The origins of industrial automation were relay-contact control circuits for production functions. Such devices had a specific unpleasant sound of work. The logic of work was fixed, and with the slightest deviation from the given algorithm of actions, it was necessary to radically change the entire installation chain.
With the development of technology in this area, processors have evolved greatly. This served as a catalyst for the creation of process control systems based on industrial PLC controllers.
The first such programmable controllers were used in the United States. They served to organize automation in the assembly line assembly line in the manufacture of automobiles. Applying this technology was the company "Modicon" in 1968.
Device description
Programmable logic controllers PLC is a program-controlled machine with many inputs that are connected to the object using control sensors. The outputs are connected to command execution devices . The microprocessor is an important component in the design of the controller. Its task is to collect information, transform and store it for the possibility of further development of management teams. One of the main advantages of a programmable controller is that it functions in real time!
Previously, relay controllers had cumbersome overall dimensions, performed the simplest switching operations. Their logical structure was monolithic, not changeable. The replaced PLC controllers were compact in size, the control algorithm rose to a new, complex level of performance. The process of free programming has appeared.
Logic Controller Features
When developing PLCs, the creators pursued the goal of the ability to control logical functions in a serial circuit. Currently, programmable controllers can not only perform logical operations, but also process signals in a digital representation, control various drives, engage in adjustment, and have acquired electronic operator control skills.
At the moment, devices are widely used in various directions. For example, the PLC 100 controller is designed to create automated control systems for production equipment in industry, agriculture and housing and communal services. PLCs are also used in the energy sector, in communications, and in the chemical industry. The devices have found their niche in the production and transportation of oil and gas, in safety systems, are involved in the automation of storage facilities, in food production, in the transportation sector, construction and in many other areas of human life.
Distinctive features
PLC controllers have some characteristic differences for electronic devices used in industry.
Firstly, programmable logic devices differ from parallel-functioning microcontrollers in using in the field of automated processes in enterprises with an industrial bias.
Secondly, programmable controllers are aimed at interacting with devices by means of advanced input of sensor signals and outputting them to actuators, unlike computers that are adapted for decision making due to operator control.
Thirdly, PLC controllers are distinguished from embedded systems by self-sufficiency in terms of their manufacture as an independent product, separate from equipment controlled with its help.
PLC Benefits
The programmable PLC controller is also easy to contact with the user. This is expressed in the actions for programming the PLC itself according to the principle scheme, according to logical equations and using the basic algorithmic language.
The device is adapted for operation in negative production conditions, using optical electronic isolation of inputs / outputs from external electrical circuits as its asset. This was made possible due to the controller being adapted to a wider range of operating conditions.
The advantages of programmable controllers include software mobility through the unification of programming languages, wide functionality, rapid change of modular nodes, real-time operating mode, the possibility of repair and system integration.
Device selection
When choosing a PLC, they are guided by such basic criteria as the technical capabilities of the assigned task and, of course, the cost of the device.
A huge number of manufacturers are engaged in the release of these controllers. The list includes both foreign firms and domestic ones. For example, the Russian company Aries offers a PLC 150 controller that meets all the necessary technical conditions. Also on this list are manufacturers of Elemer, Emikon, Tecon, Fastvel, NIL AP and many others.
Famous foreign manufacturers are Siemens, Mitsubishi, ABB, Omron, Schneider Electric, etc.
Over time, there has been a trend in the evolution of programmable logic controllers. They lose in overall dimensions, expand the range of functionality, add the number of compatible networks and interface shells, the idea of "open systems" is included in widespread use, the programming language is standardized, and the realized price is reduced.
It is worth noting that the advantageous distinctive features of programmable controllers from personal computers remain in the form of appointments and the presence of a technological programming code.
Principle of operation
The operation of PLC controllers is slightly different from standard microprocessor devices. The software shell of these logical controllers includes two parts. Like a computer operating system, the controller software manages work nodes, links components and deals with internal diagnostics. The PLC system shell is located in the permanent memory of the central microchip and is always ready for operation.
The programmable controller operates in cyclic mode by periodically collecting input information. This cycle has 4 stages:
- Interrogation of inputs.
- Execution of tasks set by the user.
- Setting the output parameters.
- Other supporting operations processes.
Controller Classification
Regarding I / O lines, PLC controllers are classified into:
- nanocontrollers;
- microcontrollers;
- medium controllers;
- large controllers.
Regarding the location of the input / output modules, there are:
- monoblock;
- modular;
- distributed.
Depending on the installation method and design of the PLC, there are:
- panel;
- for fastening inward on a special rail;
- for wall mounting;
- for mounting in a rack;
- not having a case (one board).