CAUTION: Connect the RS-485 cable
shield to pin 9 (board ground).
NOTE: Selection of the MODBUS
Address and Baud Rate is completed
through the gas detector setup menu,
described later. No jumpers or
hardware switch settings are required to
configure the MODBUS communications
network. This is done electronically from the front
panel display.
NOTE: For MODBUS
communications with the MRLDS-
250, the default communications
parameters are as follows.
Baud rate = 9600
Parity = no parity
Stop bits = 1
Confirm that all devices on the MODBUS
communications network (including a
Building Management System) are configured
similarly.
12 • MRLDS-250 Infrared Gas Detector I&O Manual
026-1315 Rev 4
If the MRLDS-250 is at the end of the RS-485
network, be sure to set the RS-485 terminator on the
printed circuit board (PCB) to
IN
. This applies a
terminating resistor to the end of the wires per the
requirements of the RS-485 protocol. The terminator
should be set to
OUT
for all other installation
conditions.
NOTE: Be sure to enable the
termination resistor on the device at
each end of the network (See Figure
3-7). This includes the Building
Management System (if used).
CAUTION: Care should be
exercised when changing the
terminator switch. Before powering
the gas detector, use a fine pointed
device or paper clip to slide the
switch position. Do not apply force to the switch
or push on the switch with any device. The
switch changes position up and down along the
access slot direction.
Figure 3-7
- Setting Network Termination Resistors
3.6.
Finish Installation
Once the base is mounted and all wiring is complete,
align the gas detector housing and press it onto the
base. The gas detector will snap into position,
completing all electrical connections. Ensure the top
and bottom snap locks are engaged.
NOTE: If the right cable gland was
not needed during installation and
wiring, be sure to install the
blanking plug.
CAUTION: Do not apply caulking
or other material around the gas
detector base. The gas detector
relies on air exchange through the
spaces between the base and the gas
detector housing. Do not obstruct the small
gap around the housing and the base with any
material.
