Operational Guide
22
pH
Calibration
Preparation
Pour small quantities of the buff er solutions into clean beakers. If possible,
use plastic to minimize any EMC interferences. For accurate calibration and to
minimize cross-contamination, use two beakers for each buff er solution; one
for rinsing the electrode and one for calibration. If you are measuring in the
acidic range, use pH 7.01 or 6.86 as the fi rst buff er and pH 4.01 (or 3.00*) as the
second buff er. If you are measuring in the alkaline range, use pH 7.01 or 6.86 as
fi rst buff er and pH 10.01 or 9.18 as the second buff er.
* pH 3.00 is only visible when using specifi c pH electrodes and will replace 4.01
pH buff er.
Procedure
Calibration can be performed using up to fi ve calibration buff ers. For accurate
measurements, a minimum of a three-point calibration is recommended. The
calibration buff er can be selected from the calibration buff er list that includes
the custom buff ers and the standard buff ers:
pH 1.68, 4.01 (pH 3.00), 6.86, 7.01, 9.18, 10.01 and 12.45.
The custom buff ers allow the user to calibrate in a buff er solution diff erent from
a standard one. Two custom buff ers can be set in SETUP menu. See page 23 for
more information about using custom buff ers.
The instrument will automatically skip custom buff ers which are in a ±0.2 pH
window of an already calibrated buff er.
Submerse the pH electrode approximately 3 cm (1¼”) into a buff er solution and
stir gently. Press
CAL
to enter calibration.
The “CAL” tag will appear and the “7.01” buff er will be
displayed on the third LCD line. If necessary, press the
ARROW keys to select a diff erent buff er value. The “ ”
along with “STIR” tag will be displayed and “WAIT” will
blink on the LCD until the reading is stable.
When the reading is stable and close to the selected
buff er, “CFM” tag will blink. Press
CFM
to confi rm
calibration.
After confi rming the fi rst point, the calibrated value
will be displayed on the fi rst LCD line and the second
expected buff er value on the third LCD line (i.e. pH
4.01).
