3-36 | Thermox Series 2000 WDG-IV / IVC / IVCM
4-wire connections
The connections used for the RS-485 4-wire communications on the wir-
ing card are labeled as follows:
4WTX+/2W+
4WTX-/2W-4WRX+
4WRX-
Connect all control unit 4WTX+, 4WTX-, and all 4WRX+ and 4WRX- con-
nections in parallel in a daisy chain fashion. Make the following con-
nections between the host computer and the controller in a daisy chain
fashion (see Figure 3-25):
Host Computer TX- to Controller 4WRX-Host
Computer TX+ to Controller 4WRX+
Host Computer RX- to Controller 4WTX-Host
Computer RX+ to Controller 4WTX+
Be sure to use twisted-pair cable for all connections.
4-wire termination resistor
The Series 2000 Control Unit is equipped with termination resistors that
can be used for the last control unit on the network. The switch settings
are:
SW1-1 = ON
SW1-2 = ON
SW1-3 = ON
This provides 120 ohm termination resistors in the RS-485 circuit. See
the “Option Card Installation” section in this chapter for help on how to
remove and access the display module. You may need to experiment to
get optimum performance over long lengths of communications wiring to
see if having a termination resistor on the last control unit of the network
improves communications. Remember, though, only to insert a termina-
tion resistor on the last control unit on the network, and not on all control
units on the network. The factory default setting is to have Switch 3 OFF
with no termination resistor in the circuit.
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