MTS Series 793 Application User Manual
Page 113
Test Design Considerations for Adding Calculations
MTS MultiPurpose TestWare®
Working with MPT Variables
113
Test Design Considerations for Adding Calculations to Variables
The method you use to add a given calculation to a variable has test design
implications.
Calculations created
with the Variable Editor
When you use the Variable Editor to add a calculation to a variable:
•
The calculation is applied to the associated variable before the first process
in the test procedure is run.
•
The calculation is applied to the variable only once during the execution of
the test procedure, regardless of where the variable is used in individual test
processes.
•
Each time a calculated variable is queried for its value, the expression is
evaluated. Because current values may change during the execution of a
test, the result may be unpredictable. Because of this, it is good practice to
create test procedures that maintain a “fixed” relationship between
variables, as opposed to creating test procedures in which variable values
change dynamically.
Calculations created
with the MPT Calculation
process
In contrast, when you use the MPT Calculation process to add a calculation to a
variable, the calculation is applied to the associated variable whenever the MPT
Calculation process is triggered. This means that:
•
Any test process that uses the variable but runs before the MPT Calculation
process will not have the calculation applied, and
•
The expression is evaluated only when the MPT Calculation process is
triggered.
•
The calculation is reapplied to the variable each time the associated MPT
Calculation process is triggered, so that the change to the variable value is
cumulative.