Discrete Unit Delay Function

Owning Palette: Discrete Linear Systems Functions

Installed With: Control Design and Simulation Module

Delays the input by the value that you specify for the sample period (s) of this function.

Details  Example

Dialog Box Options

Block Diagram Inputs

Block Diagram Outputs

Place on the block diagram

Find on the Functions palette

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.
sample period (s)	Specifies the length of the discrete time step, in seconds, of this function. If you enter a value of –1, this function inherits the discrete time step you specify for the simulation diagram. Otherwise, the value of sample period (s) must be a multiple of the discrete time step you specify for the simulation diagram. The default value of sample period (s) is 1.
sample skew (s)	Specifies the length of time by which you want to delay the execution of this function. The default value is 0. The value of this parameter must satisfy the following relationship: 0 ≤ sample skew (s) ≤ sample period (s)
initial condition	Specifies the output value at the first time step. The default value is 0.

Block Diagram Inputs

Parameter	Description
sample period (s)	Specifies the length of the discrete time step, in seconds, of this function. If you enter a value of –1, this function inherits the discrete time step you specify for the simulation diagram. Otherwise, the value of sample period (s) must be a multiple of the discrete time step you specify for the simulation diagram. The default value of sample period (s) is 1.
sample skew (s)	Specifies the length of time by which you want to delay the execution of this function. The default value is 0. The value of this parameter must satisfy the following relationship: 0 ≤ sample skew (s) ≤ sample period (s)
initial condition	Specifies the output value at the first time step. The default value is 0.
input	Specifies the input to the function.

Block Diagram Outputs

Parameter	Description
output	Returns the output of the function.

Discrete Unit Delay Details

The following equations define the output of this function.

y(0) = initial condition

y(t_k) = u(t_{k – 1})

where	u is the input
	y is the output
	tk = initial time + sample skew (s) + k * sample period (s), for k = 0, 1, 2, …

Feedthrough Behavior

For this function, the input input has indirect feedthrough to the output output. All other input/output pairs have direct feedthrough behavior.

Example

Refer to the SimEx discrete unit delay VI in the labview\examples\Control and Simulation\Simulation\Discrete Linear directory for an example of using the Discrete Unit Delay VI.

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