Delta OHM HD2205.2, Manual

Page: 40 / 80

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pH
AND CONDUCTIVITY MEASUREMENTS
-
MOST FREQUENT PROBLEMS
,
POSSIBLE
CAUSES AND HANDLING
Instrument functioning
ƒ When selecting some functions the “Operation reserved to the administrator” message is
displayed on the screen.
Some functions are reserved to the user registered as "Administrator". The other users cannot exe-
cute them (see the details on page 21).
ƒ Clicking on the LOG key the “Logging is disabled!” message is displayed on the screen.
The logging interval was set to 0. To enable it, open the menu “ System Parameters >> Memory and
Logging Options >> Select log interval ”, and select a log interval different from zero.
pH measurement
The average life of a pH electrode is about one year according to the use and maintenance per-
formed.
The electrodes used at high temperatures or in highly alkaline environments have a shorter life.
It is recommended to condition the new electrodes for half day by immersing them, before use, into
a buffer at 6.86pH or 4pH.
Calibrate the electrode with solutions closer to the values being measured. A new electrode must
always be calibrated at neutral pH (6.86pH) first point, and at least a second point.
Generally, the pH electrodes have a body in glass: handle them with care to avoid breakage. In par-
ticular, the membrane (the sensitive element housed in the end part of the electrode) is made of very
thin glass.
Some of the most frequent problems and their possible solutions are reported below.
Wrong pH measurement . Carry out the following checks:
ƒ Check that the diaphragm is not obstructed and possibly clean it using the HD62PT solution.
ƒ
Check that the reference system is not contaminated. In case of a filling type electrode, re-
place the electrolyte with the suitable solution.
ƒ Check that no air bubbles are present in the electrode tip and that it is sufficiently immersed.
Dirt residuals deposited on the membrane can alter the measurement: use the HD62PP solution for
protein cleaning.
Slow response or wrong measurements . Possible causes are aging or erosion of the membrane or
a connector short circuiting.
Storage. Keep the electrode immersed in the HD62SC solution.