Veeco MS40 Operation And Maintenance Manual page 127

5.2 DRIFT AND NOISE DETERMINATION
5.2.1
Examine the straight line approximations of Sec. 5.1.4 to determine that
1-min segment of the output curve having the greatest slope. This greatest
slope is measured in scale divisions per minute and is called the drift. If
the greatest slope is less than the scale divisions corresponding to 2% of
full scale of the recorder, the total (absolute) change in output over the
20-min period is determined. The total change is divided by 20 is then called
the drift.
5.2.2
For each 1-min segment of the curve, determine the maximum (absolute)
deviation of the recorded curve from the straight-line approximation.
5.2.3
The average of these maximum deviations, multiplied by 2, is called the
noise (scale divisions).
Note: In determining the noise, neglect any large deviation (spike) which
occurs less frequently than once in any 5-min interval.
5.3 MINIMUM DETECTABLE SIGNAL
The minimum detectable signal is taken to be equal to the sum of the
absolute values of the drift and of the noise. It should be measured in scale
divisions. If the sum is less than the scale divisions corresponding to 2%
of full scale, then the scale divisions corresponding to 2% of full scale is
called the minimum detectable signal.
5.4 SENSITIVITY DETERMINATION
5.4.1 Arrangement of Apparatus
The leak detector is connected to an auxiliary system. (Frequently, the
auxiliary system is included with the leak detector as an integral part
thereof).
The system should contain a minimum of rubber or other polymeric
surfaces. Preferably, such surfaces should consist only of the exposed
surfaces of an O-ring or O-rings. Accordingly, the "Leak Isolation Valve"
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