Emerson AMS Trex Device Communicator User Manual page 134

Loop Diagnostics application
September 2021
134
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Figure 4-4: Power a HART transmitter
The Trex unit measures both voltage and current from the HART + pwr terminals. An
internal 167 Ohm resistor is used when the Trex unit powers the device.
CAUTION
Do not insert a resistor in parallel with either the HART + pwr or HART terminals on the
Trex unit, or in parallel with the device's communication terminals. This will interfere with
the current measurements and may prevent communication.
Figure 4-5: Measure voltage on an externally-powered HART transmitter
A. Voltage source
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