Traditional PLC uses ladder diagrams and statement lists to make programming easy, and has the advantages of short system software development cycle and on-site debugging of programs. Traditional PLCs also have the disadvantages of being unable to support communication interfaces such as I2C and SPI and being relatively expensive. In view of the above shortcomings of traditional PLC, this article uses STM32 series chips to construct the PLC module hardware system circuit and design the software module to design an embedded PLC module. PLCs with modular design have the advantages of small size , low cost, and the ability to access I2C devices. At the same time, they still use the traditional development method of ladder diagrams, providing engineers with a new choice for development projects.
Common PLC modules include:
Power module
Provides internal power to the PLC, and some power modules can also provide power for input signals.
I/O module
It is the input/output module module, I represents input and o represents output. I/O modules can be divided into discrete modules, simulation modules and special modules. The modules can be mounted on a rail or rack with multiple slots, with each module plugged into one of the slots based on the number of points.
memory module
It mainly stores user programs, and some memory modules can also provide auxiliary working memory for the system. Structurally, all memory modules are connected to the CPU module.
Backplane and rack modules
As the name suggests, during the installation process of various PLC modules, the base plate and rack module act as the base plate and provide a bus for communication between modules. Some connections between multiple backplanes use interface modules, some use bus interfaces. It varies from manufacturer to manufacturer, but PLC varies by type.
In addition to the above modules, PLC also has special intelligent or functional modules. For example, A/D (model) module, D/A (model) module, high-speed counting module, position control module, temperature module, etc. These modules have their own CPU. By pre-processing or post-processing the signals, the control of the PLC CPU can be simplified and complex program control quantities can be simplified.
The types and characteristics of smart modules also vary widely. PLC with excellent performance has a variety of types and excellent performance.
After the communication module is connected to the PLC, it can communicate between the PLC and the computer, between the PLC and the PLC, can communicate with other control units such as frequency converters and temperature controllers, and can also form a local area network. The communication module represents the network function of the PLC and represents an important aspect of the current PLC performance.
The specifications of the main chassis of box-type small PLCs vary depending on the number of I/O points that can be provided by integrating the above modules into one chassis. The box-type PLC does not contain a CPU, but also has an I/O expansion box that is used only as a power supply and I/O unit. Expansion box specifications vary depending on the number of I/O points.
Application of PLC module in magnetic iron ore separation process
Read fuel consumption meter data
The fuel consumption meter has a CAN port output. In addition to being displayed on the front end, the measured data is also output through the CAN port. Since the free communication port of the PLC belongs to the RS-485 protocol port, a communication port is connected between the two communication ports. CAN to RS-485 module. To use the communication port for data communication, first initialize the free port accordingly in the subroutine SBR_ 5, turn on the interrupt, and read the data in the reception completion interrupt subroutine INT_ 6.
PC monitoring and data storage
According to the system settings
According to the design requirements, the data collected by the PLC needs to be displayed in real time on the host computer and stored in the database for call. This system uses Siemens’ WinCC host monitoring and configuration software. After configuration, each display
The parameter values, configuration and display screen are shown in Figure 3.
Keywords in this article: lora digital transmission terminal