Hanna Instruments HI 120 - Manual (Page 15)

15
Calibrate the instrument often, 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 DUE” tags are blinking during measurement.
• If “OUT CAL RANGE” message blinks during pH measurement (the
measurement range is not covered by current calibration).
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 7.01 or 6.86 as first buffer
and pH 4.01 or 1.68 as second buffer. If you are measuring in the alkaline range,
use pH 7.01 or 6.86 as first buffer and pH 10.01/9.18 or 12.45 as second buffer.
For extended range measurements (acidic and alkaline), perform a five-point
calibration by selecting five of the available buffers.
PROCEDURE
If 0.001 pH resolution is selected, each selected standard buffer value can
be updated in according with the value on the production lot certificate at
25 ºC (77 ºF). Press 2nd then SET key when a standard pH buffer with
0.001 resolution is selected. The buffer value will start blinking and it can
be changed with the ARROW keys in a ±0.020 pH window.
Calibration has a choice of 7 memorized buffers: pH 1.68, 4.01, 6.86,
7.01, 9.18, 10.01, 12.45 and 2 custom buffers.
The custom buffers are a special option that allows the user to calibrate in
a buffer solution different from a standard one. Up to two custom buffers
can be set in SETUP menu (see page 27). When selected during
calibration, the “CUSTOM C1” or “CUSTOM C2” tags are displayed on the
LCD and the custom buffer value can be changed in a ±1.0 pH window,
around the set value.
For accurate measurements it is recommended to perform a five-point
calibration. However, at least a two-point calibration is suggested.
The instruments will automatically skip the buffers used during calibration
and the buffers which are in a ±0.2 pH window, around one of the
calibrated buffers.
pH CALIBRATION