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Hot-filament ionization gauge
The hot-filament ionization gauge, sometimes called a hot-filament gauge or hot-cathode gauge, is the most widely used low-pressure (vacuum) measuring device for the region from 10−3 to 10−10 torr. It is a triode, whereas the filament is the cathode.
''Note: Principles are mostly the same for hot-cathode ion sources in particle accelerators to create electrons''
== Function ==
A regulated electron current (typically 10 mA) is emitted from a heated filament. The electrons are attracted to the helical grid by a DC potential of about +150 volts. Most of the electrons pass through the grid, and collide with gas molecules in the enclosed volume, causing a fraction of them to be ionized. The gas ions formed by the electron collisions are attracted to the central ion collector wire by the negative voltage on the collector (typically a minus 30 volts). Ion currents are on the order of 1 mA/Pa. This current is amplified and displayed by a high-gain-differential amplifier/electrometer.
This ion current will differ for different gases at the same pressure; that is, a hot filament ionization gauge is composition-dependent. Over a wide range of molecular density, however, the ion current from a gas of constant composition will be directly proportional to the molecular density of the gas in the gauge.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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