The programmable controllers produced by Siemens are also widely used in China, with applications in metallurgy, chemical industry, printing production lines, and other fields. Siemens' PLC products include LOGO, S7-200, S7-1200, S7-300, S7-400, S7-1500, etc. The Siemens S7 series PLC has small size, fast speed, standardization, network communication capability, stronger functionality, and high reliability. The S7 series PLC products can be divided into micro PLCs (such as S7-200), PLCs with small-scale performance requirements (such as S7-300), and PLCs with medium to high performance requirements (such as S7-400).

Programmable controllers are generated by the needs of modern production, and the classification of programmable controllers must also meet the requirements of modern production.
Generally speaking, programmable controllers can be classified from three perspectives. One is to classify based on the control scale of the programmable controller, the other is to classify based on the performance of the programmable controller, and the third is to classify based on the structural characteristics of the programmable controller.
Control scale
It can be divided into large machines, medium-sized machines, and small machines.
Mini computers: The control points of mini computers are generally within 256 points, suitable for single machine control or small system control.
Siemens mini computers have S7-200: processing speed of 0.8~1.2ms; Memory 2k; digital quantity 248 points; 35 analog channels.
Medium sized computer: The control points of a medium-sized computer are generally not greater than 2048 points, which can be used for direct control of equipment and monitoring of multiple programmable controllers at the next level. It is suitable for medium or large control systems.
Siemens mid-range computer has S7-300: processing speed of 0.8~1.2ms; Memory 2k; digital quantity 1024 points; 128 analog channels; Network PROFIBUS; Industrial Ethernet; MPI。
Mainframe: Mainframe control points are generally greater than 2048 points, which can not only perform complex arithmetic operations but also complex matrix operations. It can not only be used for direct control of devices, but also for monitoring multiple programmable controllers at the next level.
Siemens mainframes have S7-1500 and S7-400: processing speed of 0.3ms/1k words;
Memory 512k; I/O points 12672;
control performance
It can be divided into high-end machines, mid-range machines, and low-end machines.
Low gear machine
This type of programmable controller has basic control functions and general computing capabilities. The working speed is relatively low, and the number of input and output modules that can be carried is relatively small.
For example, the S7-200 produced by SIEMENS in Germany belongs to this category.
Mid-range machine
This type of programmable controller has strong control functions and strong computing capabilities. It can not only perform general logical operations, but also complex trigonometric, exponential, and PID operations. The work speed is relatively fast, the number of input and output modules that can be carried is also relatively large, and there are also many types of input and output modules.
For example, the S7-300 produced by SIEMENS in Germany belongs to this category.
High end machine
This type of programmable controller has powerful control functions and powerful computing capabilities. It can not only perform logical operations, trigonometric operations, exponential operations, and PID operations, but also perform complex matrix operations. The work speed is very fast, and there are many input and output modules that can be carried. The types of input and output modules are also very comprehensive. This type of programmable controller can accomplish large-scale control tasks. It is generally used as a main station in networking.
For example, the S7-400 produced by SIEMENS in Germany belongs to this category.