Transaction logging

I am logging data from our compressors to a data base using transaction groups.

My question is , can I calculate interval run time by finding that last time the compressor was started (already logging compressor running in 15 second intervals - "Compressor_Running") and when the compressor stops, within the transaction group using a triggered expression or do I need to do this in Ignition outside of transactions ?

You should do this outside of transactions. The simplest tool is your database's lead() or lag() functions, that will allow you to find the timestamps where the condition changed.

If your transaction group is only logging running/not running, consider using a triggered transaction to only log the start/stop events. Virtually identical calculations, but much less data to chew through.

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I am already using triggered events but our suggestion gave me a different idea on how to get what I am looking for.