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5.2.4
Cable requirements
All mounting methods:
•
Shield connection at drive terminal to 0V
•
Shield connection at encoder to 0V
•
It is recommended that the shielded cable should be run in a continuous length to the terminal,
to avoid the injection of noise at intermediate pigtails and to maximise the shielding benefit.
•
The shield connections ("pigtails") to the drive and encoder should be kept as short as possible
Mounting with no isolation:
•
Shield connected to ground at both ends. The connection must be made by direct fixing of the
cable to the grounded metal parts, i.e. to the encoder body and the drive grounding bracket as
shown in Figure 5-5 on page 32, "Pigtails" must be avoided. The outer sheath of the cable
should be stripped back enough to allow for the ground clamp to be installed. The shield
connection should not be broken. The ground clamps should be located as close as possible to
the drive and encoder.
•
It is essential that the shielded cable should be run in a continuous length to the terminal, to
avoid the injection of noise at intermediate "pigtails" and to maximise the shielding benefit.
Under no circumstances should the cable shield connection be omitted at any end of the
cable, since the noise voltage may well be sufficient to destroy the line driver and
receiver chips in the encoder and the drive.
CAUTION
Cable shield ground connection
For all mounting methods, grounding of the feedback cable shield has added benefits. It can protect
the drive and encoder from induced fast electrical transients, and prevent radiated radio-frequency
emission. However it is essential that it be carried out in the correct manner as explained above
and as shown in Figure 5-5.
Connecting the cable shield to ground at both ends carries the risk that an electrical fault
might cause excessive power current to flow in the cable shield and overheat the cable.
There must be an adequately rated safety ground connection between the motor/
encoder and the drive.
WARNING
Recommended Cable
The recommended cable for feedback signals is a twisted pair, shielded with an overall shield as
shown below.
Figure 5-4 Feedback cable, twisted pair
Using this type of cable allows for the connection of the outer shield to ground and the inner shields
to 0V at both the drive and encoder.
Ensure that feedback cables are kept as far away as possible from power cables and
NOTE
avoid parallel routing.
SI-Universal Encoder User Guide
Issue: 2
Cable overall shield
Twisted
pair
cable
Twisted pair shield
Cable
31
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