Rockwell Automation 57C442 Data Highway Plus Interface Module - Manual (Page 59)

J-1
Appendix J
Recommendations For Reducing Noise On
The Cable System
We recommend that all drive systems using 57C442 Data Highway Plus
Interface Modules and/or 57C443 AutoMax Allen-Bradley Remote I/O Scanner
Modules should be provided with 1770-SC station connectors installer per item 2
below. All drives which are connected using Data Highway Plus or Allen-Bradley
Remote I/O should include part number 43825-TC ferrite cores installed per item
3 below.
Installation recommendations:
1. When installing either the 57C442 or 57C443 module into the card rack,
make sure that its holddown screws are properly tightened at all times. The
basic design of the AutoMax has a floating ground on the backplane rather
than a solid DC ground like the PLC-5 does on its backplane. In AutoMax, it
has always been the case that the cards retaining screws have always had to
be tightened down tightly so that we could insure a good ground connection.
Also make sure that the AutoMax rack is properly grounded.
2. Always install an AB 1770-SC station connector box near the AutoMax rack
so that the drop cable from the AutoMax to the station connector box does
not exceed a length of 10 foot. Connect the drop cable and the trunkline
cables as specified in the installation manual for the station connector box.
This will result in the shield of the drop cable being isolated from the network
in the Station Connector box. Make sure that the station connector box is
grounded as specified. Follow the Installation Guideline documents that AB
has for Data Highway Plus and RIO networks as well as the Station
Connector Box. Guideline documents are AB publications 1770-2.20C for
the 1770-SC Station Connector Box, 1770-4.1 for Industrial Automation
Wiring and Grounding Guidelines and 1770-6.2.2 for Data Highway/Data
Highway Plus/Data Highway II/Data Highway-485 Cable.
3. The AB drives group recommends that a common mode choke be installed
at each drive. This common mode choke is a ferrite core, part number
165482. It is made by Dexter-Permag and is Dexter-Permag part number
43825-TC. The drives group recommends that 4 turns of the network cable
be dressed through this ferrite core.
Where poor installation and wiring practices are suspected and problems exist
after items 1, 2 and 3 have been implemented, additional ferrite beads, Fair-Rite
Products Corporation number 2643626502, as discussed in publication 1770-4.1,
can be added. In some cases, slowing the network speed down from 230 kbaud
to 115 kbaud has helped, as well.