Programmable logic controller:
Block diagram:
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Explanation: PLCs are industrially hardened microcomputers that perform discrete or continuous control functions in a variety of processing plant and factory environments.
PLC architecture consists of the following main units.
1. Power supply: Power supply unit converts power line voltages to those required by the solid state components.
2. Input / Output system: Inputs are real world signals of sensors. These signals can be Analog or Digital, low or high frequency, continuous or momentary. Outputs can be of discrete, register or analog.
3. Central Processing Unit (CPU): It performs the tasks necessary to fulfill the PLC functions such as scanning, I/O bus traffic control, program execution, peripheral and external device communications, and data handling and self-diagnostics.
4. Memory Unit: This is the library where the application program, input data, as well as output data are being stored.
5. Programmer Unit: Programmer unit provides an interface between the PLC and user during program development, start-up and trouble shooting