PURPOSE: To enable accurate pressure measurement, by surrounding a gauge bowl with a conducting screen of the earth potential to eliminate mutual interfer ence with other devices during the use of an ion gauge bulb.
CONSTITUTION: A filament 1, a grid 2, three electrodes of an ion collector 3 of a gauge bulb are surrounded with a conducting screen 4 of the earth poten tial to isolate them electrically from other devices in a vacuum chamber. With such an arrangement, the members of the gauge bulb which otherwise electri cally affects other devices are surrounded with this conducting screen 4 to be isolated electrically from other devices instead of mechanically isolating the gauge bulb from other devices. This enables the avoiding of mutual interfer ence between the gauge bulb and other devices to eliminate the need for mechan ical isolation thereof from the vacuum chamber and the suspension of other devices during the pressure measurement thereby enabling accurate pressure measurement.
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