Rockwell Automation LC-Series Linear Motor - Manual (Page 35)

Item Number 814036 - Rev C
Troubleshooting 3-5
5. Repeat previous oscilloscope procedure comparing B-C to A-C. In this
case A-C should lead B-C by 60
o
. The shapes and peak voltages should
be approximately the same. Note that probe common = C. Pay attention
to the specified phasing direction.
Calculating the Back EMF Constant:
1. The Back EMF calculation is compared to the motor’s rated Back EMF
constant. This check gives an indication that the electromagnetic
installation aspects are correct for the magnet strength, air gap, and coil
windings. Since the force constant is a direct relationship to the Back
EMF constant, this also checks for correct force constant. The
calculation is based on analyzing one motor electromechanical cycle.
Since a problem can occur at any point along the motor travel, also
check that the Back EMF waveshape is consistent throughout the
whole travel.
2. Reference the Back EMF test precautions.
3. Drive power OFF.
4. Disconnect the motor leads from the drive.
5. Using a storage oscilloscope, connect one channel across any two phase
leads.
6. Move the motor at a very steady and constant speed in either
direction by hand. This is the motor’s phase-phase Back EMF.
7. Capture and analyze one electrical cycle.
Figure 3.2 Motor Back EMF Cycle.
V
(pK - pK)
one cycle
time (sec)