3-10
Malfunctions Not Indicated by a Fault
Test points on the Main Control Board (TP12 – Encoder Phase B (ENCB)
and TP15 – Encoder Phase A (ENCA)) can be used to monitor the
frequency and phase relationships of the encoder. An oscilloscope should be
used to monitor these signals with respect to AGND (TP57). The
waveforms should be logic level signals, 0 to 5V square-waves.
The frequency is proportional to speed and the pulse rate of the encoder,
referred to as the “Pulse/Rev” rating on the nameplate. The speed of the
motor can be calculated by: Speed (RPM) = [Frequency (Hz) x 60]/[Pulses/
Revolution].
The direction of rotation is determined by the phase relationship of ENCA
to ENCB. ENCA and ENCB should always be 90 Degrees out of phase with
each other. If ENCA leads ENCB by 90 Degrees then the direction of
rotation is defined as forward. If ENCB leads ENCA by 90 Degrees then the
direction of rotation is defined as reverse. Waveform 1 shows forward
rotation with ENCA as the top waveform. Waveform 2 is reverse rotation
with ENCA as the top waveform.
The following table lists malfunctions, symptoms, and possible solutions.
!
ATTENTION:
Extreme care must be used when probing the
test points on any board. Improper techniques may result in
damage to the circuit and personal injury. Do Not attempt probe
tests that are not listed here. Damage to extremely sensitive
circuits may cause unpredictable drive operation and unintended
motor rotation.
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