Rockwell Automation LZ Series Linear Motors - Manual (Page 24)

Publication LZ-UM001A-EN-P - January 2008
24 Troubleshooting
7. Compare the phase resistance readings to the cold resistance
specification of the specific coil model.
The three reading should be about the same and comparable to the cold
resistance specified for your model. When the coil is hot the resistance
reading should still be balanced and but may be as mush as 30 … 40%
higher than the cold resistance. 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 Tests When the LZ motor phases are internally connected in a Y configuration
(LZ-xxx-x-xxx-D/E-x-x-x-x). 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 Wave Comparison Test
1. See the Motor Phasing Diagram on page 18. Certain measurements in
this test will be inverted.
2. Turn the drive power OFF.
3. Disconnect the motor leads from the drive.
4. With a 2 channel oscilloscope, compare U-V to W-V voltage by
connecting the leads, and slowly and steadily moving the motor by hand,
in the phasing direction specified in Motor-Hall Phasing and Sequence.
W-V should lead U-V by 60
o . The shapes and peak voltages should be
approximately the same. Note that probe common = V.
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 the motor power disabled and the leads
disconnected, permanent magnet motors can generate high
back EMF voltage when moving due to external forces.