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4.2.2
pH Calibration Modes
The instrument has two calibration modes for choice: 3-point calibration (3P) and 5-point calibration mode (5P).
Users can make the selection in parameter settings P1.4 (refer to section 7.3)
a)
3-point Calibration Mode
The 3-point calibration mode is the most commonly used. Users can adopt 1 to 3 points to calibrate as needed.
In the 3-point calibration mode, the 1
st
point must be 7.00 pH (or 6.86 if using NIST). Then choose other calibration
solutions to conduct 2
nd
and 3
rd
points (see Table-3 for details). In the process of calibration, the meter will display
the electrode’s slope in acid and alkaline ranges.
Table-3 3-point 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
b)
5-point Calibration Mode
In 5-point calibration mode, users can adopt 1 to 5 points of calibration, and can choose calibration buffer
solutions at any sequence. Typically, 5-point calibration is recommended when testing strong acid or strong
base solutions.
4.2.3
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 measurements (≤ ±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 about a week or longer. In the following cases, the meter must be re-calibrated:
a)
The electrode hasn’t been used for a long time or the electrode is brand new.
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 big difference between the temperature of the test sample and the temperature of the buffer
solution that is used in the last calibration.
4.2.4
Calibration Reminder Function
Preset the interval between calibrations (starting from the time when you set it), and then the meter will remind
you to calibrate at the end of that interval. For details, please see P1.2 (Section 7.3). When the preset time is
reached,
Er6
icon will be displayed at the lower right corner of the LCD (as showed in Figure-8). At the time,
the meter can still be operated. It is just reminding you to do calibration in order to ensure the accuracy. After
calibration, the
Er6
icon will disappear; To make it disappear, users can also choose “No” in P1.2 in parameter
setting.
