Shadowing Practice: PLC Programming #5: User-Defined Data Types (UDTs) Explained - Learn English Speaking with Video

Hello and welcome back to the channel.

In today's video, we'll be continuing our PLC tutorial series.

And today we'll be looking at user -defined data types, UDTs, which are a super important concept in PLC programming.

Okay, so today's tutorial is going to be a little bit different

because I've been doing a lot of code along tutorials in this series, but today's video is going to need to feature a fair bit of structured text,

which I haven't gone super deep into on the channel. And

so I think what would be more valuable than sharing the

writing of this code line by line is talk about the concept and show it in a practical use environment.

And then I'll explain to you the code I generated for this.

start very high level with the concept,

a user defined data type is essentially a grouping of tags that you want associated with a shared type of device.

So a very common example is in a big chemical plant, you'd make a user defined data type for every valve, every pump and motor.

And sometimes you go even more generic and you say every two state device is going to have auto manual commands,

it'll have alarms, overrides, and a whole bunch more features.

Every single device of this type is going to have these things.

So you bunch a bunch of features together for shared objects in a data type.

The example that I'm going to show with you guys today is going to be alarms.

This is very common, regardless of the size of your system, to want a bunch of shared alarms in your factory.

So if you're building a little standalone system, there still could be 15, 20 things that go wrong with it.

And if you're controlling an entire factory from this PLC, there could be hundreds or thousands of things that could go wrong with it.

So in TIA Portal, there's a folder called PLC data types over on the left in the system tree.

In Rockwell, I think there's a section called UDTs, user -defined data types.

And most other PLC platforms, it'll be pretty clear.

It'll be something that says data types.

And when you make a new one, you go to add new data type.

I've already generated the base code for alarm.

And here's where I think it's really clear what's going on.

You're saying, what does every alarm have?

that's going to trigger it initially

and then it's going to need to give me the option to acknowledge

that alarm and say yep i've seen it because

when you trigger an alarm the most normal response case is

that a light would turn on to say hey i'm in

alarm state you would shut down the logic until someone had come over

and said i see the alarm it's okay to resume

So then there will be this bit tracking if that alarm is active, if it has not yet been acknowledged.

And then when someone does try to acknowledge it, we need to retain that bit because there's a chance someone hits acknowledge, but the trigger condition is still active.

In that case, we need to see that it's been acknowledged, but not yet cleared.

sort of SCADA software so you can track alarms over time

and then we'll just give a couple identifying things so id

and message could just be like enumerated one through 20

and message could be like here's the thing that just happened

so you put that information again on an HMI

and we'll say every alarm in our system we want to share these

and you can see we have booleans we have long date say no matter how many alarms we make,

we want to keep track of all of these alarms.

And then to show where this gets really useful, we make a data block, we make a global database apologies.

And we say, hey, we're going to store all the information about all these alarms inside of this database.

So I go and make an array of 20 alarms.

And right off the bat, I get 20 individual Initially,

I have one of these tied to a physical push button.

I have another one tied to a PLC bit.

I could come right in here and I could say this is actually my third alarm.

It doesn't matter.

And then we'll say and this ID is two.

And you can see this is the default timestamp it loads in at.

So this has never been triggered.

OK, but I get all of this information for 20 objects, 21, really, just by making an array from zero to 20 of alarm.

I can make infinite numbers of that data type and I get all of those tags populated every time.

And then I made one individual outside of the array to say current alarm

because a really common thing in big systems in particular is alarm fatigue

and so many alarms go off when something shuts down

that you lose sight of what has happened most recently or what the most critical one is.

So I made a separate one and for the sake of this demonstration today this will be really valuable whatever triggered last.

So you can see the last alarm that I triggered was the button trigger, the one that's tied to the button.

So I'm going to drag that off to the side, we'll pull that back up later.

But now we've created a bunch of these objects, right, they live in this DB alarms, but we're not doing anything with them yet.

And this is where the structured text is going to come in.

So buckle up.

An important thing to understand is for loops are not super easy to

something kind of brute force with like counter variables and move blocks.

But almost the whole reason structured text became a thing.

And in Siemens, it's called SCL structured command language.

It is Siemens version of structured text, all the syntax people can calm down.

The reason structured text kind of emerged as a viable PLC programming language is

because loops and other sort of more advanced programming concepts are really tricky to do in ladder.

Rockwell does have a four block, but honestly, if you can pick up a little bit of structured text, you're going to be a better PLC programmer anyways.

And I'll talk you through what's happening here.

And let's talk through how you would want alarms in your factory to work.

Any alarm goes off in my system and I want it to activate the alarm light, the, hey, you have an alarm and it hasn't been acknowledged light.

So that's my light zero right here.

last alarm that occurred is into my current alarm field.

Okay, this is partly for me for this tutorial.

So I can keep it up over here on the right and show you how this code works.

But this is also a very real world scenario where you'd want to keep track of whatever the last alarm

that went off was and show that on the HMI

or you might want to do it where the first right the oldest unacknowledged alarm was

that might be more useful if you're doing like root cause analysis.

pretty easily in structured text.

And what we're going to do here is we're going to talk through the code

that I have set up in my alarm processing routine.

And then if you're doing this in kind of a follow along fashion, feel free to pause and copy it.

Um, and then But anyways, the first thing we're going to do is we're just going to check the local time.

This is useful when we're doing time comparisons later.

And then we're going to reset the light to zero.

So the way functions work, and this is in a function, not a function block, the way functions work is they don't have memory.

So we're going to start every scan of the alarm logic as if there is no alarm active.

And so we're going to turn the light off unless we find

that one of the alarms is active as we iterate through on our for loop.

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that's when we'll turn the light back on as we'll see in a bit.

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Okay.

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And then latest time and latest index are just going to be, they're going to be checkers for us to see if we've iterated through the whole loop.

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And if we found alarms that have gone off more recently than the kind of initial time, right?

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The default time when you first set up a new tag.

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Okay.

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So hopefully that or Python programming, Arduino.

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Hopefully this looks pretty familiar to you at the beginning.

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Now, the meat of what the alarm handler is doing for us is it's iterating from zero to 20, right?

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Because we made an array of zero to 20 alarms.

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So important to note, If you made a new array with 50 new alarms and you call them something different, you do need to make a new version of this

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or at least update this counter with your new array size and you need to point it at the right input tags.

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Okay.

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But anyways, for zero to 20, which is going to iterate through all of our alarms in our database of alarms.

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First, we're going to check if the trigger is active.

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So if it's actively having the alarm condition trigger it, and it hasn't already been active so if the triggers on

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but we've already seen

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that it's active on past cycles doesn't make sense to do all this initial stuff again

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but what we'll do then is we'll say okay active is true we'll reset acknowledged

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because even if for some reason it had been previously acknowledged the alarm is still occurring

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so we'll make that false and then we'll set the time stamp

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that this alarm has last gone off at as temp time so this will give us a snapshot of the triggered.

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Then we'll also say if acknowledge is true, or this is something I forgot to mention, acknowledge all.

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So what I have physically is two push buttons, one I'm going to use to trigger one of the alarms.

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The other one I want to use as an acknowledge all button.

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Okay, if you've been in an industrial environment, it's very normal for a cabinet to have like an alarm acknowledge push button on the outside.

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So I have an acknowledge all push button here.

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So if I acknowledge just or I press acknowledge all,

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then I want acknowledged acknowledged past tense to go equal to true and then I can reset acknowledge equal to false.

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Again, acknowledged is that intermediate value that's checking to see if acknowledged has been true, then I should reset the thing.

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If trigger is not currently active and acknowledged is true, then we want to set active back equal to false.

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And we don't really need an and if active check here

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because there's no harm in setting a value that's already false equal to false again.

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So And then again, if we get any alarm that is currently active, let's have our active alarm light just be on.

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And then this little bit here is just for us to be able to track the most recently triggered

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and active alarm and move it into our global alarm.

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So that's this line down here, whatever our latest time and latest alarm indexes, let's go ahead and copy that whole thing into the current alarm.

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And then the last thing we'll do is we'll assume ACK all is equal to false, right?

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So if we detect that it's true, we'll go ahead and reset it at the end.

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This we could actually delete most likely now that I'm reading it to you, but we're going to leave it as is because I know this is working.

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So I put all that logic in a function I called alarm handler.

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And then in main, I call two things, I call the alarm handler, and then I call another function called alarm setup.

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And this one I made purely for the sake of demonstrating how this works.

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Okay.

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So like I I'm the first one tied to zero on my PLC.

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I'm going to use it to simulate the trigger for alarm zero.

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And then I made a memory tag called trigger one, I'll use that to simulate triggering alarm one.

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And then my other push button tied to input one, I'll use that as the acknowledge all signal.

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Okay, again, I hope this is making sense in terms of why to use it, I set up alarm zero and alarm one to be a button trigger and a PLC bit trigger.

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I trigger them here on the left, you'll see them populate this current alarm on the right, and you'll get a good sense of the benefit of a UDT.

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So if I push the start push button, you can see on the left side there that activates alarm zero in the field, my output, my light is on now.

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And if I go ahead and press stop, all that'll trigger acknowledge all the light is off.

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And what you can see in current alarm here in the bottom right, is we got an updated timestamp and it says, hey, the button trigger was the last alarm to go off.

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Now, if I modify to one, what's cool is the light just turned on in the field.

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So the same output triggered, that's my, hey, an alarm is active and hasn't been acknowledged yet.

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And here you can see PLC bit trigger is the last alarm that got triggered.

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And the ID is one, and I got an updated timestamp.

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So again, I'll press acknowledge, but it's not going to actually trigger condition is still true.

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If I modify to zero, the trigger condition goes away.

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Now I can clear the thing.

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So I'm able to generate a lot of alarms with shared logic very quickly

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and they all have a trigger and acknowledge and active acknowledge timestamp.

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They have all these shared conditions

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and I know they're going to work the same way thanks to the UDT that I generate.

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But I can still reference the individual tags under each of those alarms and use them to program unique functionality.

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So if only one or two of these alarms need to open up a vent valve or stop a certain pump, I could still do that with these UDTs.

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Hopefully that's a useful practical tutorial for you.

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Apologies, this is a little bit of a chaotic tutorial, but this is honestly a pretty tricky one to teach

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because I didn't want to get super in the weeds on structured text with you

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and the lines and the use cases between UDTs and function blocks and instance data blocks do get a little bit blurry.

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that you want every device of a certain type to have access to, to one master data type tag,

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like an alarm that needs a trigger, acknowledge, active, and timestamp.

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It's also totally common practice to create UDTs, data types for devices like alarms, pumps, motors, valves, analog sensors,

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and combine that with function blocks.

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So it's not either or user defined data types or function

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be combined and that's how you can make some really powerful clean well -structured code okay

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so i still hope this practical tutorial was useful for you as always

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if you have questions

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or there are things i forgot to cover in this feel

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free to ask them in the comments below i'll get back

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to you as soon as i can let me know what

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you want to see next on the channel in the comments

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and please don't forget to leave a like on the video subscribe to the channel

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if you're finding this content useful thanks for watching good luck with your projects and see you next time Bye.

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