c. Connect a jumper wire between TB-3 (RTD RTN) and TB-4 (RTD-SNS). Connect a
second jumper wire between TB-7 (REF IN) and TB-8 (SOL GND).
d. Place the sensor back in the process liquid. If diagnostic measures such as
GLASSFAIL or REF WArn appear, turn off the sensor diagnostics.
• If the symptoms disappear, interference was coming into the transmitter
along one of the sensor wires. The measurement system can be operated
permanently with simplified wiring.
• If symptoms still persist, go to Step 4.
4. Check for extra ground connections or reduced noise.
a. The electrode system is connected to earth ground through the process. If other
ground connections exist, there are multiple paths and ground loops are present.
Noise enters the measurement either by a direct connection, usually between
the cable and grounded metal, or by an indirect connection, usually EMI/RFI
picked up by the cable.
b. If the sensor cable is run inside conduit, there may be a short between the cable
and the conduit. Re-run the cable outside the conduit. If symptoms disappear,
then a short exists between the table and the conduit. Likely a shield is exposed
and is touching the conduit. Repair the cable and reinstall it in the conduit.
c. To avoid induced noise in the sensor cable, run it as far away as possible from
power cables, relays, and electric motors. Keep sensor wiring out of crowded
panels and cable trays.
d. Occasionally, noise can travel into the transmitter housing from the metal it is
mounted on. The noise is then radiated into the transmitter electronics. If
isolating the transmitter from its metal mounting eliminates the symptoms,
move the transmitter to a different location or mount it with isolating materials.
e. If ground loop problems persist, consult the factory. A visit from an experienced
service technician may be required to solve plant-induced problems.
Temperature reading is inaccurate
1. To troubleshoot temperature problems, refer to tEMP HI and tEMP LO.
2. Calibrate the temperature response of the sensor.
3. If necessary, automatic temperature compensation can be temporarily disabled and
the transmitter placed in manual temperature compensation. For manual
temperature, choose a temperature equal to the average temperature of the
process. The resulting pH reading will be in error. The more variable the
temperature and the further from pH 7, the greater the error.
HART communications problems
1. If the 375 or 475 communicator software does not recognize the 5081 pH/ORP
transmitter, order an upgrade from Rosemount at 800 999 9307.
2. Be sure the HART load and voltage requirements are met.
a. HART communications requires a minimum 250 ohm load in the current loop.
b. Install a 250 - 500 ohm resistor in series with the current loop. Check the actual
resistor value with an ohmmeter.
Diagnostics and troubleshooting
72 Rosemount 5081
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