I am seeing an Err-2 on my pH instrument. What does it mean?

An Error 2 means that the calculated asymmetry potential is outside the acceptable range. The Asymmetry Potential (AS), also referred to as the millivolt offset, is an indication of the condition of the reference electrode. Theoretically when the electrodes are placed in a pH 7 buffer, the millivolt output from the electrode pair (pH and reference) should be zero. Some of the causes of the millivolt offset are depletion of the Potassium Chloride (KCl) from the reference electrolyte or the reference electrolyte becomes poisoned with the process solution. When the millivolt offset is +/- 30mV, it is advisable to replace the reference electrode. The correction limits of the EXA pH analyzers are +/-120mV. Outside this range an E2 error message will appear on the second line display.

Possible Causes of Error:

1. Bad Buffer 7 (zero buffer).
2. Reference Electrode is too old and out of acceptable limits.
3. Reference Electrode is poisoned or damaged.
4. Bad wiring or Electrode Cable is faulty (bad isolation).
5. Solution Ground Electrode (Post) is coated, dirty or connection is faulty.

Suggested Remedies:

1. Clean pH electrodes in 5 - 10% HCl solution or Muratic Acid.
2. Replace Reference Electrode.
3. Check wiring connections and replace Electrode Cable if needed.
4. Clean Solution Ground, check wiring connection and replace if faulty.

For further assistance, please contact Yokogawa's technical support center at support@us.yokogawa.com or 1-800-524-7378.