MID-7654/7652 Servo Power Motor Drive User Guide
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Note
If you require other encoder power voltages, reference an external power supply to the Digital
Ground signal on the 8-pin encoder terminal block.
The MID-7654/7652 supports differential inputs for Phase A, Phase B, and Index signals. You can easily
accommodate encoders with various phase relationships by swapping the signals and/or connecting
them to the inverting inputs as required by your application. The Index signal must occur when both
Phase A and Phase B signals are low, as shown in Figure 14. If the Index polarity is inverted, try
reversing the Index and Index signals on differential encoders or using the Index input on single-ended
encoders.
Figure 14 shows the proper encoder phasing for CW (forward) motor rotation.
Figure 14.
Encoder Signal Phasing, CW Rotation
Closed-loop servo applications require consistent directional polarity between the motor and encoder
for correct operation. The National Instruments motion control standard directional polarity is as
follows:
•
Positive = forward = clockwise (CW) facing motor shaft
•
Negative = reverse = counter-clockwise (CCW) facing motor shaft
Refer to Figure 8 for a depiction of clockwise and counter-clockwise rotation.
When connecting the encoder wiring to your MID-7654/7652, use shielded wire of at least 24 AWG.
You must use cables with twisted pairs and an overall shield for improved noise immunity and enhanced
encoder signal integrity. Figure 15 shows twisted pairs in a shielded cable.
Figure 15.
Shielded Twisted Pairs
Phase A
Phase B
Index
Shield
+5 V
Encoder Index
Encoder Index
Encoder B
Encoder B
Encoder A
Drain
Encoder A
Digital
Ground
