Hanna Instruments HI 255 - Manual (Page 12)

12
pH CALIBRATION
Calibrate the instrument frequently, especially if high accuracy is required.
The instrument should be recalibrated :
• Whenever the pH electrode is replaced.
• At least once a week.
• After testing aggressive chemicals.
• If “CAL” “INTV” tags are blinking during measurement.
Every time you calibrate the instrument use fresh buffers and perform an
electrode Cleaning Procedure (see page 45).
PREPARATION
Pour small quantities of the buffer solutions into clean beakers. If possible, use
plastic or glass beakers to minimize any EMC interferences.
For accurate calibration and to minimize cross-contamination, use two beakers
for each buffer solution. One for rinsing the electrode and one for calibration.
If you are measuring in the acidic range, use pH 7.01or 6.86 as first buffer and
pH 4.01 as second buffer. If you are measuring in the alkaline range, use pH
7.01 or 6.86 as first buffer and pH 10.01 or 9.18 as second buffer.
PROCEDURE
Calibration has a choice of 5 memorized buffers: pH 4.01, 6.86, 7.01, 9.18
and 10.01.
It is recommended to perform a two or three-point calibration. However, the
instrument also allows a one-point calibration, as described on page 14.
Select pH range by pressing RANGE.
THREE-POINT CALIBRATION
_ Immerse the pH electrode and the temperature probe
approximately 4 cm (1½”) into a buffer solution of
your choice (pH 4.01, 6.86, 7.01, 9.18 or 10.01)
and stir gently. The temperature probe should be
close to the pH electrode.
• Press CAL. The “CAL” and “
1
BUF
” tags will appear and
the “7.01” buffer will be displayed on the secondary
LCD.
• If necessary, press the ARROW keys to select a different buffer value.
BUFFER pH
1
BUF
pH CAL