WHAT are the advantages plcs have over relay system?

Learn about some of the advantages that PLC systems have over a relay system.

There are many advantages that a PLC system holds over a relay system. Today, we will dive into some of the advantages of PLCs. One of the first and simplest advantages is reliability.

1. Reliability

The internal relay systems of a PLC are solid state. This means that the relay function is not mechanical like conventional relay systems and components.

Traditional mechanical relays wear out much faster than the electronics in a solid state relay. Every time a mechanical relay opens and closes, the contacts will arc slightly. The arcing can eventually destroy the contact. This is simply not the case with the solid state type relays found in our PLC systems.

2. Ease of Troubleshooting

Another advantage of a PLC system is the ease of troubleshooting. In a PLC system, a good technician can read through the programming and usually figure out what is and isn’t working.

In a relay system, there will be several more wires plus the relays and possibly other components that aren’t needed in a PLC. This makes finding problems much harder.

Each physical relay needs a minimum of four wires to operate and function.

A relay output card on a PLC sends out one wire to the output device.

You can only imagine how much easier it is to troubleshoot the PLC system with multiple outputs versus the relay system with four times the number of wires.

3. Easy Expandability

One of the best features that a PLC system has over a traditional relay system is versatility with the programming and easy expandability. For example, if you wanted to add a timer to make a motor turn on after five seconds, you would just add it to the program and set it to five seconds in the PLC.

For a relay system, you would have to add an entirely new physical component. On top of that, you would have to add all of the proper wiring to make that timer work for the specific motor. This also makes expanding a system much cheaper. Not only for component costs but labor savings as well. If you have a relay system, someone will have to be paid to install a wire all of the new components.

4. Smaller Size

The physical size requirements of a PLC system are far smaller than a cabinet needed for relay logic circuitry.

Most of the physical relays, timers, counters, and controllers from a relay logic system are all contained in the PLC itself.

Depending on the machine, a cabinet containing the PLC can easily be a third of the size of a relay logic cabinet. Possibly even smaller.

Let’s look back at what we now know. PLCs are much more reliable and are way easier to troubleshoot.

The mechanical functions of relays simply wear out over time. Plus, the wiring required to operate a relay system is much more complicated than a PLC system. This can also cause higher costs to install and upgrade due to extra labor costs.

One of the major advantages is the versatility of a PLC with its programming and internal relays, timers, counters, among other features.

I hope you have enjoyed this newest installment from RealPars. Please check back soon for more useful videos. Thank you so much for your valuable time visiting our website. Please share your thoughts and ideas or questions directly in the comments.

With so much love and excitement,

The RealPars Team

By Kevin Cope

By Kevin Cope

Instrument Mechanic

Posted on July 16, 2018

By Kevin Cope

Instrument Mechanic

Posted on July 16, 2018

5 Actionable Tips for Getting a PLC Programming Job with NO Experience

5 Actionable Tips for Getting a PLC Programming Job with NO Experience

In this blog post, you’ll learn about the mindset that helped me getting a PLC programming job with NO experience. This is my personal experience as someone who searched for a job in this field and as an employer who reviews resumes and interviews candidates for a variety of projects. So let’s get started!

Open PLCs: Unlocking the Power of Industrial Automation

Open PLCs: Unlocking the Power of Industrial Automation

Programmable Logic Controllers (PLCs) have been the backbone of control systems for a long time. However, traditional PLCs have been known for their close architecture which results in limited flexibility in programming and also integrations with other systems. This...

What is an Open PLC?

What is an Open PLC?

To program a PLC, I need to write a program on my computer and download it to the PLC. To be able to write the program on my computer, I need programming software, right? I can not just open up my laptop and start writing codes. For example, to write code in C++ on my...

RealPars is the world's largest online learning platform for cutting-edge industrial technologies. 

[email protected]
+31 10 316 6400
Mon - Fri  8:30 am to 5:30 pm (CET)

Rotterdam Science Tower,
Marconistraat 16,
3029AK Rotterdam, The Netherlands



Terms of Service






Sign in


Contact Us

Help & Support

Refund & Cancellation Policy

© 2023 RealPars B.V. All rights reserved.

Created with coffee and tea in Rotterdam.