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


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Learn how the Timer and Schedule group execution types work.

Video recorded using: Ignition 8.1


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[00:00] In this video, we are going to take a look at the update rate of transaction groups. Everything that transaction groups do is driven by the group's execution scheduling. This small section around the top of the action tab, drives everything that a group does. There are two modes for scheduling group execution, a basic timer, and a schedule. The basic timer allows you to run the group at a set rate, while the schedule can be times of day or ranges of times, which will then run at a rate that you specify. This execution scheduling can be thought of as the beating heart of the group. It dictates things such as the OPC subscription rate, and drives all evaluation. For example, if we set the group to run at a one minute rate, every minute the group would first come in and evaluate it's pre-trigger conditions, then it would look at the trigger configuration, first the on change tag conditions, and then the specific trigger condition.

[01:09] If these were true, or in this case not enabled, it would go on to evaluate the triggered expression items. And then finally, it would interact with the database as defined on the action tab. In timer mode, we simply specify a rate that we want the group to run in, by entering in a numeric value and adjusting the units. In schedule mode, we can specify times of day or ranges of times. For example, if we wanted to run at 8:00 AM, and then continuously from 12:00 PM to 3:00 PM, we could put in a schedule such as this. Since we have a range, we need to specify a rate for how the group will run during that range. Let's say we wanted every 15 minutes. One interesting point about the scheduling system as opposed to the timer, is that the execution aligns to your specified start time on the update rate. So for example, we'll know that we will get recordings at 12:15, 12:30, 12:45, and so on.

[02:11] Contrast that with timer mode, where without the use of a special triggering expression item, it's impossible to specify exactly when the group should run. It's all a function of when the group first starts running, and its update rate. Although these options are fairly straightforward, it's important to understand that these are the foundation for the group. And so nothing else in this group is going to run faster than what the schedule dictates. Remember, a great amount of flexibility can be derived by using the timer in conjunction with expression items and the triggering system, both of which are covered in other videos.

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