The Mcleod gauge, Pirani gauge, and Ionization gauge III — Lesson 3

This lesson covers the techniques of measuring low pressure, focusing on the operational principle of the ionization gauge. It explains how this gauge, which operates in the range of 10 power minus 6 to 10 power minus 2 Pascal, measures such low pressure. The lesson also discusses the working principle of the ionization gauge, its construction, and its similarity to an ordinary triad vacuum tube. It further explains the concept of plate current and grid current, and how the ratio of these two currents provides information about the pressure inside the chamber. The lesson concludes with a numerical problem related to the pneumatic displacement gauge, demonstrating how to measure very small displacement.

Video Highlights

01:16 - Explanation of the operational principle of the ionization gauge
05:38 - Steps to measure very low pressure using the ionization gauge
09:26 - Calculation of the maximum displacement and outlet tube diameter
22:50 - Conclusion of the discussion on the ionization gauge
24:59 - Introduction to a problem on the pneumatic displacement gauge
32:50 - Solution of the problem on the pneumatic displacement gauge

Key Takeaways

- The ionization gauge is used to measure very low pressure in the range of 10 power minus 6 to 10 power minus 2 Pascal.
- The operational principle of the ionization gauge involves the emission of electrons from a heated cathode, leading to gas ionization and the creation of positive and negative ions.
- The ratio of the plate current to the grid current provides information about the pressure inside the chamber.
- The proportionality constant, known as the sensitivity of the gauge, is obtained through empirical relationships.
- The pneumatic displacement gauge is used to measure very small displacements, with the maximum displacement calculated using the Graneek and Evan's formula.