The working principle of pH meter (water quality analysis instrument)
The pH value of water depends on the amount of dissolved substances, so the pH value can sensitively indicate the change of water quality. The change of pH value has a great impact on the reproduction and survival of organisms, and also seriously affects the biochemical function of activated sludge, that is, the effect of treatment. The pH value of 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=HOH-, that is, decompose into hydrogen ions and hydroxide ions. In a neutral solution, the concentrations of hydrogen ions H and hydroxide ions OH- are both 10-7 mol/l, and the pH value is the negative number of the logarithm of the hydrogen ion concentration with base 10: 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, the solution is alkaline if there is an excess of hydroxide ions. The pH value is usually measured by the potentiometric method, usually using a constant potential reference electrode and a measuring electrode to form a galvanic cell. The electromotive force of the galvanic cell depends on the concentration of hydrogen ions and also on the pH of the solution. The plant has adopted CPS11 pH sensor and CPM151 pH transmitter. There is a special glass probe sensitive to pH on the measuring electrode, which is made of special glass that can conduct electricity and permeate hydrogen ions, and has the characteristics of high measurement accuracy and good anti-interference. When the glass probe comes into contact with hydrogen ions, an electric potential is generated. The potential is measured against a reference electrode with a silver wire suspended in a silver chloride solution. If the pH value is different, the corresponding potential is also different, which is converted into a standard 4-20mA output through the transmitter.
