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2017

In response to user voice :

 

Introduction :

Event frames are really useful to find out when some events happen for a specific time range.

However, it´s not possible to run an anaylsis in that event frame while the event frame is running.

Here is a workaround of how you can actually do it. The trick is to run the analysis under certain condition and link this analysis to an event frame.

Intuitively, we try to build an analysis based on an event frame but that is not possible if we want to run calculation during the event frame. We will see instead how to run an event frame based on a analysis.

That will allow us to do some calculations during an opened event frame.

 

 

Problem description:

Let´s say we want to do some calculation over a time range for a periodic signal.

But the time range is not fixed and the period of the signal can change over time.

In others words, we don’t know the explicit start and the end times of the calculation.

The only thing we know is that we want to run the calculation (to find the integral of the ‘sinusoid’ signal in our example) while the signal is increasing and stop the calculation when it’s decreasing.

Let’s plot a graph to summarize what we want to achieve:

 

In our example, we will use instead the Sinusoid signal from the PI Interface for Random, Fractal, Station, Sinusoid Data:

 

 

As the period of the signal is not always the same we can’t use a fixed time range.

We will have to retrieve the start and the end times using another tag.

 

In this example we have a variable Trigger2 linked to a PI Tag called ST2. (This PI Tag will be needed if we want to create later on an event frame.)

This variable is equal to 1 when the condition of the calculation is met, otherwise it’s equal to 0.

Here we simply define Trigger2 in that:

  • If the previous value in the archive of the tag Sinusoid is lower than the current value of Sinusoid then the value of Trigger2 is equal to 1

  • If not; Trigger2 is equal to 0

If we were working with a “real “signal, the only difference would have been the variable Trigger2. It would have to take into account the noise present on the signal. We should have ended up with something like that:

Then comes the trick of this analysis:

 

We create a variable startdate. This variable has to be mapped to a PI Tag (Calcultime in the example) because we will need to store it in the archive. Do not forget in AF to set the Value Type of this tag to “DateTime”.

Thanks to the analysis, we will store the actual timestamp of the Sinusoid tag if the trigger is equal to 0. If not, we won´t send any data to the PI Data Archive.

That way, after the Trigger2 variable jumps from 0 to 1 (in other words, when the Sinusoid signal starts increasing) we won´t update the timestamp in the archive.

The value stored in the archive is the beginning of our integral calculation.

Then, we can use this timestamp to run our calculation from Calcultime to now ‘*’.

Now it’s time to put everything together in a table understand for a better understanding:

While Trigger2 is set to 0 (when the Sinusoid value is not increasing) we store the current PI Time of the Sinusoid tag. The result in Calcultime and PI Time column are the same.

WhileTrigger2 is equal to 1, we don´t send the PI Time anymore to the archive so the value of Calcultime is the last value stored in the archive. This value corresponds to the beginning of our integral calculation Tot2.

 

Please note that the analysis scheduler is set on Event-Triggered. Indeed, we don’t know how long is the time range of the calculation of the integral so it´s important not to set it to periodic in that case.

Now we are running the integral of the signal from Calcultime to now. We can see the result Tot2 increasing in real time:

 

 

About the precision of the calculation:

In our example, we decide to compare the previous event in the archive and the current value of the tag..

That way, the precision of the integral depends on the configuration of the Sinusoid tag (scan class, exception/compression parameters, etc)

 

Link an event frame to this calculation:

It´s possible to link that calculation to an event frame so we can easily find when the calculation was running or not.

To do that, you should create a PI Tag linked to the variable Trigger 2 in my example. Actually I already did that in the previous part but this should be done if you want to use the event frame.

Then we can backfill the data and we can when the calculation was running in the last 2 days :

Thanks to the event frame, we can easily find when the calculation was running or not using Coresight for instance :

 

Please note that this method is quite heavy in configuration and required 2 tags at least per Analysis.

The possibility to run some calculations during an opened event frame will be added to the next release of Analytics (2017 R2)

This article was written using a Virtual Learning Lab (VLE) virtual machine. If you have your own PI System, great! You're welcome to follow along with what you've got, but if you'd like to access the machine used to build this article, you must have a subscription to the VLE. You can purchase a subscription for 1 month or 1 year here. If you've already got a subscription, visit the My Subscription page and start the machine titled "UC 2017 Hands-on Lab: Tips and Tricks with PI Builder and PI System Explorer". Once provisioned, connect with the credentials: user: pischool\student01 password: student. You can work from the full manual for the lab by downloading it here.

 

Software Versions Used in this Article

Product
Version
PI System Explorer2017 - 2.9.X
PI Asset Framework2017 - 2.9.X

 

Introduction

When building an Element template, it can be hard to figure out how to configure PI Point attributes. If you have a consistent tag naming convention, substitution parameters can be used directly, but what do you do if you don’t have a consistent naming pattern? You could bind the attribute to its appropriate tag by hand, but this might give you headaches down the line when you try to improve the template and don't see your improvements echo to all of the elements based on the template. This article works through the best method of configuring these data references when you're in this situation. We're going to demonstrate this by adding a new Attribute named Discharge Pressure to the Compressor Template, change the Units of Measure to psig, and make it Data Reference PI Point.  Then add a child-Attribute to this Attribute called Tag Name. If you find yourself in this situation while building an Asset Framework database in the future, follow this article to ensure you use best practises when doing so. In a nutshell:

The Bad Way - Hard-coded PI Point Data References

On the Element TemplateOn a Specific Element
badTemplate.pngbadElement.png

 

The Good Way - Soft-coded PI Point Data References

On the Element TemplateOn a Specific Element
goodTemplate.pnggoodElement.png

 

Prepare a "PI Servers" Element to Hold PI Data Archive Configuration

It's useful for any PI AF Database to have the PI Data Archive names held inside attribute values. This makes it a whole lot easier if you ever have to move to another PI Data Archive with a different name. You'll just need to change a single attribute value to migrate your entire database! You'll only need to do this step once for your database, then you'll be able to reuse it for all configuration int he future.

  1. Open PI System Explorer
  2. Press the Ctrl+1 key combination to go to the Elements view.
  3. Create an Element PI Servers based on the PI Server Template, and name it PI Servers. Hint: If you're doing this on your own system, you'll have to also create the PI Server template. Head to the Library, and create an Element Template called "PI Servers" and give it a single attribute of string type called "Server1".
    1.png
  4. Click on the PI Servers element, then click on the Attribute tab in the Attribute Viewing pane.  Enter the server name into the Server1 Attribute.
    2.png

 

Add a New Attribute on Your Element Template

  1. Press the Ctrl+3 key combination to navigate to the Library view.
  2. Select the Compressor Template under Element Templates.
  3. Click on the Attribute tab in the Attribute Viewing pane.
  4. Right click anywhere on the white space in the Viewing Pane and select New Attribute Template.
  5. Select the Attribute, press the F2 key, and type Discharge Pressure.
  6. For the Data Reference select PI Point.  Click inside the combo box for Default UOM and type in psig.
    3.jpg
  7. Select the Discharge Pressure Attribute and set the Data Reference to PI Point.  Click the Settings button, then in the PI Point Data Reference dialog type %@\PI Servers|Server1% in the field next to the Data Server (this grabs the value of Server1 that we ended up with in the above steps), and then type %@.|Tag Name% in the field next to the Tag Name. If this syntax doesn't make much sense now, don't worry. We're going to create a sub-attribute later called "Tag Name" that this substitution syntax will grab.
  8. One last thing, it is a best practice to never to use <default> units for a measurement.  So click on the Source Units combo-box and select psig from the available units of measure.
    7.png
  9. Click the OK Button. Note: The "quick" way to do the above steps is (once you become familiar with the syntax), is to delete the text under the Settings button and type \\%@\PI Servers|Server1%\%@.|Tag Name%;UOM=psig directly.
  10. Select the Discharge Pressure Attribute.  Right click and select New Child Attribute Template.  Press the F2 key and type Tag Name.  Change the Value Type to String. Under Properties select Hidden. Normally you would mark Attributes as Hidden if they are not important for end users to see. In our case end users don’t need to see the Tag Name as long as the Discharge Pressure attribute is displaying correctly. However, it's sometimes useful to leave this "Tag Name" attribute as visible - some users like being able to see which point this attribute is bound to.
    4.png
  11. Press the Ctrl+S key combination to Check In your changes.

 

Configure the Tag Name Attribute for a Specific Element

  1. Press the Ctrl+1 key combination to go to the Elements view.
  2. Select the first compressor element (name starts with K) in the Browser pane (Facility1>Area1>Rotating Equipment) then click on the Attribute tab in the Attribute Viewing pane.
    9.jpg
  3. Select the child-Attribute Tag Name, press the F2 key, and type cdt158 for the value.  Press the F5 key to refresh.  The Discharge Pressure Attribute is now receiving data.

 

Conclusion

Once this is configured, you would use PI Builder to manually bind the tag names to your desired tags. Following the above procedure greatly enhances the ease of management of your AF Database, and is considered best practise at the time of the publishing of this article. If you run into any issues when working through this or have any questions, you're welcome to post a comment!

 

Further Resources

  • If you're interested in learning PI AF, check out the online course
  • For a great article on tips and tricks with PI AF, check out this post
  • The full manual used to resource this post can be downloaded here

 

This article was written and adapted from materials originally developed by Ales Soudek and Nick Pabo.

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