Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Hence, a programmable logic controller is which programmable logic controller specialized computer used to control machines and processes. It therefore shares common terms with typical PCs like central processing unit, memory, software and communications.
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Unlike a personal computer though the PLCis designed to survive in a rugged industrial atmosphere and to be very flexible in how it interfaces with inputs and outputs to the real world. The components that make a PLC work can be divided into three core areas. PLCs come in many shapes and sizes. They can be so small as to fit in your shirt pocket while more involved controls systems require large PLC racks. For our consideration, we’ll look at the more modular rack based systems. O modules that simply slide into the rack and plug in.
The rack is the component that holds everything together. Depending on the needs of the control system it can be ordered in different sizes to hold more modules. Like a human spine the rack has a backplane at the rear which allows the cards to communicate with the CPU. The power supply plugs into the rack as well and supplies a regulated DC power to other modules that plug into the rack. The most popular power supplies work with 120 VAC or 24 VDC sources.
The brain of the whole PLC is the CPU module. This module typically lives in the slot beside the power supply. Manufacturers offer different types of CPUs based on the complexity needed for the system. The CPU consists of a microprocessor, memory chip and other integrated circuits to control logic, monitoring and communications. The CPU has different operating modes. In programming mode it accepts the downloaded logic from a PC.