KROHNE OPTISENS PH 8590 - Manual (Page 35)

SERVICE
5
35
OPTISENS PH 8590
www.krohne.com 03/2012 - 4001931401 MA OPTISENS PH 8590 R01 en
Service
5.1 Maintenance
5.1.1 Cleaning
• Slight dirt residues or dust: Rinse the sensor tip with tap water and clean it with a soft tissue.
• Oily and greasy coatings: Remove with a warm soap solution and rinse with water.
• Hardness deposits or metal hydroxide deposits: Remove with 10% citric acid or hypochloric
acid and rinse with water.
5.1.2 Aging and re-calibration
During operation, but already during storage, pH electrodes age due to poisoning effects of the
inner buffer system. Therefore it is important to re-calibrate the electrode in regular intervals as
described on page 29.
When the electrode becomes too old to provide reliable measurements, the signal converter
displays an error message after the calibration procedure. In this case, the electrode has to be
exchanged.
Aging effects pH electrodes: Aging effects pH electrodes: Aging effects pH electrodes: Aging effects pH electrodes:
• Decrease of slope Decrease of slope Decrease of slope Decrease of slope due to abrasion, drying, corrosion of glass bulb coating and leaching: The
slope should be > 50 mV/pH. An optimal value is 59 mV/pH at 25°C / 77°F. When the slope
drops below 50 mV/pH, an error message is displayed and the electrode has to be exchanged.
The slope of the electrode is displayed after each calibration procedure.
• Shift of zero point Shift of zero point Shift of zero point Shift of zero point due to leaching / contamination of reference half cell or increased
resistance between glass bulb and reference half cell: The zero point should lie between
-58...+58 mV at pH 7. An optimal value is 0 mV at pH 7.
The zero point of the electrode is displayed after each calibration procedure.
.book Page 35 Monday, March 19, 2012 2:01 PM