PLC Device and Application
1 Introduction
A Programmable Controller (PC) is basically a central processing unit (CPU) containing a program and connected to input (I/O) devices (I/O Devices). The program Controls the PC so that when an input signal from an input device turns on ,the appropriate response is made .The response normally involves turning on an output signal to some sort of output device. The input devices could be photoelectric sensors , pushbuttons on control panels, limit switches, or any other device that can produce a signal that can be input into the PC. The output devices could be solenoids, switches activating indicator lamps, relays turning on motors, or any other devices that can be activated by signals output from the PC.
For example, a sensor detecting a product passing by turns on an input to the PC. The PC responds by turning on an output that activates a pusher that pusher that pushes the product onto another conveyor for further processing. Another sensor, positioned higher than the first, turns on a different input to indicate that the product is too tall. The PC responds by turning on another pusher positioned before the pusher mentioned above to push the too-tall product into a rejection box.
Although this example involves only two inputs and two outputs, it is typical of the type of control operation that PCs can achieve. even this example is
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