Metrohm 900 Touch Control Manual - Manual (Page 420)

29.11 Electrode test for pH electrodes (ELT)
￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭
404 ￭￭￭￭￭￭￭￭
900 Touch Control
Rating
Excellent electrode Good electrode Usable electrode
Max. slope 101.0 % 102.0 % 103.0 %
Response time 60 s 75 s 90 s
Lower limit Uoff –20 mV
Upper limit Uoff 20 mV
Electrode type "Non-aqueous"
Streaming potential 3.0 mV 4.5 mV 6.0 mV
Drift 5.0 mV/s 7.0 mV/s 9.0 mV/s
Min. slope 88.0 % 80.0 % 70.0 %
Max. slope 120.0 % 130.0 % 140.0 %
Response time 60 s 75 s 90 s
Lower limit Uoff –50 mV
Upper limit Uoff 100 mV
Table 16 Possible errors during the electrode test
Test criterion Message Remedy
Buffer pH 9:
The drift in stirred solution is > 1 mV.
General problem ￭ Connect an electrode.
￭ Replace the defective electrode
cable.
￭ Clean the diaphragm (see leaflet
for the electrode).
￭ Replace the electrode.
Buffer pH 9:
–10 mV < U(not stirred) < 10 mV
and
The sum of the drift values after 1, 2,
3 and 4 min is < 12 mV/min.
Short circuit Replace the electrode.
A response time does not fulfill the
limit value for the rating Usable
electrode. Glass membrane / Diaphragm Clean the diaphragm (see leaflet for
the electrode).
The pH values are not defined for all
the buffers at the temperature mea-
sured. No buffer data Repeat the electrode test at a tem-
perature at which the pH values of
all the buffers are defined.
All the slopes fulfill the limit values
for the rating Usable electrode.
and
Uoff is outside the preset limits.
Unsuitable reference electrode ￭ Repeat the electrode test with a
suitable reference system.
￭ Replace the contaminated refer-
ence electrolyte.
￭ Select Electrode type = Cus-
tom and adjust the limits for
Uoff.