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Process Control and Instrumentation - Engineering

Q1:

Pirani gauge is used for the measurement of

A very high pressure.

B high vacuum.

C liquid level under pressure.

D liquid level at atmospheric pressure

ANS:B - high vacuum.

A Pirani gauge is used for the measurement of high vacuum.

Explanation:

  • Pirani Gauge:
    • A Pirani gauge is a type of thermal conductivity gauge used to measure the pressure in a vacuum system.
    • It operates based on the principle that the thermal conductivity of gases varies with pressure. As pressure decreases (in a high vacuum), the thermal conductivity also decreases.
    • The gauge measures the heat loss from a heated filament due to the presence of gas molecules. The rate of heat loss is directly related to the gas pressure in the system.
    • Pirani gauges are typically used in the pressure range from around 10^-3 to 10^3 Torr (approximately 10^-3 to 10^3 mbar), making them suitable for measuring high vacuum conditions.
  • Applications:
    • Pirani gauges are commonly used in various industries and scientific applications where precise measurement of vacuum levels is crucial. This includes semiconductor manufacturing, vacuum coating processes, analytical instruments, and research laboratories.
  • Not Suitable for:
    • Pirani gauges are not designed for measuring very high pressures or pressures at atmospheric levels. For high-pressure measurements, other gauges such as mechanical pressure gauges or transducers are used.

Conclusion:

Therefore, a Pirani gauge is specifically used for measuring high vacuum, where its thermal conductivity-based principle provides accurate and reliable pressure measurements in the low-pressure range typical of vacuum systems.