The 6 Essential Parts Of Every PLC System

Manufacturing has come a long way from the old assembly lines used a decade ago, and the automation of manufacturing processes has been a big part of that.

As a result, the quality of products has increased and the efficiency at which they can be made has increased tenfold. Programmable Logic Controllers, or PLCs, are an essential part of this automation process and are an essential part of any modern manufacturing business.

In this guide we’ll be going through 6 of the essential parts that make up a PLC system, so you can increase your understanding and implement that knowledge in building your own.

Essential parts of every PLC system - 39898983

A Processor or Central Processing Unit (CPU)

The central processing unit, or CPU, is essentially ‘the brain’ of any PLC System. It tells the parts what to do and holds all the information that we need to make the automated process work. They function by using a programming language that can vary between CPUs.

There have been attempts to standardize this language, but ultimately there are still 5 different languages being used. These languages are Structured Text (ST), Function Block Diagram (FBD), Sequential Function Chart (SFC), Instruction List (IL), and Ladder Diagram (LD). If you are buying a CPU from a manufacturer be sure that its programming language is right for your process.

Inputs And Outputs (I/O)

Inputs and outputs refer to the materials that we interact with that make the process work. An input module, for instance, could be a button or a switch, while an output module could be a motor or a light. An input module or assembly has two functions; to receive external signals from field devices, and to display an input point status. An output module executes commands and controls the manufacturing processes.

There are two types of (I/O) relationships — analog and specialty. Analogue I/O controls things that are responsible for a range, based on other factors that also have a range. For instance, an Analogue I/O could control the speed of a motor based on temperature or pressure. Specialty I/Os perform specific tasks like counting at high speed. This can also include Digital I/Os that operate using binary change.

Power Supply

The Power Supply, as you might have guessed, supplies the PLC with power letting it operate. They most commonly supply the system with 24VDC or 120VAC of line voltage and are continuously monitored to make sure they are operating properly.

Programming Tools/Unit

Most PLCs require some programming software that allows you to troubleshoot your PLC in the event of a malfunction. This used to come in the form of small portable devices, but nowadays, they’re more often than not built into the system themselves. These programs can also include simulation environments to make sure that your PLC will work correctly when you begin to run it.

Human Machine Interface

A Human-machine Interface, or HMI, is a system part that allows a user to adjust, control, or troubleshoot their machine. It normally involves a screen to display information and a touchpad or keyboard to input commands.


Most PLCs contain parts that aid in networking, that is communicating with other devices in their system. These can be as simple as running a wire from component to component or as complex as controllers systems communicating via a shared memory block. More complex decentralized systems generally work better and provide a faster response time.

Final Thoughts

In sum, PLCs are more relevant than ever, so it’s essential you get up to scratch on the parts that make them tick. Hopefully, this short guide will provide you with enough information to get started, so you can make an informed decision when investing in your own PLC.