Watlow PPC-2000 - Manual (Page 109)

PPC-2000 User’s Guide Chapter 2: Hardware Installation
Doc.# 30002-00 Rev 2.3 Watlow Anafaze 85
Signal Common
Each controller and the converter should be connected to the
signal common to insure they can properly interpret the signals
on the network. Pin #1 in the RJ12 connectors connects the
signal commons of all the PPCs to each other. At the converter
connect the signal common to the common of the converter’s DC
power supply.
The communications ports are optically isolated from the
sensors and the rest of the PPC circuitry, so connecting the
communications commons together will not create a ground
loop.
Termination
In some installations, particularly when transmission lines are
long, the transmission lines must be terminated. The receive
lines at the converter or host device should be terminated in the
converter, the connector to the host device, or the device itself.
Typically the converter documentation provides instructions
for termination.
The PPC receive lines can be terminated by setting a jumper on
the last PPC-2010 module. To terminate the lines for port 1, set
jumper JU1 on the last PPC-2010 module on the network to the
A position. This places a 120 ohm resistor across the receive
lines. To terminate the line for port 2, set jumper JU2 on the
last PPC-2010 module on the network to the A position. This
places a 120 ohm resistor across the receive lines. See PPC-
2010 Jumper Settings on page 18.
Alternately, the line may be terminated externally on the 485
terminal block by placing a termination resistor across the
receive line screw terminals near the last PPC. See Figure 2.70
on page 81. The value of the termination resistor should be
equal to the impedance of the communications cable used.
Values are typically 120 to 200 ohm.