I am getting an Err-3 on my pH instrument. What does it mean?

The Error 3 is related to the slope value on a pH loop, indicating that the slope value is outside of the allowable range. The Slope (SL), also referred to as the efficiency of the electrode, is an indication of the condition of the pH electrode. The slope is displayed in a percentage (%) value, with 100% SL being ideal.  When the electrode is new, the slope should be in the upper 90% range.  As the electrode ages and loses efficiency, the slope and response of the electrode will start to decrease.  The slope value is updated each time a two-point calibration is performed and usually only small changes in the slope value should be noticed. The allowable range for slope is 70% - 110% of theoretical.

The possible causes for an Error 3 are as follows:

  1. Coated or dirty Measuring Electrode
  2. Measuring Electrode (Glass) is too old and slow to respond.
  3. Measuring Electrode (Glass) is 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 Measuring Electrode
  3. Check wiring connections and replace Electrode Cable if needed.
  4. Clean Solution Ground Post, check wiring and replace if faulty.

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

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