A Pirani gauge and a Penning gauge are both types of pressure gauges used to measure low-pressure levels. However, they operate based on different principles and have distinct characteristics:

Pirani Gauge:

Principle: The Pirani gauge operates based on the thermal conductivity of the gas. It consists of a heated wire that is exposed to the gas being measured. As the gas molecules collide with the wire, they transfer heat away from it, causing the wire’s resistance to change. The change in resistance is then used to determine the pressure.

Penning Gauge:

Principle: The Penning gauge operates based on the ionization of gas molecules in a magnetic field. It consists of a discharge electrode and a collector electrode placed in a magnetic field. When a voltage is applied between the electrodes, gas molecules are ionized, and the resulting ions are accelerated towards the collector electrode. The ion current is then used to determine the pressure.

Source: Wikipedia  –  https://en.wikipedia.org/wiki/Penning_gauge