- If the glass impedance is less than about 20 megohms, the glass has cracked
and the electrode must be replaced.
- If the glass impedance is greater than about 20 megohms, the sensor is
probably in good condition. Go to Step 5.
5. Check transmitter performance by simulating pH inputs. See Section 8.1.7.
• If the transmitter performs satisfactorily, go to Step 6.
• If the transmitter does not respond to stimulated inputs, replace the board stack.
6. If the transmitter responds to simulated inputs, the problem must lie with the
sensor or the interconnecting wiring. Verify the interconnecting wiring point to
point. Fix or replace bad cable. If the cable is good, replace the pH sensor.
SLOPE Err HI
SLOPE Err HI means that a two-point buffer calibration attempt has failed. The slope is too
high (> 62 mV/pH) for a good measurement.
Troubleshooting SLOPE Er HI
1. Repeat the calibration.
a. Inaccurate buffers can cause a low slope. Repeat the calibration using fresh
buffers. Alkaline buffers, pH 10 or greater, are particularly susceptible to
changing value in air or with age. If a high pH buffer was used in the failed
calibration, try a lower pH buffer when repeating the calibration. For example,
use pH4 and 7 buffer instead of pH 7 and 10 buffer.
b. Allow adequate time for readings in buffer to become constant. If the sensor was
in a process substantially colder or hotter than the buffer, allow at least 20
minutes for readings in the buffer to stabilize. Alternatively, place the sensor in a
container of water at ambient temperature for 20 minutes before starting the
calibration.
c. Be sure the correct buffer values are being entered during calibration. To
minimize errors caused by entering the wrong buffer values, use the
autocalibration procedure.
d. Verify that the temperature reading is accurate. Compare the sensor reading
against a thermometer known to be accurate. Recalibrate if necessary.
• if the second calibration was successful, an error was made during the first
attempt.
• If the second calibration fails, go to Step 2.
2. There is a remote possibility of a problem with the autocalibration program. Repeat
the calibration using the manual calibration procedure.
• If manual calibration was successful when autocalibration failed, the problem
might be with the sensor electronics. Call the factory for assistance.
• If manual calibration is not possible, go to Step 3.
3. Check the transmitter performance by simulating pH inputs. See Section 8.1.7.
• If the transmitter performs satisfactorily, go to Step 4.
• If the transmitter does not respond to stimulated inputs, replace the board stack.
Diagnostics and troubleshooting
66 Rosemount 5081
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