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The 301C controller communicates with gas sensors over a Modbus
RS‐485 network. This transmission line requires that 120Ω termina‐
tion resistors be fitted at both ends of each network segment to ab‐
sorb the signal and thus prevent reflections. Fortunately, the control‐
ler makes network termination simple as resistors are included on the
board. These can be switched in and out of network by moving the
"EOL" jumpers as shown in the figure on page 12. More information
on RS‐485 wiring is published by Maxim Integrated in the TUTORIAL
763 Guidelines for Proper Wiring of an RS‐485 (TIA/EIA‐485‐A) Net‐
work .
Settings for Specific Transmitters
Honeywell Sensepoint XCD Transmitters must be configured for 9600
baud, no parity, and a unique address. Honeywell XNX Universal
Transmitters must be configured for 9600 baud and a unique address.
Information on configuring each transmitter is in the associated tech‐
nical manual.
Some sensors consume multiple addresses on the 301C controller.
Specifically, the 301EM consumes 4 addresses regardless of the num‐
ber of sensors connected. Additionally, the IAQPoint2 consumes 3
addresses if fitted with the optional temperature / humidity sensor.
Please allocate proper address spacing for applications utilizing a mix‐
ture of sensors on a single system.
Relay Output
The relay output can withstand up to 5A at 30Vdc or 250Vac resistive
load. Relays can be used to activate horns and strobes. Although each
relay is programmed with a default setting (below), they can be con‐
figured using the controller programming menu.
14
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