Channel History And Persist: What Happens When Values (Settings) Are Changed?

[ledbelly2142]

If I change the values on a channel "history" (stored in RAM) and or "Persist" (stored on your hard drive in the DAQFactory install folder), will I lose the history from that point backward?

I changed the Persist value in a channel from 100,000 to 1,000,000... and I lost the data going back in history from the point in time when I changed the value.

How can I change these values without losing history?

Thanks

[AzeoTech]

Correct. If you change these values, the current history / persist file is cleared out. This is because of how the data is stored depends on the size of the history/persist. This is why persist (and history for that matter) work so fast. The downside is that you can't resize it. There is an assumption here that once you are in production you wouldn't be resizing it.

[ledbelly2142]

That makes sense. Does logging to a CSV have the same storage value as the persist file? Meaning, the persist file uses 16 bytes for each measurement (or 1.6 megs for a persistent length of 100,000), is this true for the CSV logging file?

The storage difference (I think) would be that you have control over disk storage with persistence, the CSV logging file will go until there is no more disk space.

Is this correct?

Thanks

[AzeoTech]

No. CSV is ASCII so it takes one byte for each character you see when you open the file. It also typically only has one time data point for a number of channels, where persist files are per channel.

Persist files are really only designed to allow you to maintain historical data in DAQFactory for viewing in graphs and the like without having to write scripts to load your log files. They are not designed to be accessed outside of DAQFactory and are not designed for archival storage. CSV and other logging files are designed for long term logging.