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Creating an Asset Health Calculation Type Variable

Calculation variables are used in asset health report calculations and can be derived from four sources. These sources are:

•	Calculation

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Filter

•	Global variable

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Join path

A calculation type variable is a variable that itself uses a calculation to provide a value to the main calculation. For example, you might want to use this type of variable in a complex calculation with multiple variables that also need processing. Factor tables, minimum/maximum limits, and weighting can be applied to calculated variables that produce a numeric result.

Note: Calculation variables cannot use another calculation variable as an input.

This topic describes how to create a calculation type variable.

To Create a Calculation Type Variable

1.	Open an asset health calculation and select the Calculation tab.

2.	Make sure that editing is enabled.

3.	Click New. The Calculation Variable dialog appears.

4.	Enter a name for the calculation variable.

Note: The calculation variable name can only contain letters and numbers, must not contain spaces or special characters, or start with a number.

5.	Enter a brief description for the calculation variable.

6.	In Source of the derived value list, select Calculation. The window changes accordingly.

7.	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

8.	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.

9.	If the type of expression is 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:

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Calculation indicators (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 Asset Health 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”.

Example:

To enter a calculation that takes the average of two inputs, you would type:

(Input1 + Input2) / 2

The variables “Input1” and “Input2” are placeholders for data. When the calculation is evaluated, APM gets the current values of the inputs.

10.	Select the Factor Table tab to convert the derived value using a factor table. For more information, see Defining a Factor Table for an Asset Health Variable.

11.	On the Limits and Weighting tab, enter any maximum or minimum values applied to this variable, and weighting factors, if needed. For more information, see Assigning Calculation Variable Limits and Weighting.

12.	On the Null Value tab, select the behavior when the value for the variable returns a null value. For more information, see Assigning Null Value Behavior.

13.	On the Notes tab, you can enter any additional information about this calculation variable.

14.	When you are finished, click OK to save the variable and close the dialog.