Discrete First-Order Hold Function
Owning Palette: Discrete Linear Systems Functions
Installed With: Control Design and Simulation Module
Extrapolates the value of the output signal based on the first derivative of the input signal.
| 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) |
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) |
| input | Specifies the input to this function. |
Block Diagram Outputs
| Parameter | Description |
|---|---|
| output | Specifies the output of the system. |
Discrete First-Order Hold Details
The following equation defines the output of this function.
| where | y is the output |
| u is the input | |
| t is the current simulation time | |
| ti is the initial simulation time | |
| tk = ti + sample skew (s) + k * sample period (s), for k = 1, 2, 3, … | |
 |
Feedthrough Behavior
All input/output pairs of this function have direct feedthrough behavior.
Example
Refer to the SimEx first-order-hold VI in the labview\examples\Control and Simulation\Simulation\Discrete Linear directory for an example of using the Discrete First-Order Hold VI.
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