9
8
CALIBRATION
pH CALIBRATION
For greatest accuracy, it is recommended to frequently calibrate the
instrument. For a faster procedure, it is possible to calibrate at 1
point, but it is always a good practice to calibrate at 2 points.
For a two-point calibration two of the following pH buffers can be
used: pH 4.01, pH 7.01 (or 6.86), pH 10.01 (or 9.18).
In the case of a two-point calibration in the acidic range (from 0 to
7 pH), use pH 7.01 (or 6.86) buffer as first solution and pH 4.01
buffer as second solution. If testing in the alkaline range (from 7 to
14 pH), use pH 10.01 (or 9.18) buffer as second solution.
Due to electrode conditioning time, the electrode must be kept
immersed a few seconds to stabilize. The meter is equipped with a
stability indicator and the user will be guided step by step with easy
indications on the LCD during the calibration. This will make the
calibration a simple and error-free procedure.
PROCEDURE
1. Rinse the electrode with a portion of the first calibration buffer or
clean water. Dip the tip (4 cm/1½") of the electrode into a
beaker containing the solution.
2. Press (ALT+) CAL when the meter dis-
plays pH measurement.
3. Enter the password (if different from "0000") with the arrow keys.
4. Press CFM to confirm the password or (ALT+) CAL to exit.
5. If password is correct, the meter displays "7.01pH" on the
secondary LCD with the "BUF 1" and "CAL" indications. The
primary LCD shows the uncalibrated pH reading.
Note
: The pH buffer value (displayed on the secondary LCD) varies
with temperature. For example, at 20
°
C it shows 4.00 -7.03 -
10.06, at 25
°
C it shows 4.01-7.01-10.01.
6. Select the first buffer solution value with
or
if necessary.
7. When the "CFM" symbol blinks, the read-
ing is stable and calibration can be
confirmed.
8. Press CFM to confirm the first buffer.
9. If everything is satisfactory the LCD will
display "Stor" and then the expected
value for the second buffer (two-point
calibration). If a wrong solution or elec-
trode has been used or if the buffer is
polluted, "WRONG" will be displayed to
alert the user.
10. If a single point calibration is required,
press (ALT+) CAL to exit the calibration
mode and maintain the previous slope
calibration. The instrument then checks
the electrode parameters and advises user
of possible abnormalities by "old probe"
and "dead probe" indications.
11. Press
or
to select the second buffer value. The meter will
display the "BUF 2" indication.
12. Rinse the electrode with some of the second buffer solution or clean
water.
13. Dip the tip (4 cm/1½") of the pH electrode into a beaker
containing the second buffer.
14. When the "CFM" symbol blinks, press CFM
to confirm the second calibration point.
15. The LCD will display "Stor". The instrument checks the electrode
parameters and advises the user of possible abnormalities by "old
probe" and "dead probe" indications (in these cases, repeat the
calibration procedure with fresh buffers). If everything is satisfactory
the meter is calibrated and it returns to normal operational mode.
Note
: To abort the calibration procedure and leave the calibration data
unchanged, press ALT and CAL before confirming the first point.
CALIBRATION ERROR MESSAGES
If the "old probe" or "dead probe" messages are displayed, or if the
WRONG tag blinks during calibration, check the electrode by following
the conditioning and maintenance procedures and repeat calibration.
If calibration can not be successfully performed, the pH electrode
might have to be replaced.
Note
: See "GLP" section for more details about "old probe" and "dead
probe" messages.