
D12
EX-IR
Gas Transmitter with IR Smart Sensor
Dec 2019 ( 85-0004 Rev A)
26
RS485 Multi-drop Connection
RS485 permits up to 32 devices to be connected on the same bus and can be used to connect a Modbus
master to multiple transmitters. Size the power supply and wiring according to the power required for
each transmitter. Voltage at the transmitter’s terminals must not drop below 12v. This connection
requires the communication jumper. See Figure 9 on page 18 for location and placement of the jumper.
The Modbus polling address is set through the operator interface (see Modbus Menu on page 70).
Note: 4-20mA signaling is shown disconnected below, but may be operated concurrently if connected to a
4-20mA receiver using a 3-wire or 4-wire connection (see Figure 12 and Figure 13 on pages 21 and 22).
Figure 17. Example RS485
“M
ulti-drop
”
connections
Supply
24 VDC
DCS, SCADA, or
Computer System
(Modbus master)
Sig.Com.
B(+)
A(-)
Not at End of Bus - Unterminated
Install the transmitter’s communication
jumper block in the “RS485 Unterminated”
position if it
IS NOT
at the end of the bus
(see Figure 9 on page 18).
RS485 Adapter
(typical)
+
-
End of Bus - Terminated
Install the transmitter’s communication
jumper block in the “RS485 Terminated”
position if it
IS
at the end of the bus (see
8
7
3 Sig.Com.
2 B(+)
1 A(-)
D12 TB1
D12 TB1
8
7
3 Sig.Com.
2 B(+)
1 A(-)
D12 TB1
8 V+ (12-30 VDC)
7 Gnd
6 mA(-)
5 mA(+) (12-30 VDC)
4 Remote Reset
3 Signal Com.
2 RS232-Rx/RS485-B
1 RS232-Tx/RS485-A