ALL-TEST PRO
®
31 User Manual
©2011, ALL-TEST Pro, LLC www.alltestpro.com rev 2011-11F 26
V. Additional Functions and Features
Electro-Magnetic Interference (EMI):
It is electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals,
as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to
be induced in other circuits. This interrupts, obstructs, or otherwise degrades or limits the effective
performance of those other circuits.
NOTE: These voltages can come from cables of other energized machines lying in the same cable tray
as the cables for the machine being tested.
The EMI feature of the ALL-TEST PRO® 31 measures if there is any EMI present in the motor system,
which may cause errors in ALL-TEST PRO® 31 or ALL-TEST IV PRO ™ readings.
Facts about EMI:
· EMI may cause non-repeatable or unsteady test results.
· A constantly changing value for impedance during testing indicates either the shaft is still rotating or there
is EMI present from another cable.
· EMI is a ‘floating’ voltage, which will often have a value above the ground reference (0 Volts).
· The EMI may be sinusoidal depending upon the cause for the EMI (see Figure 3).
· EMI values over 1 Volt should be investigated and corrected whenever possible.
· EMI values above 10 milli-Volts may interfere with test results.
If the impedance values are constantly changing,
1
st
Verify that the rotor of the motor being tested is not turning, and
2
nd
Test for EMI using the following procedure:
Figure 3: Electro-Magnetic Induction
0 Volts
0.4 milli-Volts
0.2 milli-Volts
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