Hanna Instruments HI 3512 - Manual (Page 33)

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It is recommended to calibrate the instrument frequently, especially if
high accuracy is required.
The EC range should be recalibrated:
• Whenever the EC 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 EC
measurement (the measurement range is not covered by current
calibration, if feature is enabled in SETUP).
Note: TDS and Resistivity readings are automatically derived from the
EC reading and no specific calibration is needed.
PROCEDURE
HI 3512 instrument offers a choice of 7 memorized standards
(0.00
µ
S/cm, 84.0
µ
S/cm, 1.413 mS/cm, 5.00 mS/cm,
12.88 mS/cm, 80.0 mS/cm and 111.8 mS/cm).
For accurate EC measurements, it is recommended to perform an offset
calibration and slope calibration in the nearest value standard solution
of the samples readings (two-point calibration).
The instrument will automatically recognize the standards and skip the
standard used during calibration.
• Pour small quantities of selected standard solutions into clean
beakers. For accurate calibration use two beakers for each standard
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
standard solution to be used for the first calibration point.
TWO-POINT CALIBRATION
• It is better to perform the first point calibration as offset calibration.
• Tap the probe repeatedly to remove any air bubbles that may be
trapped inside the sleeve.
• For offset (zero) calibration, just leave the dry probe in the air.
E C E C E C E C E C CALIBRATION CALIBRATION CALIBRATION CALIBRATION CALIBRATION