The working principle of pH meter in water quality analyzer
There are two installation methods for pH meters: flow type and immersion type. The sewage treatment plant generally adopts immersion installation. For example, the pH meter of the sewage treatment plant is installed in the outlet overflow tank of the oxidation ditch, where the pH value is representative and the water flow is stable, which will not cause significant impact on the pH meter.
The working principle of pH meter
The pH value of water varies with the amount of dissolved substances, so the pH value can sensitively indicate changes in water quality. The change in pH value has a significant impact on the reproduction and survival of organisms, and also seriously affects the biochemical function of activated sludge, which affects the treatment effect. The pH value of wastewater is generally controlled between 6.5 and 7. Water is chemically neutral, and some water molecules spontaneously decompose into hydrogen ions and hydroxide ions according to the following formula: H2O=H++OH -. In a neutral solution, the concentrations of hydrogen ion H+and hydroxide ion OH - are both 10-7mol/l, and the pH value is the negative logarithm of the hydrogen ion concentration at the base of 10: pH=- log, so the pH value of a neutral solution is 7. If there is an excess of hydrogen ions, the pH value is less than 7, and the solution is acidic; On the contrary, if there is an excess of hydroxide ions, the solution will be alkaline. The pH value is usually measured by the potentiometric method, using a constant potential reference electrode and a measuring electrode to form a primary battery. The magnitude of the primary battery electromotive force depends on the concentration of hydrogen ions and also on the pH of the solution.
There is a special pH sensitive glass probe on the measuring electrode, which is made of special glass that can conduct electricity and penetrate hydrogen ions. It has the characteristics of high measurement accuracy and good anti-interference. When the glass probe comes into contact with hydrogen ions, a potential is generated. The potential is measured using a silver wire suspended in a silver chloride solution as a reference electrode. Different pH values result in different potentials, which are converted into standard 4-20mA output through a transmitter.
