Hot-cathode ionization vacuum gauges

Fig. 3.13 Schematic diagram and potentiai curve in a hot-cathode ionization vacuum gauge...

In all those measurement instruments which use the ionization of gas molecules as the measurement principle (cold-cathode and hot-cathode ionization vacuum gauges), strong magnetic leakage fields or electrical potentials can have a major influence on the pressure indication. At low pressures it is also possible for wall potentials which deviate from the cathode potential to influence the ion trap current. 

Hot-Cathode Ionization Gauges. For pressures below approximately lO " Pa, it is not possible, except under carehiUy controlled conditions, to detect the minute forces that result from the coUision of gas molecules with a soHd wall. The operation of the ion gauge is based on ionisa tion of gas molecules as a result of coUisions with electrons. These ions are then subsequendy collected by an ion collector. Ionisa tion gauges, used almost exclusively for pressure measurement in high, very high, ultrahigh, and extreme ultrahigh vacuums, measure molecular density or particle dux, not pressure itself. 

Bayard-Alpert gauge (vacuum technology) A hot cathode ionization gauge using a fine-wire ion collector to minimize X-ray effects in the gauge. 

Hot cathode ionization gauge (vacuum technology) An ionizahon vacuum gauge in which the electrons for ionization are obtained from a thermoelectron-emitting hlament. 

Gauges. Because there is no way to measure and/or distinguish molecular vacuum environment except in terms of its use, readings related to gas-phase concentration ate provided by diaphragm, McCleod, thermocouple, Pitani gauges, and hot and cold cathode ionization gauges (manometers). 

The cold cathode ionization gauge has offsetting advantages relative to the hot cathode type. It is insensitive to mechanical vibrations, is not susceptible to an inrush of air in the event of a vacuum accident (that can destroy the healed filament in the hot cathode type) and is less susceptible to harm from contaminants. 

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