2.
Removing diaphragm blockages:
Blocked reference system for reference electrode diaphragms can be mechanically
cleaned (does not apply to IsFET pH sensor, teflon diaphragms or open ring electro-
des):
•
Use a small key file.
•
Only file in one direction.
3.
Check for air bubbles in the glass electrode:
air bubbles indicate incorrect installation. Therefore check the installation position:
•
Permitted: 15° to 165° to the horizontal.
•
Not permitted: horizontal installation or installation with the plug-in head pointing
downwards.
4.
Check for reference system reduction:
The inner metal lead of the reference system (Ag/AgCl) of a combination electrode or a
separate reference electrode is usually light-brown and matt. A silver-coloured refe-
rence system is reduced and therefore defective. The cause is a current flowing through
the reference element.
Possible causes:
•
Incorrect operating mode of the measuring instrument (PM pin connected, but still
unsymmetrical operating mode ("without PML") selected. See functional description,
Field A6 on p. 32.
•
Shunt in measuring cable (e. g. through humidity) between reference line and groun-
ded screen or PM line.
•
Measuring instrument defective (shunt in reference input or entire input amplifier
downstream of PE).
Preliminary redox calibration work
A soiled or coated redox electrode can be cleaned mechanically:
•
Carefully use mechanical means to clean metal pins or surfaces which have deposits
on them, e.g. with fine abrasive sheets or a glass fibre brush.
•
Do not clean redox measuring surfaces chemically. After chemical cleaning, e.g. with
acid, a redox electrode requires a long period before it reaches a stable operating
point again.
Execution of calibration
The different types of calibration and their execution are described from page 82.
