The Mcleod gauge, Pirani gauge, and Ionization gauge II — Lesson 2

This lesson covers the principles and applications of two low-pressure measurement devices: the Pirani gauge and the McLeod gauge. The Pirani gauge operates on the principle of thermal conductivity of gases, which reduces at low pressures. The lesson explains the operational principle of the Pirani gauge, its limitations, and the precautions needed while using it. The McLeod gauge, on the other hand, measures low pressure indirectly by measuring the temperature of a filament. The lesson also includes a numerical problem on the McLeod gauge, demonstrating how to calculate gauge reading for a given absolute pressure. The lesson emphasizes the need for careful handling and calibration of these devices for accurate measurements.

Video Highlights

01:29 - Pirani gauge's schematic depiction
13:56 - Limitations and precautions of the Pirani gauge
26:22 - Introduction to the McLeod gauge
32:04 - McLeod gauge's schematic depiction

Key Takeaways

- The Pirani gauge measures low pressure based on the reduction in thermal conductivity of gases at low pressures.
- The McLeod gauge measures low pressure indirectly by measuring the temperature of a filament.
- Both gauges require careful handling and calibration for accurate measurements.
- The Pirani gauge is not suitable for high pressure measurements due to insignificant changes in thermal conductivity.
- The McLeod gauge can measure absolute pressure by calculating the length of the region containing the gas.