Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS - Manual (Page 79)

Installing the Assembly
Chapter 6
6Ć29
the proper polarity for loss-of-feedback detection at the 1771-ES
expander. If you use the opposite analog output signal orientation, you
will not be able to utilize the loss-of-feedback detection feature.
WARNING: Always utilize the loss-of-feedback feature.
Without loss-of-feedback detection, if encoder or tachometer
feedback is lost, unexpected axis motion can occur, resulting in
damage to equipment and/or injury to personnel.
Limit the cable lengths to 50 feet. If your application requires a cable
length greater than 50 feet, contact your local Allen-Bradley
representative.
Grounding Cable Shields
Figure 6.17 is a pictorial representation of the shielded cable connections.
Mount a ground bus directly below the I/O chassis to provide a
connection point for cable shield drain wires and the common connections
for the input circuits. Connect the I/O chassis ground bus through 8 AWG
wire to the central ground bus to provide a continuous path to ground.
The tachometer cable is broken into three segments because of the
connection to the drive and potentiometer in the middle of the cable.
Connect these cable shield segments together as shown. Connect the
shield to ground only at the I/O chassis end. Do not connect the shield to
the drive.