Alternate modbus wiring for existing installations, Figure 8: recommended modbus wiring, Power supply – RKI Instruments 65-2619RK-CH4-4 User Manual
Page 41: Modbus controller
65-2619RK-CH4-4 M2 Transmitter Operator’s Manual
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Figure 8: Recommended Modbus Wiring
Alternate Modbus Wiring For Existing Installations
Although the wiring shown in Figure 8 is recommended, it is possible to wire the M2 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 9 below for this wiring configuration. In this configuration, the wire between the
“C” terminal on the M2 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.
Figure 9: Alternate Modbus Wiring
C NC NO
C NC NO
C NC NO
ALARM 2
ALARM 1
F
AIL
A B C
RS 485
PWR/SIG
S
T
O
XIC O
X
Y
See
Detector
Wiring
24 VDC
Power Supply
D
Modbus
Controller
0
D
1
Input
Terminals
Common
C NC NO
C NC NO
C NC NO
ALARM 2
ALARM 1
F
AIL
A B C
RS 485
PWR/SIG
S
T
O
XIC O
X
Y
See
Detector
Wiring
To
Additional
M2s
C NC NO
C NC NO
C NC NO
ALARM 2
ALARM 1
F
AIL
A B C
RS 485
PWR/SIG
S
T
O
XIC O
X
Y
See
Detector
Wiring
24 VDC
Power Supply
D
Modbus
Controller
0
D
1
Input
Terminals
Common
C NC NO
C NC NO
C NC NO
ALARM 2
ALARM 1
F
AIL
A B C
RS 485
PWR/SIG
S
T
O
XIC O
X
Y
See
Detector
Wiring
To
Additional
M2s