Oakton PH550 - Page 9

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Table-3 Calibration Mode
USA
NIS
Calibration
icon
When to adopt
1-Point
Calibration
7.00 pH
6.86 pH
accuracy≤ ±0.1 pH
2-Point
Calibration
7.00 pH and
4.00/1.68 pH
6.86 pH and
4.01/1.68 pH
Measuring range: 0 to 7.00 pH
7.00 pH and 10.01 pH
6.86 pH and 9.18 pH
Measuring range: >7.00 pH
3-Point
Calibration
7.00pH, 4.00/
1.68 pH and 10.01 pH
6.86pH, 4.01/
1.68pH, 9.18 pH
Wide measuring range
How often to calibrate
The frequency that you need to calibrate your meter depends on the tested samples, condition of
electrodes, and the requirement of the accuracy. For High-Accuracy meaustements (≤ ±0.02pH), the
meter should be calibrated before test every time; For ordinary-accuracy measurements (≥±0.1pH), once
calibrated, the meter can be used for several days before recalibration. In the following cases, the meter
must be re-calibrated:
a) The electrode hasn’t been used for a long time or a new electrode is connected.
b) After measuring strong acid (pH<2) or strong base (pH>12) solutions.
c) After measuring fluoride-containing solution and strong organic solution
d) There is a significant difference between the temperature of the test sample and the temperature of
the buffer solution that is used in the last calibration.