2.History and development
• Before the PLC, the automation control system was mainly composed of time relays, contactors, position switches, current relays, voltage relays, middle relays, speeding relays, control buttons, air switch and so on.
•Learning outcome:
•Understand roughly about PLC technology including applications, history and development, hardware and software.
•Can design a simple ladder diagram to control the motor to start and stop.
•The PLC have been widely used In the power system , such as intelligent electric meter with PLC.
•intelligent e lectric meter s with PLC
• In these applications, the PLC replaced the hardwired logic with relay ladder logic, a programming language visually resembling the hardwired logic reduced the time for designing a control system from 6 months down to 6 days.