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Compares an input signal to user-specified limits and returns information on whether the test passed or failed, and where it failed. The step accepts time-domain signals, frequency-domain signals, and scalar values as input. You can specify the limits as signals or as scalar values. You also can specify user-defined limits. In LabVIEW SignalExpress, other steps can create limits.

Details  

Dialog Box Options

Block Diagram Inputs

Block Diagram Outputs

Dialog Box Options

Parameter	Description
View	View—Specifies how to display the results of the limit test. You can select from the following options: Graph—(Default) Displays the results of the limit test as a graph. Results table—Displays the results of the limit test as a table.
Limit Test	Displays the result of the limit test operation. The four plots show the original input signal, the points where the limit test operation failed, and the two limit signals, respectively. This graph appears when you select Graph from the View pull-down menu.
Limit test results	Limit test results—Displays each signal in the limit test and whether or not the signal passed the test. This table appears when you select Result table from the View pull-down menu.
Autoscale Y-scale	Scales the y-axis of the display graph. The default is to autoscale the Y-scale.
all tests	Indicates if the tests passed or failed.
Input	The following options apply to the LabVIEW SignalExpress step: Input signal:—Specifies the input scalar value. Upper limit:—Specifies the upper limit scalar value. Lower limit:—Specifies the lower limit scalar value. Limit:—Specifies the single limit scalar value.
Input type	The following options apply to the Express VI: Time Waveform—Select this option to perform limit testing on a time domain signal. Frequency Waveform—Select this option to perform limit testing on a frequency spectrum. Scalar—Select this option to perform limit testing on a single scalar value.
Configuration	Contains the following options: Limit Setup—Contains the following options: Limits source—Selects the type of scalar signal to use as limits. Options include: Input Scalars and User Defined Constants. Compare mode—Selects the comparison mode. Options include: Between Limits, Outside Limits, >Lower Limit, and <Upper Limit. The default is Between Limits. Limits window based on—Specifies the limits as two individual limits or by a single limit and a range that a set of gain and offset values defines. Options include: Two Limits and Single Limit & Range. Upper constant—Specifies the value of the upper limit constant. This option appears when you select User Defined Constants. The default is 1. Input value—Displays the value of the input. Lower constant—Specifies the value of the lower limit constant. This option appears when you select User Defined Constants. The default is –1. Limit constant—Specifies the single constant value that in conjunction with the gain and offset values defines the two limit values. Relative range specs—Contains the following options: Upper gain—Gain value that when applied to the single limit signal calculates the upper limit signal. The default is 1.1. Lower gain—Gain value that when applied to the single limit signal calculates the lower limit signal. The default is 900m. Upper offset—Offset value that when added to the single limit signal calculates the upper limit signal. The default is 0. Lower offset—Offset value that when added to the single limit signal calculates the lower limit signal. The default is 0.
Advanced	Contains the following option: Limits Inclusion—Contains the following options: Upper inclusive—If you place a checkmark in this checkbox, this step specifies if a signal point that is exactly on the upper limit signal passes. If you remove the checkmark from this checkbox, this step specifies that the signal point failed. Lower inclusive—If you place a checkmark in this checkbox, this step specifies if a signal point that is exactly on the lower limit signal passes. If you remove the checkmark from this checkbox, this step specifies that the signal point failed.
Actions	Contains the following options: Action on failed—Contains the following options: Stop project after failed occurs—Specifies to stop running the project after the signal fails the limit test the number of times specified in the times control. times—Specifies the number of times for the signal to pass or fail the limit test before LabVIEW SignalExpress stops the project. Action on failed—Specifies the action to perform when the signal fails the limit test the number of times specified in the times control. none—Specifies to take no additional action. snapshot of inputs—Specifies to take a snapshot of the current inputs of the Limit Test step. snapshot of all signals in project—Specifies to take a snapshot of all signals in the project. Action on passed—Contains the following options: Stop project after passed occurs—Specifies to stop running the project after the signal passes the limit test the number of times specified in the times control. times—Specifies the number of times for the signal to pass or fail the limit test before LabVIEW SignalExpress stops the project. Action on passed—Specifies the action to perform when the signal passes the limit test the number of times specified in the times control. none—Specifies to take no additional action. snapshot of inputs—Specifies to take a snapshot of the current inputs of the Limit Test step. snapshot of all signals in project—Specifies to take a snapshot of all signals in the project.

Block Diagram Inputs

Parameter	Description
Input	Specifies the input signal.
error in (no error)	Describes error conditions that occur before this VI or function runs.
LowerScalar	Specifies the scalar value that this Express VI uses as the lower limit.
UpperScalar	Specifies the scalar value that this Express VI uses as the upper limit.

Block Diagram Outputs

Parameter	Description
test passed	Indicates the result of limit mask testing.
error out	Contains error information. If error in indicates that an error occurred before this VI or function ran, error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out front panel indicator and select Explain Error from the shortcut menu for more information about the error.
Limit Test	Returns the input signal, the upper and lower limits, and the failures.

Limit Test (Scalar) Details

Use the Limit Test step to test if an input signal that is a time-domain waveform, a frequency-domain spectrum, or a scalar value is within a user-specified range.

Output Signal Types

Limit Test returns a group of signals named limit test results. This group of signals contains the following elements:

• failed signals—Signal or group of signals that indicates the location of the limit test failures.
• upper limit—Copy of the upper limit signal used to perform the limit test.
• lower limit—Copy of the lower limit signal used to perform the limit test.

Limits

The Limit Test signal types depend on the input signal type.

If the input is a time-domain signal or frequency-domain spectrum, there are four possible limit options:

• The limits are input signals of the same type as the input signal. For example, you can compare a time-domain signal to two time-domain input signals.
• The limits are scalar inputs, and this step compares the input signal to these values element by element. For example, you can compare a time-domain signal to two measured DC values.
• The limits are user-defined signals of the same type as the input signal. You can define the limit signals by clicking the Define Upper Limit, Define Lower Limit, or Define Single Limit buttons. The Define Signal dialog box appears, and you can define a limit signal based on user-defined points. Use this dialog box to create a limit signal made up of a series of line segments that connect these points.
• The limits are user-defined constants. In this case, this step compares the input signal to these constant values element by element.

If the input is a scalar value, two possible limit options are available:

• The limits are scalar inputs, and this step compares the input value to these scalar values. For example, you can compare a DC measurement to two measured peak values.
• The limits are user-defined constants. In this case, this step compares the input value to these constant values.

Compare Mode and Limits Inclusion

Limit Test has four compare modes. These modes indicate if a signal or value is between limits, outside limits, greater than a lower limit, or lower that an upper limit. You can choose the exact limit values to include or not include in the test. These limit values result in a failing or passing test where the input value equals the limit value.

Defining a Limit Range from a Single Limit

You can define a set of upper and lower limits from a single limit using the gain and offset scaling parameters. Select the limits based on Single Limit & Range to enable the user-defined scaling parameters.

Limits Defined in a Logarithmic Frequency Scale

When defining user-defined limits for a frequency-domain signal, this step defines the limits as a series of line segments that connect user-defined points. By default, the step assumes the frequency axis is linear so a linear relationship exists between the frequency and the magnitude or phase values. The Freq. axis is logarithmic checkbox indicates to display a logarithmic frequency axis and define the limit signals so the connection between the points appears as straight lines in the logarithmic frequency scale. You can define the limits in a logarithmic frequency scale if you want to test the asymptotic roll-off of a filter, typically a straight line in a decibel versus logarithmic frequency scale.