What are the basic operations of a PLC controller?

Many production lines, machine functions, or processes across several industries from theme park rides to factory assembly lines utilise a Programmable Logic Controller (PLC). This type of industrial computer control system makes automating operations simpler, as it monitors input devices and makes decisions in order to effectively control the condition of output devices. Implementing a PLC into any production or mechanical process will be very beneficial. Read on to learn more about the basic operations of a PLC, so you can see how a bespoke control panel could help your business. 

Operations of a PLC 

A PLC works by following four key steps: 

  • The input scan verifies the status of all input devices linked to the PLC  
  • Program scan executes the user-created logic 
  • Output scan – energises or de-energises all output devices connected to the PLC 
  • Housekeeping – including communicating with programming terminals and internal diagnostics 

Common components of a PLC


The processor is the most important part of the PLC, without it the control panel would be unable to function. Different types of PLC will come with a different processor depending on its intended uses and the scale of the application. Its main function is to determine key elements of the PLC like available memory, programming functions, processing speed, and the size of the application logic to name a few examples. 

Input assembly 

The PLC system’s controller receives signals from the processor via the input assembly. It can have various types of inputs based on the exact programming and it includes different pressure sensors, operator inputs, and switches. Also, input can be split into analogue and digital categories with each being managed by its own specific class. 

Output assembly 

Output assembly takes the data produced by the PLC and transmits it to other applications. Also known as the actuator, outputs aren’t received at their end destination in the same way that they are sent. Again, based on the input type the output can either be analogue or digital. 


A rack in a PLC is used to keep different components in one place, it can also be called housing. It’s essential that the rack is carefully designed to ensure it can effectively handle the components it needs to and is strong enough to hold more than one PLC bricks. With this in mind if you know you need a PLC for your operations, it is always best to get a professional industrial control panel design. This will give you full confidence that your PLC system and all its parts are made specifically for the needs of your processes and business. So, it will be as efficient, long-lasting, and cost effective as possible. 

Programming device 

The programming device as the name suggests is the component that programs the PLC as each system comes with its own software and code. The programmer makes the different logic and implements it in different units. It is essential that this device is in full working order and is programmed in the correct way for the PLC to function effectively.

What are some examples of input/output devices? 

Input device 

A device used to input data and control signals into a computer system is known as an input device. Examples include but are not limited to: 

  • Proximity sensors 
  • Photoelectric sensors 
  • Limit switches 
  • Pressure switches 
  • Temperature switches 
  • Level switches 

Output device 

The role of an output device is to communicate data processing results and outcomes from an information processing system and translate it into an understandable form. Examples of output devices include: 

  • Actuators 
  • Motor starters 
  • Valves 
  • Horns and alarms 
  • Fans 
  • Pumps 
  • Printers 

Why do you need a PLC? 

There are many advantages for businesses who decide to implement a PLC into their processes: 

  • PLCs increase the functionality of controls without taking up a lot of space in your facility 
  • They can calculate, count, compare analogue process values as well as complete relay switching tasks 
  • It’s easier to modify control logic whenever you need to with a PLC 
  • Simple trouble shooting capabilities 
  • No need for rewiring and adding extra hardware for every new logical configuration 
  • They are sectional, meaning you can mix and match to find the ideal combination of input and output devices to suit your operation 



Do you think a PLC is right for your business and processes? The team at FESS are experts in control panel build and installation services. We can help design the most suitable PLC for your requirements and seamlessly integrate it with your existing processes. Contact us today to discuss your needs or if you have any questions. Alternatively, you can book a free site survey with us online and we can assess any other ways we could help you make your operations more efficient and cost effective. 

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