1.5 Field Communicator connections
In order for the Field Communicator to interface with the THUM
Adapter, the wired device must be powered.
The Field Communicator must be put into poll mode and should use
the THUM Adapter address of 63.
1.6 Power supply
• Minimum loop load of 250 Ohms.
• The THUM Adapter communicates via and derives power from a
standard 4–20 mA/HART
®
loop. The THUM Adapter causes a small
voltage drop on the loop which is linear from 2.25 V at 3.5 mA
to 1.2 V at 25 mA. Under fault conditions, the maximum voltage
drop is 2.5 V. The THUM Adapter will not affect the 4–20 mA signal
under normal or fault conditions as long as the loop has at least
a 2.5 V margin at the maximum loop current (25 mA for a typical
4–20 mA/HART device).
• Limit the power supply to 0.5 Amps maximum and voltage to 30
Vdc.
Loop current
THUM Adapter voltage drop
3.5 mA 2.25 V
25 mA 1.2 V
1.7 Load resistor
If required, add a load resistor as shown in Figure 6-8, Figure 6-11
and Figure 6-12. The resistor should be adequately rated for the
application (1 W minimum) and be compatible with the supplied
splice connector which accepts wire sizes from 14 to 22 AWG.
1.8
Loop
To ensure proper operation, the THUM Adapter should not be
installed on a HART
®
loop with other active HART masters. HART
masters that are active periodically, such as a field communicator can
be used on a loop with a THUM Adapter.
Quick Start Guide May2024
6 www.emerson.com
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