Veeco MS40 Operation And Maintenance Manual page 125

3.4.3 Virtual Leak
The semblance of a leak due to the evolution of a gas or vapor within a
system.
3.5 LEAK RATES
3.5.1 Leak Rate
The mass rate (also called "throughput"; differentiated from volume rate
of flow (liters/sec) also called pumping speed ), in Torr liters/sec (or Pa
m3/sec) at which a specified gas passes through a leak under specific
conditions.
3.5.2
The mass rate of flow, through a leak, of atmospheric air of dew point less
than -25°C under standard conditions specified as follows: the inlet
pressure shall be less than 760 Torr ±5%, the outlet pressure shall be less
than 10 Torr and the temperature shall be 23±3°C.
3.5.3
Short path leaks having standard air leak rates less than 10-6-10-7 Torr
liters/sec (10-7-10-8 Pa m3/sec) are of the molecular type (see Sec 3.4.1.3).
Consequently, helium (mol. wt 4) passes through such leaks more rapidly
than air (mol. wt 29) and a given flow rate of helium corresponds to a
smaller flow rate of air. In this recommendation, helium flow is measured
and the "equivalent standard air leak rate" is taken as (4/29)´ = 0.37 times
the helium leak rate under standard conditions (see Sec 3.5.2).
3.8 SENSITIVITY TERMS
3.8.1 Sensitivity
The sensitivity of a device is the change in output of the device divided by
the change in input which caused the response.
3.8.2 Minimum Detectable Signal
An output signal due to incoming search gas which is equal in magnitude
to the sum of the noise and the drift.
3.8.3 Minimum Detectable Leak (or Minimum Detectable Leak Rate)
The smallest leak, as specified by its standard air leak rate, that can be
detected unambiguously by a given leak detector. The minimum
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Standard Air Leak Rate
Equivalent Standard Air Leak Rate
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