Ametek Thermox TM2000, User Manual

Page: 52 / 170

3-30 | Thermox TM 2000 Oxygen Analyzer
RS-485 Communications Connections
The Series 2000 control unit has the ability to communicate with other
computers that use the same protocol and have the same hardware in-
terface. See the Serial Communication Appendix for information on the
RS-485 serial communications protocol.
2-wire connections
The connections used for RS-485 2-wire communications on the wiring
card are labeled as follows:
4WTX+/2W+
4WTX-/2W-
Connect all the 2-wire pluses (+) and all the 2-wire minuses (-) in parallel
with all the devices in a daisy-chain fashion, including all the control units
on the network and the host computer. In addition, on the host computer
connect the receive and transmit terminal block connections (see Figure
3-26). Be sure to use twisted-pair cable for all connections.
2-wire termination resistor
The Series 2000 control unit is equipped with a termination resistor that
can be used for the last control unit on the network. Switch 3 on SW1 of
the display module allows you to place a 120 ohm termination resistor
into the RS-485 circuit:
Switch 3 of SW1 = On (Termination Resistor In Circuit)