What is pirani gauge? working principle

The Pirani gauge is a widely used instrument for measuring vacuum pressure in the range of 10^-4 to 1000 Pa. It operates based on the principle of thermal conductivity, where the heat transfer rate from a heated filament to the surrounding gas depends on the gas pressure.

Working Principle:

  1. Heated Filament: A thin metal filament (typically tungsten or platinum) is heated electrically by passing a current through it.
  2. Heat Transfer: The heated filament transfers heat to the surrounding gas particles through collisions.
  3. Pressure Dependence: The rate of heat transfer depends on the pressure of the gas. Higher pressure means more gas particles, leading to faster heat transfer and a lower filament temperature.
  4. Resistance Change: The filament’s resistance changes with temperature, and this change is measured using a Wheatstone bridge circuit.
  5. Pressure Measurement: The measured resistance change is calibrated to provide a corresponding pressure reading.

Advantages of the Pirani Gauge:

  • Simple and robust design
  • Wide measurement range
  • Fast response time
  • Relatively inexpensive

Disadvantages of the Pirani Gauge:

  • Accuracy decreases at higher pressures
  • Susceptible to contamination and outgassing
  • Cannot distinguish between different gas types

Applications of the Pirani Gauge:

  • Vacuum coating processes
  • Leak detection systems
  • Refrigeration systems
  • Chemical analysis equipment
  • Spacecraft and satellites

Other Important Information:

  • The Pirani gauge was invented by Marcello Pirani in 1906.
  • Several variations of the Pirani gauge exist, including the pulsed Pirani gauge and the cold cathode Pirani gauge.
  • The Pirani gauge is often used in conjunction with other vacuum gauges, such as the ion gauge, to cover a wider pressure range and improve accuracy.

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