Oldham OLCT 200 User Manual page 28

series with the output from HART modem board, preferably at the controller end of the
current loop. Adding the additional resistor at the controller allows the HART handheld
to be connected anywhere in the loop, because it must have the full 250 ohm load after
its connection point to function properly. If the additional resistor is added at the
transmitter, in TB1, the HART handheld will only be able to access variables locally, at
the transmitter. The example in 2-15 shows a 100 ohm resistor added to the output
loop since the controller has a 150 ohm terminating resistor installed from the factory.
Figure 2-13: 10-0351 HART Modem Option
Instructions for Accessing Process Variables with HART Handheld Device
The HART handheld can access process variables from anywhere in the 4-20 mA loop
as long as the handheld device is on the modem side of the 250 ohm load. Process
variables are accessed by attaching the leads to the signal (+) and common (-) wire.
Typically the process variables are accessed either at the transmitter or at the
controller.
At the transmitter end of the 4-20 mA loop unscrew the cover on the OLCRT 200
explosion-proof enclosure. Find the two HART connection points located next to TB1
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