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Defining the Calculation

In APM, four types of expressions can be used to create a calculation: VB.NET, C#, stored procedure, and VB scripts. Note that APM recommends using VB.NET or C# scripts rather than VB scripts whenever possible, due to their increased functionality.

This topic describes how to define the calculation for a triggered or asset degradation calculation.

To Define the Calculation

1.	Make sure that editing is enabled.

2.	Open the calculation for which you want to define.

3.	Select the Calculation tab. For example:

4.	Select the type of expression. A calculation can be based on:

•	VB.NET – Inputs and functions defined on the Calculation tab can be used to create a formula that is calculated at run time. This is the default option

•	C# – Inputs and functions defined on the Calculation tab can be used to create a formula that is calculated at run time

•	Stored procedure – The expression is provided in a stored procedure that receives its inputs at runtime and returns a value

5.	For VB.NET and C# expressions, you must also select the expression type. Your options are “Simple expression” (for single-line commands) or “Complete class” for more complex scripts.

With the Complete class option, a starter script template is provided automatically, which you can edit as needed. You can also click Regenerate from Template to reset the formula to the starter script.

The template scripts include DebugData statements that you can augment to output trace messages when the Check (Test) or Check (Live) method is invoked to test the calculation.

Tip: You can view the template scripts by opening the Enterprise window, clicking the Administration menu and then Calculation options. For more information, see Defining Calculation Options.

6.	If the type of expression is a VB.NET, C#, or VB script, in the text box provided, type in the mathematical formula or function that the reading will use.

If you are entering a function, see Using Logical Operators in Calculations.

If you are using a formula, you can use three elements:

•

Calculation variables (a name that represents data from another asset input): enter a variable name for each input that you want to use in the calculation. Each calculation variable must begin with a letter, cannot contain a period (.), must not exceed 20 characters, and must be unique within the calculation. For example, for an age variable, you might enter “Age1”. You will link a source to the variable in the next step. For more information about calculation variables, see Creating Calculation Variables.

•	Operators (such as, add or multiply): Type the operator in the format shown in Using Logical Operators in Calculations.

•	Constants (that is, a fixed value used in the calculation): enter the value of the constant in the calculation. For example, to divide by two, you would enter “2”.