65-2646XL-05-04 M2A Transmitter Operator’s Manual
Chapter 8: RS-485 Modbus Output
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50
Alternate Modbus Wiring For Existing Installations
Although the wiring shown in Figure 11 is recommended, it is possible to wire the M2A into a
Modbus system with only 4 wires in situations where a pre-existing system is being replaced and
wiring is already in place. This should only be done if wiring for a system that is being replaced is
already installed and it is not practical to run another wire. See Figure 12 below for this wiring
configuration. In this configuration, the wire between the “C” terminal on the M2A and the
Common terminal on the Modbus controller is omitted. Instead, the Common terminal on the
Modbus controller is connected to the “-” of the 24 VDC power supply.
The ground jumper must
be installed in this wiring configuration.
Figure 12: Alternate Modbus Wiring
Adding an M2A to an Existing M2 Modbus Installation with Alternate
Wiring
An M2A can be wired into an existing M2 Modbus system. The shape of the terminal PCB will be
different but the wiring connections are identical and the ground jumper on the M2A must still
remain installed.
+
-
S
+
PW
R
/S
IG
+
-
S
+
PW
R
/S
IG
A
B
C
RS
4
8
5
A
B
C
RS
4
8
5
+
-
10-30 VDC
Power Supply
Modbus Controller
D1
Common
D0
Input
Terminals
TO
X
IC
O
X
Y
C
NC
N
O
AL
A
R
M
1
C
N
C
NO
AL
A
R
M
2
C
NC
N
O
FA
IL
See
Detector
Wiring
C
NC
N
O
AL
A
R
M
1
C
N
C
NO
AL
A
R
M
2
C
NC
N
O
FA
IL
To
Additional
M2As
+
TO
X
IC
O
X
Y
+
See
Detector
Wiring
