Selecting the right control system is crucial for future-proofing your automation efforts. When scoped appropriately, you’ll avoid costly errors and unnecessary guesswork. Two of the most popular options are smart relays and Programmable Logic Controllers (PLCs). Keep reading to learn what’s best for your specific applications.

Smart Relays vs. PLCs: Basic Overview

At their core, both smart relays and PLCs manage and oversee industrial processes. While they share the same purpose, the technology that powers them and the range of tasks they can handle are quite different.

Smart Relays

Smart relays are small, compact devices installed directly on electrical circuits. Also referred to as "mini-PLCs" or "logic relays," they let you wirelessly control different connected devices, simple machines, and applications.

Smart relays are designed to execute simple programs or schedules, making them ideal for industrial environments where efficiency is a top priority. Unlike more complex control systems, smart relays don't require or accept sophisticated input, which makes them easier to implement. They’re a convenient choice for those seeking to add wireless control and basic PLC-like functionality to their electrical systems.

Programmable Logic Controllers (PLCs)

PLCs are specifically designed for industrial automation and control. As the name implies, these devices can be programmed to perform various tasks, from simple on/off controls to complex process management.

PLCs are equipped with a central processing unit (CPU), input/output (I/O) modules, and a power supply, allowing them to interface with various sensors, actuators, and other industrial equipment.

What sets PLCs apart from smart relays is their greater programmability. You can easily tweak and optimize them to accommodate changing processes or more advanced control strategies. Need to integrate with other automation systems like Supervisory Control and Data Acquisition (SCADA) or Human-Machine Interfaces (HMIs)? No problem! PLCs can be reprogrammed on the fly to keep up with your changing needs.

Choosing Between Smart Relays & PLCs: Key Questions to Ask Yourself

The deeper you go into the world of industrial automation, the more apparent the differences between smart relays and PLCs become. Here are two key differences you need to know about:

Do I Need Adaptability and Power or Size and Simplicity?

One of the biggest differences between smart relays and PLCs is their adaptability. PLCs are designed to be versatile, allowing for easy reprogramming and reconfiguration. This makes them an excellent choice in environments where requirements evolve over time.

On the other hand, smart relays are typically less flexible, cost less, and their predefined logic primarily defines their functionality. However, unlike PLCs, you won’t need extensive programming knowledge or specialized training to work with them.

Configuring and programming a PLC typically involves a basic understanding of ladder logic, function block diagrams, or other programming languages. This presents a steeper learning curve for some organizations, especially those with limited technical resources.

In short, a PLC system is recommended for industrial processes that require frequent changes, while a smart relay is suitable for basic needs and on a basic budget.

Do I Want Basic Controls or a Highly-Integrated System?

Another key distinction between smart relays and PLCs is their ability to integrate with other automation systems and technologies.

PLCs are designed to seamlessly integrate with a wide range of devices and systems, including SCADA, HMIs, and even enterprise-level software. This allows for a more streamlined and efficient automation process, where data can be easily shared and analyzed across different system components.

We should note PLCs often come equipped with advanced communication protocols—like Ethernet, DeviceNet, or Profibus—enabling them to connect and exchange information with other industrial devices and control systems.

Smart relays, on the other hand, are a bit more limited in terms of integration. They're often restricted to specific communication protocols, like sending errors over Wi-Fi. And, while you can still integrate them with other systems, it's not quite the same level of connectivity and data exchange you'd get with a PLC-based solution.

PLCs vs. Smart Relays: Pros & Cons

To make the right call between smart relays and PLCs, you need to weigh the pros and cons—not just the specs on paper, but what works best for your industrial environment.

Pros of Smart Relay Systems

• Size: Smart relays are often more compact, so If space is at a premium, writing your logic so that it can be handled by a smart relay rather than a PLC can help keep your tools in scope.
• Simplicity: Smart relays are celebrated for their simple design and easy operation, making them appealing for tasks needing basic control functions.
• Savings: Compared to PLC systems, smart relays are generally more affordable, offering a budget-friendly alternative, especially for smaller industrial setups.

Cons of Smart Relay Systems

• Limited Features: Smart relays lack the control features and programming capabilities for advanced industrial applications like motion control and high-speed data collection.
• Limited Flexibility: Smart relays have a more constrained level of flexibility than PLCs, as their predefined logic primarily defines their functionality.
• Limited Efficiency: Smart relays do not integrate well with other systems like SCADA or HMI, making the automation process less efficient.

Pros of PLCs

• Improved Integration: PLCs are designed to seamlessly integrate with a wide range of other automation systems, enabling more efficient and streamlined processes through data exchange and centralized control.
• Advanced Diagnostic Tools: Most PLCs come equipped with diagnostic tools that can quickly identify and troubleshoot problems, reducing downtime and improving overall system performance.
• Centralized Control: PLC systems provide centralized control over multiple processes and devices, simplifying the management of complex industrial automation systems.

Cons of PLCs

• Higher Cost: PLC systems are typically more expensive than smart relay systems, which can be a significant factor for smaller businesses or applications with limited budgets.
• Training Requirements: Programming and operating PLCs require specialized knowledge and training, which can be challenging for organizations with limited technical expertise.
• Vulnerability to Cyber Threats: PLC systems, being more complex and integrated with other systems, may be more susceptible to cyber-attacks, posing potential safety and security risks.

Don’t Leave Your Industrial Automation Strategy to Chance: Find the Right Fit with Wistex

At Wistex, we know the choice between smart relays and PLCs is a big decision—one that can have a significant impact on the effectiveness of your industrial automation strategy. Before going with one over the other, keep the following in mind:

Understand Your Automation Needs

The first step in choosing the right control system is genuinely understanding your specific automation requirements. Smart relays are a practical choice for simpler, straightforward applications, while PLC systems excel in more complex, dynamic, and interconnected environments. Take a moment and assess the complexity of your processes. Do you need any wiggle room when it comes to programming? Are you looking to integrate with other systems in your facility? Once you have a clear understanding of your automation needs, you can make a more informed decision.

Common Applications for Smart Relay Systems

• Motor Control: Smart relays are widely used in industrial applications to control the operation of motors, such as pumps, fans, and compressors.
• Lighting Control: Smart relays are a popular choice for controlling lighting systems in industrial and commercial buildings, providing simple and reliable control over lighting circuits.
• Process Control: In industrial ovens, furnaces, and other process control applications, smart relays are used to regulate temperature, pressure, and other process variables.

Common Applications for PLC Systems

• Intelligent Building Systems: PLC systems can easily be integrated with next-generation building management systems, streamlining both control and energy optimization of your HVAC, lighting, climate controls, and other “smart” building solutions.
• Process Manufacturing: For chemical processing, oil/gas refining, and wastewater treatment, PLCs offer a better way to manage complex control and monitoring tasks.
• Packaging: PLC systems are a popular choice in packaging facilities, as they help control and manage your filling and sealing machines, conveyor systems, and labeling devices.

Plan for the Future, Avoid Common Pitfalls

One of the biggest mistakes companies make when choosing a new automation system is not thinking long-term. They get so caught up in what they need here and now that they forget to consider how their needs might change over time.

When you're weighing the pros and cons of smart relays and PLCs, don't just focus on the immediate benefits; think about the bigger picture.

Smart relays might be easier to set up and get running, but will they still be the right fit a few years from now? As your automation environment grows and evolves, you might regret that decision when you're stuck with a system that can't keep up.

You don’t want to overcomplicate things. If a smart relay can handle everything you need, there may be no point in spending extra for a PLC.

Take a look at your automation strategy and be honest about where you see it heading. A PLC might be the way to go if you expect big changes and growth. But if you're pretty sure your needs will stay the same, a smart relay will suffice—the key is to find a sweet spot between simplicity and scalability.

The Wistex Advantage

Don't leave your industrial automation strategy to chance! Whether you're looking to upgrade an existing setup or design a new one from scratch, Wistex is here to roll up our sleeves and make it happen. Start a conversation today. Together, we’ll assess your building’s requirements, find a solution that delivers the greatest return on investment, and help create a more reliable, future-proof automation solution.