, but is cyclically heated up to a certain temperature threshold by an increasing voltage ramp. When the threshold is reached, the heating voltage is switched off and the sensor cools down again.
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A McLeod gauge is a scientific instrument used to measure very low pressures, down to 10 −6 Torr (0.133 mPa). It was invented in 1874 by Herbert McLeod (1841–1923). [ 1 ] McLeod gauges were once commonly found attached to equipment that operates under vacuum , such as a lyophilizer .
Its definition and measurement are often discussed in ultraviolet photoelectron spectroscopy literature, for example [2] As the vacuum level is a property of the electron and free space, it is often used as the level of alignment for the energy levels of two different materials. The vacuum level alignment approach may or may not hold due to ...
The word "gauge" or "vacuum" may be added to such a measurement to distinguish between a pressure above or below the atmospheric pressure. Both mm of mercury and inches of water are common pressure heads, which can be converted to S.I. units of pressure using unit conversion and the above formulas.
Vacuum permittivity, commonly denoted ε 0 (pronounced "epsilon nought" or "epsilon zero"), is the value of the absolute dielectric permittivity of classical vacuum. It may also be referred to as the permittivity of free space , the electric constant , or the distributed capacitance of the vacuum.
The types of physical measurements required under the Rockwood definition are similar to those required under the Trasatti definition, but they are used in a different way, e.g. in Rockwood's approach they are used to calculate the equilibrium vapour pressure of the electron gas. The numerical value for the absolute potential of the standard ...