S7-300 is one of the programmable logic controller (PLC) series products produced by Siemens in Germany. Its modular structure, easy to implement distributed configuration, high cost-effectiveness, strong electromagnetic compatibility, and good shock resistance make it an economical and practical solution in a wide range of industrial control fields.

Product characteristics

For modular small and medium-sized control systems with low performance requirements, different grades of CPUs can be equipped, and different types of expansion modules can be selected. Up to 32 modules can be expanded, with integrated backplane bus, network connection - Multipoint Interface (MPI), - PROFIBUS or - Industrial Ethernet. All modules can be accessed through the programmer PG without slot restrictions.

Product Features

Short cycle time and high processing speed; The instruction set is powerful (including over 350 instructions) and can be used for complex functions; The product design is compact and can be used in situations with limited space; Modular structure for more flexible design; CPU modules of different performance levels are available for selection; Functional modules and I/O modules can be selected; There are module types that can be used in harsh outdoor conditions.

CPU module

Various CPUs have different performance, for example, some CPUs integrate digital and analog input/output points, while others integrate communication interfaces such as PROFIBUS-DP. There are status fault indicators, mode switches, 24V power terminals, battery boxes, and memory module boxes on the front panel of the CPU (some CPUs do not have them)

Signal Module (SM)

Digital input module: 24V DC, 120/230V AC

Digital output module: 24V DC, relay

Analog input module: voltage, current, resistance, thermocouple

Analog output module: voltage, current

Functional Module (FM)

The functional module is mainly used for process signal processing tasks that require strict time requirements and high memory capacity.

-Counting: Counter module

-Positioning: fast/slow feed drive position control module, electronic cam controller module, stepper motor positioning module, servo motor positioning module, etc

Siemens PLC S7-300 Selection

1、 Selection of model

（1） Types of Siemens PLC S7-300

Siemens PLC is divided into two types based on its structure: integrated and modular, and on-site installation and control room installation according to the application environment; According to CPU word length, it can be divided into 1 bit, 4 bit, 8 bit, 16 bit, 32 bit, 64 bit, etc. From an application perspective, selection can usually be based on control functions or input/output points.

The I/O points of the integrated Siemens PLC are fixed, so the user has less choice and is used for small control systems; Modular PLC provides multiple I/O cards or cards, so users can reasonably select and configure the I/O points of the control system. Its function expansion is convenient and flexible, and it is generally used in large and medium-sized control systems.

（2） Selection of input/output modules

The selection of input and output modules should consider consistency with application requirements. For example, for input modules, consideration should be given to signal level, signal transmission distance, signal isolation, and signal power supply side