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MODEL SOLU COMP II SECTION 6.0
CALIBRATION
6.3 AUTO CALIBRATION — pH
6.3.1 Purpose
1. New sensors must be calibrated before use. Regular recalibration is also necessary.
2. Use auto calibration instead of manual calibration. Auto calibration avoids common pitfalls and reduces errors.
6.3.2 Definitions
1. AUTO CALIBRATION. The analyzer recognizes the buffers and uses temperature-corrected pH values in the
calibration. The table lists the buffers the Solu Comp II recognizes.
Note 1: NIST is National Institute of Standards, DIN is Deutsche Institute für
Normung, JSI is Japan Standards Institute, and BSI is British Standards
Institute.
Note 2: pH 7 buffer is not a standard buffer. It is a popular commercial buffer
in the United States.
The Solu Comp II also measures noise and drift and does not accept calibration data until readings are sta-
ble. Calibration data will be accepted as soon as the pH reading is constant to within 0.02 units for 10 sec-
onds. The stability settings cannot be changed.
2. SLOPE AND OFFSET. Once the Solu Comp II suc-
cessfully completes the calibration, it calculates and
displays the calibration slope and offset. The slope is
reported as the slope at 25°C. Figure 6-1 defines the
terms.
6.3.3 Procedure
1. Obtain two buffer solutions. Ideally the buffer pH val-
ues should bracket the range of pH values to be meas-
ured.
2. Remove the sensor from the process liquid. If the
process and buffer temperatures are appreciably dif-
ferent, place the sensor in a container of tap water at
the buffer temperature. Do not start the calibration until
the sensor has reached the buffer temperature. Thirty
minutes is usually adequate.
3. Calibrate the sensor by using the procedure on the following page.
pH at 25°C Standard(s)
(nominal pH)
1.68 NIST, DIN 19266, JSI 8802, BSI (see note 1)
3.56 NIST, BSI
3.78 NIST
4.01 NIST, DIN 19266, JSI 8802, BSI
6.86 NIST, DIN 19266, JSI 8802, BSI
7.00 (see note 2)
7.41 NIST
9.18 NIST, DIN 19266, JSI 8802, BSI
10.01 NIST, JSI 8802, BSI
12.45 NIST, DIN 19266
FIGURE 6-1. Calibration Slope and Offset
48