Veeco MS40 Operation And Maintenance Manual page 120

10. Vacuum Testing - A leak detecting procedure in which the enclosure
11. Mass Spectrometer Leak Detector - A mass spectrometer adjusted to
12. Spectrometer Tube - The sensing element of a mass spectrometer
13. Ion Source - That part of a spectrometer tube in which tracer gas is
14. Noise Level - In the case of a leak detector, the spurious output,
15. Background - In the case of a leak detector, the spurious output,
16. Minimum Detectable Pressure Change - The pressure producing an
17. Minimum Detectable Leak
18. Probe Test - A leak test in which the tracer gas is applied by means
19. Probe - A tube having a fine opening at one end, used for directing a
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under examination is evacuated, a tracer gas applied to the outside
surface of the enclosure, and the gas detected after entering the
enclosure.
respond only to a tracer gas. Helium is commonly used as the tracer
gas, and thus the instrument is normally referred to as a helium leak
detector
leak detector.
ionized preliminary to being detected.
expressed in suitable terms, exhibited by the detector in the absence
of an output due to tracer gas.
expressed in suitable terms, due to the response to other gases than
the actual gas being used for probing. The background may be
inherent in the detector, or accidental.
indication of three times the noise level.
a. The size of the smallest leak, expressed in terms of mass flow
per unit time that can be unambiguously detected by a leak
detector in the presence of noise and background.
b. The product of the minimum detectable pressure change and the
pumping speed at the detector
of a probe (see below) so that the area covered by the tracer gas is
localized. This enables the individual leaks to be located.
stream of tracer gas.
a-ii