KROHNE SMARTSENS PH 8510 EN - Manual (Page 24)

5
SERVICE
24
SMARTSENS PH 8510
www.krohne.com 11/2013 - 4002544402 - MA SMARTSENS PH 8510 R02 en
Service
5.1 Maintenance
5.1.1 Cleaning
• Slight dirt residues or dust: Rinse the sensor tip with demineralised water and clean it with a
soft tissue.
• Oily and greasy coatings: Remove with a warm soap solution and rinse with demineralised
water.
• Hardness deposits or metal hydroxide deposits: Soak the sensor tip including diaphragm in
10% citric acid or hypochloric acid for a couple of minutes and rinse the complete glass shaft
of the sensor with demineralised water.
• Biological fouling: Soak the sensor tip including diaphragm in 10 % pepsin solution for
minimum 3 hours and afterwards rinse the complete glass shaft of sensor with demineralised
water.
5.1.2 Aging and re-calibration
During operation, but already during storage, pH sensors age due to poisoning effects of the
inner buffer system. Therefore it is important to re-calibrate the sensor in regular intervals.
Consider status messages and diagnostic information.
When the sensor becomes too old to provide reliable measurements, an error message (see on
page 17) appears after the calibration procedure. In this case, the sensor has to be replaced.
Aging effects of sensor: Aging effects of sensor: Aging effects of sensor: Aging effects of sensor:
• Decrease of slope Decrease of slope Decrease of slope Decrease of slope due to abrasion, drying, corrosion of glass tip 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 rises above -50 mV/pH, an error message is displayed and the sensor has to be
replaced.
The slope of the sensor is displayed after each calibration procedure.
• Shift of zero point Shift of zero point Shift of zero point Shift of zero point due to strong temperature changes, leaching and contamination of
reference half cell or increased resistance between glass tip 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 sensor is displayed after each calibration procedure.
INFORMATION!
Recalibrate the sensor after each cleaning procedure
.book Page 24 Monday, November 18, 2013 2:46 PM