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.
1.5
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 55 Vdc.
Loop current
THUM Adapter voltage drop
3.5 mA
2.25 V
25 mA
1.2 V
1.6
Load resistor
If required, add a load resistor as shown in Figure 8 on page 10, Figure 12 on
page 13, and Figure 16 on page 15. 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.
1.7
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
September 2020
6
Emerson.com/Rosemount
Summary of Contents for THUM
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