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MODEL 3081 pH/ORP SECTION 12.0
TROUBLESHOOTING
4. 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.
5. If ground loop problems persist, consult the factory. A visit from an experienced service technician may be
required to solve plant-induced problems.
12.5.9 Temperature Reading Is Inaccurate
A. To troubleshoot temperature problems, refer to Section 12.4.6.
B. To calibrate the temperature response of the sensor, refer to Section 7.4.
C. If necessary, automatic temperature compensation can be temporarily disabled and the transmitter placed in manual
temperature compensation. Refer to Section 8.5. 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.
12.5.10 HART Communications Problems
A. If the Model 275 Communicator software does not recognize the Model 3081pH/ORP transmitter, order an upgrade
from Rosemount Measurement at (800) 999-9307.
B. Be sure the HART load and voltage requirements are met.
1. HART communications requires a minimum 250 ohm load in the current loop.
2. Install a 250-500 ohm resistor in series with the current loop. Check the actual resistor value with an ohmmeter.
3. For HART communications, the power supply voltage must be at least 18 Vdc. See Section 2.5.
C. Be sure the HART Communicator is properly connected.
1. The Communicator leads must be connected across the load.
2. The Communicator can be connected across the power terminals (TB-15 and TB-16).
D. Verify that the Model 275 is working correctly by testing it on another HART Smart device.
1. If the Communicator is working, the transmitter electronics may have failed. Call Rosemount Analytical for
assistance.
2. If the Communicator seems to be malfunctioning, call Rosemount Measurement at (800) 999-9307 for assistance.
12.5.11 No Display
A. Be sure power requirements are being met.
1. The positive voltage lead must be connected to TB-16.
2. Check dc voltage requirements and load restrictions. Refer to Section 2.5.
B. Check for bad connections between the circuit boards. Refer to Section 2.2. Be sure the ribbon cable between the
display and CPU boards is firmly seated in the socket on the CPU board. Be sure the socket connection between the
CPU and analog boards is firm.
C. If power is correct and connections are good, check the 4-20 mA output signal
If the signal is correct and only the display is not working, replace the display board (PN 23652-01).
If there is no response to pH changes, replace the electronic board stack (PN 23574-02).
12.5.12 Display Segments Missing
Replace the display board (PN 23652-01).