Fluid Components Intl ST51A - HART Connections; Figure 19 - Single Connection and Multidrop HART Setups

INSTALLATION ST51A/ST75A/ST75AV Mass Flow Meters
22 Fluid Components International LLC
HART Connections
Connect the installation HART wiring to the appropriate J8 terminals depending on the application.
● Single Connection – The instrument supplies power to the loop and controls the current as well. For this application connect HART+
to J8-1 and HART- to J8-3.
● Network (Multidrop) Connection – The instrument receives loop power from the network, and controls the current. For this
application connect EXT_HART+ to J8-3 and EXT_HART- to J8-2.
The block diagram in Figure 19 below shows the single connection and multidrop HART setups. Use a 250 Ω 1%, ≥ 0.3 W resistor as shown in the
diagram below only if the external HART interface/wiring does not have this resistance built-in (HART requires a minimum loop resistance of 230 Ω).
See also Figure 17, page 19 and Table 3, page 21. If using a handheld HART communicator/calibrator connect it to the line as described
by the manufacturer’s instructions.
C
ABLING RECOMMENDATION
Use a shielded, twisted-pair instrument grade wire (min. 24 AWG for runs less than 5000 ft/1500 m; min. 20 AWG for longer distances). The RC
value of the wire (Total Resistance x Total Capacitance) must be less than 65 µs (not a concern for point-to-point topology with a run less than
328 ft/100 m). A cable designed for HART/RS-485 such as Belden 3105A is recommended for complex setups or particularly long runs or both.
Note:
The HART communications digital signals are superimposed on top of the channel #1 current loop (4-20 mA) output.
When HART communications is in use, the HART current loop channel #1 MUST be configured as FLOW to comply
with the HART protocol. The channel #1 current loop output is configured as FLOW by default at the factory.
Figure 19 – Single Connection and Multidrop HART Setups
C01208-1-1
ST51A/75A/75AV
HART
J8-1
J8-2
J8-3
ST51A/75A/75AV
HART
J8-1
J8-2
J8-3
ST51A/75A/75AV
HART
J8-1
J8-2
J8-3
ST51A/75A/75AV
HART
Network P.S.
24 VDC
HART
Master
J8-1
R
LOAD
HART
I/O
J8-2
J8-3
ST51A/75A/75AV
HART
HART Master
+
HART
I/O
–
J8-1
J8-3
4-20 In
HART+HART–
(a) HART Single Connection
(b) HART Network, Multidrop