Introduction to plc
Programmable Logic Controller is a digital computing operation electronic system specially designed for application in industrial environments. It uses a programmable memory that stores instructions for performing operations such as logic operations, sequence control, timing, counting, and arithmetic operations, and controls various types of mechanical equipment or production through digital or analog input and output. process.
power supply, central processing unit CPU, memory, input unit, output unit
When the programmable logic controller is put into operation, its working process is generally divided into three stages, namely, input sampling, user program execution and output refresh. Completing the above three phases is called a scan cycle. During the entire run, the CPU of the programmable logic controller repeatedly performs the above three phases at a certain scan speed.
The hardware of the PLC controller itself adopts the building block structure, and has a motherboard, a digital I/O template, an analog I/O template, a special positioning template, a barcode recognition template, etc., and the user can expand on the motherboard as needed. Or use the bus technology to equip the remote I/O slaves to get the desired number of I/Os.
While implementing various I/O controls, the PLC also has the ability to output analog voltage and digital pulses, enabling it to control a variety of servo motors, stepper motors, variable frequency motors, etc. that can receive these signals, plus a touch screen. With the support of the human-machine interface, Schneider's PLC can meet your needs at any level of process control.
(1) Open-loop control of switching quantity
The open-loop control of the switch is the most basic control function of the PLC. The PLC's command system has powerful logic computing capabilities, making it easy to implement various logic control methods such as timing, counting, and sequencing (stepping). Most PLCs are used to replace the traditional relay contactor control system.
(2) Analog closed-loop control
For the analog closed-loop control system, in addition to the switching input and output, there must be analog input and output points, so that the sampling input and the regulated output can realize the continuous adjustment of parameters such as temperature, flow, pressure, displacement and speed. With control. The current PLC not only has this function for large and medium-sized machines, but also some small-sized machines.
(3) Intelligent control of digital quantity
When the control system has a rotary encoder and a pulse servo device (such as a stepping motor), the PLC can realize the function of receiving and outputting high-speed pulses to realize digital control. The advanced PLC also specially developed a digital control module to realize the curve. The interpolation function has recently introduced a new type of motion unit module, and also provides a programming language for digital control technology, making PLC digital control easier.
(4) Data collection and monitoring
Since PLC is mainly used for on-site control, it is very necessary to collect field data. On this basis, the PLC can be connected with the host computer or touch screen, and the current value of these data can be observed, and statistical analysis can be performed in time. The PLC has a data recording unit that can be inserted into the unit using a memory card of a general personal computer to store the collected data. Another feature of PLC is the self-test signal. With this feature, the PLC control system can realize white diagnostic monitoring, reduce system failures, and improve system reliability.
Three characteristics of future PLC technology
1. Miniaturization and integration are getting higher and higher: With the market demand for micro and integration, PLC technology is more integrated into industrial, automotive, communication and other products. The characteristics of PLC products are control and data processing. While satisfying the functions, the technical requirements are also more refined.
2. Intelligent PLC technology: With the development of AI technology, more products are given intelligent functions, and PLC is no exception. For example, if it is applied to the intelligent I/O module of the industrial control PLC and the intelligent temperature control module on the vehicle, the future intelligent PLC technology will have more application scenarios.
3. Diversified PLC technology: including programming language and tools related to PLC. With the deepening of application scenarios, one or several programming languages cannot realize all functions, and customized PLC products will increase. PLC module The technology will also increase.
Nowadays, PLC technology is developing rapidly. According to statistics, there are more than 300 PLC manufacturers and more than 500 PLC products in the world. The United States, Europe and Japan are the main production sites with a market share of over 60%. The United States has A-B companies, General Electric, Modicon; Germany's Siemens, AEG; France's TE; Japan's Mitsubishi, Omron, Panasonic, etc. are well-known PLC suppliers.