Rockwell Automation LC-Series Linear Motor - Manual (Page 34)

Item Number 814036 - Rev C
3-4 Troubleshooting
• Compare the phase resistance readings to the cold resistance
specification of the specific coil model. If the three readings are
balanced but much different than specified, the reason may be a special
coil model or due the cable resistance (if much higher.) To rule out the
cable resistance, disconnect the field cable at the coil assembly interface
and repeat the procedures at the coil.
Motor Back EMF Test Waveshape/Phasing and Calculating Back EMF Constant
Anorad motor phases are internally connected in a Y configuration. The
neutral of the Y is not accessible without the use of a resistor star network.
This is why all measurements are performed phase-to-phase.
Each phase can consist of single windings (coils) or multiple sets in series or
parallel. Performing a Back EMF voltage magnitude and phase sequence test is
a good indicator of correct internal wiring.
Back EMF Test
1. Refer to Motor Phasing Diagram on page 2-21. Certain measurements
in this test will be inverted.
2. Drive power OFF.
3. Disconnect the motor leads from the drive.
4. With a 2 channel oscilloscope compare A-B to C-B voltage by slowly
and steadily moving the motor by hand in the specified phasing
direction. C-B should lead A-B by 60
o
. The shapes and peak voltages
should be approximately the same. Note that probe common = B.
IMPORTANT
Do not perform coil or insulation electrical stress tests
(Megger or Hi-Pot test) without first consulting with
Anorad technical support or engineering.
ATTENTION
!
Even with motor power disabled and leads disconnected,
permanent magnet motors can generate high Back EMF
voltage when moving due to external forces.