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. In their passage from the filament to the grid, the electrons collide with gas molecules in the gauge envelope, 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.
Read more about this topic: Hot-filament Ionization Gauge
Famous quotes containing the word function:
“Science has fulfilled her function when she has ascertained and enunciated truth.”
—Thomas Henry Huxley (1825–95)
“To look backward for a while is to refresh the eye, to restore it, and to render it the more fit for its prime function of looking forward.”
—Margaret Fairless Barber (1869–1901)
“Of all the inhabitants of the inferno, none but Lucifer knows that hell is hell, and the secret function of purgatory is to make of heaven an effective reality.”
—Arnold Bennett (1867–1931)