Emerson Rosemount Smart Wireless THUM, Reference Manual, Page: 21 / 60

Reference Manual
00809-0100-4075, Rev BA
October 2010
3-3
Smart Wireless THUM Adapter
Remote Mount
1. Install the HART device according to standard installation practices,
being sure to use an approved thread sealant on all connections.
2. The THUM Adapter should be mounted as shown in Figure 3-2 on
page 3-2.
3. Connect the THUM Adapter to the wired device using standard
practices. Wire running from the THUM Adapter to the wired device
must be shielded or in conduit.
4. Ground the Remote Mount Kit per local practices.
5. Connect the THUM Adapter to the HART wired device using the
wiring diagrams below. See Figure 3-19 through 3-26 on the following
pages.
6. Close the housing cover on the HART wired device, so that metal
touches metal, but do not over tighten to prevent damaging the unit.
NOTE
Two splice connectors are included with the THUM Adapter. The first is a two
connection splice. The second is a three connection splice for use with a
resistor, if there is not enough resistance in the loop. Both of these splice
connectors can accept 14 to 22 gauge wire. See wired device reference
manual for information on the required loop resistance.
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.
Loop Current THUM Adapter voltage drop
3.5 mA
25 mA 2.25 V
1.2 V