Vaisala PTU300 - Manual (Page 59)

Chapter 3 ________________________________________________________________ Installation
VAISALA ________________________________________________________________________ 57
RS-422/485 Interface
The RS-422/485 interface enables communication between an RS-485
network and the PTU300 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 PTU300 main board cannot be used and connected
when RS-485 module is connected. Service port operates normally.
1102-023
Figure 32 RS-485 Module
The following numbers refer to Figure 32 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