8
Diagram - 10
Chart - 5 Three-point calibration mode
USA standard
NIST standard
Icons
Suited range
One-point
calibration
7.00 pH
6.86 pH
Accuracy
≤
±0.1pH
Two-point
calibration
7.00 pH→4.00 or 1.68pH
6.86 pH
→
4.01 or 1.68pH
Range<7.00pH
7.00 pH→10.01 or 2.45pH 6.86 pH
→
9.18 or 12.45pH
Range>7.00pH
Three-point
calibration
7.00pH→4.00 or1.68pH
→10.01 or12.45pH
6.86pH
→
4.01or 1.68pH
→
9.18 or 12.45pH
Large Range
4.2.3. Calibration intervals
Calibration intervals depend 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 re-calibrated in the following situations:
(a) New probe, or probe that is unused for a long period of time
(b) After measuring acids (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
4.2.4. Due calibration
Preset calibration interval (begin from the date of last calibration) to remind due
calibration in a preset period in parameter setting P1.4 (clause 7.3). During due
calibration,
Er5
icon appears on LCD (see Diagram
– 9). The meter can not
continue operation and
Er5
icon disappears until the calibration is done, or
when select
“No” in parameter setting P1.4.
4.2.5. Check calibration date
Check the date and time of last calibration to decide whether new calibration is
needed. Please refer to parameter setting P1.5 (clause 7.3).
4.3. pH Calibration (take three-point calibration as an example)
4.3.1. The 1
st
point calibration
（
a
）
Press key to enter into the calibration mode, CAL 1 blinks at the top
right of LCD and “7.00 pH” blinks at the bottom right of LCD, indicating using
pH 7.00 buffer solution to make the 1
st
point calibration.
（
b
）
Rinse pH electrode in pure water, allow it to dry, and submerge it in
pH7.00 buffer solution. Stir the solution briefly and allow it to stay in the buffer
solution until a stable reading is reached. LCD displays , press to
finish 1
st
point calibration, meter goes to measurement mode, the bottom left of
LCD indicating , See Diagram
– 10.
Diagram - 9
