7 Maintenance
Mycom S CPM 153
90
Hauser
7.1.3
Calibration
Calibration is necessary:
•
after electrode replacement
•
after downtimes (Caution: a pH glass electrode may not be stored in a dry environ-
ment.)
•
At reasonable intervals, dependent on the process. The required interval can range
between several times a day to once every three months. At the start, calibrate more
often, and keep the results in the operations logbook. The data of the last 30 calibra-
tions are also saved in the calibration logbook. Slowly extend the intervals depending
on the deviations which occur during calibration.
Preliminary pH calibration work
1.
Remove dirt and deposits:
The selection of cleaning agent depends on the type of fouling. The most frequent
fouling and the associated cleaning agents are listed in the table below:
!
Note!
•
Only clean redox electrodes mechanically. Chemical cleaning applies a potential to
the electrode that takes several hours to decay. This potential causes measuring
errors.
•
Do not clean IsFET sensors with compressed air.
Type of contamination
Cleaning agent
"
Caution!
Danger of sensor destruction. No acetone may be used to clean an IsFET pH sensor (CPS 401), otherwise
the material may be damaged.
Greases and oils
Substances containing tensides (alkaline) or water-
soluble organic solvents (e.g. alcohol)
#
Warning!
Danger of caustic burns! Protect your hands, eyes and clothing when you use the following detergents.
Calciferous deposits, metal hydroxide deposits,
heavy biological deposits
3% HCl
or with ChemoClean:
HCl (10%) in injector thinned to approx. 3%
Sulphide deposits
Mixture of hydrochloric acid (3%) and
thiocarbamide (commercially available)
Protein deposits
Mixture of hydrochloric acid (0.1 molar) and
pepsin (commercially available)
Fibres, suspended substances
Water under pressure, poss. with surface-active
agents
Light biological deposits
Water under pressure
