How to Choose a PLC: 8 Control Panel Tips for Engineers & Purchasers
by Simcona on Sep 19, 2023 2:47:57 PM
Integrating a control system is an interesting topic – many people have their favorites.
Everyone involved knows the basic value of PLCs (programmable logic controller) – they check off functionalities that are key to continuous industrial operation. But what sets the many, many options apart when you’re building for a material handling control system or a similar automation control panel?
Starting with the classic cost-vs.-features argument, you must understand these factors before you truly know how to choose a PLC:
How to Choose a PLC – 8 Criteria
The PLC is the heart of many industrial control panels. To use your operational data wisely and keep motors, interfaces, and other components safe, focus on these purchase factors:
- Affordability vs. functionality
- Ease of programming/software
- Communication protocol
Start the PLC selection process with a drawing of the process or equipment. A good schematic will point out field devices and physical requirements for hardware locations. You can also use it to determine the necessary number of analog and discrete devices.
1. Affordability vs. Functionality
You and each of your co-workers fit snugly into a certain position and role. The machine maintenance guys aren’t drafting technical drawings, and the CFO isn’t making $200,000 per year to sweep the factory floor.
Your PLC has a defined job, too. It's essential to strike a balance between affordability and functionality. Here are three places to look first:
If your PLC will oversee an entire factory, a high number of I/Os is essential. If it’ll only manage eight safety switches, it only needs eight matching outputs.
The number of I/Os will in turn dictate how big of a chassis your PLC will need.
Distance matters, too. Will your system use local and remote I/Os, or only local? This will depend on the distance between its subsystems and the CPU.
Your application may have special needs – or lack thereof – when it comes to processing speed. Are speed and efficiency non-negotiables for your PLC’s job role? For example, automation processes that demand quick thinking might benefit from PLCs with:
- Fast scanning times
- Deft execution of instructions
- High-speed counters
Most controllers don’t come with a power supply. Once you’ve settled on a broad idea of what you want your PLC to do, refer back to your power requirements.
In some PLCs, a single supply powers all connected modules via busing in the backplane. In other systems, separate wiring connects each module to various power sources on the rack.
No matter your method, don’t allow an insufficient or faulty power supply into your hardware. A bad source could cause damage, memory loss, and poor performance in the PLC and other devices.
Overall, your PLC control panel’s price should match the industrial demands you plan to put on it – and nothing more. While it’s tempting to spring for a fancy PLC, remember that 80% of features in the average software are never or rarely used.
The waiting game isn’t very fun … and you almost always lose.
Like many devices, PLCs are at the mercy of the electronic component shortage that started in 2020. Well into 2023, some PLC buyers are still seeing lead times of up to a year.
Depending on how specific your functional requirements are, it might pay to not be picky with PLCs. You certainly shouldn’t risk safety or serious quality issues, but settling for an alternative might get your project out the door months sooner.
Partnering with a panel manufacturer with a robust supply network can significantly reduce wait time as well as future regret. It’s more likely to have the expertise, agility, and capacity to track down a readily available alternative that doesn’t compromise quality.
3. Ease of Programming/Software
The ease with which your engineering team can program your PLC can make or break your project's success.
When choosing control components, weigh the simplest options first. PLC panels offer a lot more to the user than a simple relay or timer, but only if they know how to program it.
Some PLCs come with user-friendly interfaces, while others have a steeper learning curve. And while some companies offer complimentary software packages, others require a paid subscription. A smart investment will account for not just the sticker price, but also training, a temporary (hopefully) dip in productivity, and updates.
Which programming languages are usable with your potential PLC and its software? If your team is unfamiliar with it, will that cause delays or mistakes?
The programming framework of your PLC also affects:
Take the temperature of your team’s situation, then recommend the right tech for the right people at the right time.
4. Present- and Future-Proofing
In many industrial machines, these are equally important.
Start with your project’s current state – is there an existing system in place, or are you implementing a PLC from scratch? Carefully check your potential purchase for compatibility with the existing system (if any). Certain controllers don’t play well with others, so you’ll save time and rework by knowing this up-front.
Your needs today might not be the same as tomorrow, so look for ways to future-proof the PLC system as well. Opting for a controller that allows for expandability can be a game-changer in long-term efficiency.
There are many ways you can make your automation system scalable and avoid expensive overhauls:
- Using I/O or explanation modules so you can have more input/outputs
- Flexible expansion racks
- Easy integration of communication interfaces
This scalability ensures that your automation system can adapt to future requirements without requiring a complete overhaul. Being able to adjust the system as your project evolves ensures nobody’s left with an obsolete paperweight a few years down the line.
5. Communication Protocol
Your PLC's communication protocol is the language it shares with your system. In life, all languages can be effective, but only if the listener understands and can give feedback. You could fly to Japan and start an English conversation with a baggage handler, but the listener might lack the fluency to carry that conversation.
Likewise, your PLC should match your system’s communication needs:
- What other networks or devices does the PLC need to be able to communicate with?
- How do they communicate with external devices?
- How important is data to your operation? Is data collection a significant aspect of process efficiency?
- Security … see tip #6 below.
Some controllers come with communication parts; others do not. There are too many protocols available to list, but you’ve probably heard of Can bus, Profibus, and Ethernet (one of the few with internet capability). Some applications use more than one.
Whatever the case, it's vital that your PLC can "talk" to your system efficiently.
When 95% of the world’s cybersecurity breaches are due to human error, why not add some machine-based backup for that trove of data?
PLCs play a huge role in industrial automation and IoT (Internet of Things). With 5G increasing the bandwidth of connected devices, and more companies relying on data clouds and remote workers, IoT devices are facing greater cybersecurity risks.
If IP protection or user security is a top priority for your operations, it's essential to invest in a PLC that offers robust defense features. A look at typical, traditional manufacturing or industrial control system “security” shows you why:
- Most controllers don’t require access authentication or support encryption. Any hacker or careless employee with network access could threaten the business’s well-being.
- An amazing number of workstations still use Windows XP or another outdated operating system.
- Most companies don’t patch PLCs for vulnerabilities because the engineers place network stability above all other needs. Patching controllers can disrupt production and lead to reliability issues.
Fortunately, there are ways to modernize your system to prevent shady data access and misuse:
- Avoid permission “slips” – Explore all access options for your application and team, such as multifactor authentication, username-password combos, & digital certificates
- Use secure communication protocols – Like encrypted connections & e-signatures
- Update PLC firmware & software – Use the latest versions so you don’t miss a security patch or bug fix!
- The more they know – Educate ALL users and stakeholders on cybersecurity best practices, and enforce the rules
Protection features can seem expensive, intrusive, or downright annoying, but so are security breaches. The terrifying numbers bear that out.
The industrial workplace can be harsh for machines and electronics, just like it can for humans.
You might have limited options for the build of your PLC if it must endure demanding conditions.
PLC failure is usually due to exposure to:
- Extreme temperatures
- Chemicals or oil
- Electromagnetic interference
Most PLCs by nature are ruggedized for physical performance, but your application may have unique challenges. The typical operating range for a PLC is 32-130 °F, so if your project’s environment will be noticeably higher or lower, investigate special-case products. You can also look at the material construction and relevant ratings or compliances to gauge the reliability of the PLC.
The higher-quality your purchase is, the more likely you’ll enjoy continuous operation.
We’re not here to tell you what the best PLC brand or manufacturer is. But it’s worth noting that most major manufacturers come with a hefty price tag. As you window-shop, stay sharp for signals of whether the brand’s size actually equates to quality.
Identifying the top PLC manufacturer comes down to your application’s specifics and level of complexity. While many companies can produce a basic PLC, fewer can craft one that integrates seamlessly into intricate applications.
This is especially true when safety is critical. Are you controlling a factory that’s got 10-ton lifts over workers’ heads? Are you managing a rail car system that carries millions of people annually? A brand you trust is worth its weight in steel.
If your own manufacturing operation lacks experience with the type of PLC you need, check out the maker’s level of tech support. Give bonus points to those with robust training resources and a maintenance or warranty program.
If it’s too close to call between two candidates, go with the one whose company has history on its side. A financially stable company with proven success will ensure you’re not left holding a faulty PLC and nobody to answer for it.
Controlling Costs vs. Controlling Your Panel
Splurging on unnecessary features can strain your budget without adding worthwhile value to your operations. However, lowballing your system with a cheap, underperforming PLC will hurt its ability to process quickly, withstand harsh conditions, and crunch important data numbers.
Just like hiring and communicating with humans, the most successful PLC integration is one set up to succeed – on Day 1 and Day 1,000. A high-performance system from a reputable manufacturer almost always saves time, money, and headaches in the long run.
For more knowledge on effective PLC panel design and implementation, check out our full resource hub:
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