Installation manual

5
Reference Manual
00809-0100-4075, Rev CA
Section 1: Introduction
March 2014
Introduction
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.
Power supply
Minimum loop load of 250 Ohms.
The THUM Adapter communicates 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.
Load resistor
If required, add a load resistor as shown in Figure 3-20, Figure 3-22, and Figure 3-24. The resistor
should be adequately rated for the application (1W minimum) and be compatible with the
supplied splice connector which accepts wire sizes from 14 to 22 AWG.
When adding a load resistor, ensure that uninsulated conductors do not contact the enclosure
and/or other exposed metal parts.
Loop current THUM Adapter voltage drop
3.5 mA 2.25 V
25 mA 1.2 V