Hanna Instruments HI 21 Series - Manual (Page 20)

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Three-point Calibration
• Proceed as described above but do
not quit calibration by pressing CAL.
Note The meter will automatically skip the two buffers that were
used to prevent errors.
• After the second calibration point
is confirmed, immerse the pH elec-
trode and the Potential Matching Pin
into the third buffer solution (e.g.
pH 10.01) and stir gently.
Note The electrode should be submerged
approximately 4 cm (1½") in the so-
lution. The temperature probe should
be located as close as possible to the
pH electrode.
• Only when the reading is stable the
probe indicator " " will stop flash-
ing (after about 30 seconds) and the
"CFM" indicator will start blinking.
• Press CFM to confirm the calibration; if the reading is close
to the selected buffer, the meter stores the reading, adjust-
ing the 2
nd slope point and the calibration process is ended
with the offset and the 1 st and 2 nd slope of the meter cali-
brated.
If the reading is not close to the se-
lected buffer, "WRONG
BUF
" will
blink.
Note During calibration, the secondary LCD displays the selected
buffer value. By pressing LCD the temperature can be dis-
played. This will allow you to check the buffer temperature
during calibration.
Two-point Calibration
• Proceed as described above for one-point cali-
bration, using pH 7.01 as the first point, but do
not quit calibration by pressing CAL at the end.
Note The meter will automatically skip the buffer that was used for
the first calibration to prevent errors.
• After the first calibration point is con-
firmed, immerse the pH electrode with
the Potential Matching Pin into the sec-
ond buffer (e.g. pH 4.01) and stir gently
Note If you are not going to perform a three-point calibration, it is
recommendable to use pH 4.01 buffer if you are going to mea-
sure acid samples, or use pH 10.01 buffer for alkaline samples.
Note The electrode should be submerged ap-
proximately 4 cm (1½") in the solution.
The temperature probe should be located
as close as possible to the pH electrode.
• Select the 2 nd buffer value on
the secondary display by press-
ing or (e.g. pH 4.01).
• Only when the reading is stable
the probe indicator " " will stop
flashing (after about 30 seconds) and
the "CFM" indicator will blink.
• Press CFM to confirm the calibration; if the reading is close
to the selected buffer, the meter stores the reading, adjust-
ing the slope point and the secondary LCD will display
the expected third buffer value.
If the reading is not close to the se-
lected buffer, "WRONG
BUF
" will
blink.
• Press CAL and the calibration pro-
cess is ended with the offset and the
1
st slope of the meter calibrated.