At former epoch, before PLC is found, control systems at industry applies conventional network, which in the form of network relay. By using this network, we require many places and many components, besides need many cables also to string up it is and many releasing cost that is big enough to make a conventional control system.
PLC in finding around year of 1968 and company that is firstly makes is Schneider electric by the name of MODICON (Digital Modular of Controller). After the time/date of that is automation network many changes, and increasingly simple. As according to the name, this controller earns in program to apply logic, it is of course understandable logic by PLC. Logic that is most popular and many in using in PLC is Ladder logic, or doorstep logic. very Popular doorstep logic, because is adaptation from contact logic and relay. If you understood about contact logic and relay, you are not too difficult to comprehend programming PLC. Here also applies ladder logic program PLC to. In general usage of unlimited PLC, now control PLC is not merely limited to control ON/OFF (digital/discrete), PLC here and now can control magnitude (analogue) for example motor speed, level tank, big value of aperture valve and others. At the moment PLC often applied for controller sequential, and monitoring plant.
Sequential Control/ Drum sequencer
PLC ahead created to make control sequential or drum sequencer, which if using network relay and timer, hence inefficient. Mean a lot of relay and timer require, depends on how many step at the sequence (drum sequencer I debate later). If would apply PLC, enough one PLC, relay and timer can be replaced with software in PLC. ‘PLC can replace relay and timer', because PLC has relay and timer virtual in it.'
Monitoring Plant
PLC is also able to be applied as one of component for monitoring plant. Ably its receiving magnitude value data from sensor/transmitter. as well as can communicate with other peripheral, hence by connecting PLC with HMI (Human machine Interface), we can monitor condition of plant. now a lot of producer HMI, started from only sells software only, until selling its(the hardware is also, and most HMI now supports communications with Merk PLC distinguised like mho, Omron, and others. One Of Merk HMI which distinguised is: WinCC (mho), Wonder ware, Proface, LG, and others. Usually producer PLC produces also its(the HMI.
