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Trigger – On Value Change
Learn how to configure a Transaction Group to only trigger when a value has changed, using either the Timer or Schedule option of the Execution Scheduling setting.
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[00:00] When using Transaction Groups it is often useful to only have the group execute when the tag values being monitored have changed. This could be any tag value in the transaction group itself or it might be a specific tag or a set of tags that you want to monitor. Here I have a historical transaction group logging three Integer values and a Boolean value to my database at a one second rate. I can configure this transaction group to only execute when any of the values I am monitoring changes. This can be configured in the Trigger section of the transaction group. The first and simplest method of restricting group execution is to have the transaction group, Only evaluate when values have changed. Enabling the group of this configuration will cost the group to execute the first time. I'll not execute again until any of my tag values here change, like so.
[01:09] I can go even further and restrict the group to only execute if a specific tag or tags change value. I can change the mode from, All tags to Custom. I can now press this Select tags button and choose which tags needs to change for my transaction group to execute. I can select say, Integer A and Boolean A. Now the group will only execute when either of those values change. It does not require that both of them change, it is an either, or scenario. The third way we can limit a transaction group's execution is via a trigger set up on a specific tag. So for example, if we wanted the group to execute only if Integer C changed value, I could enable my trigger by toggling the setting, which now requires this group to, Execute on a trigger.
[02:06] I can then use this dropdown and choose Integer C to be my trigger item. If I set my trigger configuration to be, Active on any change, anytime my Integer C see has changed value my trigger condition will be met and the transaction group will execute. With my trigger configuration on Integer C like this, the group would act the same as if I had selected Integer C as part of my selected tags list above. However, both of these settings can be used together for finer grain control. So to summarize, in this particular configuration we have selected Integer A and Bullion A in the top on change condition. And then down below, we've set Integer C as our specific trigger condition. When used together, this means that the group will first look at these two values, Integer A and Bullion A And only when one of those have changed, we'll look at the Integer C value.
[03:06] If Integer C has changed as well, the group will then execute. With all of these conditions combined, there's a great deal of flexibility in restricting group execution and logging data only when you need to.