PLCs are solid-state machines called programmable logic controllers that are used in industrial settings to make logical decisions for control purposes. The PLC was adopted right away by the automobile sector and is now widely used in a variety of sectors. Relays, solid-state electronics, or small computers were once needed to do tasks that the PLC can now complete. PLCs are compact, robust machines that don't require fans, air conditioning, or electrical filtration to function.

There are three parts to programmable logic controllers. The CPU, the power source, and an input/output (I/O) section make up this PLC.

The Processor

The PLC system's processor, sometimes known as the brain, is a solid-state device created to carry out a variety of production, machine tool, and process control tasks. These tasks were formerly carried out by conventional electromechanical devices, relays, and the wire that accompanied them. The PLC is a far more popular option because processors can easily do the same tasks in a larger range of control operations.


The power supply provides DC electricity (around 5V) for the processor to use. A portion of the I/O and devices attached to the service port of the PLC are powered internally through the processor. The processor retains the ladder-diagram program after it is entered until the user modifies it using one of the programming tools. In the event of a power outage or power off, the programme remains unaffected.

The Power Supply

A Programmable Logic Controller's power supply transforms the input source power into the voltages needed for internal circuitry. In rare circumstances, it also offers an isolated VDC supply to power switches, other indicators, and DC input circuits. The PLC's power supply is a crucial part of how the PLC functions.

The PLC Input/Output (I/O)

A PLC's internal circuits would be severely impacted by electrical noise, such as power line spikes or load kick-back, because the CPU of a PLC runs at extremely low voltage levels. The PLC's input/output (I/O) section is crucial in this situation. The CPU is shielded from electrical noise by the I/O, which includes inputs and outputs. Status signals are noise-filtered in the I/O section, voltage levels are verified, and CPU decisions are made and executed. The status of the PLC inputs is provided to a storage area in the CPU, and the status of the outputs is driven by a similar stored status in the CPU.

Pushbuttons, limit switches, and sensors from the outside world are attached to the PLC input modules. These modules monitor the state of the input signals and send a stored image to the input components of the ladder logic when the state changes. The Programmable Logic Controller's input parts mimic the behavior of relay contacts. The output modules in the I/Os then "activate" the output elements, producing the desired output signals to operate loads like motor controllers, contactors, solenoids, and pilot lights. Ladder logic generally takes one word of memory per instruction. Series contacts are ANDed and parallel contacts are ORed for each instruction.

There are programmable logic controllers with I/Os up to 1000 and operating voltages ranging from 12V to 240V AC or DC.

PLC Programming

Programming is easy with Programmable Logic Controllers. They communicate in a relay ladder language that is remarkably reminiscent of magnetic relay technology. Without much training or experience, engineers, technicians, and electricians can learn to programme the PLC. Compared to relay or solid-state electronics, employing programmable logic controllers has many benefits. Changes in a PLC can be made rapidly and frequently without changing the controller's hardware. PLCs are reusable, and they have indication lights at key diagnostic areas that help with troubleshooting. It is dependable, made for an industrial setting, and simple to maintain. The Programmable Logic Controller is adaptable and capable of carrying out numerous tasks in addition to saving money.