Inficon Transpector XPR 3+, Operating Manual, Page: 72 / 130

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Transpector XPR 3+ Operating Manual
Ionization probability factors can be approximated by substituting the relative ion
gauge sensitivities for various gases.
Table 4-5 gives relative ion gauge
sensitivities for some common gases.
NOTE: This table lists relative ionization gauge sensitivities for selected
molecules. The data was compiled from
Empirical Observations on the
Sensitivity of Hot Cathode Ionization Type Vacuum Gauges by R. L.
Summers (NASA Technical Note NASA TN D5285, published in 1969).
Similar, although more limited, lists of ionization sensitivities can be found
in the books by O’Hanlon (Chapter 8, Section 1.1) and Drinkwine and
Lichtman (Table I, page 5).
HINT: Actual ionization probabilities vary significantly depending especially on the
ionizer and the electron energy. For best accuracy, measure the relative
ionization probability using a hot cathode ionization gauge (calibrated for
nitrogen) to monitor a known pressure of the substance of interest. The
ratio of the gauge reading to the known true pressure is the relative
ionization probability. To determine the true pressure, use a gauge which is
gas species independent (for example, a capacitance manometer) or a
gauge with a known sensitivity factor (for example, a spinning rotor gauge).