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Vacuum Gauge

in Transducers / 1 Comment

For pressure measurement below atmosphere or vacuum, different gauges are available. Manometers and bell gauges can go up to 0.1 Torr. Diaphragm gauges are usable up to a pressure of 10-3 Torr. For pressure below this value, electrical gauges like Pirani or Ionization Gauges are used. Vacuum measurement is broadly classified into Mechanical Type, Thermal Type, Ionization Type, and Radiation Vacuum Gauge.

Thermal Types

The heat conductivity of gases is independent of its pressure, at normal pressure. But, heat conductivity starts falling as the pressure is lowered t 10 Torr and below. The reason behind this is less collision between gas molecules within the wall and also their small number in a specific volume. The energy is carried to the walls of the container due to this collision. Thus, lesser number of molecules will be available to take the heat away from the source.

At low pressures, the heat loss that occurs from a hot wire mounted in a glass or metal tube is due to the following factors.

  • Convection
  • Conduction through the lead mines
  • Radiation
  • Conduction in the gas

Out of these, convection is comparatively negligible. A new clear wire has a small surface emissivity and is god for producing high temperature at low gas pressures. Due to oxidation and carbonization, the surface tends to deteriorate. This causes error of the device at low pressure ranges.

Discussion 1 Comment

  1. adekolurejo ezekiel

    i want the information on vacuum to be sent to me regularly

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