Calibration of ph electrode – Hach-Lange SI627 P User Manual

Page 20

4. Operation

The buffer
temperature
can be intro-
duced by the

, keys.

The display
shifts automa-
tically when
the reading is
stable.

Press

to perform a
3-point calibra-
tion.

Introduce the
code 100

Notes: During calibraTIOn instrument is in hold state:
• Current output is frozen at 21 mA or at last value.
To quit the hold state it is necessary to return to mEASURE.
Press ESC to quit the calibration, from any screen, without
storing data.
For practical reasons, CRISON recommeds to select
temperature manually during calibraTIOn, even if you have
an ATC probe connected (Pt 1000)

4.7. 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 19).

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 recom-
mend 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 sensitivity in acid and alkaline regions.

CALIBRATING

pH 4.00 19°C

SLOPE

59.26 mV/pH

CALIBRATE

CODE 000

M E A S U R E

pH 7.34 25.2 °C

INSERT 1 st BUFFER
25°C

CALIBRATING

pH 7.02 19°C

INSERT 2 nd BUFFER

INSERT 3d BUFFER

ASYMMETRY POT.

0 mV

CALIBRATION OK

si627 P_HACH_LANGE_Ed.0510.indd ANG:16

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