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Check Against Reference

Check that model signal tracks reference signal during simulation

  • Library:
  • Simulink Design Optimization / Model Verification

    Simulink Design Optimization / Signal Constraints

  • Check Against Reference block

Description

Check that a signal remains within the tolerance bounds of a reference signal during simulation.

  • If all bounds are satisfied, the block does nothing.

  • If a bound is not satisfied, the block asserts, and a warning message appears in the MATLAB® command window. You can also specify that the block:

    • Evaluate a MATLAB expression.

    • Stop the simulation and bring that block into focus.

During simulation, the block can also return a logical assertion signal.

  • If all bounds are satisfied, the signal is true (1).

  • If a bound is not satisfied, the signal is false (0).

You can add Check Against Reference blocks on multiple signals to check that they track reference signals.

You can also plot the reference signal on a time plot to graphically verify the signal tracking.

This block and the other blocks in the Model Verification library test that a signal remains within specified time-domain characteristic bounds. When a model does not violate any bound, you can disable the block by clearing the assertion option. If you modify the model, you can re-enable assertion to ensure that your changes do not cause the model to violate a bound.

If the signal does not satisfy the bounds, you can optimize the model parameters to satisfy the bounds. If you have Simulink® Control Design™ software, you can add frequency-domain bounds, such as the Bode magnitude, and optimize the model response to satisfy both time-domain and frequency-domain requirements.

The block can be used in all simulation modes for signal monitoring but only in Normal or Accelerator simulation mode for response optimization.

Ports

Input

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Signal to check against the reference signal specified in Amplitudes and Times during simulation.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | fixed point | enumerated | bus

Output

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Output signal indicating if the input signal is within bounds of the specified assertion signal. At each time step, the output is returned as one of the following:

  • True (1) if assertion succeeds, that is, all bounds are satisfied

  • False (0) if assertion fails, that is, a bound is violated

The output signal data type is Boolean if, in the Simulink model, in Configuration Parameters, Implement logic signals as Boolean data is selected. Otherwise, the data type of the output signal is double.

Dependencies

To enable this port, select the Output assertion signal parameter.

Data Types: Boolean | double

Parameters

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Use the plot to view:

  • System characteristics and signals computed during simulation — Click this button before you simulate the model to view the system characteristics or signal.

    You can display additional characteristics, such as the peak response time, by right-clicking the plot and selecting Characteristics.

  • Bounds — You can specify bounds on the Bounds tab or by right-clicking the plot and selecting Bounds > New Bound. For more information on the types of bounds you can specify, see the individual reference pages.

    You can modify bounds by dragging the bound segment or by right-clicking the plot and selecting Bounds > Edit Bound. Before you simulate the model, click Update Block to update the bound value in the block parameters.

Typical tasks that you perform in the plot window include:

  • Opening the Block Parameters dialog box by clicking or selecting Edit.

  • Finding the block that the plot window corresponds to by clicking or selecting View > Highlight Simulink Block. This action makes the model window active and highlights the block.

  • Simulating the model by clicking . This action also linearizes the portion of the model between the specified linearization input and output.

  • Adding a legend on the linear system characteristic plot by clicking .

Open the plot window instead of the block parameters when you double-click the block in the Simulink model.

Use this parameter if you prefer to open and perform tasks, such as adding or modifying bounds, in the plot window instead of the block parameters. If you want to access the block parameters from the plot window, select Edit or click .

For more information on the plot, see the Show plot parameter.

Programmatic Use

Parameter: LaunchViewOnOpen
Type: character vector
Value: 'on' | 'off'
Default: 'off'

Open the Response Optimizer to optimize the model response to meet design requirements specified on the Bounds tab.

See Also

Bounds Tab

Check that the input signal to the block tracks the reference signal specified in Amplitudes and Times during simulation. The software displays a warning if the signal does not track the reference signal.

  • When this parameter is disabled, the reference signal is disabled and the software stops checking that the input signal tracks the reference during simulation.

  • To view only the reference signal on the plot, disable Enable assertion.

The reference signal appears on a time plot if you select Show plot, as shown in the figure.

Plot of the specified reference signal

Dependencies

To use this parameter, select Enable assertion in block parameters. When Enable assertion is disabled, the reference signal is not used for assertion but continues to appear on the plot.

Programmatic Use

Parameter: EnableReferenceBound
Type: character vector
Value: 'on' | 'off'
Default: 'on'

Time vector for the reference signal in seconds, specified as a monotonically increasing vector of positive values. You can also specify a MATLAB expression that evaluates to a vector. Specify the corresponding amplitudes using the Amplitudes parameter. The Times vector must have the same dimension as the Amplitudes vector.

Programmatic Use

Parameter: ReferenceTimes
Type: vector
Value: vector of positive values | MATLAB expression
Default: linspace(0,10)

Amplitude of the reference signal, specified as a real and finite vector, corresponding to the time vector specified in Times. You can also specify a MATLAB expression that evaluates to a vector. The Amplitudes vector must have the same dimension as the Times (seconds) vector.

Programmatic Use

Parameter: ReferenceAmplitudes
Type: vector
Value: vector | MATLAB expression
Default: 1-exp(-linspace(0,10)/2)

Absolute tolerance used to determine bounds as the input signal approaches the reference signal, specified as a positive real scalar. During simulation, the signal must remain within upper and lower limits respective to the reference signal given by

yu = (1 + RelTol)yr + AbsTol

yl = (1 – RelTol)yrAbsTol

Here:

  • yr is the value of the reference at a certain time.

  • yu is the upper tolerance bound corresponding to that time point.

  • yl is the lower tolerance bound corresponding to that time point.

  • RelTol sets the relative tolerance between input and reference signal amplitudes at each time step. To set RelTol, use the Relative tolerance parameter.

  • AbsTol sets the absolute tolerance between input and reference signal amplitudes at each time step. To set AbsTol, use the Absolute tolerance parameter.

The block asserts if the signal violates these limits.

Programmatic Use

Parameter: AbsTolerance
Type: scalar
Value: positive real scalar
Default: eps^(1/3)

Relative tolerance used to determine bounds as the input signal approaches the reference signal, specified as a positive real scalar. During simulation, the signal must remain within upper and lower limits respective to the reference signal given by

yu = (1 + RelTol)yr + AbsTol

yl = (1 – RelTol)yrAbsTol

Here:

  • yr is the value of the reference at a certain time.

  • yu is the upper tolerance bound.

  • yl is the lower tolerance bound.

  • RelTol sets the relative tolerance between input and reference signal amplitudes at each time step. To set RelTol, use the Relative tolerance parameter.

  • AbsTol sets the absolute tolerance between input and reference signal amplitudes at each time step. To set AbsTol, use the Absolute tolerance parameter.

The block asserts if the signal violates these limits.

Programmatic Use

Parameter: RelTolerance
Type: scalar
Value: positive real scalar
Default: 0.01

Assertion Tab

Enable the block to check that bounds specified and included for assertion on the Bounds tab are satisfied during simulation. Assertion fails if a bound is not satisfied. A warning, reporting the assertion failure, appears at the MATLAB prompt.

If the assertion fails, you can optionally specify that the block:

  • Execute a MATLAB expression, specified in Simulation callback when assertion fails (optional).

  • Stop the simulation and bring that block into focus, by selecting Stop simulation when assertion fails.

This parameter has no effect if you do not specify any bounds.

When this parameter is disabled, the block no longer checks that specified bounds are satisfied. The block icon also updates to indicate that assertion is disabled.

In the Simulink model, in the Configuration Parameters, the Model Verification block enabling parameter lets you enable or disable all model verification blocks in a model, regardless of the setting of this option in the block.

Dependencies

This parameter enables:

  • Simulation callback when assertion fails (optional)

  • Stop simulation when assertion fails

Programmatic Use

Parameter: enabled
Type: character vector
Value: 'on' | 'off'
Default: 'on'

MATLAB expression to execute when assertion fails.

Because the expression is evaluated in the MATLAB workspace, define all variables used in the expression in that workspace.

Dependencies

To enable this parameter, select Enable assertion.

Programmatic Use

Parameter: callback
Type: character vector
Value: MATLAB expression
Default: ''

Stop the simulation when a bound specified on the Bounds tab is violated during simulation, that is, when assertion fails.

If you run the simulation from a Simulink model window, the Simulation Diagnostics window opens to display an error message. The block where the bound violation occurs is highlighted in the model.

Because selecting this option stops the simulation as soon as the assertion fails, assertion failures that might occur later during the simulation are not reported. If you want all assertion failures to be reported, do not select this option.

Dependencies

To enable this parameter, select Enable assertion.

Programmatic Use

Parameter: stopWhenAssertionFail
Type: character vector
Value: 'on' | 'off'
Default: 'off'

Output a Boolean signal that, at each time step, is:

  • True (1) if assertion succeeds, that is, all bounds are satisfied

  • False (0) if assertion fails, that is, a bound is violated.

The output signal data type is Boolean only if, in the Simulink model, in the Configuration Parameters, the Implement logic signals as Boolean data parameter is selected. Otherwise, the data type of the output signal is double.

Selecting this parameter adds an output port to the block that you can connect to any block in the model.

Use this parameter to design complex assertion logic. For an example, see Verify Model Using Simulink Control Design and Simulink Verification Blocks (Simulink Control Design).

Programmatic Use

Parameter: export
Type: character vector
Value: 'on' | 'off'
Default: 'off'

Extended Capabilities

Introduced in R2011b