Apera Instruments PH850, User Manual, Page: 8 / 20

6
Chart - 3 pH standard buffer solution series
Calibration guide icons
pH standard buffer solution series
USA series (USA) NIST series (NIS)
Three-point
calibration
1.68 pH and 4.00 pH 1.68 pH and 4.01 pH
7.00 pH 6.86pH
10.01 pH and 12.45 pH 9.18 pH and 12.45 pH
4.2.2. Three-point calibration
The instrument can perform 1-3 points calibration. The first point calibration must use 7.00 pH (or 6.86 pH)
standard solution, then select other standard solution to perform the second and the third point calibration.
See chart – 4.
Chart - 4 Three-point calibration mode
USA standard NIST standard Icons ! Suited range !
One-point
calibration
!"##$%&$ '"('$%&$
Accuracy
≤
±0.1pH
Two-point
calibration
!"##$%&)*"##$+,$-"'(%&$ '"('$%&)*"#-$+,$-"'(%&$
Range<7.00pH
!"##$%&)-#"#-$+,$."*/%&$ '"('$%&)0"-($+,$-."*/%&$
Range>7.00pH
Three-point
calibration
!"##%&)*"##$+,-"'(%&$
)-#"#-$+,-."*/%&$
'"('%&)*"#-+,$-"'(%&$
)0"-($+,$-."*/%&$
Large Range
4.2.3. Calibration frequency
Calibration frequency depends on the sample, the electrode performance, and the required accuracy. For
high accuracy measurements (≤ ±0.03pH), the meter should be calibrated immediately before taking a
measurement. For general accuracy (≥±0.1pH), the meter can be calibrated and used for approximately
one week before the next calibration.
The meter must be recalibrated in the following situations:
(a) New probe or probe that has not been used for a long time
(b) After measuring acid (pH<2) or alkaline solutions (pH>12)
(c) After measuring a solution that contains fluoride or a concentrated organic solution
(d) If the solution’s temperature differs greatly from the calibration solution temperature.