Transfer Function Function
Owning Palette: Continuous Linear Systems Functions
Installed With: Control Design and Simulation Module
Implements a system model in transfer function form. You define the system model by specifying the Numerator and Denominator of the transfer function equation.
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 single-input single-output (SISO) or multiple-input multiple-output (MIMO). The default value is SISO. |
Feedthrough | Configures the function to be either a Direct or Indirect feedthrough function. Enable this control by selecting a parameter from the Parameters list and then selecting Terminal from the Parameter source pull-down menu. If you select Configuration Dialog Box from the Parameter source pull-down menu, LabVIEW disables this control and calculates the feedthrough behavior automatically. Refer to the Details section for a description of the parameters that determine the feedthrough behavior of this function. |
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. |
Transfer Function | Specifies the transfer function in terms of numerator and denominator polynomial functions.
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reset? | Sets the model state(s) to 0, when TRUE. |
Block Diagram Inputs
Parameter | Description |
---|---|
reset? | Sets the model state(s) to 0, when TRUE. |
input u(k) | Specifies the input to the system. input u(k) must be a vector of length m, where m is the number of inputs. |
Transfer Function | Specifies a transfer function model. This input accepts either a block diagram constant or a model you created using Control Design VIs and functions. |
Block Diagram Outputs
Parameter | Description |
---|---|
output y(k) | Returns the current output of the system. This vector must be of length r, where r is the number of outputs. |
state x(k) | Returns the states of the system. |
Transfer Function Details
For SISO models, this function uses the following equation to calculate the output:
For MIMO models, this function calculates the output as H = [Hij]
where | b0…bm are the coefficients of the numerator polynomial |
a0…an are the coefficients of the denominator polynomial | |
m is the order of the numerator | |
n is the order of the denominator | |
s is the Laplace transform variable | |
i is the index number of the input | |
j is the index number of the output |
Feedthrough Behavior
The values you specify for the Numerator and Denominator subparameters determine the feedthrough behavior of this function. Given m as the order of the Numerator and n as the order of the Denominator:
- If n = m, all input/output pairs have direct feedthrough behavior.
- If n > m, the following input/output pairs have indirect feedthrough behavior.
- input — output
- input — states
- If n < m, LabVIEW returns an error.
When you use the configuration dialog box to configure n and m, LabVIEW verifies that the feedthrough behavior is correct. For example, if you set the Feedthrough parameter to Indirect, and you set n equal to m, LabVIEW changes the Feedthrough parameter to Direct.
If you define the transfer function programmatically, LabVIEW does not adjust the feedthrough behavior for you. You must ensure that you specify the proper feedthrough behavior for the orders of n and m you specify.
Example
Refer to the SimEx transfer function VI in the labview\examples\Control and Simulation\Simulation\Continuous Linear directory for an example of using the Transfer Function VI.