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Assigning a Calculation Variable Null Value Behavior

From time to time, an asset health calculation variable might return a null value. To avoid errors or unexpected results, you can determine what happens when a null value occurs by choosing to not calculate the value at all, use a default value, or apply a VB or stored procedure against the value. You can also assign a maximum value to use for variables that have a null value.

Null values are also considered in asset health availability indexes. These indexes produce a percentage based on the number of non-null calculation variables compared with all variables for a given calculation. For example, for ten total variables of which two are null-values, the remainder (eight) divided by the total represents an availability index of 80%. Availability indexes are displayed within asset health report tables.

For more information about creating calculation variables, see Creating Calculation Variables.

This topic describes how to assign null value behavior to a triggered or asset degradation calculation.

To assign null value behavior to an asset health calculation, see

To Assign a Calculation Variable Null Value Behavior

1.	Make sure that editing is enabled.

2.	Open the calculation variable for which you want to assign a calculation variable null behavior.

3.	Select the Null Value tab. For example:

4.	Select the option that best reflects the expected behavior when the value for this calculation variable is null:

•	Do not calculate a value: The value will be excluded in the calculation.

•	Use the following value as the derived value for this variable instead: Enter a numeric value that will be substituted when a null value occurs.

•	Handle the null value in the calculation function: The null value will be addressed within the VB script or stored procedure of the calculation itself.

Note: For multi-level variables where the primary variable is assigned “Use the following value” and it calls a secondary variable that is assigned “Handle the null value in the calculation” yet the secondary variable is not actually handled in the calculation, the primary calculation variable’s null value behavior is assumed.

5.	If you selected either Use the following value as the derived value for this variable instead or Handle the null value in the calculation function, you can select and enter a value for Use the following value as the maximum value for the variable instead.