Ask the experts: PLCs

Josh Kingsley:
For more information about this and to learn more about how to set up the software, please visit eaton.com/AutomationCompass. Our next question is going to come from Gloria. How are PLCs used in correlation with safety applications? Adam, we'll have you take that one.

Josh Kingsley:
All right, so we're going to jump back to you, Travis. We'll get into one more question for you. This one's coming from Miguel. How can I control a variable frequency drive with a PLC?

Travis Quinn:
Sure. Great question, Miguel. So there are actually a couple of different ways that you can control the speed or control VFD in general or variable frequency drive that's in a PLC. The first method that's commonly used is hardware control, and the second method would be Fieldbus communications. If you just need an enabled signal and maybe a separate signal to control the actual speed of the drive, I'd probably use hardware control. However, if more signals are needed, I would definitely go with the Fieldbus controls such as Modbus TCP or Ethernet IP. Traditionally however, nano PLCs, which we're commonly referring to within this episode do not actually have Fieldbus control, at least not as a master. However, the easyE4 will be launching Modbus TCP master control soon. Up to you, Josh.

Josh Kingsley:
Nice. Sounds like a great feature. 

Josh Kingsley:
All right. Can we help Gloria out with our question about are PLCs used in correlation with safety applications?

Adam Bainbridge:
Yeah, great. To answer your question, Gloria, that is a good one, a very difficult one, but very important. Safety is a huge concern and there's a bunch of different ways to solve it. The first thing I'll point out as far as PLCs go, there are safety rated PLCs on the market, and those are used to monitor safety conditions and control safe outputs. But, you don't always need a safety rated PLC for applications with safety requirements. In many applications safety relay is a great choice to use in conjunction with the PLC and whatever motor control you may be using.

Adam Bainbridge:
A good example would be a conveyor. If you need an emergency stop on that conveyor motor, and that's the only safety requirement you have, then using an emergency stop safety relay with whatever SIL rating your application requires is probably the most cost effective solution. Now, where the PLC comes into play. If you have a lot of safety requirements, a lot of safety inputs, a lot of safety outputs, the PLC can really save you time and effort when configuring those applications. But, most of the time you only have one or two safety requirements. And I think the relay is a great choice.

Josh Kingsley:
Okay, perfect. So just to expand a little bit. It sounds like the most important thing if you're working with a safety application or requirement, it's just really important to do all the research and the quantifying upfront, correct?

Adam Bainbridge:
Yeah. There's two ways to go about this. Sometimes your end user will have a specification, whether it be SIL 1, SIL 2, or a performance level, such as performance level E, those are done with letters. So typically, ask the end user if there's a specification or there's safety surveys that can be conducted to help determine what those requirements are. And, once you have those requirements in hand, you can choose the right products, the right combination of products that meet those levels.

Josh Kingsley:
So, get your risk parameters in order. All right, thank you, Adam. And, for anybody who's just joining us right now. This is session two of Ask the Expert by Eaton for PLCs. And, don't forget for more information, please visit eaton.com/easyE4 and eaton.com/AutomationCompass. It looks like our next question's going to be back to Adam again. And, this one's coming from Sarah. Why is data logging feature so commonly used with a nano PLC?

Adam Bainbridge:
Good question, Sarah. This one comes up a lot more and more these days, that the traceability and applications is really becoming an important requirement. And, each industry has different requirements and different needs for different data logging features, and there are different ways to accomplish it. 

If you're in a process industry such as wastewater treatment, there may be legal requirements that you have to track how much pollutants, what the levels of chemicals are at any given moment in time. And, that's really important as a legal requirement.

In other situations such as manufacturing, just knowing how many parts are produced, how many defects were made is really important. The good news is, it's getting easier to do. As far as nano PLCs are concerned, it's becoming more common to have SD cards built right in. 

Our easyE4 uses a micro SD card, which you can get very inexpensively and in very large sizes. So, they'll hold a lot of data and you can capture that data right in the easyE4. You can timestamp the data, you can track it. There's really a lot of power there. Additionally, once you have these on board, you can extract that data using a higher level SCADA system, which gives you a lot of capacity to share that data with other systems within your facility as well.

Josh Kingsley:
Perfect. All right. We threw a lot of acronyms in there, I just want to pick on one here in particular, what's a SCADA system?

Adam Bainbridge:
It's a supervisory control and data acquisition, and a SCADA system is typically used in conjunction with PLCs in large process environments. So, it doesn't do the real-time control that a PLC does and control the inputs and outputs. However, it might start and stop the process. But, most importantly, it handles alarming and monitoring all the data that multiple PLCs and different processes might have within that facility. Really, it just pulls it all in so you can get a view of that plant or that process all in one screen in an instant.

Josh Kingsley:
Perfect. All right. So the next question is coming from Arturo. Are you planning to make any major ECS soft code assist software updates soon?

Adam Bainbridge:
Yeah, that's a great question. I think, obviously a big trend is IoT, internet of things, and making a lot more things easier to use using those new tools that we have available. I think across the board, this isn't just ECS soft code assist, but that one is absolutely included. Being able to back up your projects, being able to more easily interact with products using the cloud, using new use cases. So really across the board, looking at how we can make our products easier to use with new technologies that are available.

Josh Kingsley:
All right. So software is a focus is what I'm hearing.

Adam Bainbridge:
Absolutely it is.

Josh Kingsley:
All right, Travis, I've got one for you. This one's coming from, Jesus. What's the best, most cost-effective way to start thinking about and learning how to program Eaton's PLCs.

Travis Quinn:
Sure. Great question Jesus. The best way to most cost effectively look at which type of PLC system that you want to use is start by actually looking at what the requirements of your system are. if you only need, let's say us then, a 100 IO points, you probably going to want to look at a nano PLC system with some expansion IO.

Travis Quinn:
However, even if you need a little bit more than that, and maybe your throughput on calculations are slightly more than the nano PLC allows for, I would start looking at the micro level or a small level PLC. Really what you need to do is break down how many IO points you need, what features you need and as well as the horsepower so to say that you need in your PLC.

Josh Kingsley:
Thank you very much, Travis.

Travis Quinn:
Absolutely.

Josh Kingsley:
Next question that we have - what kind of sensors work with PLCs? Travis, this is going to be a good question for you as well. This one's coming from Simon.

Travis Quinn:
Another good question, Simon. Like the last question, some of those IO points obviously can be sensors. So, the sensors that do work with PLCs would be anything from analog sensors to digital sensors, to also sensors that communicate using fieldbus controls, such as Ethernet IP, or maybe IO link. Eaton in particular does have a solid line of photoelectric and proximity sensors as well as limit switches.

Photoelectric sensors are commonly used for instance, with a counter to count parts, going through a process where you probably don't want to have physical contact with the sensor. A lot of common places where you'll find these types of sensors are definitely in food and beverage industries. 

Otherwise the prox switches that I was referring to, or proximity switches, are used to indicate the presence of a metallic object, such as maybe a metal arm moving into a desirable location on a machine.

And then lastly, the limit switches that I was referring to previously are used to indicate the presence of any physical object in a specific location. However, it does require contact with the object because those limit switches themselves do have physical arms that need to rotate to trigger the sensor to be on or off. An example where you might want to use those switches would be on a packaging machine to count boxes moving down the line.

Josh Kingsley:
Okay, perfect. Well, it sounds like there are plenty of applications you can get into using PLCs and sensors and it's almost like they communicate together well.

Travis Quinn:
Absolutely.

Josh Kingsley:
Good stuff. The next question's coming in from Juan, and this is a two-part question. How redundant is the PLC and what about the PLC using HART, which I'm assuming is the Highway Addressable Remote Transducer Protocol. Adam, I'll let you do that one.

Travis Quinn:
Yeah, to answer the first question. When we're talking specifically about our nano PLCs, and this is really across the industry. There really isn't a way to set those up in a redundant application. Typically, you need to go up to micro or small to have those redundant capabilities. And, it's really a lot to do with software. You need to have the IO split wired to two exact clones of the actual hardware. And then the software kind of keeps them in sync, and it knows which processors are in control. Then if something fails, it switches over to the second PLC. So, there are different levels of redundant PLCs.

We had a question about codices earlier, codices absolutely supports redundant PLCs, and you can use those in Eaton's micro and above programmable logic controllers. So it absolutely is possible. And it's fairly easy to set up. The physical installation is honestly the trickiest piece of solving that. The second about HART, yep, HART is a communication protocol as Josh alluded to. What was the specific question there? How does it relate to PLCs?

Josh Kingsley:
Yeah, no. So the question is, yeah, HART with a PLC. And I think it's just an ask for an overview about using HART with PLC.

Adam Bainbridge:
Yeah. It's pretty uncommon. I will say Eaton's PLCs do not include Hart protocol communication standard, but you can get gateways to translate that to Ethernet IP, Modbus TCP, and that is typically how we see them integrated. I think that answers your question. Typically you'll need some kind of gateway to translate it into something the PLC speaks. I'm sure there are PLCs out there that have HART cards built in, but it's really not very common.

Josh Kingsley:
Okay, perfect. Travis, got another question that I can ask you. What kind of upfront checklists would you have that you would recommend using? If you're going to build an infrastructure that's going to have a PLC. What are the things that you want to make sure you're considering?

If you're putting together an automation process with a machine, what's the checklist that you would start with if you were going to integrate a PLC? If you're building a system from scratch, what is the approach that you would take to build architecture fundamentally correct?

Travis Quinn:
Another great question. The first thing I would definitely a different look at is the type of sensors, the type of speed of the application. Also, the throughput, how fast you actually need that data calculated? All those things definitely go into what PLCs and what equipment that you need. 

For instance, if you have a conveyor application, where you have a box that you just need to control the speed of all the boxes going down the line need to just go maybe 15 miles an hour and you just need to start and stop it, I'll probably then look at the nano PLC.

However, if you have maybe a packaging machine or a boxer, which needs maybe a little bit of motion control and it needs to be able to calculate some of those function blocks inside the PLC a little bit quicker, you're going to need to bump up to a micro level. 

Then, of course you need to look at how many IO points you need as well with your sensors. So, it really does boil down to IO points, the speed of your application, as well as throughput of calculations.

Adam Bainbridge:
I’d like to chime in here.

Travis Quinn:
Okay, take it.

Adam Bainbridge:
I often see people getting very comfortable with a certain class of PLC. Usually it's a micro because they're very powerful, they're very flexible, and they apply those kinds across the board for the most part. But, oftentimes a nano PLC can solve those requirements. I urge you as technology certainly improves to just look at what the requirements truly are and open it up because you could save a significant amount of money because there are huge price differences as you change classes of PLCs.

Travis Quinn:
Great point, Adam.

Josh Kingsley:
So Adam, quick follow-up to that. We're throwing out all these different classifications of PLCs. We've heard of micro and nano, how many classifications are there?

Adam Bainbridge:
Travis mentioned them earlier. There's nano, micro, small and large. To be honest, that doesn't mean a whole lot to a lot of people. Really the differences, IO counts for the most part. But, even that line is getting pretty blurry and really the biggest difference is just how they program, whether it's registered-base or not, or tag-based. 

The programming type, specifically around the memory addressing, really defines that, so definitely largest for automating an entire production line such as automotive manufacturing. There will be a huge rack with thousands of IO. That one's pretty clear. Nano and micro is a little bit blurry and kind of the same with small. I'm sorry I don't have a better answer for you because there is a lot of overlap and it really just depends on what you're trying to do.

Josh Kingsley:
Yes, so personal preference application, and then having a good support system behind you. To me, that did answer the question and it's just really important to make sure you put all your thought upfront when you're building and architecting a system.

Adam Bainbridge:
Yes.

Josh Kingsley:
A quick reminder for those of us just joining us. This is session two of Ask the Expert for PLCs, and don't forget for more information, please visit eaton.com/easyE4 and eaton.com/AutomationCompass. Our next question is going to be about software programming. I think I'll give both of you guys a chance to give your thoughts on this. This one comes from Alley. They've started learning Ladder Logic, but they're trying to take their PLC programming to the next level.

Adam Bainbridge:
I'll take that one. Ladder Logic is a great way to learn, because it has a very sequential flow. It executes the first rung on the ladder, then the second, then the third, then the fourth. And, it's really easy to see that in your mind and understand how the program's going to execute. 

You can understand how certain checks are happening, because it reads like a book. It starts at the top left, goes right to left, top to bottom. We are all very much programmed in our heads to think that way. So, when looking at a ladder chart, we can see very easily these are the steps the PLC is going to take. That has a lot of advantages because it's easier for us to quickly understand how that program works.

When you want to take it to the next level. Yes, different programming languages really open up. Modern computing has multi-threaded things where it's kind of thinking about a couple of different things at once. You can break that sequential flow a lot easier and really control multiple different things at the same time.

So, different languages are better at doing that. You know, I like Ladder, because like I said, it flows very easily. But, I'll tell you, for doing math operations and really computing a lot of numbers, Structured Texts is the best. I look at it thinking, "What am I doing? Am I just looking at binary inputs and checking them all in a certain sequence?" I'll typically use Ladder, it's what I'm comfortable with. But, if I see there's a lot of math, floating point math to manipulate, I jump right to Structured Text. 

The good news is that with a lot of modern PLCs you can mix and match, including the easyE4. You can write blocks of code in Structured Text and then write it in Ladder, kind of mix and match. So, you can get the best of both worlds in a lot of cases.

Josh Kingsley:
Yes.

Travis Quinn:
And, then I'll just add onto that a little bit. 

Once you're also start getting a little bit more involved, if you are starting with Ladder, I'd say the next step, which is definitely useful more in Ladder than it is in Structured Text, is easyE4 in Easysoft itself. There is a feature, which allows you to actually go online and view the data. You can actually manipulate operations using simulators, and it's a lot more easy to see and visualize then within Structured Texts. 

However, another thing to note is, as you are trying to really maximize and get as much out of your PLC as you can, Ladder Logic is actually faster than maybe Function Block diagrams, and Structured Text is faster than Ladder. So, there are little nuances that you can actually do to really try to get the most out of your PLC that you can. That's where I see things going when you're trying to go to the next level.

Josh Kingsley:
Perfect. So quick follow-up question for Adam, you did mention that you can interchange the different. These are programming languages, right?

Adam Bainbridge:
Yep.

Josh Kingsley:
So, you can interchange the different programming languages. Do you have to have something that marries all of them together? Does the Easysoft do that or is there another method that you can use to make everything work? Because this is a little bit beyond my personal scope. This is sounding pretty complicated, if you could just dig into that a little more.

Adam Bainbridge:
It is. That's absolutely the easiest way to do it, but it limits you in some ways. So, this is again some of those differences between the layers of PLCs. At Easy you have a main program, right? And you can call another program, in the Easy it's called the function block. You can call another function block within that program. When you're in your main program and you create a math block that's just doing a simple conversion. 

Let's say it's adding two numbers together and dividing them both by two to get an average or something like that. You would place that block in the main program and then elsewhere you can edit that code for that block in a different language. The main program is the one executing, when it gets to that rung, it will move to that block and then execute its code.

That's the simplest way, right? When you move on to more advanced programs like CODESYS, there's a whole Task Manager. It's really complicated, super powerful, but you can create different tasks that run off of all kinds of different triggers. You can have them triggering, you can have one program triggering every millisecond, another every five, another every 50. Or you can have event-based triggers where if an input changes state, then it triggers that program to run. And you really get a lot more power, but it gets difficult to manage. You have to be careful, because if you put everything in  a 0.01 millisecond task, and you have 5,000 lines of code in four programs, it's never going to finish executing the processor. It typically won't let it execute that. And, you start to get variations on what you expect. So, you really have to put a lot of thought when you have that flexibility to make sure that you're not over running the processor and starting to get unexpected or untimely outcomes.

Josh Kingsley:
Okay, perfect. So looks like we got another question coming in. This one's from Eric. Can you describe a bit about the API functionality?

Adam Bainbridge:
Okay. So an API is a standardized programming interface, right? This is used a lot in the IoT world. In fact, if you have an Amazon Alexa at home or some of those tools, they all use APIs. What they do is it creates a standard way of interfacing two different things together. If you have a smart light bulb and a smart speaker, there's an API that's written to kind of link the two together. It's a standardized language. 

When we move on to the Easy, it's the same thing. We have the standard programming interface that can be linked up to all of these other smart IoT things. And, it standardizes your program and the tags within that program to talk to those other devices. It really opens up beyond common industrial protocols what you can communicate and how you can link devices together.

Travis Quinn:
Yep. Just to add a little more clarity. What our APIs and our Java APIs really they do is they are objects of code as Adam was describing that basically just help you get inputs, output and send it to via an HTML file or something similar to that. You can manipulate and gather data in programs such as Excel. Otherwise, you can also link it maybe to a custom web pages server. So they are definitely handy tools and something very useful once you get to learn the easyE4 itself.