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The automation of many different processes, such as controlling machines or factory assembly lines, is done through the use of smallcomputers called a programmable logic controllers (PLCs). This is actually a control device that consists of a programmablemicroprocessor, and is programmed using a specialized computerlanguage. A modernprogrammable logic controller is usually programmed in any one of several languages, ranging from ladder logic to Basic or C. Typically, the program is written in a development environment on acomputer, and then is downloaded onto the programmable logic controller directly through a cable connection. The program is stored in the programmable logic controller in non-volatile memory.Programmable logic controllers typically contain a variable number of input/output (I/O) ports, and are usually Reduced Instruction Set Computer (RISC) based. They are designed for real-time use, and often mustwithstand harsh environments on the shop floor. The programmable logic controller circuitry monitors the status of multiple sensor inputs, which control output actuators, which may be things likemotor starters, solenoids, lights and displays, or valves.
This controller has made a significant contribution to factory automation. Earlier automation systems had to use thousands of individual relaysand cam timers. In many cases, a PLC allows all of the relays and timers within a factory system to be replaced with a single controller. Today, programmable logic controllers deliver a wide range offunctionality, including basic relay control, motion control, process control, and complex networking, as well as being used in distributed control systems (DCS).
Digital signals yield an on or offsignal, which the programmable logic controller sees as Boolean values, those with only two states: true or false. Analog signals may also be used, such as those from devices like volume controls,...