Do PH meters/acid meters have to be calibrated? What are the methods of calibration?
pH measurement is usually a colourimetric method (pH paper or cuvette) and electrode method. Colourimetric method, of course, do not calibrate, while the electrode method must be calibrated, because the electrode method of pH measurement is the unknown solution and the known pHs value of the standard solution in the measuring cell to compare the measurement, which is the electrode method of pH measurement of the "operational definition" of the decision.
There are many types of pH meters with different meter designs and different operating procedures, so the operation of a pH meter should be carried out correctly and in strict accordance with its operating instructions. In specific operation, calibration is an important step in the operation of pH meter. Table 1 data is the accuracy of 0.01 level, after measurement and calibration of the pH meter in the uncalibrated and calibrated measured values, from which we can see the importance of calibration.
Although there are many types of pH meters, but their calibration methods are used two-point calibration method, that is, the choice of two standard buffers: one is the pH7 standard buffer, the second is the pH9 standard buffer or pH4 standard buffer. The meter is first positioned with the pH7 standard buffer, and then the second standard buffer is selected according to the acidity or alkalinity of the solution to be measured. If the solution to be measured is acidic, the pH4 standard buffer is used; if the solution to be measured is alkaline, the pH9 standard buffer is used. If the pH meter is manually adjusted, the operation should be repeated several times between the two standard buffers, until there is no need to adjust its zero and positioning (slope) knob, the pH meter can accurately display the two standard buffer pH value. Then the calibration process is finished. Thereafter, the zero and position knobs should not be moved during the measurement. If it is an intelligent pH meter, there is no need for repeated adjustments, because it has internal storage of several standard buffer pH values to choose from, and can be automatically recognised and automatically calibrated. However, attention should be paid to the selection of standard buffer and the accuracy of its preparation. Intelligent 0.01 level pH meter generally have three to five kinds of standard buffer pH value in memory, such as the KL-016 type pH meter of Kelilong company.
Secondly, special attention should be paid to the temperature of the solution to be measured before calibration. In order to correctly select the standard buffer, and adjust the temperature compensation knob on the panel of the meter, so that it is consistent with the temperature of the solution to be measured. The pH value of the standard buffer solution is different at different temperatures.
