Why should the pH meter be calibrated regularly?

Why should pH meters be calibrated regularly? The accuracy and life of the pH meter depend on the pH electrode, and the price varies greatly. However, in many cases, the improper use method leads to inaccurate measurement. Generally, the pen-type pH meter has been adjusted before leaving the factory and can be used directly. The pH meter must be re-adjusted after a period of use, and the time depends on the solution being measured and the frequency of use. After a period of use, the electrode of the pH meter is asymmetrical, and the potential will change greatly, so it must be calibrated regularly. The frequency of pH electrode calibration and calibration depends on the sample, the performance of the pH electrode and the accuracy requirements for measurement. For high precision measurement (≤±0103pH), it should be calibrated in time; for general precision measurement (≤±011pH), it can be used continuously for two weeks or even longer after one calibration. Calibration of the pH electrode is not necessary as often as the measurement shows that the pH value is accurate. First test the standard solution that is closer to the measured solution, and determine whether recalibration is required according to the size of the error. Re-calibrate in the following cases: ① Replace with a new pH electrode. ② Measuring concentrated acid (pH< 2) Later, or measure concentrated lye (pH> 12) Later. ③After measuring solutions containing fluoride or concentrated organic solutions. ④ When the temperature of the measured solution is too different from the temperature of the standard solution (or room temperature).