Vaisala DMT340 - Manual (Page 62)

User's Guide _______________________________________________________________________
60 ___________________________________________________________________ M210704EN-G
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 operates
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.
1
2
3