Detect Zero Crossing Function

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LabVIEW 2011 Control Design and Simulation Module Help

Edition Date: June 2011

Part Number: 371894F-01

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Owning Palette: Nonlinear Systems Functions

Requires: Control Design and Simulation Module

Detects a zero crossing according to the trigger type you specify. A zero crossing occurs when the input signal you specify crosses the x-axis.

This function detects a zero crossing for both fixed and variable step-size ordinary differential equation (ODE) solvers. For variable step-size solvers, this function also forces the ODE solver to evaluate the simulation and update the simulation output when the signal crosses zero. If this function detects a zero crossing in the direction the trigger type parameter specifies, this function resets the ODE solver.

Details Example

Dialog Box Options

Block Diagram Inputs

Block Diagram Outputs

Dialog Box Options

Parameter	Description
Polymorphic instance	Specifies whether this function is Scalar or Vector. The default value is Scalar.
Parameters	Lists all the parameters associated with this function. Select a parameter from this list to configure the parameter. When you select a parameter, the parameter and its associated Parameter source control appear in the Parameter Information section of the configuration dialog box.
Preview	Displays a graphical preview, if available, of the function output or configuration.
Parameter Information	Contains the parameters you can configure for this function. You must select a parameter from the Parameters list to make that parameter and its associated Parameter source control visible in the Parameter Information section of the configuration dialog box.
Parameter source	Specifies whether you configure this parameter using the Configuration Dialog Box or a Terminal on the simulation diagram. The default value is Configuration Dialog Box. If you select Terminal, LabVIEW displays an input for that parameter on the simulation diagram, and you can wire values to that input to configure this function programmatically. If you select Configuration Dialog Box, LabVIEW removes that input from the simulation diagram. You then must set the value for this parameter inside the configuration dialog box.
trigger type	Specifies when this function resets the ODE solver. Note that if you wire an array to the input parameter of this function, the trigger type you specify is applied to all the signals in the array. However, if you wire an array to the input parameter and you need to specify more than one trigger type, you must configure a trigger type for each signal in the array. You can choose from the following options: rising—The ODE solver resets when the input crosses zero with a positive slope. falling—The ODE solver resets when the input crosses through zero with a negative slope. either—The ODE solver resets when the input crosses zero with either a positive or negative slope. none—(Default) The ODE solver does not reset.
offset	Specifies the value around which this function detects a crossing. This function detects a crossing if the following equation is true: sgn(u(t–1)–offset(t)) ≠ sgn(u(t)–offset(t))

Block Diagram Inputs

Parameter	Description
trigger type	Specifies when this function resets the ODE solver. Note that if you wire an array to the input parameter of this function, the trigger type you specify is applied to all the signals in the array. However, if you wire an array to the input parameter and you need to specify more than one trigger type, you must configure a trigger type for each signal in the array. You can choose from the following options: rising—The ODE solver resets when the input crosses zero with a positive slope. falling—The ODE solver resets when the input crosses through zero with a negative slope. either—The ODE solver resets when the input crosses zero with either a positive or negative slope. none—(Default) The ODE solver does not reset.
input	Specifies the signal to which you want to apply the function.
offset	Specifies the value around which this function detects a crossing. This function detects a crossing if the following equation is true: sgn(u(t–1)–offset(t)) ≠ sgn(u(t)–offset(t))

Block Diagram Outputs

Parameter	Description
crossed?	Returns TRUE if the input signal crossed zero in the direction that the trigger type parameter specifies, depending on the type of ODE solver. For fixed step-size ODE solvers, crossed? returns TRUE if the input signal crossed zero during the last time step. For variable step-size ODE solvers, crossed? returns TRUE when the input signal reaches zero. crossed? returns FALSE in all other situations. If crossed? is TRUE, the ODE solver resets.

Parameter

Description

crossed?

Returns TRUE if the input signal crossed zero in the direction that the trigger type parameter specifies, depending on the type of ODE solver. For fixed step-size ODE solvers, crossed? returns TRUE if the input signal crossed zero during the last time step. For variable step-size ODE solvers, crossed? returns TRUE when the input signal reaches zero. crossed? returns FALSE in all other situations.

If crossed? is TRUE, the ODE solver resets.

Detect Zero Crossing Details

Feedthrough Behavior

All input/output pairs of this function have direct feedthrough behavior.

Example

Refer to the SimEx detect zero crossing VI in the labview\examples\Control and Simulation\Simulation\Nonlinear directory for an example of using the Detect Zero Crossing VI.