At high pressures the cathode erodes and the production of secondary electrons depends on the
surface of the cathode and it has to be cleaned quite often to get reproducible results.
Since the ring current of a Penning gauge is very high (1 A or so), it has a high sensitivity and
the discharge current may be inexpensively measured without an amplifier down to 10–4 Pa.
The discharge is generally not stable in crossed field gauges. In the early designs the discharge
became erratic below 10–3 Pa, and was often extinguished completely at 10–4 Pa.
Therefore better designs were invented with the aim of increasing the active volume of the
discharge and reducing discontinuities
became erratic below 10–3 Pa, and was often extinguished completely at 10–4 Pa.
Therefore better designs were invented with the aim of increasing the active volume of the
discharge and reducing discontinuities.