30
SECTION 3,
continued
3.3
pH Calibration
Hach recommends a daily two- or three-point calibration using
buffers that bracket the sample pH. Store and compare the daily
slope values to verify that the electrode is working properly.
3.3.1
Performing a Calibration Using Automatically Recognized Buffers
1. Prepare two or three pH buffers according to the electrode
instruction manual. Choose from 1.68, 4.01, 7.00 (or 6.86),
10.01, and 12.45 pH buffers.
Note: Use a 6.86 or 7.0 pH buffer for the mid-range buffer. To view or
change the setting for the mid-range buffer see Section 3.2.
2. Turn the instrument on. From the pH Reading mode, press
CAL
.
CAL
and flashing
?
will appear in the upper display
area, along with
Standard
and
1
.
3. Place the pH electrode in one of the buffers.
4. Press
READ
. The instrument will automatically recognize the
calibration buffer value. The temperature and pH values will
be updated until a stable reading is reached.
Note: The pH values for the buffers are given for 25 °C. If the calibration
buffer temperature is not 25 °C, the pH values displayed for the
buffers will reflect the correct pH value for the calibration buffer
temperature.
Note: If the meter is measuring in pH mode, it automatically moves to the
next calibration step when the reading stabilizes (indicated by three
beeps). If measuring in mV mode, the meter beeps three times
when the reading stabilizes. Press
ENTER
to accept the reading.
5. When the reading has stabilized or been accepted, the
standard number will change to
2
.
6. Remove the probe from the first buffer and rinse with
deionized water. Place the probe in the second buffer.
7. Press
READ
. The temperature and pH values will be updated
until a stable reading is reached.