The composition of various online analyzers varies greatly due to their principle of operation, the object of analysis and their complexity. The basic components are generally composed of four parts (see figure), ① Sampling, pre-treatment and feed system. It takes a representative sample from the process and makes it conform to the analyzer’s requirements for sample status or conditions. ②Analyzer. Converts the amount of composition or physical properties of the sample into a measurable electrical signal. ③ Power supply and electronics. Supply power to each part of the instrument, control the work of each part of the instrument, amplify the electrical signal sent by the analyzer, and output to the display, recorder, or send to the automatic controller or electronic computer at the same time. ④Display and recorder. It is used to display and record the electric signal representing the composition or physical quantity.