Calibration Of Ph Electrode - HACH LANGE si629 P Manuel D'utilisateur

4. Operation

4.6. Calibration of pH electrode

To measure pH correctly, the electrode and instrument set
needs to be calibrated regularly with buffer solutions.
The instrument is capable of one-, two- and three-point ca-
libration. The calibration parameters are stored in the me-
mory until a new calibration is performed.
If an anomaly occurs during calibration an error message
will appear on-screen (see page 30).
One-point calibration
This form of calibration is acceptable when pH values
around that of the buffer used are being measured.
One-point calibration only corrects the asymmetry potential
of the electrode.
Two-point calibration
This is the most common type of calibration. We recommend
pH 7 for the first buffer, and pH 4 or 9 for the second,
depending on whether you will be working in the acid or
alkaline region.
In addition to asymmetry potential, calibration with two
buffers also compensates the electrode slope or sensitivity
loss.
Three-point calibration
This type of calibration is recommended when measurements
are made across the entire pH scale. It is also used when a
great deal of accuracy is required in a certain region. For
the first point pH 7 is recommended. For the second and
third points, two of the remaining values must be chosen (pH
2.00, 4.01, 9.21, 10.90, at 25˚C). Three-point calibration
compensates the asymmetry of the electrode and its sensiti-
vity in acid and alkaline regions.
Notes: During calibration the instrument is in Hold state:
• Limit and cleaning contact relays are opened. (Alarm OFF).
• Current output is frozen at the value programmed in Hold.
To quit the Hold state it is necessary to return to measure.
The Current output 4 to 20 and the Relays will activate in 10 sec.
For practical reasons, during calibraTION, we recomends to intro-
duce the buffer temperature manually despite the ATC probe (Pt
1000/Pt 100) is connected.
20
si629 P_HACH_LANGE_Ed.0510.indd ANG:20 si629 P_HACH_LANGE_Ed.0510.indd ANG:20
M E A S U R E
pH 7.34 25.2 °C
Introduce the
CODE 000
code 100
CALIBRATION
The buffer tem-
INSERT 1 st BUFFER
perature can
25°C
be introduced
by the keys
CALIBRATING
PH 7.02 19°C
The display
shifts automa-
tically when
the reading is
stable.
INSERT 2 nd BUFFER
CALIBRATING
PH 4.00 19°C
INSERT 3d BUFFER
Press ENT to perform
a 3-point calibration.
SLOPE
59.26 MV/PH
ASYMMETRY POT.
0 MV
CALIBRATION OK
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