This lesson is part of the Tags in Ignition course. You can browse the rest of the lessons below.


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Driven Tag Group


Learn how to configure a Driven Tag Group, a Tag Group that varies in execution rate based on some condition.

Video recorded using: Ignition 8.1


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[00:00] Sometimes we don't want our Tags to execute 24/7, we want to execute at different rates at different times based on some condition. For this ignition has a Driven Tag Group. Tags and Driven Tag Group will execute at one rate when the condition is true. And another rate when the condition is false. You can see I have these pressure and temperature Tags derived from the PLC, as well as a machine status Tag. These Tags are running at a one second rate, and that's fine. But when the machine is turned off, I'd like to turn down the polling rate a bit, or maybe even stop polling completely. To do this, we'll open up the Tag Group Editor. And you can see we have our default Tag groups. But I'm going to add another one. And I'll name it Driven Tag Group. And we'll change the mode to driven. Now once we do that, you can see that a few other properties pop up. Namely, we now have two rates, our regular rate and our Leased/Driven Rate. The Leased/Driven Rate is the one that's going to run when our driving comparison is true. And the normal rate is how often will run when the driving comparison is not true. Now for our comparison to work, we'll have to fill out all three of these properties. And I'll set my driving expression to be based on that machine status Tag, we can click on the Edit icon on the right. And then we can select our machine status Tag. And this is all I need in here. So hit Apply Changes. And we want to change a rate based on when the machine status Tag is true. So I'll have a comparison of equal and a value of one. So when our machine status is equal to one, now I'll leave our Leased/Driven Rate at one second. So when a machine status is one, we'll run at one second rate. But when it's not true, then we'll run at a different slower rate. And I'll set that to 5000 milliseconds or five seconds. Now, before I hit OK, I wanted to mention this One-Shot property. If this is true, then when our driving comparison becomes true, we will collect the Tag values once rather than at the rate, then the Tag group will wait for the comparison to become false and then true again, to collect the Tag value one more time. We'll leave that as false, and then hit OK to submit our group. Now you can see our Tags are still running at that one second rate. But this is because we haven't actually assigned our new Tag group to these Tags. We'll select both Tags, and then go and edit the Tags. And then you can see here we'll have our Tag Group, we'll set it to the new Driven Tag Group that we just created. And then when we hit OK, then you can see that these Tags are going to start running at a different rate because our machine status is off. If we turn our machine status back on, then you can see that they will move into the faster rate and start running at a one second rate again. Now what if I want to do something a little bit different until these Tags do not run at all when the machine is off. To do this, we can go back and edit our original Tag Group here. And we can set our rate to a value of zero. That means don't collect the Tag values while we're off. I'll hit OK down at the bottom. And then if I change my machine status to false, then you can see the Tag values will stop updating. In future videos, we'll look at additional applications for these Driven Tag Groups.

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