Introduction to Programmable Logic Controllers

Hello everyone, this is the first video for the basic PLCs course. Now for this video what I'm going to do is talk about the PLCs and their introduction and then the following videos will be more heavily into the programming and other things that are important to the PLC environment. Now first of all if you're not familiar with the PLC, a PLC is known as a programmable logic controller. And at its core, it's an industrial computer with a high degree of reliability, and it's capable of running a program without interruption 24-7 in a 365-day environment. Now, it's pretty much a computer that you're going to program, and it will run that program pretty much every day of every second of every hour in an environment that is pretty much going to be an industrial environment. But it can be multiple different types of environments. Now these were created as cost-effective alternatives to relay-based systems a few years after transistors became more commonplace. So pretty much what that's saying is we used to have things like this, and there probably are some places that still use relay boards like this. And it's not that it's bad, it's just that this was condensed into something like this. A smaller, pretty much smaller computer that can accomplish the same work, but it's a lot smaller and a lot more reliable. Now, at first, these PLCs, this is a PLC here. These were simple and easy to set up, but as the needs of the business change and the manufacturing floor complexities became apparent, these evolved. Now, they come in different sizes, different manufacturers. We'll talk about that on the next page. But these require a dedicated person. I underlined it down here. They now require a dedicated person, and that's you watching this, that knows PLC programming to not only create the program, You need to optimize it for the specific project and then be able to change it depending on the business needs. That's what you're going to have to be able to learn for this course. You have to not only create a program, you have to optimize it, and then you have to be able to change it. Those are the three main steps that you have to do to become a PLC programmer. Now, there are different brands, as I said. Two of the most popular, I have them listed here. I have Allen Bradley by the Rockwell Automation. and then i have semantic by siemens there are many many many types of different plc brands but these are probably the two that are are the biggest i would say now allen bradley are are heavily used in north america so if you're in the united states you'll probably see more of the allen bradley if you go overseas you'll probably see more of the siemens plcs because of the standard in european and asian regions Now what I also have listed here is just different shapes and sizes and brands of PLCs. So this is Siemens. This is just a small Siemens PLC. Probably will maybe be about eight inches across, something like that, just to give you a size. We now have medium. This is a medium one here. This is I believe Allen Bradley. Allen Bradley PLC medium size. And then we have a large Allen Bradley PLC here. So they can get even larger than this. They can get even smaller than this. and then there's different manufacturers that make them, depending on what you're trying to do with them. Obviously, the larger you go, the cost also increases, and the complexity increases. Now, starting at the top, you may be able to program the PLC. You can do it in multiple different languages. I have a couple listed here. So we have ladder logic, function block diagrams, structured text, but ladder logic should be the first language you master. And that's something that you should have also covered in the motor controls class, which is the prerequisite for this course. If you haven't, then we can talk about that, but the ladder logic is the most important and I believe the first language you should master. Now I put a reason here. I said the reason is it's the most widely spread type of PLC programming due to its roots back to the relay logic that I showed you the relay board before. It's simplicity to implement and the ease of debugging. Now not to jump too fast, but you're going to be programming something like this. This is just an example. Now if you've taken motor controls or even electrical controls for example, this is very similar to your structure, the wiring that you accomplish in those courses. So for example, you could draw a line almost down the center. You could see some most of your switches on the left hand side. You can see majority of your loads on the right hand side. It's not exact. It's not exact to the motor controls and electrical controls courses. But, for example, these look like normally closed, and they're very similar. to normally close wherever you see them. These look like normally open that you're used to, and they're very similar to the normally open. And these look like the different loads that you have, the circle that you use in the motor controls course. You may put M for motor starter, for example. You may put T for timer, depending on what you have. R for a red light, depending on what you have. But in PLCs, they all use them. pretty much the same symbol here if you can see that they don't put m for motor starter and t for timer they have different symbols for motor controls but plc's they all use the same pretty much so there's some similarities but we'll talk about the differences when we get to the programming page now what's important about this is you're going to be creating this now in some instances it may already be created for you and you're going to be debugging and troubleshooting. But for this course, I want you not only to be able to debug, I want you to be able to create. So you're going to be able to create things like this in your first couple of labs. Now to do that, you need a software environment to be able to program the PLC in. And that brings us to the bottom. Now, Allen Bradley, again, since we're in North America and we're in the United States, I want you to be able to use the Allen Bradley. That's going to be majority of what we're going to be focusing on. But the environment that Allen Bradley has, it has multiple different environments. So you may be used to some that I have listed here. I have RSLogix 5, 500, 5000, Studio 5000. There's multiple environments depending on the PLC that you're using. But in these environments, this is where you're going to be doing the programming. This is where you're going to be accomplishing this. So in our course, we're going to be using the Studio 5000. because that's what we have in the labs and we're going to be using Allen Bradley PLCs because again we're in North America in the United States. Now when you guys come to the lab you'll see something like this by the time you get into the Studio 5000. Now unfortunately this is something that's paid. It's pretty expensive software so you won't be able to do it from home unless I find maybe a simulation or something that you can do that's very similar to the Studio 5000 that's free. But when you come to the labs you're going to be opening your project from the Studio 5000 and in here in this Studio 5000 is where you're going to be programming your systems that you want to be able to accomplish in the lab. Now I put the other just another star here I said again if since we're in North America and we're using Allen Bradley you We're going to be using the Studio 5000. So it just takes you piece by piece. It says Alan Bradley is a PLC type. Studio 5000 is a programming environment and ladder logic is the programming language. So those are the three things that we're going to be intertwining the whole time. So before I talk about the PLC block, now this is what your PLC is going to look like. There's different types. Again, I showed you on the last page there's three or four different types. um just listed there um so they don't all look like this but they all have the same kind of format to them now again before i get into this i want you all to understand that you're going your main job is to be able to go into a software environment something like studio 5000 be able to program either something completely brand new you or the program may already be there and you're going to be troubleshooting it and and solving the problem with that program that's the main job of the of the plc's course it's for you to not only be able to go into the plc environment and program a plc correctly you need to also be able to troubleshoot a program that's already been created so we'll talk more about that in the in the next video but for now i just want you to see a plc block this is just the overall plc example that i have for you Now there's some different names here that I want to talk about. So first of all, there's a power supply to a PLC. Now this thing has to be plugged in. It has to be getting voltage from somewhere. So there's a power supply unit on the PLC and it converts the incoming power to suitable levels for the PLC components. So the power supply section of the PLC takes the incoming voltage, whatever it may be, and then brings it down to certain voltages for these all these components and everything else that's on here to work. Now there's a chassis that's on here this provides a modular housing for the PLC modules and helps with the assembly as well. So these can extend longer they can be wider just depending on what type of PLC you have and how many different slots you have. Now there's a CPU, it's not listed on here, but there's a CPU known as the Central Processing Unit. And what that is, is it's going to be the brain. So the brain of the whole system. So when you do a program, the CPU or the Central Processing Unit is what's going to execute your program. So it's going to understand what you did with your program and then execute it in the real world. Now there are other IOs, so they call it input, output, and communication modules. So they have different inputs that you're going to wire to your PLC. There's different outputs that you're going to wire to your PLC. And these, again, I'll talk about this in a little bit, but they can be either something known as digital or analog. But these are the input and output communication modules. They're pretty much going to be receiving signals. So your input, You're going to be taking like a switch, for example, wiring it to the input slot, wherever you decide to wire it to. Program it, and that's going to turn on or off something at the output. But you have to physically connect something to the input and output. And I'll give you a very good example in the next couple of pages that I have. Now, there are a lot of other things. There's different controllers. There's mode key switches. For example, when you're programming, you can be in different modes. So you can be in something known as like offline mode. So that's where I would like you to do your programming initially. So you're going to be programming when the system is offline. You can do something called run. So after you finally do your programming, you can upload it to the PLC, and then you can put it in run mode. And there's different things going on. So when you're in run mode, you cannot program. So you need to be in the offline mode to be able to program. In run mode, your system's running the program that you actually created, but again, you can't do anything to it. You can't actually edit the program while it's in the run mode. And we'll talk more about that inside the Studio 5000. But this PLC can be broken down into many, many little parts, and each of them has their own little definition to them. So I have a slide for you or a page for you that will talk about that. But I just want to get you familiar with some of the... some of the terminology. So they use the word power supply, CPU, chassis, IO, slots. Slots are different inputs and output slots that you could have on the PLC. And then later on we'll talk about analog outputs and digital outputs and things like that. Now what I have here is just some of the definitions. So you can pause the video if you'd like to see any of these definitions from the PLC blog. But I just wanted to put, I put this here just for an overall explanation of what you're going to be doing. Now, I just want you to follow along with this. So you're going to have a computer that you're going to create a program and upload it to the PLC. So this whole center block here, imagine is the PLC. It has a CPU, it has memory, and then that's where your program and all the data is going to go into. So you're going to be on a programming device. computer obviously on the computer you're going to enter the software environment and that will take you inside this PLC where you can program and upload and download and do all the things for the PLC now once your software once your program is ready you're going to be wiring physical inputs and outputs to the PLC depending on how you programmed it that's the main this is the whole whole course pretty much the next 16 weeks is this right here You're going to be programming from the program. You're going to have physical, these are real world physical buttons and float switches and limit switches. And these are real world outputs, the solenoid motor starters and lights and speakers and your program, depending on how you program, it's going to communicate these to these. That's the whole job of the PLC. Now, let me give you an example. You can have a real world push button. This first push button. Your program could actually get this push button to turn on this light. So it doesn't have to go just straight across. It doesn't have to be number one to number one, number two to number two. Your program can, you can, you can tell your program here that if I push one button, I can turn this light on. If I push the second button or if I don't press it, for example, the solenoid energizes. It's all dependent on your program here. Now. Two last examples that I have. These are just some definitions that I recommend that you write down or make some notes about, but the PLC is going to take digital inputs or or analog inputs, and that will control the output voltage and output current and turn things on and off depending on what you input to them. So as I showed you on the last page that I had, I had some physical inputs. So I could have called them digital inputs, for example, the buttons, they can either be on or off. So with those buttons, if I don't press them, or if I press them, I only have two options. So I will treat that as a digital input. Now, if I press it, it will allow voltage to pass through that button and turn something on and the plc will see that it's an on and if that comes on i can do something at the output and again you can pause the video if you like to look through here but these are all very important i talk about the output voltages for the plc output current load considerations i won't go into depth and to read all these individual things but again they're all very important so in the lab environment you're going to have the digital and analog inputs and outputs already wired for you. But in the real world, it's not going to be like that. So this is a very important page that you need to read through. But let me give you an example. This is one example I want to give you. Here's an example of a PLC. We have the power supply section. So it's already been powered. This is the first slot. It's called slot zero. It has a CPU and that remote. or that switch that I talked about before. You can be in offline or test mode or run mode. That's what this will do. There's ethernet slots and other communication that you can do on it. But I want you to look here. So this slot number one says DC, 24 volts DC input. So this is the PLC here pretty much. This is the PLC slot that we're going to be focusing on. Now here's pretty much what's going to happen. If you can see here, these are all real world physical buttons. Some normally open, some normally close. Now, you're going, so pretty much what's going to happen is you're going to have an external DC power supply. And you can say this is 24 volts for this to work. Now, let's follow this. Let's see what the PLC does. This first push button is wired to channel zero. So it's physically wired. Imagine a screw is right here. This is a button that is physically wired to channel zero of this PLC. Now, what does that do? The PLC says if voltage is able to pass through here, since this is open, it cannot. But if voltage was able to pass through here, the PLC would see that as on or will see it as true if the voltage passed through. So the only way for that to come on, this little light right here to come on, is if this button's pressed. and right now it's in an open stage but if i was able to press this the voltage from here would pass through and turn channel zero to true so the plc sees true as a one and false as a zero so as since it's a zero it will see this as off and again it depends on your programming and lots of other factors but in this example i want to show you if the button is open this plc will be off now we can look at the next one on channel one i tied another button into it i see it as open the light is off now on the third button what do i have i have something that is normally closed so the voltage and current can pass through this button immediately so 20 this is 24 volts it's an external dc power supply it's 24 volts this is dc power supply 24 volts and the current can pass through here and since it can pass through immediately the plc sees it as on you can see there's a different color hopefully between these two so the plc can see this is on and since it's now on in your program you can say hey when when channel 2 becomes on i want you to do something to my output and we'll talk about that on the next page so it's really dependent on what you're wiring into and what your program does so for example let's look through Maybe another one down here on channel 5. The DC power supply will pass the 24 volts through this switch and turn on channel 5. And you can see that channel 5 is a different color. This is off, off, on, off, off, on, off, off. And this is just a common ground, for example, that the negative goes to. So depending on the physical state of these buttons, the PLC will turn things on and off. And depending on how you program, you can do things at your output. Now PLC typically is going to have, they can be, they can be different numbers, but typically you're going to see numbers zero through 15. So a total of 16 different options that you have here. And this is based on the 16 bits input register. So this is something else that's going on inside of the PLC, but it pretty much sees zeros as off and ones is on. So we could see this as be channel zero, for example, channel zeros off. Channel 1 is off. Channel 2 is on. Channel 0, 1, 2, 3 is off. 4 is off. And then, for example, 5 is on. So this is what's going on inside the PLC. You can see this when you get into the Studio 5000 if you want to change bits and force bits and toggle bits and all these other things that you can do with your program. But the main sequence of what's going on is you're going to have physical inputs that change the states of the PLC. And depending on these change states and your program, you can do things at the output. So imagine on that last page that I had, I turned on channel. Let me go back and look. We turned on. Let's see here. Channel two. So this button was already closed and channel 2 came on. In my program, so the middleman, remember there's an input section, there's an output section, and the middleman's your program pretty much. I can say in my program that if channel 2, 24 volts DC input, if channel 2 comes on, I can in my program turn on channel 0 at the output. You see how this is a different color than the rest? I can turn on channel 0. and since this is connected to a 24 volts dc output i will now have 24 volts coming out from this section and what they did on this in this specific example they tied from here they tied it to a coil and they tied it back to ground and then back down so pretty much i that button that i had on the last page since it's closed it turned on channel number two in my program i can say hey if channel number two comes on turn on channel zero at the output and since this is a 24 volt dc output it will turn on this coil and i tied it to a real world device it will turn on this dc relay coil and apply 24 volts here and they continued they turned on a 24 volt relay and then they had this relay connected to another dc power supply with a contact or a motor starter here that has high current so it's dependent on what you have as your load For example, a relay is very small, not that high of current, but you can't just tie, again, we'll talk about this a little bit more later, but you can't just tie from here to a big motor starter and go back, or four motor starters in parallel or whatever and go back, because this has a certain current that it can output, and if you exceed that, you'll damage the system, or nothing will work correctly. But something small like a light or a DC relay, this probably uses maximum. maybe one amp two amps something small like that can work properly and then go back but it's also dependent on the plc type as well and the manufacturer it will it will tell you how much output current you have but typically it's up to two or three amps something like that now this is just one example and what i have for you is this is the um output section so the 24 volt dc output Again, you can pause the video and look through any of these pages that I have, but this is the end of the video one.

But it can be multiple different types of environments. Now these were created as cost-effective alternatives to relay-based systems a few years after transistors became more commonplace. So pretty much what that's saying is we used to have things like this, and there probably are some places that still use relay boards like this. And it's not that it's bad, it's just that this was condensed into something like this.

A smaller, pretty much smaller computer that can accomplish the same work, but it's a lot smaller and a lot more reliable. Now, at first, these PLCs, this is a PLC here. These were simple and easy to set up, but as the needs of the business change and the manufacturing floor complexities became apparent, these evolved. Now, they come in different sizes, different manufacturers.

We'll talk about that on the next page. But these require a dedicated person. I underlined it down here. They now require a dedicated person, and that's you watching this, that knows PLC programming to not only create the program, You need to optimize it for the specific project and then be able to change it depending on the business needs.

That's what you're going to have to be able to learn for this course. You have to not only create a program, you have to optimize it, and then you have to be able to change it. Those are the three main steps that you have to do to become a PLC programmer.

Now, there are different brands, as I said. Two of the most popular, I have them listed here. I have Allen Bradley by the Rockwell Automation.

and then i have semantic by siemens there are many many many types of different plc brands but these are probably the two that are are the biggest i would say now allen bradley are are heavily used in north america so if you're in the united states you'll probably see more of the allen bradley if you go overseas you'll probably see more of the siemens plcs because of the standard in european and asian regions Now what I also have listed here is just different shapes and sizes and brands of PLCs. So this is Siemens. This is just a small Siemens PLC.

Probably will maybe be about eight inches across, something like that, just to give you a size. We now have medium. This is a medium one here.

This is I believe Allen Bradley. Allen Bradley PLC medium size. And then we have a large Allen Bradley PLC here. So they can get even larger than this. They can get even smaller than this.

and then there's different manufacturers that make them, depending on what you're trying to do with them. Obviously, the larger you go, the cost also increases, and the complexity increases. Now, starting at the top, you may be able to program the PLC.

You can do it in multiple different languages. I have a couple listed here. So we have ladder logic, function block diagrams, structured text, but ladder logic should be the first language you master. And that's something that you should have also covered in the motor controls class, which is the prerequisite for this course. If you haven't, then we can talk about that, but the ladder logic is the most important and I believe the first language you should master.

Now I put a reason here. I said the reason is it's the most widely spread type of PLC programming due to its roots back to the relay logic that I showed you the relay board before. It's simplicity to implement and the ease of debugging. Now not to jump too fast, but you're going to be programming something like this. This is just an example.

Now if you've taken motor controls or even electrical controls for example, this is very similar to your structure, the wiring that you accomplish in those courses. So for example, you could draw a line almost down the center. You could see some most of your switches on the left hand side.

You can see majority of your loads on the right hand side. It's not exact. It's not exact to the motor controls and electrical controls courses. But, for example, these look like normally closed, and they're very similar.

to normally close wherever you see them. These look like normally open that you're used to, and they're very similar to the normally open. And these look like the different loads that you have, the circle that you use in the motor controls course. You may put M for motor starter, for example.

You may put T for timer, depending on what you have. R for a red light, depending on what you have. But in PLCs, they all use them. pretty much the same symbol here if you can see that they don't put m for motor starter and t for timer they have different symbols for motor controls but plc's they all use the same pretty much so there's some similarities but we'll talk about the differences when we get to the programming page now what's important about this is you're going to be creating this now in some instances it may already be created for you and you're going to be debugging and troubleshooting.

But for this course, I want you not only to be able to debug, I want you to be able to create. So you're going to be able to create things like this in your first couple of labs. Now to do that, you need a software environment to be able to program the PLC in.

And that brings us to the bottom. Now, Allen Bradley, again, since we're in North America and we're in the United States, I want you to be able to use the Allen Bradley. That's going to be majority of what we're going to be focusing on.

But the environment that Allen Bradley has, it has multiple different environments. So you may be used to some that I have listed here. I have RSLogix 5, 500, 5000, Studio 5000. There's multiple environments depending on the PLC that you're using.

But in these environments, this is where you're going to be doing the programming. This is where you're going to be accomplishing this. So in our course, we're going to be using the Studio 5000. because that's what we have in the labs and we're going to be using Allen Bradley PLCs because again we're in North America in the United States.

Now when you guys come to the lab you'll see something like this by the time you get into the Studio 5000. Now unfortunately this is something that's paid. It's pretty expensive software so you won't be able to do it from home unless I find maybe a simulation or something that you can do that's very similar to the Studio 5000 that's free. But when you come to the labs you're going to be opening your project from the Studio 5000 and in here in this Studio 5000 is where you're going to be programming your systems that you want to be able to accomplish in the lab. Now I put the other just another star here I said again if since we're in North America and we're using Allen Bradley you We're going to be using the Studio 5000. So it just takes you piece by piece.

It says Alan Bradley is a PLC type. Studio 5000 is a programming environment and ladder logic is the programming language. So those are the three things that we're going to be intertwining the whole time. So before I talk about the PLC block, now this is what your PLC is going to look like.

There's different types. Again, I showed you on the last page there's three or four different types. um just listed there um so they don't all look like this but they all have the same kind of format to them now again before i get into this i want you all to understand that you're going your main job is to be able to go into a software environment something like studio 5000 be able to program either something completely brand new you or the program may already be there and you're going to be troubleshooting it and and solving the problem with that program that's the main job of the of the plc's course it's for you to not only be able to go into the plc environment and program a plc correctly you need to also be able to troubleshoot a program that's already been created so we'll talk more about that in the in the next video but for now i just want you to see a plc block this is just the overall plc example that i have for you Now there's some different names here that I want to talk about.

So first of all, there's a power supply to a PLC. Now this thing has to be plugged in. It has to be getting voltage from somewhere.

So there's a power supply unit on the PLC and it converts the incoming power to suitable levels for the PLC components. So the power supply section of the PLC takes the incoming voltage, whatever it may be, and then brings it down to certain voltages for these all these components and everything else that's on here to work. Now there's a chassis that's on here this provides a modular housing for the PLC modules and helps with the assembly as well. So these can extend longer they can be wider just depending on what type of PLC you have and how many different slots you have. Now there's a CPU, it's not listed on here, but there's a CPU known as the Central Processing Unit.

And what that is, is it's going to be the brain. So the brain of the whole system. So when you do a program, the CPU or the Central Processing Unit is what's going to execute your program. So it's going to understand what you did with your program and then execute it in the real world.

Now there are other IOs, so they call it input, output, and communication modules. So they have different inputs that you're going to wire to your PLC. There's different outputs that you're going to wire to your PLC.

And these, again, I'll talk about this in a little bit, but they can be either something known as digital or analog. But these are the input and output communication modules. They're pretty much going to be receiving signals. So your input, You're going to be taking like a switch, for example, wiring it to the input slot, wherever you decide to wire it to.

Program it, and that's going to turn on or off something at the output. But you have to physically connect something to the input and output. And I'll give you a very good example in the next couple of pages that I have. Now, there are a lot of other things. There's different controllers.

There's mode key switches. For example, when you're programming, you can be in different modes. So you can be in something known as like offline mode. So that's where I would like you to do your programming initially.

So you're going to be programming when the system is offline. You can do something called run. So after you finally do your programming, you can upload it to the PLC, and then you can put it in run mode. And there's different things going on. So when you're in run mode, you cannot program.

So you need to be in the offline mode to be able to program. In run mode, your system's running the program that you actually created, but again, you can't do anything to it. You can't actually edit the program while it's in the run mode.

And we'll talk more about that inside the Studio 5000. But this PLC can be broken down into many, many little parts, and each of them has their own little definition to them. So I have a slide for you or a page for you that will talk about that. But I just want to get you familiar with some of the... some of the terminology. So they use the word power supply, CPU, chassis, IO, slots.

Slots are different inputs and output slots that you could have on the PLC. And then later on we'll talk about analog outputs and digital outputs and things like that. Now what I have here is just some of the definitions. So you can pause the video if you'd like to see any of these definitions from the PLC blog. But I just wanted to put, I put this here just for an overall explanation of what you're going to be doing.

Now, I just want you to follow along with this. So you're going to have a computer that you're going to create a program and upload it to the PLC. So this whole center block here, imagine is the PLC. It has a CPU, it has memory, and then that's where your program and all the data is going to go into.

So you're going to be on a programming device. computer obviously on the computer you're going to enter the software environment and that will take you inside this PLC where you can program and upload and download and do all the things for the PLC now once your software once your program is ready you're going to be wiring physical inputs and outputs to the PLC depending on how you programmed it that's the main this is the whole whole course pretty much the next 16 weeks is this right here You're going to be programming from the program. You're going to have physical, these are real world physical buttons and float switches and limit switches. And these are real world outputs, the solenoid motor starters and lights and speakers and your program, depending on how you program, it's going to communicate these to these.

That's the whole job of the PLC. Now, let me give you an example. You can have a real world push button.

This first push button. Your program could actually get this push button to turn on this light. So it doesn't have to go just straight across.

It doesn't have to be number one to number one, number two to number two. Your program can, you can, you can tell your program here that if I push one button, I can turn this light on. If I push the second button or if I don't press it, for example, the solenoid energizes.

It's all dependent on your program here. Now. Two last examples that I have.

These are just some definitions that I recommend that you write down or make some notes about, but the PLC is going to take digital inputs or or analog inputs, and that will control the output voltage and output current and turn things on and off depending on what you input to them. So as I showed you on the last page that I had, I had some physical inputs. So I could have called them digital inputs, for example, the buttons, they can either be on or off.

So with those buttons, if I don't press them, or if I press them, I only have two options. So I will treat that as a digital input. Now, if I press it, it will allow voltage to pass through that button and turn something on and the plc will see that it's an on and if that comes on i can do something at the output and again you can pause the video if you like to look through here but these are all very important i talk about the output voltages for the plc output current load considerations i won't go into depth and to read all these individual things but again they're all very important so in the lab environment you're going to have the digital and analog inputs and outputs already wired for you. But in the real world, it's not going to be like that.

So this is a very important page that you need to read through. But let me give you an example. This is one example I want to give you.

Here's an example of a PLC. We have the power supply section. So it's already been powered.

This is the first slot. It's called slot zero. It has a CPU and that remote.

or that switch that I talked about before. You can be in offline or test mode or run mode. That's what this will do. There's ethernet slots and other communication that you can do on it.

But I want you to look here. So this slot number one says DC, 24 volts DC input. So this is the PLC here pretty much. This is the PLC slot that we're going to be focusing on. Now here's pretty much what's going to happen.

If you can see here, these are all real world physical buttons. Some normally open, some normally close. Now, you're going, so pretty much what's going to happen is you're going to have an external DC power supply.

And you can say this is 24 volts for this to work. Now, let's follow this. Let's see what the PLC does. This first push button is wired to channel zero. So it's physically wired.

Imagine a screw is right here. This is a button that is physically wired to channel zero of this PLC. Now, what does that do? The PLC says if voltage is able to pass through here, since this is open, it cannot. But if voltage was able to pass through here, the PLC would see that as on or will see it as true if the voltage passed through.

So the only way for that to come on, this little light right here to come on, is if this button's pressed. and right now it's in an open stage but if i was able to press this the voltage from here would pass through and turn channel zero to true so the plc sees true as a one and false as a zero so as since it's a zero it will see this as off and again it depends on your programming and lots of other factors but in this example i want to show you if the button is open this plc will be off now we can look at the next one on channel one i tied another button into it i see it as open the light is off now on the third button what do i have i have something that is normally closed so the voltage and current can pass through this button immediately so 20 this is 24 volts it's an external dc power supply it's 24 volts this is dc power supply 24 volts and the current can pass through here and since it can pass through immediately the plc sees it as on you can see there's a different color hopefully between these two so the plc can see this is on and since it's now on in your program you can say hey when when channel 2 becomes on i want you to do something to my output and we'll talk about that on the next page so it's really dependent on what you're wiring into and what your program does so for example let's look through Maybe another one down here on channel 5. The DC power supply will pass the 24 volts through this switch and turn on channel 5. And you can see that channel 5 is a different color. This is off, off, on, off, off, on, off, off. And this is just a common ground, for example, that the negative goes to.

So depending on the physical state of these buttons, the PLC will turn things on and off. And depending on how you program, you can do things at your output. Now PLC typically is going to have, they can be, they can be different numbers, but typically you're going to see numbers zero through 15. So a total of 16 different options that you have here.

And this is based on the 16 bits input register. So this is something else that's going on inside of the PLC, but it pretty much sees zeros as off and ones is on. So we could see this as be channel zero, for example, channel zeros off. Channel 1 is off.

Channel 2 is on. Channel 0, 1, 2, 3 is off. 4 is off.

And then, for example, 5 is on. So this is what's going on inside the PLC. You can see this when you get into the Studio 5000 if you want to change bits and force bits and toggle bits and all these other things that you can do with your program.

But the main sequence of what's going on is you're going to have physical inputs that change the states of the PLC. And depending on these change states and your program, you can do things at the output. So imagine on that last page that I had, I turned on channel. Let me go back and look.

We turned on. Let's see here. Channel two.

So this button was already closed and channel 2 came on. In my program, so the middleman, remember there's an input section, there's an output section, and the middleman's your program pretty much. I can say in my program that if channel 2, 24 volts DC input, if channel 2 comes on, I can in my program turn on channel 0 at the output. You see how this is a different color than the rest?

I can turn on channel 0. and since this is connected to a 24 volts dc output i will now have 24 volts coming out from this section and what they did on this in this specific example they tied from here they tied it to a coil and they tied it back to ground and then back down so pretty much i that button that i had on the last page since it's closed it turned on channel number two in my program i can say hey if channel number two comes on turn on channel zero at the output and since this is a 24 volt dc output it will turn on this coil and i tied it to a real world device it will turn on this dc relay coil and apply 24 volts here and they continued they turned on a 24 volt relay and then they had this relay connected to another dc power supply with a contact or a motor starter here that has high current so it's dependent on what you have as your load For example, a relay is very small, not that high of current, but you can't just tie, again, we'll talk about this a little bit more later, but you can't just tie from here to a big motor starter and go back, or four motor starters in parallel or whatever and go back, because this has a certain current that it can output, and if you exceed that, you'll damage the system, or nothing will work correctly. But something small like a light or a DC relay, this probably uses maximum. maybe one amp two amps something small like that can work properly and then go back but it's also dependent on the plc type as well and the manufacturer it will it will tell you how much output current you have but typically it's up to two or three amps something like that now this is just one example and what i have for you is this is the um output section so the 24 volt dc output Again, you can pause the video and look through any of these pages that I have, but this is the end of the video one.

Transcript for:Introduction to Programmable Logic Controllers

Transcript for:
Introduction to Programmable Logic Controllers