Emerson Rosemount 644, Reference Manual

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78
Reference Manual
00809-0200-4728, Rev RA
Section 6: Troubleshooting
April 2015
Troubleshooting
6.3 Troubleshooting the 4-20 mA/HART output
Table 6-1. Rosemount 644 Troubleshooting Table for 4-20 mA Output
Symptom or
issue Potential
source
Corrective action
Transmitter
Does Not
Communicate
with Field
Communicator
Loop
Wiring

Check the revision level of the transmitter device descriptors (DDs) stored in
your communicator. The communicator should report Dev v4, DD v1
(improved), or reference “Field Communicator” on page 3-2 for previous
versions. Contact Emerson Process Management Customer Central for
assistance.

Check for a minimum of 250 ohms resistance between the power supply and
Field Communicator connection.

Check for adequate voltage to the transmitter. If a Field Communicator is
connected and 250 ohms resistance is properly in the loop, then the
transmitter requires a minimum of 12.0 V at the terminals to operate (over
entire 3.5 to 23.0 mA operating range), and 12.5 V minimum to communicate
digitally.

Check for intermittent shorts, open circuits, and multiple grounds.
High Output
Sensor
Input
Failure or
Connection

Connect a Field Communicator and enter the transmitter test mode to check
for a sensor failure.

Check for a sensor open or short circuit.

Check the process variable to see if it is out of range.
Loop
Wiring

Check for dirty or defective terminals, interconnecting pins, or receptacles.
Power
Supply

Check the output voltage of the power supply at the transmitter terminals. It
should be 12.0 to 42.4 Vdc (over entire 3.75 to 23 mA operating range).
Electronics

Connect a Field Communicator and enter the transmitter status mode to
isolate module failure.

Connect a Field Communicator and check the sensor limits to ensure
calibration adjustments are within the sensor range.
Erratic Output
Loop
Wiring

Check for adequate voltage to the transmitter. It should be 12.0 to 42.4 Vdc at
the transmitter terminals (over entire 3.75 to 23 mA operating range).

Check for intermittent shorts, open circuits, and multiple grounds.

Connect a Field Communicator and enter the Loop test mode to generate
signals of 4 mA, 20 mA, and user-selected values.
Electronics

Connect a Field Communicator and enter the transmitter test mode to isolate
module failure.