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WARNING: The membrane should be stretched and pressed firmly
against the sensor platinum cathode. The membrane SHALL NEVER separate
from the cathode!
After a certain period of service, the sensor may have the volume of electro-
lyte reducing due to leakage through pinholes or ruptures in the membrane, which
necessitates electrolyte replacement.
Remove the membrane assembly from bushing 6, drain the remaining elec-
trolyte and wash the assembly with distilled water. Fill the membrane assembly
with new electrolyte.
Electrolyte composition: KCl, chemically pure – 14 g; KOH, chemically pure –
0,2 g; versene – 0,15 g; distilled water – up to 0,1 dm
3
. Filter the solution.
2.6.4 Replacement of the membrane assembly and teflon film
2.6.4.1 Replacement of the membrane assembly may be necessary in case
of mechanical damage (cracks, ruptures) or overstretching of the membrane. A
faulty membrane manifests itself in analyzer reading instability, high analyzer read-
ings in the null solution and longer time of response during DOC measurement.
Unscrew and remove the protective bushing from the sensor as per Fig.2.3.
Remove the membrane assembly form the inner case and drain the electrolyte.
Check the teflon film for damage.
The film should be firmly pressed against the cathode, in a wrinkle-free man-
ner. Damaged film should be replaced.
Once the teflon film is removed, check the sensor electrode to see if they
look as follows:
platinum cathode 1 (Fig.1.1b) sealed in a glass tube should be clean;
silver anode 2, coiled over the tube should be gray.
If necessary, clean the electrodes with a wad of alcohol-soaked cotton.
WARNING: NEVER use any abrasive for cleaning electrodes!
2.6.4.2 Damaged teflon film should be replaced with new one from spare
parts kit. To do this, place it on the cathode, press the film edges firmly against the
side surface of the glass tube and, holding the edges by hand, wind around 5-6
laps of caprone thread making 2-3 knots. Cut off with scissors surpluses of teflon
film not closer than 3-5 mm from caprone.
WARNING: NO rupture or hole in teflon film in the platinum cathode ar-
ea are permissible!
