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MODEL 3081 pH/ORP SECTION 12.0
TROUBLESHOOTING
12.4.10 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 Flowchart-SLOPE Err HI
A. Repeat the calibration.
1. 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 pH 4 and 7 buffer instead of pH
7 and 10 buffer.
2. 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.
3. Be sure the correct buffer values are being entered during calibration. To minimize errors caused by entering the
wrong buffer values, use auto calibration procedure described in Section 7.5.
4. Verify that the temperature reading is accurate. Compare the sensor reading against a thermometer known to be
accurate. Recalibrate if necessary. See the procedure in Section 7.4.
If the second calibration was successful, an error was made during the first attempt.
If the second calibration fails, go to step B.
B. There is a remote possibility of a problem with the autocalibration program. Repeat the calibration using the manual
calibration procedure in Section 7.6
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 C.
C. Check transmitter performance by simulating pH inputs. See Section 12.8.
If the transmitter performs satisfactorily, go to step D.
If the transmitter does not respond to simulated inputs, replace the board stack (PN 23574-02).
D. 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 cable is good, replace the pH sensor.
12.4.11 Std Err
Std Err means the reference electrode voltage has changed drastically. Typical causes are exposure to poisoning agents,
sulfides or cyanides, or prolonged exposure to high temperature.
Troubleshooting Flowchart-Std Err
Troubleshooting depends on the type of sensor.
If the sensor is rebuildable...
Replenish the electrolyte solution and replace the liquid junction. Calibrate the sensor.
If the sensor can be calibrated, the problem has been corrected.
If the sensor cannot be calibrated, replace the sensor. If the sensor has separate measuring and reference
electrodes, replace only the reference electrode.