What to do when you receive a pH slope error message on the analyzer.
Typical Result:
- Common- Sensor needs to be cleaned and recalibrated, see How to Clean and Calibrate your Zirkon® pH Sensor
- Less Common- Sensor is old, replace sensor
pH slope error
Cause: After calibration, the slope was not within 50…65mV/pH
Suggested remedies: Check buffers, check temperature, check sensor cable, repeat calibration, change sensor
The slope depends on temperature – at low temperatures it is smaller than at high temperatures. Therefore, an improperly set temperature compensation or a defective temperature sensor will lead to a slope error. A low slope can also be the result of contact problems, or more accurately if the insulation is not high enough.
Note: A slope error might also occur if your buffer solutions were not the same temperature as the temperature probe in the Argon Stabiflow® apparatus. To avoid this, place your buffer solutions in a beaker containing water from your process for about 10 minutes to allow them to reach the same temperature as the temperature probe on the Argon Stabiflow®. To check calibration settings go to:
Main menu > Cal > Cal pH.
Damaged cable insulation, or water inside the connector, or worse, inside the instrument, can cause signal loss and hardware damage.
Note: If the instrument issues a calibration error (zeropoint or slope), check the INFO menu in the calibration menu. It lists the results of the last calibrations with date and time and helps determine whether the current results are following a general trend or if the current results differ greatly from previous results, making a damage or some calibration error more likely.
If these causes can be ruled out, then the focus turns towards the sensor, especially towards the pH membrane which might be coated or worn out. Check it for discoloration and damages, and clean it if necessary. If cleaning or regeneration did not improve the results, you will have to exchange the sensor.