PLC vs. Relay-Based Control Systems: Making the Right Choice for Industrial Applications

Hard-wired logic has been widely used in the industrial sector for many years, and can still be a good choice. Many industrial businesses have switched to programmable logic controllers (PLCs) for their automation and control needs. But how do you know which is best for your business?

We compared PLCs vs relay-based control systems to help you make the right choice for your industrial applications.

Key Differences Between PLC and Relay-Based Controls

The global PLC market is growing, and by 2026, the market size should amount to over 15.5 billion USD.

A quick look at these key differences between PLC control systems and relay-based automation highlights why PLC systems are often the better choice.

Versatility

PLC systems offer more programming flexibility and, therefore, more versatility. You can easily program or reprogram them as needed; no rewiring or replacement is necessary. Relay-based controls, on the other hand, will require rewiring to match the logic change.

Accuracy

PLCs are prized for their accuracy, even in more complex systems. They are less prone to failure than traditional relay-based systems. PLCs are also better for extreme environments. They are more resistant to vibration, temperature fluctuations, and changes in humidity levels than traditional relay systems.

Reliability

Mechanical relays tend to wear out. PLCs, on the other hand, are very reliable, and even when things go wrong, built-in diagnostics make them easier to troubleshoot than relay-based controls.

Several types of relays can be used inside PLCs, too. The most common are electro-mechanical, which are great for handling high currents.

Cost-Efficiency

When it comes to cost-efficiency, there are two factors to consider: initial costs and running costs. Relays, particularly smart relays, are more cost-effective initially. However, PLCs typically offer more durability, reliability, flexibility, and scalability, which equals better cost-efficiency in the long term.

Integration

Relay logic is ideal for smaller and simpler control systems. But for larger and more complex systems, PLCs are the better choice. PLCs easily integrate with other industrial control systems, including Supervisory Control and Data Acquisition (SCADA) systems and Human-Machine Interfaces (HMI).

Response Times

In industrial automation and control, efficient response times are crucial. PLCs process inputs and outputs in real-time. They offer faster response times than conventional relay-based control systems. Built-in redundancy measures mean they maintain operations in the event of a system failure.

When to Use PLCs vs. Hardwired Relays

Hardwired relays offer affordability, simplicity, and reliability in smaller, simpler settings. There’s no software to manage, making it resistant to cyberattacks. However, programmable logic controllers are the way to go for more complex industrial automation operations.

PLCs are the popular choice because they are suitable for complex logic and sequencing, diagnostics, and integration capabilities. They’re easy to troubleshoot and modify, and can save you money in the long term. They can save space, too, by replacing relays, counters, timers, and other components. 

PLCs are particularly useful for businesses that require accurate data analysis, with remote monitoring and management. And because they allow predictive maintenance, they are essential for businesses that cannot risk unplanned downtime.

Case Studies: Upgrading Legacy Systems for Increased Efficiency

PLCs have come a long way since they were first introduced into the industrial sector. That’s why businesses across the US and worldwide are upgrading their legacy systems. Today’s modern, more sophisticated PLCs and improved control panel design increase efficiency across industries.

Here are two examples.

Automotive Parts Manufacturer

A leading automotive parts manufacturer decided to upgrade their production line with a modern PLC system. Their primary goals were to 1) streamline operations, 2) improve quality control, and 3) reduce downtime.

Let’s look at what the new PLC system they installed achieved:

• Various manual processes became automated. This reduced their cycle times and increased production.
• Real-time monitoring could detect and correct any defects earlier in the production process.
• The new PLC system gave them feedback mechanisms that improved their overall product quality.
• Predictive maintenance features minimized unexpected failures and reduced unscheduled downtime.

Chemicals Company

A U.S.-based chemicals company found that its outdated plant control system was impacting operational efficiency. It could no longer support the plant’s growing demands. They looked for an economical solution to address these limitations.

The newer PLC system they installed did the following:

• It improved the plant’s operational efficiency.
• It offered advanced functionalities that improved process monitoring and control.
• Best of all, it leveraged data analytics to optimize the plant’s productivity.

Conclusion

The choice between relay-based control systems and PLCs comes down to how complex your systems are and your need for scalability. But while hardwired relays still offer affordability and reliability in simpler setups, PLCs are best-suited for complex automation and control settings.

Modern PLC systems and custom control panels are making a difference in all industrial applications.

AEC is a licensed ETL 508A panel building shop. From custom industrial control systems and panels to standard automation and control components and services, we have everything needed to meet modern demands. Contact us today for more information.