Wednesday, April 18, 2012

OSIsoft PI OPC Interface and sub-second data

I found out today that the PI-OPC Interface supports sub-second data. I'd imagine that this comes as no surprise to many of you, but it certainly does to me.

OSIsoft PI has supported the archival of sub-second data for quite some time. And for cell culture/fermentation processes, sub-second data is overkill. Cell culture happens over the course of days, production culture...weeks. Fermentations happen in hours, so very few things happen in between seconds.

Actually, there was this one time there was a rupture disk on a pasteurizing unit that had a setting of 50psi. When the transfer of media through the pasteurizer failed, due to the rupture disk, the highest pressure reading on OSIsoft PI was 29psi. As it turns, there was a pressure spike that happened on a sub-second basis, and was not captured... I suppose some large-scale manufacturing activities may require sub-second data for troubleshooting.

But ever since moving to sub-second data, it has been a pain because an event may happen at

18-Apr-12 01:24:03.5566

but if you were searching between

18-Apr-12 to 18-Apr-12 1:24, then you'd miss this event.

As is, people despise typing out more characters for specifying time. And in cell culture processes, it is simply not necessary. But as OSIsoft PI evolves to serve multiple industries, nuisances like sub-second data start cropping up.

In any case, the way to specify a sub-second scan-rate is at the interface. In the case of the PI-OPC Interface, you can specify the scan class as a fraction. If you wanted to specify scan rates at 1/10th, 1, 2, 5, 10, 30 and 60 seconds, your interface configuration file should read:

/f=0.1 /f=1 /f=2 /f=5 /f=10 /f=30 /f=60

Then any tag that you want to scan 10 times per second should have location4=1 (since 0.1 is the first scan class).

In any case,

  • Few cell culture/fermentation processes require sub-second scan rates.
  • Well duh: a PI system capable of archiving sub-second data has interfaces engineered to deliver data at sub-second scan rates.

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