Limit Test

LabVIEW SignalExpress

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Limit Test

Tests an input signal or value against user-specified limits and returns information on whether the test passed or failed and, in the case of a failure, where it failed. Limit Test accepts time-domain signals, frequency-domain signals, and scalar values as inputs. You can specify either signals or scalar values for the limits, and you can define the limits or use other signals in the project as the limits.

Details

Parameter

Description

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

[View: Graph] 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.

Displayed signal—Specifies the signal(s) to display in the preview graph(s). This option appears only when you select a group of signals for the input.
Note If the input signals include scalar values that depend on the values of input waveform signals, you cannot specify to display all signals in the preview graph(s).

Limit test results

[View: Results table] Displays each signal in the limit test and whether or not the signal passed the test.

Autoscale y-axis

[View: Graph] Specifies whether to autoscale the y-axis on the Limit Test graph.

selected test

Indicates whether the test of the signal displayed on the Limit Test graph passed or failed. This indicator appears only when you test a group of signals.

all tests

Indicates if the tests passed or failed.

Input

The following options apply only to the Limit Test step in LabVIEW SignalExpress:

Input signal—Specifies the input signal or scalar value.

Upper limit—[Limits source: Input Signals, Input Scalars] Specifies the upper limit signal or value.

Note When a LabVIEW SignalExpress project runs continuously, LabVIEW SignalExpress reads the Upper limit and Lower limit only on the first iteration of the project. If you select a limit signal that continuously changes, LabVIEW SignalExpress uses only the first iteration of the signal to perform the limit test.

Lower limit—[Limits source: Input Signals, Input Scalars] Specifies the lower limit signal or value.
Limit—[Limits source: Input Signals, Input Scalars AND Limits window based on: Single Limit & Range] Specifies the single limit signal or value.

Input type

The following options apply only to the Limit Test Express VI in LabVIEW:

Time Waveform—Specifies to perform limit testing on a time domain signal.
Frequency Waveform—Specifies to perform limit testing on a frequency spectrum.
Scalar—Specifies to perform limit testing on a single scalar value.

Configuration

Contains the following options for configuring the limits for the limit test:

Limit Setup—Contains the following options:
- Limits source—Specifies the source of the limits for the limit test. You can select from the following options:
  - Input Signals—Uses output signals from previous steps or Express VIs as the limits.
  - Input Scalars—Uses output scalar values from previous steps or Express VIs as the limits. You specify the scalar values on the Input page.
  - User Defined Signals—Uses signals you define for the limits. If you set Limits window based on to Two Limits, click the Define upper limit and Define lower limit buttons to display the Define Signal dialog box and interactively define the limit signals. If you set Limits window based on to Single Limit & Range, click the Define single limit button to display the Define Signal dialog box and interactively define the limit signal.
  - User Defined Constants—(Default) Uses constant values that you specify for the limits. If you set Limits window based on to Two Limits, use the Upper constant and Lower constant fields to specify the limits. If you set Limits window based on to Single Limit & Range, use the Limit constant field to specify the limit.
- Compare mode—Specifies the comparison mode Limit Test uses to compare the input signal to the limits you specify. You can select from the following options:
  - Between Limits—(Default) Determines whether the input signal is between the limits you specify.
  - Outside Limits—Determines whether the input signal is outside the limits you specify.
  - >Lower Limit—Determines whether the input signal is above the lower limit you specify.
  - <Upper Limit—Determines whether the input signal is below the upper limit you specify.
- Limits window based on—Specifies how you define the limits used for the limit test. You can select from the following options:
  - Two Limits—Specifies that you define two limits for the limit test.
  - Single Limit & Range—Specifies that you define a single limit and a range of gain and offset values for the limit test.
- Upper constant—[Limits source: User Defined Constants AND Limits window based on: Two Limits] Specifies the value of the upper limit constant. The default is 1.
- Lower constant—[Limits source: User Defined Constants AND Limits window based on: Two Limits] Specifies the value of the lower limit constant. The default is –1.
- Limit constant—[Limits source: User Defined Constants AND Limits window based on: Single Limit & Range] Specifies the single constant value that, in conjunction with the Relative Range Specs, defines the limit values.
- Define upper limit—[Limits source: User Defined Signals AND Limits window based on: Two Limits] Displays the Define Signal dialog box, which you can use to define the upper limit signal interactively.
- Define lower limit—[Limits source: User Defined Signals AND Limits window base on: Two Limits] Displays the Define Signal dialog box, which you can use to define the lower limit signal interactively.
- Define single limit—[Limits source: User Defined Signals AND Limits window base on: Single Limit & Range] Displays the Define Signal dialog box, which you can use to define the limit signal interactively.
Relative Range Specs—Contains the following options:
- Upper gain—[Limits window base on: Single Limit & Range] Specifies the gain value to apply to the single limit to calculate the upper limit. The default is 1.1.
- Lower gain—[Limits window base on: Single Limit & Range] Specifies the gain value to apply to the single limit to calculate the lower limit. The default is 900m.
- Upper offset—[Limits window base on: Single Limit & Range] Specifies the offset value to add to the single limit to calculate the upper limit. The default is 0.
- Lower offset—[Limits window base on: Single Limit & Range] Specifies the offset value to add to the single limit to calculate the lower limit. The default is 0.

Advanced

Contains the following options:

Limits Inclusion—Contains the following options:
- Upper inclusive—Specifies whether a value that is exactly on or equal to the upper limit passes the limit test. Place a checkmark in this checkbox to pass a value that is on or equal to the upper limit.
- Lower inclusive—Specifies whether a value that is exactly on or equal to the lower limit passes the limit test. Place a checkmark in this checkbox to pass a value that is on or equal to the lower limit.
Timing information—Contains the following options for time-domain and frequency-domain signals:
- Freq. axis is logarithmic—Sets the display graph frequency axis to logarithmic and, when the Limits source is User Defined Signals, computes the limit values between the definition points so the resulting segment appears as a straight line in a logarithmic frequency representation. For example, you can use this to create asymptotic limits fitting filter roll-off in decibels per decade. This parameter appears only if the input signal is a frequency-domain signal.
- Ignore timestamp—Forces the timestamp of the input signal to 0 so you can define the limit signals relative to the beginning of the input signal. This parameter appears only if the input signal is a time-domain signal.

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 you specify.
- 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 you specify.
  - 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 you specify.
- 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 you specify.
  - 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.

Limit Test Details

Output Signal Types

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

failed signal—The input signal(s) or value(s). If you graph failed signal, the graph includes the input signal, the limits, and the portions of the signal that failed the limit test.
upper limit—The upper limit used to perform the limit test.
lower limit—The lower limit used to perform the limit test.

Limits

The type of limits you can define for the Limit Test depend on the input signal type.

If the input is a time-domain or frequency-domain signal, you can use the following types of limits:

Output signals of the same type as the input signal—You can use output signals from other LabVIEW SignalExpress steps or LabVIEW VIs as the limits. For example, you can compare a time-domain signal to two other time-domain signals.
Output scalar values—You can use output scalar values from other LabVIEW SignalExpress steps or LabVIEW VIs as the limits. Limit Test compares the input signal to the scalar values element by element. For example, you can compare a time-domain signal to two measured DC values.
User-defined signals of the same type as the input signal—You can define 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.
User-defined constants—You can define constant values for the limits. Limit Test compares the input signal to the constant values element by element.

If the input is a scalar value, you can use the following types of limits:

Output scalar values—You can use output scalar values from other LabVIEW SignalExpress steps or LabVIEW VIs as the limits. Limit Test compares the input signal to the scalar values element by element. For example, you can compare a time-domain signal to two measured DC values.
User-defined constants—You can define constant values for the limits. Limit Test compares the input value to the 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 than 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 you use user-defined signals as limits for a frequency-domain signal, Limit Test defines the limits as a series of line segments that connect user-defined points. By default, Limit Test 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 specifies whether 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.

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