Programmable Logic Controllers are simply industrial computers, being the basic component of every control system. Their main task is to run programs and communicate with other devices within a given system, such as inverters, remote I/O systems, HMI panels or SCADA systems. PLCs comprise a processor that computes all logical and arithmetical operations. Taking their mechanical construction and application into account, Programmable Logic Controllers can be divided into compact PLCs for simple applications, compact PLCs with an integrated HMI panel for workflow virtualisation and modular PLCs designed to operate within medium and large systems.
PLCs supervised by a real time operating system can control machinery and equipment in both open and closed systems. Each controller is equipped with a communication port as a standard. This port can be used for programming and communication with other devices. Controllers with programmable memory are used to monitor and control complex processes.
A PLC monitors inputs, makes decisions on the basis of a user program and controls outputs during automated processes. The controller analyses inputs on the basis of data sent from a program, analyses input states and uses input modules to collect data from analogue and discrete measuring sensors. The data is then sent via modules and communication connections, and programs are run on the basis of the collected parameters and data regarding a given process or a machine. In the next stage, control signals are generated according to the program calculation results, which are then sent via output modules to actuators. Moreover, PLCs carry out software and hardware diagnostic tasks.