Numeric Limit Test Step

TestStand 2019 Help

Edition Date: May 2019

Part Number: 370052AA-01

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The Numeric Limit Test step calls a code module that returns a single measurement value.

After the code module executes, the Numeric Limit Test step type compares the measurement value to predefined limits. If the measurement value is within the bounds of the limits, the step type sets the step status to Passed. Otherwise, it sets the step status to Failed.

Configuring the Step

Use the Numeric Limit Test edit tabs in the TestStand Sequence Editor and the Edit Numeric Limit Test dialog box in a TestStand User Interface to customize the type of comparison and limits TestStand uses to set the step status.

A Numeric Limit Test step uses the Step.Result.Numeric property to store the measurement value. A code module can set the value of Step.Result.Numeric in the following ways:

  • LabVIEW Adapter—Specify Step.Result.Numeric as the Value expression for a Numeric output of a VI on the LabVIEW Module tab.
  • LabWindows/CVI, C/C++ DLL, .NET, ActiveX/COM, or Sequence Adapter—Pass Step.Result.Numeric as a reference parameter to a subsequence or code module.
  • LabVIEW or LabWindows/CVI Adapter—The LabVIEW and LabWindows/CVI Adapters update the value of Step.Result.Numeric automatically after calling legacy code modules. The LabVIEW Adapter updates the value of Step.Result.Numeric based on the value of the Numeric Measurement element of the Test Data cluster the VI returns. The LabWindows/CVI Adapter updates the value of Step.Result.Numeric based on the value of the measurement field of the tTestData parameter it passes to the C function.
  • All Adapters—Use the TestStand API to set the value of Step.Result.Numeric directly in a code module.

By default, the step type uses the value of the Step.Result.Numeric property as the numeric measurement to compare the limits against.

Step Properties

In addition to the common custom properties, the Numeric Limit Test step type defines the following step properties:

  • Step.Result.Numeric—The numeric measurement value. Usually, you set this value in the code module.
  • Step.Result.Units—A label that indicates the unit of measurement.
  • Step.RawLimits.Low, High, Nominal—The limit values stored with the default TestStand format of %.16g. These properties are used to compute the low and high limit values that are used with the EQT (== +/-) comparison type.
  • Step.Limits.Low, High, LowExpr, HighExpr, UseLowExpr, and UseHighExpr—The limits for the comparison.
  • Step.Comp—The type of comparison, such as EQ.
  • Step.CompExpr—The comparison operation using an expression.
  • Step.UseCompExpr—The step uses the expression to compare the measurement values.
  • Step.InBuf—An arbitrary string the LabVIEW and LabWindows/CVI Adapters pass to the test in the Input Buffer control or tTestData structure of legacy code modules. This property exists to maintain compatibility with previous test executives. Usually, code modules you develop for TestStand receive data as input parameters or access data as properties using the TestStand API.
  • Step.DataSource—A numeric expression the step type uses to set the value of Step.Result.Numeric. The default value of the expression is "Step.Result.Numeric", which has the effect of using the value the code module sets. You can customize this expression when you do not want to set the value of Step.Result.Numeric in the code module.

You can use a Numeric Limit Test step without a code module, which is useful when you want to limit-check a value you have already acquired. To set up this limit check, select <None> as the module adapter before you insert the step in the sequence and configure Step.DataSource to specify the value you have already acquired.

Note Note  The type for measurement and limit values must be double-precision, 64-bit floating-point values, and cannot be signed or unsigned 64-bit integers.

See Also

Calling Legacy LabVIEW Code Modules

Calling Legacy LabWindows/CVI Code Modules

Step Types You Can Use with Any Module Adapter

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