Chapter 3 _______________________________________________________________ Installation
VAISALA _______________________________________________________________________ 61
RS-422/485 Interface
The RS-422/485 Interface enables communication between an RS-485
network and the DMT340 transmitter. The RS-485 interface is isolated
and offers a maximum communications rate of 115 200 bits/s. (For
maximum bus length of 1 km, use bit rate 19200 b/s or less.)
When selecting an RS-232 to RS-485 converter for the network, avoid
self-powered converters, as they do not necessarily support the needed
power consumption.
NOTE
RS-232 User Port on DMT340 main board cannot be used and
connected when RS-485 module is connected. Service port is operating
normally.
1102-023
Figure 41
RS-422/485 Module
The numbers refer to Figure 41 above:
1
=
Flat cable pins
2 = Selection
switches
3
=
Screw terminals for wiring
NOTE
The data lines on earlier versions of the RS-422/485 module are marked
A and B instead of D1+ and D0-. When the line is idle, D1+ has positive
voltage compared to D0-.
When connecting the module, be prepared to swap the D1+ and D0-
wires if you have a communication problem.