An online pH meter is an instrument used to measure the pH value of a solution. The online pH meter works on the principle of a primary battery. The electromotive force between the two electrodes of the primary battery is based on Nernst's law, which is not only related to the properties of the electrode itself, but also related to the concentration of hydrogen ions in the solution. There is a corresponding relationship between the electromotive force of the primary battery and the concentration of hydrogen ions, and the negative logarithm of the concentration of hydrogen ions is the pH value. Online pH meter is a common analytical instrument widely used in agriculture, environmental protection and industry. There are two installation methods of online pH meter: flow-through type and immersion type. Sewage treatment plants generally use immersion installations. For example, the pH meter of the sewage treatment plant is installed in the outlet overflow tank of the grit chamber. The pH value here is more representative and the water flow is stable. It will not affect the pH meter cause a big impact. Online pH meter. Regular maintenance is helpful for the accurate measurement of the instrument and prolongs the service life of the instrument. It should be noted that the special cable between the sensor and the transmitter cannot be damp, otherwise the high-resistance low-voltage signal of the electrode will not be transmitted to the transmitter. Online pH meter. If the electrode is not being measured, the protective sleeve should be put on, which can keep the electrode in a wet state, which is beneficial to prolong the service life of the electrode. Every month or so, the electrode should be cleaned. First, spray the attachment with soft water, then soak the electrode in the cleaning solution for a period of time, and then wash it with clean water. The sensor holder should also be cleaned. Online pH meter. After each cleaning, a buffer solution should be used for calibration. The manufacturer generally provides two bottles of standard solutions, one with a pH value of 7, used to calibrate the zero point of the instrument; the other with a pH value of 4, used to calibrate the signal output slope of the instrument . Online pH meter.