• If the message remains, go to Step 4.
4. Confirm that the problem is with the remote preamplifier. Wire the pH sensor
directly to the transmitter. Change the menu from PAMP=SnSr to trAnS for the test
and return it to SnSr afterwards.
• If the error message clears, the remote preamplifier is faulty. Replace the
preamplifier.
• If the error message remians, the sensor has failed. Replace the sensor.
SLOPE Err LO
SLOPE Err LO means that a two-point buffer calibration attempt has failed. The slope is too
low (<40 mV/pH) for a good measurement.
Troubleshooting SLOPE Err LO
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 pH 4 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 temperatures for 20 minutes before starting the
calibration.
c. Be sure the correct buffer values are being entered during calibration.
• If the second calibration was successful, an error was made during the first
attempt.
• If the second calibration fails, go to Step 2.
2. Check wiring. Connections to TB-10, TB-7, and TB-8 are particularly important.
Recalibrate the sensor.
• if the wiring was the only problem, the sensor should calibrate.
• If the message persists, go to Step 3.
3. Inspect and clean the senor. Recalibrate the sensor.
• If the sensor was dirty, it should calibrate after cleaning.
• If the message persists, go to Step 4.
4. Check for a faulty sensor.
• If a spare sensor is available, connect it to the transmitter. Use the auto
calibration procedure to calibrate the sensor.
- If the new sensor cannot be calibrated, the transmitter is faulty. Go to Step 5.
- If the new sensor can be calibrated, the old sensor has failed.
• If a spare sensor is not available, measure the glass impendance (GIMP). See
Section 8.1.7.
Diagnostics and troubleshooting
Instruction Manual 65
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