Hello all,
We are using a PI Server as a replacement for our DeltaV Continous Historian.
I have a few questions:
1. How can I determine the sample rate at which DeltaV sends data to PI? I know this depends on module scan rate, but is there another sample rate I can look at.
2. Anyone knows the sample rate at which PI Server collects and display data?
I am trying to determine if we are missing pressure spikes on the PI due to samping delays. But I do not have proof the sampling time. Thank you
Thank you kindly
It depends on your interface from PI to DeltaV.
The most common interface, PI OPC-DA, is a client to the DeltaV OPC server that subscribes to changes in the source data or polls based on scan class setting, excdev, and compdev settings for the PI tag to determine how to react to changes in source data (when to read from the OPC server, when to send to PI server, and then when to archive).
You are correct that the value cannot be updated faster than the scan time of the source module.
To translate the existing compression and sampling frequency in DeltaV to PI, look at the DeltaV historical configuration for all tags (this can be bulk exported):
1. Sampling Period = Scan Class (location parameters)
2. Data Compression Deviation = compdev
3. Data Compression Collect at least every = compmax
Make sure to set excdev and excmax according to OSI recommendations (based on compdev and compmax).
Be careful about using advise tags scan class, as I'm not sure how the required change in value to advise can be configured at the interface or DeltaV server.
In reply to Youssef.El-Bahtimy:
Thanks for responding
For the tag here is the information I found in PI. The module scan is set to 1 seconds.
scan: 1
compdev: 0.4
compmax: 28800
I am not sure I understand what these numbers mean.
www2.emersonprocess.com/.../WP_PIProtocolConv_FAQ.pdf I am also reading here on page 13 " Protocol Converter retrieves data from the Continuous Historian every 5 seconds." But like you mentioned it depends on how we are interfaced PI to DeltaV.
How can I find out if we using Continous Historian or PI OPC-DA to interface to DeltaV?
Thanks so much for your help.
In reply to DCS Newbie:
Darrell,
You mentioned that you were replacing the DeltaV Continuous Historian with an OSI PI server.
Does this mean that you will decommission the existing DeltaV Continuous Historian? If so, how will you provide historical trends to the operators in the control room with only the PI Server (especially trends embedded into operator graphics which are very useful)?
Or are you an OSI PI Enterprise user and will use PI as the historian within the DeltaV?
Youseff's recommendation for getting the current settings was good. You may also want to grab an export of engineering units and scale values for importing into PI as well.
Depending on use of OPC DA or OPC HDA, the actual population of data into the PI Server may be different. The HDA interface may update in chunks, but is getting the data directly from the Continuous Historian (meaning it cannot be decommissioned).
Michael
In reply to Michael Moody:
The Protocol converter document you cite does not really pertain to your situation (that is if I understand the situation correctly). The protocol converter (which I'm not even sure is still supported after v 10 of Dv) allows DeltaV Continuous historian to provide data to PI clients as if it were a PI server.
You mention that you are replacing your continuous historian. Typically, sites that wish to integrate to site or enterprise PI, keep their local DeltaV continuous historian for the purpose of supporting DeltaV historical clients like Process History View, but then also use a PI OPC interface (either DA which connects directly to DeltaV OPC DA or PI OPC HDA which connects to DeltaV OPC HDA/DeltaV Continuous Historian) to get information up to enterprise historian.
There are a myriad of choices to connect to enterprise PI, and depending on which version of DeltaV you are running, some of these are productized solutions created between OSI and Emerson. V 12.3.1 for example, introduces the advanced continuous historian, which looks a lot like the Legacy historian, but obviously offers more functionality. This option would allow a PI-to-PI interface of local advanced (PI) historian to enterprise PI, which is probably the most robust way to integrate.
www3.emersonprocess.com/.../c_main.html
I would contact your local Emerson representative to discuss your options in detail (since it does depend on Deltav version) to ensure you get the best advice, especially regarding redundancy and ease of administration.
By the way, the parameters you mention in PI mean:
scan: 1 - this means the module is to be scanned. 0 means it is not.
compdev: 0.4 - this mean values that differ by more than 0.4 will only be archived (generally)
compmax: 28800 - this means that if the value does not differ by more than 0.4 for 28800 seconds a value will be archived anyway.
Thank you Youssef and Michael for responding. I really apprecaite this forum. For a newbie like myself its like entering college again learning. But it is fun
I will talk to my PI adminstrator to get a better understanding how we are setup.
Thank you
Happy to hear you are finding the community so useful, Darrell. Feel free to pass the word around :)
Best Regards,
Rachelle McWright: Business Development Manager, Dynamic Simulation: U.S. Gulf Coast