or stroboscope (fig. 7-66), to measure the speed of a
Before operational testing the unit, thermometers
should be placed at each bearing location and at the
mid-point of the stator as a minimum. The ambient
temperature should be recorded for each thermometer.
Once the unit is placed in operation the temperature of
each location should be frequently noted and recorded.
Any unusual/rapid temperature rise must be
investigated and corrected before the test can be
NOTE: Check bearing temperatures frequently
during operation. Temperatures should not exceed
Testing Phase Current Balance
During operation, the phase current of the unit
should be checked to ensure they are within normal
operating limits. When testing dc machines, you need
to have an ammeter installed prior to testing the values
of the phase currents. When testing ac machines, a
clamp-on ammeter (fig. 7-67) can be used.
Figure 7-67.--Clamp-on ammeter.
The current in any phase, at rated load, should not
differ from the arithmetic average of the maximum and
minimum current values by more than that shown in
Table 7-8.--Maximum Allowable Difference in Phase Currents
Figure 7-66.--Type 1531-AB strobotac.