Dynamic inclusion of PI tags in a PI ACE calculation

Discussion created by fabiano.batista on Sep 7, 2012
Latest reply on Sep 7, 2012 by fabiano.batista

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Hi folks,

I am building a PI ACE calc to perform calculations on tags that are not initially specified in the PI ACE calculation configuration. This is how I am planning it:

- Calculation context is started

- In the initialization phase, it search for tags and build a point list for the tags that match a certain attribute mask (using PI-SDK)

- Every N minutes (clock based), perform the calcs and output the results.

- A separate thread would be continuously searching for new tags to be included in the next calculation time

However, I believe I should leverage the power of PI point caching in ACE, and this is one thing that SDK is not going to give me. Is there any way to add PI ACE points on the fly into the calculation?

Also, I am concerned about performance. The type of calculation (formula used) will depend on some tag attributes. Is it a good practice to read a pipoint attribute every time a perform a calculation or it would be better to store the specific attribute value in arrays (considering that reading an array is usually faster than reading an object attribute)? Any recommendation regarding pipoint attribute reading performance?

Best regards,

Fabiano

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Asle Frantzen Sep 7, 2012 2:46 PM
Hi Fabiano

Just a quick word on how I did it when I needed to have a variable amount of input tags per context, for a context based ACE calculation.

I think you need to initialize the number of input tags you're going to use, in the actual code. A good thing here is that you can initialize aliases in the module database. If you create a setup with the maximum number of aliases/tags needed, you can fill PI tags into the aliases you need and just fill a dummy-tag into the rest of them.

Make sure you create a dummy-tag which has some default value, and which is never being updated.

Then you can either create a module database property specifying the number of actual aliases/tags in use, and just use those aliases in your code. Or you can search through all your aliases and just ignore using the ones containing the dummy-tag.

It's not 100% what you need, but maybe you can use it to get one step closer to your goal.
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- matthew.rivett @ Asle Frantzen on Sep 7, 2012 2:53 PM
  PI ACE can do anything! As Asle mentioned depending how you are triggering the calculation this may or may not work for you. I load tag dynamically and it works fine because it's clock based. Haven't seen any performance issues.
  
  This example loads aliases from the module database but you could search for tags using the SDK instead. A bus can have different numbers of generators so it had to be dynamic.
  
  I give up on posting code properly. I'm not sure what I'm doing wrong...
  
  #Region "INITIALIZATION"
  
  Private Sub LoadGenerators()
  
  ' load all the generators for this bus
  
  Try
  
  ' first I need to get the generator module below the current bus module
  
  Dim modGenerators As PISDK.PIModule
  
  modGenerators = PIACEBIFunctions.GetPIModuleFromPath(Context & "\generator")
  
  GeneratorsOnThisBus = New GeneratorsOnBus()
  
  Dim GeneratorOnThisBus As GeneratorOnBus
  
  ' loop through all the modules in the generator module
  
  ' create a new GeneratorOnBus Object to be used in the vstatt calculation
  
  ' add it to the collection of all generators on this bus
  
  For Each modGenerator As PISDK.PIModule In modGenerators.PIModules
  
  GeneratorOnThisBus = New GeneratorOnBus(New PIACEPoint(Context & "\generator\" & modGenerator.Name, "g_mw"), New PIACEPoint(Context & "\generator\" & modGenerator.Name, "g_mr"), New PIACEPoint(Context & "\generator\" & modGenerator.Name, "hmrlm"), New PIACEPoint(Context & "\generator\" & modGenerator.Name, "lmrlm"))
  
  GeneratorsOnThisBus.Add(GeneratorOnThisBus)
  
  Next
  
  Catch ex As Exception
  
  PIACEBIFunctions.LogPIACEMessage(OSIsoft.PI.ACE.MessageLevel.mlErrors, "GPM ACE ERROR in vstatt check " & logFileLocation, Context)
  
  logMessage("PI ACE Error in """ & Context & """ LoadGenerators" & vbCrLf & vbCrLf & ex.ToString)
  
  End Try
  
  End Sub
  
  Protected Overrides Sub InitializePIACEPoints()
  
  Try
  
  av_kv = GetPIACEPoint("av_kv")
  
  l_kv = GetPIACEPoint("l_kv")
  
  u_kv = GetPIACEPoint("u_kv")
  
  vstatt = GetPIACEPoint("vstatt")
  
  Catch ex As Exception
  
  logMessage(System.DateTime.Now & " Error initializing PI ACE Points: " & ex.ToString)
  
  End Try
  
  End Sub
  
  Protected Overrides Sub ModuleDependentInitialization()
  
  Try
  
  ' MyBase.CalculationLimit = 1000
  
  client = New SmtpClient("mail.com")
  
  previousMessage = System.DateTime.Now
  
  LoadGenerators()
  
  Catch ex As Exception
  
  logMessage(System.DateTime.Now & " Error in ModuleDependentInitialization: " & ex.ToString)
  
  End Try
  
  End Sub
  
  #End Region
  
  #Region "GeneratorOnBus Class"
  
  Public Class GeneratorOnBus
  
  Implements IDisposable
  
  Private _g_mw As PIACEPoint
  
  Private _g_mr As PIACEPoint
  
  Private _hmrlm As PIACEPoint
  
  Private _lmrlm As PIACEPoint
  
  Public Sub Dispose() Implements IDisposable.Dispose
  
  _g_mw.Dispose()
  
  _g_mr.Dispose()
  
  _hmrlm.Dispose()
  
  _lmrlm.Dispose()
  
  _g_mw = Nothing
  
  _g_mr = Nothing
  
  _hmrlm = Nothing
  
  _lmrlm = Nothing
  
  End Sub
  
  Public ReadOnly Property g_mr() As PIACEPoint
  
  Get
  
  Return _g_mr
  
  End Get
  
  End Property
  
  Public ReadOnly Property g_mw() As PIACEPoint
  
  Get
  
  Return _g_mw
  
  End Get
  
  End Property
  
  Public ReadOnly Property hmrlm() As PIACEPoint
  
  Get
  
  Return _hmrlm
  
  End Get
  
  End Property
  
  Public ReadOnly Property lmrlm() As PIACEPoint
  
  Get
  
  Return _lmrlm
  
  End Get
  
  End Property
  
  Public Sub New(ByVal PT_g_mw As PIACEPoint, ByVal PT_g_mr As PIACEPoint, ByVal PT_hmrlm As PIACEPoint, ByVal PT_lmrlm As PIACEPoint)
  
  _g_mw = PT_g_mw
  
  _g_mr = PT_g_mr
  
  _hmrlm = PT_hmrlm
  
  _lmrlm = PT_lmrlm
  
  End Sub
  
  End Class
  
  #End Region
  
  #Region "GeneratorsOnBus Collection Class"
  
  <System.Reflection.DefaultMemberAttribute("Item")> _
  
  Public NotInheritable Class GeneratorsOnBus
  
  Inherits CollectionBase
  
  Public Sub New()
  
  MyBase.New()
  
  End Sub
  
  Public Property Item(ByVal index As Integer) As GeneratorOnBus
  
  Get
  
  Return CType(InnerList(index), GeneratorOnBus)
  
  End Get
  
  Set(ByVal Value As GeneratorOnBus)
  
  InnerList(index) = Value
  
  End Set
  
  End Property
  
  Public Sub Insert(ByVal index As Integer, ByVal GeneratorOnBus As GeneratorOnBus)
  
  InnerList.Insert(index, GeneratorOnBus)
  
  End Sub
  
  Public Function Add(ByVal GeneratorOnBus As GeneratorOnBus) As Integer
  
  Return InnerList.Add(GeneratorOnBus)
  
  End Function
  
  Public Sub Remove(ByVal GeneratorOnBus As GeneratorOnBus)
  
  InnerList.Remove(GeneratorOnBus)
  
  End Sub
  
  End Class
  
  #End Region
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  - fabiano.batista @ matthew.rivett on Sep 7, 2012 3:26 PM
    Hi Asle and Matt, thank you for your reply. In my case I am trying to build a calculation that does not require any dummy tags to be created in advance. It is a sort of "totalizer" based on ACE basically (so I can have all the benefits of ACE, such as scalability, recalculation, etc). The user will just have to create a regular tag with some specific attributes, and then the PI ACE calculation would pick that tag on the fly. I have coded it using purelly PI-SDK, but using PI ACE I will have the caching feature provided by this tool.
    
    My problem was when trying to define a PIACEPoint directly in the code, instead of using a PISDK.Pipoint. For testing purposes, without using the PIACE wizard for the tag creation, I tried to manually define a tag in the "Initailize PIACEPoint() sub. Here is my basic testing code:
    
    Public Class testclass
    
    Inherits PIACENetClassModule
    
    Private mytag As New PIACEPoint
    
    '
    
    ' Tag Name/VB Variable Name Correspondence Table
    
    ' Tag Name VB Variable Name
    
    ' ------------------------------------------------------------
    
    '
    
    Public Overrides Sub ACECalculations()
    
    mytag.Value = 2
    
    End Sub
    
    Protected Overrides Sub InitializePIACEPoints()
    
    mytag = GetPIACEPoint("sinusoid")
    
    End Sub
    
    '
    
    ' User-written module dependent initialization code
    
    '
    
    Protected Overrides Sub ModuleDependentInitialization()
    
    End Sub
    
    '
    
    ' User-written module dependent termination code
    
    '
    
    Protected Overrides Sub ModuleDependentTermination()
    
    End Sub
    
    End Class
    
    When I run the code, I get "Object reference not set to an instance of an object" error, even though the point was instanciated by using the "New" keyword.
    
    Any ideas if I can "manually" initialize a point this way"? What I am doing wrong here?
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    - matthew.rivett @ fabiano.batista on Sep 7, 2012 5:25 PM
      GetPIACEPoint is looking for a "SourceCodeName" which is created by ACE when you created a new calculation.
      
      I am beginning to think I was wrong when I said you could do this using the SDK to get tag names and created PIACEPoints. It looks like you need to use the MDB to use PIACEPoints. Even if you create a new PIACEPoint like I did in my code you still need to provide an alias in the MDB for it.
      
      My code is dynamic in a way that the number of objects can be different but the objects always contain the same aliases. I really should have read the posts a little closer.
      
      For a calculation that has a different number of inputs we do as Asle suggested. Create a bunch of aliases and use a placeholder tag in the ones we don't need to use. It's not great but I don't know of any better way.
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      - RJKSolutions @ matthew.rivett on Sep 7, 2012 5:35 PM
        Ive built projects that piggyback ACE and dynamically create 1,000's of tags but only ever have one Input...more common than you think amongst clients because of the API fanning.
        
        You should be able to create a new PIACEPoint and use the SetTag method (from my memory). Don't create a new instance in the class level variable, that might be your problem here.
        
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        matthew.rivett @ RJKSolutions on Sep 7, 2012 5:50 PM
        Rhys is correct. The properties are called Context and Alias but you can use server and tag name instead.
        Public Overrides Sub ACECalculations()
        
        Dim ptTest As PIACEPoint
        
        Try
        
        ptTest = New PIACEPoint("\\DOR\", "SINUSOID")
        
        Debug.Print(ptTest.Server)
        
        Debug.Print(ptTest.Tag)
        
        Debug.Print(ptTest.Value)
        
        Catch ex As Exception
        
        End Try
        
        End Sub
        
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        fabiano.batista @ matthew.rivett on Sep 7, 2012 6:07 PM
        Thank you guys for the detailed explanation and example.
        
        As I mentioned before, PI ACE will build the cache using values for the input tags that are created by the ACE Wizard. If I add the tag manually (using the code provided by Matt), how can we assure that this tag is being considered an input point by ACE (so that its values will be in the cache)? I am not what attribute (if any) ACE uses to inform a PIACEPoint is a input tag.
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        matthew.rivett @ fabiano.batista on Sep 7, 2012 6:17 PM
        I haven't really done any testing with caching. There's another constructor that you can specify an alias type. Maybe this is all you need to do? Someone else will need to verify.
        
        New PIACEPoint("\\DOR\", "SINUSOID", TagAliasUsedType.TagAliasAsInput)
        
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        fabiano.batista @ matthew.rivett on Sep 7, 2012 6:24 PM
        Thanks Matt. It makes sense for me. I believe this parameter will do the job.
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        nagarwal @ fabiano.batista on Sep 7, 2012 7:30 PM
        Hi Fabiano - As others have pointed you can either use the PIACEPoint constructor or the SetTag() method to dynamically create PIACEPoint instances. You can create PIACEPoints based on tags or aliases. See code below.
        
        Protected Overrides Sub ModuleDependentInitialization() 'Create PIACEPoint based on a tag using the constructor tag1 = New PIACEPoint("\\mypiserver", "sinusoid", TagAliasUsedType.TagAliasAsInput) 'Create PIACEPoint based on a tag using the SetTag method tag2 = New PIACEPoint() tag2.SetTag("\\mypiserver", "sinusoidu", TagAliasUsedType.TagAliasAsInput) 'Create PIACEPoint based on an alias relative to the context using the constructor 'Context="\\mypiserver\Aquariums\Aquarium1"; has an alias named PumpPower tag3 = New PIACEPoint(Context, "PumpPower", TagAliasUsedType.TagAliasAsInput) 'Create PIACEPoint based on an alias relative to the context using the SetTag method 'Context="\\mypiserver\Aquariums\Aquarium1"; has an alias named LightPower tag4 = New PIACEPoint() tag4.SetTag(Context, "LightPower", TagAliasUsedType.TagAliasAsInput) End Sub
        Any PIACEPoint instances created using TagAliasUsedType.TagAliasAsInput or TagAliasUsedType.TagAliasAsBoth would automatically be signed up with ACE Cache (provided you have it enabled). Make sure you initialize these instances in the ModuleDependenInitialization() method - as you want them to be created during initialization and signup for updates.
        
        Hope this helps.
        
        Regards,
        
        Nitin
        
        1 person found this helpful
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        fabiano.batista @ nagarwal on Sep 7, 2012 8:46 PM
        Thank you Nitin. This was very helpful.
        
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Dynamic inclusion of PI tags in a PI ACE calculation

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