Rockwell Automation 1770 DH,DHII,DH485 CABLE - Manual (Page 48)

Chapter 3
Constructing a Data Highway or
Data Highway Plus Cable System
3-16
Network Checkout
After you have installed your network using 1770-SC station connectors,
complete the following steps before you attach any modules to the droplines
to check the system integrity.
Important: If the trunkline is routed between several building structures,
building-to-building ground potential may differ. This checkout should be done
on a per building basis.
1. Check the resistance between the following points.
sockets 6 and 8 on each 15-socket connector
the blue and clear wires on each station connector
The readings should be 75 ohms plus the resistance of the Belden 9463
cable. Belden 9463 has a typical resistance of one ohm per 100 feet.
The resistance readings should be no less than 75 ohms +/- 1%, and no
more than 125 ohms +/- 10%. If the resistances do not fall within this
parameter, you must locate and correct the error before network start-up.
2. Remove the resistors from the end station connectors and check the
resistance between sockets 6 and 8 on any 15-socket connector on the
network. There should be infinite resistance.
3. Connect socket 8 to building steel (chassis ground). The resistance on
socket 8 should be 1,000 ohms or less, and the resistance on sockets 6 and
7 should be one meg ohms or more.
If these readings are not found, you must locate and correct the problem
before network start-up.
If the resistances are within the guidelines outlined above, you can start up the
network.