IM-P736-02 EMM Issue 3
43
VLM30 In-Line Vortex Flowmeter
Fig. 27 HART communication (example)
1 Internal ground terminal
2 Power supply, current output/HART
Output
3 Load resistance
4 Power supply/Supply isolator
5 PLC/DCS
6 Generic handheld HART communicator
7 External indicator
8 External ground terminal
9 Terminal for external terminal
3.18.8 HART
®
communication connection example
For connecting the signal voltage/supply voltage, twisted cables with a conductor cross-section of 18 to 22
AWG/0.8 to 0.35 mm
2
and a maximum length of 1500 m (4921 ft) must be used. For longer leads a greater
cable cross Section is required. For shielded cables the cable shielding must only be placed on one side
(not on both sides). For the earthing on the transmitter, the inner terminal with the corresponding marking
can also be used.
The output signal (4 to 20 mA) and the power supply are conducted via the same conductor pair.
The transmitter works with a supply voltage between 12 and 42 Vdc.
Note: Any configuration changes are saved in sensor memory only if no HART communication is taking
place. To securely save any changes, make sure that HART communication has ended before the device is
disconnected from power. The possible lead length depends on the total capacity and the total resistance
and can be estimated based on the following formula.
L =
65 x 106
-
Ci + 1000
R x C C
L Lead length is meters
R Total resistance in Ω
C Lead capacity
Ci Maximum internal capacity in pF of the HART
field devices in the circuit
Avoid installing the cable together with other
power leads (with inductive load, etc.), as well as
the vicinity to large electrical installations. The
HART Handheld terminal can be connected to
any connection point in the circuit if a resistance
of at least 250 Ω is present in the circuit. If there
is resistance of less than 250 Ω, an additional
resistor must be provided to enable communication.
The handheld terminal is connected between the
resistor and transmitter, not between the resistor
and the power supply.
1
2
3
4
5
9 8
7
6
To Next Page
