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pH CALIBRATION
It is recommended to calibrate the instrument frequently, especially if high accuracy is required.
The pH range should be recalibrated:
• Whenever the pH electrode is replaced.
• At least once a week.
• After testing aggressive chemicals.
• When calibration alarm time out is expired ‑ “CAL DUE” blinks (if feature is enabled in
SETUP).
• If “Outside Cal Range” message blinks during pH measurement (the measurement range is
not covered by current calibration, if feature is enabled in SETUP).
PROCEDURE
HI98190 and HI98191 instruments offers a choice of seven standard buffers (pH 1.68, 4.01, 6.86,
7.01, 9.18, 10.01 and 12.45). The meters allow the user to set up to five custom buffers. The set
custom buffers are the buffer values at 25 °C.
When a custom buffer is selected during calibration, the Custom functional key is displayed on the
LCD. Press Custom key in order to enter custom buffer changing mode. Use / keys to change
the value in a ±1.00 pH window, in according with the temperature reading and then Accept. Press
ESC to leave custom buffers value unchanged.
For accurate pH measurements, it is recommended to perform a calibration in maximum allowed
points. However, at least a two point calibration is suggested.
The instrument 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.
• Pour small quantities of selected buffer solutions into clean beakers. For accurate calibration use
two beakers for each buffer solution, the first one for rinsing the electrode and the second one
for calibration.
• Remove the protective cap and rinse the electrode with some of the buffer solution to be used for
the first calibration point.
FIVE POINT CALIBRATION
• Immerse the pH electrode approximately 4 cm (1½”) into a buffer solution of
your choice (pH 1.68, 4.01, 6.86, 7.01, 9.18, 10.01, 12.45 or a custom buffer)
and stir gently. The temperature probe (HI98191 only) should be close to the
pH electrode.
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