When the pH system will not autocalibrate, the meter, pH electrode and pH buffers should be checked systematically. If your meter has a millivolt mode, measure the electrode millivolts in pH buffers. In order for ORION meters to recognize pH buffers for autocalibration, millivolt (mV) limits have been placed on each buffer:
1. The electrode millivolts in a pH 7 buffer should be 0+/-30 mV.
2. The electrode millivolts in a pH 4 buffer should be 140 to 210 mV.
3. The electrode millivolts in a pH 10 buffer should be -140 to -210 mV. If the millivolt values are outside of the above ranges, clean the pH
4. electrode. If cleaning does not return the mV to an acceptable range, either manually calibrate or replace the electrode. Note: As long as the pH electrode has a slope between 92% and 102%, the electrode should be working properly. The pH buffers should be replaced if the measured millivolts are outside of the acceptable ranges. Contaminated buffers may slightly contribute to shifted millivolt values.
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