Emerson Exchange 365

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Dynamically change historian in Embedded Trend Control

Hello,

I have a customer who has several screens of embedded trends that they use for running their facility.  Currently, all of these embedded trends are pointed to 1 of the 2 DeltaV Continuous Historians.  Recently, they asked me for a way to dynamically switch the historian that the embedded trends point to like you can in Process History View.  This was along the lines of "We'd like to click a button and have the trends switch to the other historian."

I have not been able to figure out a way to do this; the trend object doesn't seem to take "defaulthost" as a server, nor can I asses a pen's properties from VBA.

Is there some method that can be used to do this?

Thank you,

Dave

• DeltaV Operate
• Process history View
• trend

dave_marshall

• 10 Aug 2015 9:50 PM
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5 Replies

• Michael Moody

  

  • 11 Aug 2015 2:50 PM

  Dave,
  
  Interesting request. Do you have more info on why they want to do this? Are the customer's two historians collecting history for the same data points (redundancy) or for different points (splitting the load)? Is the customer trying to make use of the 250 data values that come with each Op station?
  
  I was thinking the embedded trend control didn't allow for the trend pens to be modified during runtime meaning the same tags are always on the trend (unless you find a way with VBA). So, if the intent is to swap over when a historian is taken down, I can understand the request. Otherwise, I'm not sure the benefit unless they also want to dynamically change the tags on the trend.
  
  Michael

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• dave_marshall

  

  • 11 Aug 2015 3:55 PM

  In reply to Michael Moody:

  Michael,
  
  They have redundant historians and are looking for a way to switch which historian the embedded trends point to if the primary goes down. This site has 6 dedicated monitors (2 quads) to these graphics, with each graphic containing 8 embedded trends.
  
  I started poking at the embedded trend control object with VBA, but either there is no way to do it or my VBA-fu isn't strong enough. I have also considered making 2 sets of screens, one for each historian, but this seems very silly and wasteful. In addition, a clever way to switch all the screens would have to be developed.
  
  Alternatively, I'd be open to another way of displaying this data.
  
  Dave

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• Matt Stoner

  

  • 11 Aug 2015 4:14 PM

  In reply to dave_marshall:

  Dave,
  
  Not the most eligant solution but you cound configure the same trend(s) twice with the appropriate historian configured on each of those trends and then have a "global" selection of which historian to use that would change the visiblity for the associated trend objects. Then only the selectect historian trends would show up on the graphic...but yes you would have to make any changes to the trend(s) multiple times.
  
  Regards,
  Matt

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• dave_marshall

  

  • 11 Aug 2015 5:28 PM

  In reply to Matt Stoner:

  Matt,
  
  Ahhh, there is a clever idea. Is there a way to make a global parameter/variable in Operate that every Operator station would see? Or is it strictly on a per-station basis?
  
  Dave

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• Matt Stoner

  

  • 11 Aug 2015 8:04 PM

  In reply to dave_marshall:

  Dave,
  
  The only 'real' way to do this globally would be to put the selection in a parameter within a module executing somewhere (Controller or workstation) so all workstations could reference the selection.
  
  If you only want the selection by individual workstation, you can just have a variable on the User.fxg that you can reference from any graphic on the system (Main, Toolbar, Alarmban, etc) to select.
  
  Matt

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