Penning (vacuum) gauge

A cold-cathode ionization gauge. In the Penning (vacuum) gauge, an annular electrode (anode) is placed between a pair of parallel plate electrodes (cathode), and a magnetic field is applied parallel to their axes to lengthen the traveling distance of electrons. As a result, constant discharge occurs even at a low pressure, thus the Penning gauge can measure the pressure of the middle to high vacuum region or 1 to 10^-4Pa. The produced current is proportional to the pressure of the vacuum. For a TEM, the gauge is used for switching of the evacuation system from the diffusion pumping (DP) to the sputter ion pumping (SIP) because the gauge is robust and easy to use.

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