User's Manual

Chapter Two Installation
Man_455U-D Rev 3.01 Page 29
messages.
Redundant Host Pair
If the host device is duplicated as a redundant pair, with an individual host connected to an
individual 455U, then RS232 should be used - the 455U will receive and send serial
messages, however only the active 455U will transmit via the radio.
Dual Redundanct Control Connection
The DIO channels on the two units are connected - this connection forms the Dual
Redundant Control Connection.
Note: The DIO channel is not available for any other purpose when the 455U unit
is connected to a redundant module.
If the Dual Redundant Control Connection becomes disconnected, then the two units will
remain in their previous active/in-active state.
Redundant units should be connected to separate power supplies and must be connected to
separate antennas and coaxial cables.
Although only one antenna will transmit at any one time, care must be taken with the
installation of the two antennas to avoid one antenna affecting the radiation pattern of the
other. The antennas should be installed at least 2 metres (6 feet) apart.
TYPICAL REDUNDANT WIRING INSTALLATION
B
A


 Earth
+24
+12
DIO
Power
Supply
24V
PRIMARY
455U
RS485
CONNECTION TO
HOST DEVICE
_
+
B
A


 Earth
+24
+12
DIO
Power
Supply
24V
_
+
SECONDARY
455U
REDUNDANT
CONTROL
CONNECTION