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MDA-550/MDA-510
Users Manual
4. Place the probe in the magnetic probe holder. Extend
the probe holder with the included two-piece extension
rod.
Use the probe holder to keep the probe in a fixed
position and the brush in contact with the motor
shaft.
5. Make sure that it is possible to make good electric
contact with the shaft before you do the measurement.
6. Use one of the ground leads to contact the motor
chassis that is the reference ground.
When it is not possible to connect near the shaft, an
extension cord with 4 mm connections on both ends is
included for extending the connection to the ground
lead. The measurement can be done on the driven and
the non-driven end of the motor.
7. Turn on the motor.
8. Do the measurement after the motor warms up to
normal operating temperature.
With this function you can determine the number of flash-
overs that occur between shaft and motor chassis, also
referred to as electrical discharge machining. When motor
shaft voltages exceed the bearing grease insulation
capability, flash-over currents occur and cause pitting and
grooving of the bearing races.
22
Note
Tips:
•
Under direct 50/60 Hz mains operation, the shaft
voltage is normally <1 V.
•
Due to the fast edges of the switching voltage from a
motor drive, the shaft voltage for a motor powered by a
motor drive can be much higher. High Voltage can
cause large breakdown currents across the grease
barrier causing damage to the bearings.
•
Normal, unavoidable shaft voltage due to asymmetry in
the air-gap magnetic field result in peak voltages <5 V
and slower than 100 ns, which, in general, are not
damaging.
•
Voltage discharges of >15 V and transition times faster
than 50 ns can point to grease flash-over currents that
can damage bearings. However, no fixed values can be
given that can be considered damaging for the motor,
as there are many factors that influence this value.
After selecting the Motor Shaft Voltage measurement, the
display shows the voltage waveform. The voltage
peak-peak reading shows at the top of the display. Select
EVENTS ON to view the discharge event and
count the amount of discharge events. Only the discharge
events show. The readings at the top of the display show
the Volt Peak-Peak, dV/dt, and falltime or risetime as well
as the number of events/second. Expect about 20 seconds
before the number of events/second shows on the display.
Use
DEFINE EVENTS to define what is
considered a discharge event.
In this screen, select the maximum voltage change and
maximum rise or fall time that will be counted and displayed
as an event.
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