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Group Update Rate
Learn how the Timer and Schedule group execution types work.
Video recorded using: Ignition 7.9
Transcript(open in window)
[00:00] Everything that transaction groups do is driven by the groups 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 schedule can be times of day or ranges of times which then will run at a rate, very similar to the timer. 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. So this is the first step of group execution. For example, if we set the group to run at a one minute rate, every minute the group would first come in and evaluate its pre-trigger conditions, then it would look at the trigger configuration, first the on change tag conditions and then the specific trigger condition. If these were true or in this case, not enabled, it would go on to evaluate the trigger expression items and then it would interact with the database as defined on the action tab. In schedule mode we can specify specific times of day or ranges of times. For example, if we wanted to run at 8:00 a.m. and then continuously from 12:00 p.m. to 3:00 p.m., 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 schedule 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. In timer mode, 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 the group is going to run faster than what this schedule dictates. On the other hand, 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.