Addition, Modification and Removal of Calculated OPC Item(s) in Genesis 3.1

Adding acquired Item(s) to an OPC Group requires beforehand

1. The selection of an OPC Server (click here to get details on selection of an OPC Server)
2. The addition of OPC Group(s) (click here to get details on addition of an OPC Group)
3. The addition of Acquired Item(s) (click here to get details on addition of Acquired OPC Items)

1. Addition of Calculated OPC Item(s) Two methods are available to start the addition of Calculated OPC Item(s)

• Select the OPC Group to Add Items(s) to and Click on the Ribbon Button 'Add Calc. OPC Item(s)' in the Ribbon Tab 'OPC Server'




• Right-Click the OPC Group (to add item(s) to) in the 'OPC Explorer Setup' Tree Control and Select the menu 'Add, Modify and Remove Acquired OPC Item(s)'



Addition of the OPC Calculated Item




Suppose you want to compute the normalized flow from the acquired data: Flow (FY_201), Temperature (TY_201) and Pressure (PY_201).
using the formula: Flow Normalized = Measured Flow × (Temperature K Normal / Measured Temperature K) × ( Abs Measured Pressure / Abs Normal Pressure)
where Temperature K is the temperature in Kelvin ( that is Temperature C° + 273.16). Normal Pressure will be 1.033 Bar.

Here are the procedure to add this computation:


• Start the Addition of OPC Calculated Item (as described above)

  Addition of the OPC Calculated Item

  Note that the available acquired OPC items list on the left of the dialog box with Qualified Name and Short Name. The Short Names (in the screen copy, FY_201, TY_201 and PY_201) are used to make calculation easier to read and edit. The edition of Short Item Identifier is explained here

• Enter the Short Identifier for the New Calculated Data: FY_201_NORM
  
  
• Select the Acquired Data FY_201 and click on the button 'Insert Acquired Item in Expression'
  
  
• Continue to Edit the Calculated Expression by typing : * ( 273.16 / (273.16 +
  
  
• Select the Acquired Data TY_201 and click on the button 'Insert Acquired Item in Expression'
  
  
• Continue to Edit the Calculated Expression by typing : )) * (( 1.033 +
  
  
• Select the Acquired Data PY_201 and click on the button 'Insert Acquired Item in Expression'
  
  
• Finish the Edition of the Calculated Expression by typing : ) / 1.033)
  
  
• Click on the 'Evaluate button to Check Formula
  
  
  

  Evaluation of OPC Calculated Expression
  
  
  Note: in case of error, Genesis 3.1 displays the best possible explanation of the expression issue.
  
  
  

  Error in OPC Calculated Expression
  
  
  
• Click on the 'Add Item' button to Add the Item to the Calculated Item List. The Dialog Box willl then show the new configuration of the OPC group.
  
  
  

  Error in OPC Calculated Expression
  
  
  
• Confirm Calculated Items Addition with the button 'Ok'
  
  
  

  Addition of OPC Calculated Items
  
  

Additional features are available to get calculated values:

1. Use of Built-In Functions

Select one built-in function by cliccking the pull-down button of the Combobox 'Available Functions'



The function will be inserted at the caret position. Move the caret inside the function parenthesis and add an acquired OPC data using the 'Insert Acquired Item in Expression' button. Note that you can also insert calculated data (see next point)


2. Use of Calculated Data in Calculated Data

Calculated data can be used in other calculated data expression provided that ....it is computed before !!!

Taking the exemple of computing the normalized flow from the acquired data, this can be done in simpler steps:
Compute Kelvin Temperature: TY_201_K = TY_201 + 273.16
Absolute Pressure PY_201_ABS = PY_201 + 1.033
Normmalized Flow = FY_201 * ( 273.16 / TY_201_K) * ( PY_201_ABS / 1.033)

Obviously, Indirect calculated items are valid only if intermediary calculated items are already calculated and valid.