What is a PLC? Components and Working Of PLC!

Kevin Richard
Jul 1 · 3 min read

What is a PLC?

PLC Stand for Programmable Logic Unit. A PLC is an industrial digital computer that is specifically designed to operate in harsh environments and conditions. These are made to operate or automate a single process or machine function. This is generally made to replace hardwired relays, timers, and sequencers used in the rugged environment and unfavorable conditions for electrical equipment.

Components of PLC:

Components Of PLC

PLCs are small industrial computer units that are designed to perform a specific task or automate a task. PLC consists of 3 major components that perform the complete functioning of a PLC: A Processor, Power Supply and I/O Section.

A Power Supply: The Power Supply Unit of a PLC converts the input source into the required circuitry voltage. The power supply usually requires 110 Volts that is then converted into DC and transferred to the respective components.

PLC Component- Power Supply

A Processor: The Processor or the brain of a PLC performs operations from the inputs received from the Input Device. It is the main Logical unit that organizes all control activities by receiving the inputs, perform the logical decisions and controlling the outputs.

Components of PLC- Processor

I/O Section: It as the body for the brain of a PLC. The Input Section receives the information from real-world input sources like push buttons, temperature switches, sensors, proximity switches, etc. The Output Section than delivers the obtained result from the Processor in the form of output Voltage required to control the loads such as alarms, lights, solenoids, etc.

How PLC Works?

How PLC Works

The Working of a PLC generally really on its components. The power supply transfers regulated direct current power to the PLC. The power supply will generally run off of 120 VAC or 24 VDC sources. This means that depending on the PLC that is selected it will most likely be able to be powered by a standard wall outlet.

The CPU is like the brain of the PLC. This is where a microprocessor, memory chip, and other integrated circuits come together perform logic control, monitoring, and communications. The CPU of the PLC has different operating modes. Programming mode allows programs/logic to be downloaded from a PC source. Run mode is what the PLC is set to when a functional operation is desired. Since a PLC is a dedicated controller it will only process a singular program over and over again. Once the cycle through the program is called a scan time and involves reading the inputs from the other modules, executing logic based on these inputs and then updating the outputs accordingly. The CPU memory stores the program, statuses of I/O, and can store values if necessary. There are many different types of I/O configuration for a PLC.

Input devices can be either digital or analog. Digital inputs are specific values or on/off, analog inputs, on the other hand, need to have their voltage or current converted to a digital equivalent number before they can be processed. Outputs can also be both digital and analog. The digital output would turn something on or off. An analog output would be converted back to its voltage or current representation which can then be used to drive mass flow controllers, pressure regulators, position controls, and more.

Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch
Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore
Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade