Vacuum measurement – Pirani gauge application range A Pirani gauge is typically used to measure which pressure regime?

Introduction / Context:
Pirani gauges are common thermal-conductivity-based vacuum gauges used in vacuum systems for packaging, metallurgy, and research. Knowing where they apply on the vacuum scale guides proper selection and prevents misuse outside their calibrated range.

Given Data / Assumptions:

• Gauges infer pressure from gas thermal conductivity changes.
• The sensing filament is heated electrically; cooling depends on gas density.
• Calibration is gas-dependent and typically referenced to air or nitrogen.

Concept / Approach:
A Pirani gauge covers the high vacuum through rough/medium vacuum region (commonly ~10^−3 to a few tens of mbar, depending on design), where thermal conductivity varies significantly with pressure. It is not used for measuring very high pressure, nor is it a level instrument. For ultra-high vacuum (<10^−7 mbar), ionization gauges are used instead.

Step-by-Step Solution:

Verification / Alternative check:
Vacuum technology references place Pirani gauges in the rough to high vacuum range; beyond that, cold cathode/hot cathode gauges take over.

Why Other Options Are Wrong:

• Very high pressure: Outside operating principle and construction.
• Liquid level options: Different measurement category entirely.

Common Pitfalls:
Assuming “high vacuum” means UHV; Pirani covers up to high/medium vacuum, not UHV.

Final Answer:
High vacuum