ELECTRODE CONDITION & MAINTENANCE
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8. ELECTRODE CONDITION & MAINTENANCE
Electrode Condition (MW151 only)
The
MW151
displays a probe icon (unless the feature is disabled from setup) which
indicates the electrode status after calibration. The assessment of the electrode's
status remains active for 12 hours and is based on the pH electrode offset and slope
characteristics at the time of calibration.
If electrodes are not cleaned after use they will lose their accuracy and the measurement
precision of the bench meter decreases. This can be observed as a steady decrease in
the slope of the electrode.
The slope (%) indicates the sensitivity of the glass membrane, the offset value (mV) indicates
the age of electrode and provides an estimation when the electrode needs to be changed.
Milwaukee Instruments recommends that the offset does not exceed ±30 mV and that the
slope percentage is between 85-105%.
When the slope value drops below 50 mV per decade (85 % slope efficiency) or the offset
at the zero point exceeds ± 30 mV, reconditioning may return the electrode to the level of
expected performance, but a change of electrode may be necessary to ensure accurate
pH measurements.
An electrode is characterized by both its zero point and its slope and it is advisable to do a
minimum of a two point calibration for reliable measurements and better precision. Also,
the electrode condition is evaluated only if the current calibration has a minimum of two
points. Its performance is expected to slowly decrease over time.
5 bars: excellent condition
4 bars: very good condition
3 bars: good condition
2 bars: fair condition
1 bar: poor condition
1 bar blinking: very poor condition
With 1 bar it is recommended to clean the electrode and recalibrate. If after recalibrating
there is still only 1 bar or 1 bar blinking, replace the probe.
0 bar indicates that the instrument has not been calibrated on the current day or a one
point calibration has been performed with previous calibration not yet deleted.
This information can also be viewed in the GLP data.
