Measure Voltage On An Externally-Powered Loop; Measure The Control System Output - Emerson AMS Trex User Manual

•
•
4.11.1

Measure voltage on an externally-powered loop

You can use the HART terminals on the Trex unit to measure the voltage on an externally-
powered device/loop.
Note
Use the HART + pwr terminals if you want the Trex unit to power the device and measure voltage.
See Section
CAUTION!
Do not connect lead sets to the HART and HART + pwr terminals at the same time.
Procedure
1.
2.
4.11.2

Measure the control system output

Measure loop current to ensure a device or distributed control system is sending the
correct value. You can measure loop current from 0 to 25 mA on a 4-20 mA current loop.
Note
Measurements are for reference purposes only. Do not make critical process-control decisions based
on these measurements.
WARNING!
Do not connect the mA terminals on the Trex unit to a power supply that is not current limited
to 250 mA. This can blow a fuse inside the Trex unit. The repair/replacement will need to be
completed at an authorized service center.
WARNING!
Do not connect the mA terminals (ammeter) in parallel with a powered 4-20 mA current loop.
Ammeters have low resistance. This can disrupt the loop and cause devices to report incorrect
values or positioners to move unexpectedly.
Procedure
1.
User Guide
Simplify the problem by removing one or more components from the HART loop.
Attempt tasks from the "Checks after installation" section.
Isolate the device and perform tasks from "Checks before installation."
4.6.
Connect the lead set to the HART terminals on the Trex unit and to the externally-
powered device.
View the Measured Voltage section on the Loop Diagnostics screen.
Connect the lead set to the mA terminals on the Trex unit and to a connection point
on the loop.
Loop Diagnostics application
145