Vaisala HMT330 - Manual (Page 59)

Chapter 3 ________________________________________________________________ Installation
VAISALA ________________________________________________________________________ 57
0503-037
Figure 35 Relay Module
The following numbers refer to Figure 35 above:
1 = Indication led for the relay 1 or 3
2 = Relay test buttons
3 = Flat cable pins
4 = Indication led for relay 2 or 4
WARNING The relay module may contain dangerous voltages even if the
transmitter power has been disconnected. Before opening the transmitter
you must switch off both the transmitter and the voltage connected to
the relay terminals.
WARNING Do not connect the mains power to relay unit without grounding the
transmitter.
RS-422/485 Interface
The RS-422/485 interface enables communication between an RS-485
network and the HMT330 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 HMT330 main board cannot be used and
connected when RS-485 module is connected. Service port operates
normally.