The automation of various processes, such as controlling machines or factory assembly lines, is done through the use of small computers called programmable logic controllers (PLCs). This is actually a control device consisting of a programmable microprocessor and is programmed using a specialized programming language. A modern programmable logic controller is usually programmed in any one of several languages, ranging from the ladder to Basic or C. Normally, the program is written in a development environment on a computer, and then is downloaded to the programmable logic controller directly through a cable. The program is stored in the programmable logic controller in nonvolatile memory.
Programmable logic controllers typically contain a variable number of input / output (I / S), and generally reduced instruction set computer (RISC) based. They are designed for use in real time, and often must withstand hostile environments in the workshop. The programmable logic control circuit monitors the status of multiple sensor inputs, which control output actuators, which can be things like motor starters, solenoids, lights and displays, or valves.
This driver has made a significant contribution to factory automation. Earlier automation systems had to use thousands of individual relays and timers cams. In many cases, a PLC allows all relays and timers in a factory system to be replaced by a single controller. Today, programmable logic controllers offer a wide range of functions, including basic relay control, motion control, process control, and the creation of complex networks, in addition to being used in distributed control systems (DCS).
Digital signals produce a signal on or off, the programmable logic controller sees as Boolean values, which have only two states: true or false. Analog signals can also be used, such as from devices like volume controls, and these analog signals can be viewed by the programmable logic controller as floating point values. This is one way in which a computer can be a rational number, but may be inaccurate.
There are different types of interfaces that are used when people need to interact with the programmable logic controller to set up or work with him. It can be configured with simple lights or switches, or a text display. More complex systems may use a web interface on a computer with a supervisory control and data acquisition (SCADA).
Programmable logic controllers were created to serve the automotive industry. The first draft logic programmable controller was developed in 1968 by General Motors to replace wired relay systems with an electronic controller.
