4-3
Maintenance
HARDWARE
MAINTENANCE
The Model 3144 and 3244MV transmitters have no moving parts and
require a minimum amount of scheduled maintenance. Both
transmitters feature modular design for easy maintenance. If you
suspect a malfunction, check for an external cause before performing
the diagnostics as discussed later in this section. If you must return
failed transmitters or parts to a Rosemount Service Center for
inspection, repair, or replacement, refer to “Return of Materials” on
page 4-6 for more information.
Test Terminals
The test terminal, marked as TEST or T on the terminal block, and the
negative terminal accept MINIGRABBER™ or alligator clips, and
facilitate in-process checks (see Figure 2-3 on page 2-4). The test and
the negative terminals are connected across a diode through which the
loop signal current passes. The test equipment shunts the diode when
connected to the test terminals; so long as the voltage across the
receptacles is kept below the diode threshold voltage, no current passes
through the diode. To ensure that there is no leakage current through
the diode while making a test reading, or while an indicating meter is
connected, the resistance of the test connection or meter should not
exceed 10 ohms. A resistance value of 30 ohms will cause an error of
approximately 1.0 percent of reading.
Sensor Checkout
If the sensor is installed in a high-voltage environment and a fault
condition or installation error occurs, the sensor leads and transmitter
terminals could carry lethal voltages. Use extreme caution when
making contact with the leads and terminals.
To determine whether the sensor is at fault, either replace it with
another sensor or connect a test sensor locally at the transmitter to test
remote sensor wiring. Transmitters with Option Code C7 (Trim to
Special Sensor), are matched to a specific sensor. You may select any
standard, off-the-shelf sensor for use with the transmitter, or consult
the factory for a replacement special sensor/transmitter combination.
Low Output or
No Output
Sensor Element
• Connect a HART communicator and enter the
transmitter test mode to isolate a sensor failure.
• Check the process variable to see if it is out of
range.
Loop Wiring
• Check for adequate voltage to the transmitter. It
should be 12.0 to 42.4 V dc (over entire 3.90 to 20.5
mA operating range).
• Check for shorts and multiple grounds.
• Check for proper polarity at the signal terminal.
• Check the loop impedance.
• Connect a HART communicator and enter the loop
test mode.
• Check wire insulation to detect possible shorts to
ground.
Electronics Module
• Connect a HART communicator and check the
sensor limits to ensure calibration adjustments are
within the sensor range.
• Connect a HART communicator and enter the
transmitter test mode to isolate an electronics
module failure.
SYMPTON
POTENTIAL
SOURCE
CORRECTIVE ACTION
See “Safety Messages” on page 4-1 for complete warning information.
