Magnetek HPV 900 Series 2, Техническое руководство

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APPENDIX
– Selection and Mounting of Encoder
190
Differential / Single-Ended Encoder
Configurations
Drives with TerMag boards 46S04284-1020
can be configured to run with either a
differential or single-ended encoder with the
setting of the SW3 dip switches. Below are
examples of how the TerMag can be
configured to run with differential or single-
ended encoders. NOTE: each encoder
channel can be configured individually for
differential or single-ended operation.
Figure 57: Default setting of SW3 on
TerMag Board A & B with Differential and Z
with Single-Ended
Figure 58: SW3 set for ALL Differential
Input for TerMag Board
Figure 59: SW3 set for ALL Single-Ended
Input for TerMag Board
Capacitors from Electronics to Case
Do not allow capacitors from internal encoder
electronics to case, in order to minimize
ground current noise injection and minimize
the coupling of high frequency noise.
Encoders are sometimes supplied with an
internal capacitor from circuit common to case
ground to drain electrical noise from common
to building ground. However, PWM drives have
extremely high frequency noise that is coupled
to the frame and shaft of the motor. A
capacitor placed between the encoder case
and the encoder electronics will couple this
noise into the encoder, where it can interfere
with normal operation.
The result is intermittent rough operation,
motor reversal or no operation at all. The
presumption is that there is a drive or encoder
problem. An improvement is to remove any
internal encoder capacitors between electrical
common and the case.
The above analysis assumes that the electrical
wiring is correct and that the shield on the
encoder cable is properly grounded,
see
Encoder Wiring on page 30.
The scope traces in Figure 60 and Figure 61
show a noise comparison of output signals
from similar encoders with and without internal
capacitors, both connected to a motor with
typical PWM switching noise on the frame.
6 5 4 3 2 1
default
SW3
A
B
Z
on
off
6 5 4 3 2 1
SW3
A
B
Z
on
off
6 5 4 3 2 1
SW3
A
B
Z
on
off