Siemens Milltronics MFA 4p Operating Instructions Manual page 42

Technical Reference
A.1 Principles of Operation
The relationship between speed and gap of a standard probe
①
Fig. a
②
Fig. b
③
Fig. c
The resultant line indicates the threshold tolerance of the accompanying MFA 4p electronics.
For example, in Fig. a, a 100 mm (4 inch) gap requires a minimum velocity of about
10 m/minute (35 ft/minute): with a velocity of 0.61 m/minute (2 ft/minute), a maximum gap of
31 mm (1.25 inch) is possible.
Note
25.4 mm = 1 inch and 0.305 m = 1 ft
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Operating Instructions, 08/2017, A5E33988839_AB
Milltronics MFA 4p