Power Supply; Load Resistor; Bench Top Configuration - Emerson Smart Wireless THUM Adapter Quick Installation Manual

Smart Wireless THUM Adapter

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
3.5 mA
25 mA

Load Resistor

If required, add a load resistor as shown in Figure 8, 12, and 16. 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.
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.
B C
ENCH TOP
When performing bench top configuration it is suggested that you connect the THUM
Adapter to a wired device. If this is not possible, the following wiring diagrams can be used.
For bench top configuration, ensure that the power supply that you are using is limited to 0.5
Amps maximum.
Figure 2. THUM Adapter Only, Powered by a Current Source (Such as a Fluke 744)
THUM Adapter
4
THUM Adapter voltage drop
2.25 V
1.2 V
ONFIGURATION
Green
Red
Black
White
Yellow
Quick Installation Guide
00825-0100-4075, Rev DA
Ground
250 Ohm Resistor not
required, but may be
used to verify current
HART
Modem
July 2011
®
+
20 mA
Current
Source
-