©NationalInstruments Corporation 23 MID-7654/7652Servo Power Motor Drive User Guide
Note If you require other encoder powervoltages, reference an external power supply to
the Digital Ground signal on the 8-pin encoder terminal block.
TheMID-7654/7652 supports differential inputs for Phase A, Phase B, and
Indexsignals. You can easily accommodate encoders with various phase
relationshipsby swapping the signals and/or connecting them to the
invertinginputs as required by your application. The Index signal must
occurw hen both PhaseA and Phase B signals are low,as shown in
Figure 14. If the Indexpolarity is inverted, try reversing the Index and
Indexsign als on differentialencoders o r using the Index input on
single-endedencoders.
Figure 14 showsthe prop er encoder phasing for CW (forward) motor
rotation.
Figure14. Encoder Signal Phasing, CW Rotation
Closed-loop servoappl ications 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 (C W) facing motor shaft
•Negative= reverse = counter-clockwise (CCW) facing motor shaft
Refert o Figure 8 fora depiction of clockwise and counter-clockwise
rotation.
Whenconnecting the encoder wiring to your MID-7654/7652, useshielded
wire of atleast 24 AWG. You must use cables with twisted pairs and an
overallshield for improved noise immunity and enhanced encoder signal
integrity.Figure 15 shows twisted pairs in a shielded cable.
PhaseA
PhaseB
Index