Hanna Instruments HI 3512 - Manual (Page 19)

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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 “Out of cal. range” message appears on the LCD during pH
measurement (the measurement range is not covered by current
calibration, if this feature is enabled in SETUP).
PROCEDURE
The HI 3512 offers a choice of 7 standard buffers (1.68, 4.01, 6.86,
7.01, 9.18, 10.01 and 12.45 pH) and up to 2 custom buffers. The
standard pH buffers are temperature compensated during calibration.
The custom, user entered buffers are not temperature compensated
during calibration.
When a custom buffer is selected during calibration, the Custom function
key is displayed on the LCD. Press Custom key in order to alter the value
to the actual pH value at the temperature of measurement. Use
ARROW keys to change the value within a ±1.00 pH window and
then press
Accept. Press ESC to leave custom buffers value unchanged.
Press Confirm.
For accurate pH measurements, it is recommended to perform a multipoint
calibration. At least a two-point calibration is required.
The instrument will automatically skip the buffers within ±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, open the fill hole and rinse the electrode
with some of the buffer solution to be used for the first calibration
point.
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