What is the PLC?
PLC(Programmable logic controller): An industrial digital computer which has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability, ease of programming and process fault diagnosis.
The above is the definition of PLC in Wikipedia. In short, PLC is simply a special computer which is programmed to control certain processes in industries like petroleum, Steel or Automobile, which can can range from small modular devices with tens of inputs and outputs (I/O), in a housing integral with the processor, to large rack-mounted modular devices with a count of thousands of I/O, and which are often networked to other PLC and SCADA systems.
What are the components of PLC?
PLC have three components which are processor, power supply, and an input/output (I/O) section.
- Processor:Just like human's brain, the processor is the most vital components of PLC, which is a solid-state device designed to perform a wide variety of production, machine tool, and process-control functions. A wide scope and variety of control functions performed by conventional electromechanical devices, relays and their associated wiring formerly can be provided by the Processors, which make the PLC a much more popular choice.
Power Supply:Power supply of PLC converts the input source power into voltages required for internal circuitry.Beside, it can also provide an isolated VDC supply to power DC input circuits, switches and other indicators.The Power Supply of the PLC is an essential component to running the PLC.Blow are examples of Power Supplies that may be found in a PLC
- PLC Input/Output (I/O):PLC Input/Output(I/O) protects the cpu from electrical noise(spikes in the load kick-back or power lines.) which would have serious impact on a PLC's internal circuits since its CPU operates at very low voltages levels.The I/O section is where status signals are filtered to remove noise, validate voltage levels, and CPU decisions are made and put into operation. The PLC Inputs provide their status to a storage area within the CPU and outputs are driven from similar stored status in the CPU.
How the PLC work?
Suppose in such an industrial scenario, we have an electrical motor and a push button.We want the motor to turn on when pressing the button.Pressing the button again, we want the motor to turn off. This function s similar to the that of the power button on your TV remote.
Programming with PLC, we must first write a program for this operation on a computer and then download it to the CPU.Then we connect the switch to the input and the motor to the output.if we press the button, an electrical signal will be sent to the PLC. The PLC input will deliver this signal to the CPU but first must present it in a format that the CPU can process.Because the CPU is a computer system and cannot process the raw electrical signal.So it will process the data received and send the result to the output.And then, the output turns the data to a raw electrical signal again and applies that to the motor and turns it on. If we switch the button again,the process repeats and the motor will turn off.