D12
EX-IR
Gas Transmitter with IR Smart Sensor
Dec 2019 ( 85-0004 Rev A)
25
HART Multidrop 3-Wire Connections
The HART multi-drop connection permits up to 15 transmitters to communicate digitally on the same
bus, but without 4-20mA signaling. Setting the transmitter’s polling address from 1 to 15 fixes the
current loop output at 4mA. According to HART specifications, the current loop must be terminated with
a load resistor between 230 and 1100 ohms; however, transmitter specifications restrict the maximum
analog output resistance to a lower value (see Specifications). The position of communication jumper has
(Figure 9 on page 18) has no effect on HART communication. 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.
Figure 16. Example HART Multidrop 3-Wire
3-Wire Transmitter
4mA
HART SCADA/DCS
250 Ohms
+
-
HART FSK
Modem
Optional
Barrier/Isolator
for Hazardous
Locations
Loop Supply
24 VDC
D12 TB1
8
7
6
5
(12v Min.)
(12v Min.)
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
3-Wire Transmitter
4mA
D12 TB1
8
7
6
5
(12v Min.)
(12v Min.)
3-Wire Transmitter
4mA
D12 TB1
8
7
6
5
(12v Min.)
(12v Min.)