Ask the Experts: PLCs

Josh Kingsley:
Okay, wonderful. Thank you very much, Travis and Henry. Hopefully that cleared everything up for you. It looks like the next question's coming in, also from the LinkedIn world. What are the different components of a PLC? Adam, as the PM, I think that one's going to be great for you.

Adam Bainbridge:
Really good question. So, there are three main components to a PLC. There are the base devices, the communications and the expansion modules. These three devices are typically combined in different configurations for different applications but the base device is the CPU, it does all the thinking and processing of your program. 

The communication unit brings in digital information. It communicates using standard industrial protocols and delivers the status of communicating sensors to the logic program to be processed where decisions can be made. 

The expansion units, finally, are physical IO cards that take physical sensor inputs, physical relay outputs, to control contactors and motors directly. So, those are the three main components — base devices, communication units and expansions. 

Josh Kingsley:
Sounds good. We're going to go ahead and bounce over to Facebook here for this next one, this one is coming from Janice. Travis, I think that we're going to have you do this one here. What are the common applications of a PLC? As an application engineer, Travis, I think you have some good answers for this.

Travis Quinn:
Absolutely. So, a PLC can be used, pretty much, anywhere that you need to automate a process. The key thing to note there is you typically want to use the PLC in situations where you don't want to use an application-specific processor. Those situations would be either flexibility requirements or costs. 

Some examples of where you would want to use a PLC would be definitely in process control in applications such as water sanitization, HPAC systems or otherwise, food and beverage production.

Josh Kingsley:
Perfect. Okay. It looks like we're going to be hopping right back into the LinkedIn world and we're going to go to Adam with this one. So, how does an HMI communicate with a PLC? 

Adam Bainbridge:
Really good question. That can be complicated, but in the simplest terms, your PLC has a tag list or variable list that you build when you create the program. That tag lists or variable list is imported into the HMI and the HMI, using its communication drivers, synchronizes the data between the PLC and the HMI using standard industrial protocols. Ethernet/IP is a very common option in our Americas region. So, once that's imported, you have that physical layer that keeps them in sync and you can use them in either a program and synchronize that data between the two.

Josh Kingsley:
So, more than anything, it sounds like, they interface pretty well together and that they are generally made to work together. Is that a fair statement?

Adam Bainbridge:
Very easy. Simple to set up.

Josh Kingsley:
Okay. Good stuff. 

Josh Kingsley:
Back to the questions, we got Chuck Z from the Facebook world. This seems like a fairly complicated question — I have a variety of customers that deal with a variety of voltages for their applications, is there such thing as a PLC that would work for all of them?

Adam Bainbridge:
Not exactly all of them, but we're getting very close. You are correct, there are different power and power standards throughout the world. And, even within each region, different applications have different requirements. 12 volt DC is commonly used in mobile applications, some mobile refrigeration, trucking, and things like that. 24 volt AC is used everywhere in the HPAC industry. Then you have standard 120 volt, 240 volt and some high-voltage DC used in some rail and transportation industries. 

We have something we call UC, Universal Current, that accepts both AC and DC. So, with one PLC, you can take 12 volt DC, 24 volt DC or 24 volt AC, which really simplifies the choices that you need to make, the number of inventory you need to carry. And then, our high-voltage AC devices can take between 100 and 240 volts AC. Again, simplifying the selections that you need to make.

Josh Kingsley:
Okay. Good stuff. Travis, I do want to bounce to you to weigh in on this as well. All the time that you spend in the field as an application engineer, why are there so many different voltages? It's great that there are products available that can cover some of this, but why do we have to get to the point where we're recovering that way?

Travis Quinn:
Sure. Great question, Josh. A lot of it really boils down to tradition, as Adam was alluding to. The United States, historically, has a lot of your control voltage either 24 DC, otherwise, 120 AC. But ,when you go over to Europe, a lot of times their outlets, for instance, or their control voltages are, a lot of times, 220 volts AC. So, it really, again, just boils down to tradition. However, there are some benefits to using 24 DC compared to 110 AC, such as, you don't have to use gloves once you're underneath 50 volts. If you need to enter a panel using lower voltage applications, you definitely have an advantage.

Josh Kingsley:
It looks like this next question is coming back from LinkedIn, this one's from Frank. I do want to point out that this question is also something that was of great interest on the LinkedIn event poll that we sent out previously. So, again, thanks to all the viewers that we have on today, that participated in that poll. It was good to get the pre-feedback. 

This specific question is going to be about PID control. So, what Frank wants to know is what is PID control and what is a common application for implementing the control scheme with a PLC? Travis, this seems like a perfect question for you again.

Travis Quinn:
Sure. So, PID stands for Proportional Integral Derivative control. However, in 90% of the applications, usually all you need is proportional and integral control. So, proportional control directly scales the air between the set point and the feedback to increase or decrease the initial response of a system, so the reaction of a system or a step-change, if you've heard that term before. Whereas, the integral gain scales the accumulated air at that point in time. It's very useful for eliminating steady-state air that, usually, can't be corrected by proportional gain alone. 

A common application for PID control with the PLC would be, for instance, controlling the speed of an exhaust fan to maintain a temperature in a room. So, the PLC will either speed up or slow down the speed of a fan via variable frequency drive in order to blow more or less hot air out of the room, which then, of course, would increase or decrease the temperature of the room to maintain that set point that you're desiring.

Josh Kingsley:
Adam, anything to add to that?

Adam Bainbridge:
Yeah, absolutely. Proportional Integral Derivative control sounds really complicated so a lot of people may want to avoid it. Going to the application example Travis presented, of using that exhaust fan to regulate temperature in electrical control rooms. It's very easy to just slap on an on/off temperature switch. So, it turns on at a certain temperature and shuts back off. The downside is that you don't get very accurate temperature control. The temperature swings within that range and also, you don't realize any energy savings. So, having a fan run full speed is maybe okay but if you put a variable frequency drive on the system and reduce that fan to half speed, you get significant energy savings. Even if it's running the same amount of time or even half the time, you're still saving a significant amount of energy in that application.

Adam Bainbridge:
You get better temperature control, energy savings and it really isn't that complicated with modern technology to set up a simple temperature sensor, some kind of PI controller, which could be on the nano PLC or could be built into the VFD itself. It's really going to give you much more precision. And again, save you energy, which is a big deal.

Josh Kingsley:
When you're talking about saving energy in a commercial building type of setting, that can be a large amount of cost savings, correct?

Adam Bainbridge:
Yes. Motors in commercial buildings are one of the greatest loads, second to lighting. So, reducing the power consumption of any motor, by varying its speed, is a huge advantage.

Josh Kingsley:
Thanks a lot, glad to know that we have the ability to help our facility managers out there in the world. It looks like the next question is going to come in from the Facebook world and this one is from Jen. The question is, what is the difference between PLC and RTU? And I think that this is really a result of throwing a lot of acronyms around. So Adam, can you clarify please?

Adam Bainbridge:
Yes. So, PLC is a Programmable Logic Controller, RTU is a Remote Terminal Unit. They both process logic and they both control things. I would say, just traditionally, the PLC has always been easier to program, but they ultimately do very similar things. They're reading inputs, reading outputs, writing to outputs, making decisions, but the PLC uses much more standardized code, which makes them very easy to implement in sequential logic operations.

Josh Kingsley:
Travis, anything that you would add to that?

Travis Quinn:
I think Adam spelled it out pretty clearly. The PLC is definitely tuned more toward the industrial world and common applications such as IEC 61131-3 programming. Again, it's a lot more commonly used, which makes it a lot easier to pick up and tune in, calibrate, so to say, for pretty much anyone versus the RTU.

Josh Kingsley:
Perfect. It looks like we have our next question from Nelson on LinkedIn. Would I be able to debug your PLC software in Linux? If so, please inform me if I can erase EPROM or PROM memory or strictly the RAM cache memory. Adam, can you take that one please?

Adam Bainbridge:
That's definitely an in-depth question Nelson. So, you're wanting to debug it from a Linux-based system. Our EasySoft application, which interfaces with the software, is a Windows-based tool, so you can do all of the functions you described from Windows, for sure. You cannot run EasySoft on a Linux-based platform, so there is that limitation, unfortunately. 

The easyE4 does have an API, which is an application interface that allows you to interface with the device over JSON. So, many of the commands that you're asking for, you could write and interface directly with that tool and read and write data and do diagnostics. Unfortunately, it'll just be a little bit more manual, but could offer a lot of flexibility in your applications, so I think it's a very powerful feature having that API available for you to work with in those environments.

Josh Kingsley:
Travis, have you gotten into a situation like that before, where you could comment on anything further?

Travis Quinn:
Really, that's a pretty unique situation. I actually, personally, have not run across that yet. I also heard something about resetting the module, so I'll just chime in there. There's also a built-in microSD card that also can be used to reset the device. There are some manual ways of resetting the device and getting the configuration that you need, built into the device as well.

Josh Kingsley:
I'll ask a quick follow-up question. What other benefits would you have by having the microSD card reader on there? Can you preload programs, things of that nature?

Travis Quinn:
Yes. You can preload programs. You can also have little bitmaps to actually load an image when you boot. You also can log data to that card. So, there are definitely multiple features that are very useful when using that SD card.

Josh Kingsley:
All right. Any more questions from the field? It looks like we're pretty prepared to get into your in-depth specific application situation, so keep them coming.

Josh Kingsley:
Travis, I have a question for you. What's the unique PLC application that you've seen in the field? What's the most unique project that you had the opportunity to work on?

Travis Quinn:
Are we talking specifically to the easyE4? 

Josh Kingsley:
I would say, in the nano PLC space in general. What kind of scope of applications are a nano PLC going to cover? And, what's the most unique one that you've had the opportunity to work on?

Travis Quinn:
Sure. I'm not going to consider it super unique but I'd say one of the most beneficial methods that I've definitely seen is using the nano PLCs as remote IO. So, when you have a nano PLC, just the cost benefit alone with the built-in IO, you can then interact with it to read and write data or turn on and off outputs directly. This is super beneficial because then you can also run some minor logic, maybe, remotely too, in the PLC. And then, report or funnel up some of those calculations back to a main controller. So, there has definitely been customers that have used that architecture as well.

Adam Bainbridge:
And I'll add a little bit to that. Nano PLCs have really blurred the line, the current generation that is, in applications. You used to have these dedicated PID controllers, dedicated temperature controllers, dedicated flow controllers. You could have a dedicated counter, timer relays, and things like that. 

The price point is so low on these nano PLCs that you can easily consider doing a nano PLC in those simple applications to replace a counter and then, you have expandability in the future. Nano PLCs, typically, weren't very expandable. Now, with easyE4, you can get up to 190 IO points, something in that range. So, the number of IO is rarely the limiting factor anymore. It's really about processing speed and the type of control that you need. 

The nano PLC is a great fit for upgrading from simple dedicated controllers or even thinking about some PLC applications, where you just need a millisecond response time, a second response time. But, if you really need much faster, hyper accurate position control, you'll probably need to bump up to a higher class, the microplastic PLC devices.

Josh Kingsley:
Thank you very much. It looks like we did have a couple more questions come in. But, real quick, I want to say hi to people all over the world. This is awesome. We have some representation from down in the Caribbean, from the Dominican Republic. We've some African friends from Morocco. We've got South America, Peru. We've got Mexico. And, we've got a bunch of European places, Switzerland, Italy, and Russia. We have some Asian countries, India. We have Turkey, which is both European and Asian. And, Nigeria, Toronto, of course, the U.S., Spain, Tunisia. This is exciting. Glad to have so many people from all over the world tuning in to listen to Adam and Travis drop some knowledge on us.

Josh Kingsley:
The next question is can you learn to program a PLC with help from online courses or is it required to have the equipment? So, what would be the best way to learn about a PLC? This is from Zyan on LinkedIn. I think what they're asking is if you needed to learn how to program a PLC, what's the best way to go about doing that? Travis, I think you've had to learn how to program a lot of PLCs, so I'll let you answer this one.

Travis Quinn:
Sure. So, Eaton right now is definitely working on some training classes online. We do have some in-person classes, and we're working on getting a lot of that information online and available for customers to use as well. That training is very beneficial. Even if you download the software itself, you can definitely play around with it. There are built-in simulators to help you also play with that logic and you can get some feedback without having a device. But, really, if you do want to physically have it in front of you, I would always recommend trying to purchase just the basic components because I really do feel that interacting with the device is the best way to really learn about it.

Adam Bainbridge:
I want to add to that, if I can.

Josh Kingsley:
Sure Adam. Just go for it.

Adam Bainbridge:
You can download easySoft for free. The only restriction is if you do not license it, you cannot download to a device. We do have videos available online, I think there's seven at the moment on our webpage. They cover basic things like starting your first program, downloading it to a device, using basic function blocks, things like that. So, to answer your question very specifically, yes, you can learn this thing very easy. It is very simple to program. We do have tools available online where you can pick it up very quickly. But as Travis said, we do have a starter box that comes with the cable, comes with the software license and comes with a base unit device that you can purchase, if having a physical device will make it easier for you.

Josh Kingsley:
So, quick follow-up question. Now, Travis, you did mention, get the basic devices to put everything together. Are you insinuating that it would be nice to have a small motor to simulate an application? Or what do you mean when you say, have the basic devices around?

Travis Quinn:
I guess what I meant for the basic devices in that last sentence was, making sure you have the base unit. And then, we also have a variety of expansion units at the easyE4, so if you need analog outputs, for instance, we typically do not provide those on the easyE4 base unit. So, if you need some of those features, that's what I was referring to when I meant, get the basic components of what you feel you need for your application. You don't need to go out and go crazy and buy all sorts of things or get too complicated. If you're just starting out and going through some of those videos that Adam was alluding to was, the base devices that you need for your system or application are typically all you would need to get up and running.

Josh Kingsley:
Outstanding. Thanks for that clarification. Next question that we have is from LinkedIn. Any recommendations on an application or reference manual for PLC controllers for medium-voltage switchgear? Adam, can you take that one please?

Adam Bainbridge:
Any reference manuals? Was that the specific question?

Josh Kingsley:
Yes. So, recommendations on application or reference manuals for PLC controllers with medium voltage switch gear.

Adam Bainbridge:
We do have manuals for the base devices that cover implementation of the different blocks and stuff within it. Anything specific to switchgear, to be honest, no, we do not have any documentation, but feel free to reach out to Travis or me and we can help you with those applications. If there are specific functions, such as transfer schemes and monitoring, we can absolutely help and point you to the right function blocks to assist you in solving those applications. 

Josh Kingsley:
Okay. Is the best point of contact to work through the Technical Resource Center? Through you guys directly?

Adam Bainbridge:
The Technical Resource Center is always a great place to start. They have a lot of in-depth knowledge with the products. But yes, feel free to reach out to Travis or myself as well.

Josh Kingsley:
We did have a few more questions come in, that I want to try and get through. So, Amir on LinkedIn, what aspects of enhancements are still needed for a Programming Logic Controller, both hardware and software, especially when it comes to dealing with IoT issues? Adam, do you want to do that one please?

Adam Bainbridge:
What issues or enhancements?

Josh Kingsley:
Yes. What aspects of enhancements are still needed for the PLC hardware and software when you're dealing with IoT issues?

Adam Bainbridge:
Security is a big thing. That's always going to be an issue that is never going to be finished. We're going to have to continue to solve that every day and keep an eye on current threats. As Travis mentioned earlier, we already have email servers within the easyE4, so you can connect it to the internet and it can send those email messages and alerts out to any support staff or building owners or plant operators that you may wish to, that's already in there. And cybersecurity, it's been tested and it's ongoing. 

The other issue is, we'd like to do more. We'd like to get more data collection out of these devices. We have the APIs, which enables you to extract the data into the platform of your choosing. But, I think that could be simplified for the end-user and then. That's something that we're going to continue to work on. 

Josh Kingsley:
Perfect. Looks like we're going to be able to get one more in. So Travis, if you could quickly answer Ola from LinkedIn, what maintenance processes are required for a PLC?

Travis Quinn:
Typically, the PLCs themselves are sealed up pretty well. So, maintenance on a PLC, especially when it's within a panel, is very, very low. There are some PLCs that do have batteries in them, for the real-time clocks, which may burn out eventually. That's, typically, the only maintenance that they need, honestly. These PLCs have been around in the industrial industry for a very, very long time and they're, basically, bulletproof when it comes to maintenance.