How does the water quality analyzer pH meter work?

The working principle of the PH meter is as follows:

The pH of the water depends on the amount of material dissolved, so the pH can sensitively indicate changes in water quality. The change of pH has a great influence on the reproduction and survival of the organism, and also seriously affects the biochemical action of the activated sludge, that is, affects the treatment effect. The pH value of the sewage is generally controlled between 6.5 and 7. Water is chemically neutral, and some water molecules spontaneously decompose according to the following formula: H2O=H++OH-, which is decomposed into hydrogen ions and hydroxide ions. In a neutral solution, the concentration of hydrogen ion H+ and hydroxide ion OH- is 10-7 mol/l, and the pH value is the negative of the logarithm of the base of hydrogen ion concentration: pH=-log, so neutral The pH of the solution is equal to 7. If there is an excess of hydrogen ions, the pH is less than 7, and the solution is acidic; otherwise, if the hydroxide ions are excessive, the solution is alkaline. The pH value is usually measured by a potentiometric method. Usually, a reference electrode and a measuring electrode of a constant potential are used to form a primary battery. The magnitude of the electromotive force of the primary battery depends on the concentration of hydrogen ions and also depends on the pH of the solution. The plant uses a CPS11 pH sensor and a CPM151 pH transmitter. The specific structure is shown in Figure 1. The measuring electrode has a special pH-sensitive glass probe. It is made of special glass that can conduct electricity and penetrate hydrogen ions. It has high measurement accuracy and good anti-interference. When the glass probe is in contact with hydrogen ions, a potential is generated. The potential was measured by a silver wire reference electrode suspended in a silver chloride solution. The pH value is different, and the corresponding potential is different. It is converted into a standard 4-20mA output by the transmitter.

 

     The glass on the pH electrode gradually ages with time, and the gradient (the value of the change in the electrode output potential caused by the change in the pH value per unit) deteriorates, and it takes a long time to reach the stable potential. The life of the electrode is generally up to two years. In addition, the temperature also has a great influence on aging, and the degree of aging at 100 ° C for several weeks is equivalent to the degree of aging at room temperature for one year. The pH meter has the advantages of high precision, high reliability, convenient installation and maintenance, and is sensitive to pollution. It needs to be calibrated frequently. It is usually calibrated once every one to one and a half months, and the electrode is replaced every two years.