Record Previous Value on Change - All Drivers and Points

[du5tin]

In oil and gas we often have periods of time where a point doesn't change because the industry is built on process control that is 24/7. Could be a variable valve output held at 100% or a flow rate that is zero for a period of time because of an optimization program. Some drivers have scan groups or confidence polling that help work around these issues but the features are not applied consistently to all drivers. The problem we consistently have is that recorded values don't represent what the value is doing. It records the value when the point goes to steady state, which could be two weeks ago, and then doesn't record more history to help the trends properly show what the value is doing. Customers often (read: always!) ask if we can record a value on EVERY poll but the product doesn't support that. 

Hopefully this isn't patented by PI but maybe we can record a "previous value" just before the value changes so that trends more accurately reflect what the value is doing. 

[BevanWeiss]

It won't matter if it's patented by OSIsoft (PI) anymore... since they're on the same team 😉

https://www.aveva.com/en/info/aveva-agrees-to-acquire-osisoft/aveva-and-osisoft-combine-accelerating... 

But yes, the 'swing door' compression approach I find to be much more favourable to the deadband version currently in Geo SCADA Expert.

Some drivers do support adding historic event on every poll (i.e. DNP3), if you have the Historic Event setting to 'Value Change and Current Value' or something like that... towards the bottom of the Point properties tab.  You would need to turn off any historic compression however.

I think I did raise a feature request on the SCADAPack forum for some event storage settings similar to this (in the outstation).  I guess similar should apply for Geo SCADA Expert where it's the one doing the historic capture.

[sbeadle]

Thanks. Confidence polls always log values. But, we're always telling customers not to waste CPU and disk by setting up high frequency confidence polling. Just Store Changes, we say. I understand your point though. The trend is trying to draw a line between known points, so is technically correct. You could use Step traces to show the prior value.

[du5tin]

Step traces gets us part way there. But Step does not work well with Processed Pens (as opposed to Raw trends). 

O&G is very picky and maybe unsophisticated about the underlying data. They want to positively know for absolute certain that the flow rate was zero for 8 hours, not just at the beginning of the time period. Its been a struggle to teach customers understand how the system is supposed to work. "oh but all the other SCADA systems I've used prior don't do that so just make it record a value on every poll" or "we'll compress the data at a higher level in our historian. We want the OT system to maintain the highest resolution and fidelity". 

We often work around it by using RTU logging. DLOG in a SCADAPack. History points in a Floboss/ROC. DEVT blocks occasionally for DNP3 in a SCADAPack. Outside of that we do use scan groups or confidence polls or forced refreshes on drivers that support such things. Confidence polls on a large system can be problematic though.