Programmable logic controller is defined as specialized electronic devices designed for use in the control of a wide variety of manufacturing machines and systems. 3.
The PLC business is a 6.5 billion dollar industry that is growing at 20% per year. There are about 110 programmable controller venders, over 1000 vendors offering PLC add-in boards and other peripherals, and over 2000 companies developing PLC solutions. 4.
Some similarities between PLC and PC are that they both have a similar architecture, with both having a motherboard, processor, memory, and expansion slots. Some differences between PLC and PC is that a PLC has no removable or fixed storage media such as floppy or hard disk drives and PLCs do not have a monitor, but often use a human machine interface (HMI) flat screen display. 5.
The major difference is that the virtual relay used in a PLC ladder logic program is only limited by the size of the PLC memory, while the physical relay used in relay ladder logic is limited to the nuber of poles present on the relay selected. 8
. The input contacts in a relay logic diagram represent actual components and contacts present in the control system, while the input instructions in the PLC ladder logiconly represent data values stored in the PLC. 10.
The processor is the central processing unit (CPU) that handles all logical operations and performs all the mathematical computations. The power supply provides power to the processor and to the modules plugged into the rack. The input interface provides the link between the processor and the external devices that measure the conditions in the production area. The output interface is both a location for termination of wiring and a signal conditioner to provide the proper voltage and output drive power required by the output field devices. 12.
Ethernet/IP is the highest level of network control that provides the information layer for plant-wide data collection and program...
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