What does two-point calibration of a pH meter mean?
For precision pH meters, in addition to "positioning" and "temperature compensation" adjustments, there is also an electrode "slope" adjustment, which requires calibration with two standard buffer solutions. Generally, pH 6.86 or pH 7.00 is used for "positioning" calibration, and then pH 4.00 (acidic) or pH 9.18 and pH 10.01 (alkaline) buffer solutions are selected for "slope" calibration based on the acidity and alkalinity of the test solution. The specific operation steps are:
⑴ Clean and spin dry the electrode, immerse it in a standard solution with pH 6.86 or pH 7.00, and place the instrument temperature compensation knob at the solution temperature. After the indicated value is stable, adjust the positioning knob to make the indicated value of the instrument be the pH value of the standard solution.
⑵ Remove the electrode, wash and spin dry it, and immerse it in standard solutions. After the indicated value is stable, adjust the slope knob of the instrument so that the indicated value of the instrument is the pH value of standard solutions.
⑶ Remove the electrode, wash it and shake it dry, then immerse it in a pH 6.86 or pH 7.00 buffer solution. If the error exceeds 0.02 pH, repeat steps (1) and (2) until the correct pH values can be displayed in both standard solutions without adjusting the knob.
⑷ Take out the electrode and shake it dry. Adjust the pH temperature compensation knob to the temperature of the sample solution. Immerse the electrode in the sample solution, shake it, and let it stand still. After the display stabilizes, take a reading.
What is automatic calibration of pH meter?
PH meter automatic calibration can only be applied to microcomputer or computer chip pH meters. This type of pH meter has inputted various buffer solution data and operating procedures into the chip, so there is no need to view the pH values of the buffer solution. If equipped with a temperature sensor, there is no need to adjust the temperature value. Simply select one point calibration, two point calibration, or three-point calibration based on the testing accuracy of the sample solution (press the CAL key once, twice, or three times), and the instrument will automatically display the calibration end symbol. Three point calibration is a characteristic of this type of pH meter. It corrects three points, pH 7.00 (or pH 6.86), pH 4.00 or pH 10.01 (or pH 9.18), respectively, for more accurate testing across the entire pH range. When using such instruments, it is important to carefully check the specific types of the three pH buffer solutions embedded in the pH meter, such as pH 6.86 or pH 7.00, pH 9.18 or pH 10.01, and select the correct buffer solution. Some computer-based pH meters can set their own pH buffer solution, but it must be set correctly in advance, otherwise the computer cannot recognize two similar buffer solutions and calibration errors may occur. Computerized pH meters will make calibration more convenient.
