SI Transfer Function Estimation Express VI

LabVIEW 2013 System Identification Toolkit Help

Edition Date: June 2013

Part Number: 372458D-01

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Owning Palette: Parametric Model Estimation VIs

Requires: System Identification Toolkit

Estimates a discrete or continuous transfer function model for a SISO unknown system. For discrete models, this VI supports the direct, indirect, and joint input-output identification methods.

Dialog Box Options
Block Diagram Inputs
Block Diagram Outputs

Dialog Box Options

ParameterDescription
SignalsDisplays the signals used to estimate the system, including the stimulus signal, reference signal, response signal, and estimated response signal.
Signal SelectionSpecifies the signal you want to preview. Contains the following options:
  • Stimulus—Displays the stimulus signal.
  • Response (default)—Displays the response and estimated response signals.
  • Reference—Displays the reference signal.
Data typeSpecifies the data type for the input signal(s). Contains the following options:
  • Waveform (default)
  • Array
Model typeSpecifies the type of model to estimate. Contains the following options:
  • Continuous
  • Discrete (default)
Signal typeSpecifies the type of the input signals. This option is available only when you set Model type to Continuous. Contains the following options:
  • General (default)
  • Step response
SettingsSpecifies whether the dynamic system contains delay and whether stimulus signal and response signal contain initial condition parts. This option is available only when you set Model type to Continuous and set Signal type to Step response. Contains the following options:
  • System with delay?—specifies whether the dynamic system contains delay. The default is TRUE. If System with delay? is TRUE, this VI estimates the delay of the dynamic system automatically.
  • Signal with initial part?—specifies whether stimulus signal and response signal contain initial condition parts. The default is TRUE. If Signal with initial part? is FALSE, this VI assumes stimulus signal and response signal equal zero in the initial conditions.
Numerator orderSpecifies the order of the numerator of the system model. When you set Model type to Continuous and set Signal type to Step response, this VI sets the value of Numerator order to Denominator order – 1. In this case, you cannot change the value of Numerator order.
Denominator orderSpecifies the order of the denominator of the system model. When you set Model type to Continuous and set Signal type to Step response, the value of Denominator order must be 1 or 2.
Delay initial guessSpecifies the initial guess of the system delay in seconds. The default is NaN, which means no delay exists in this transfer function. This option is available only when you set Model type to Continuous and set Signal type to General.
Estimation methodSpecifies the estimation method to use for discrete systems. Contains the following options:
  • Direct (default)
  • Indirect—This option is available only when you set Model type to Discrete.
  • Joint input-output—This option is available only when you set Model type to Discrete.
Controller numeratorSpecifies the numerator coefficients of the discrete, linear controller. This option is available only when you set Model type to Discrete and set Estimation method to Indirect.
Controller denominatorSpecifies the denominator coefficients of the discrete, linear controller. This option is available only when you set Model type to Discrete and set Estimation method to Indirect.
Controller structureSpecifies the controller position in the feedback loop. If the controller is set before the dynamic system, select Feedforward-path. If the controller is set after the output, select Feedback-path. This option is available only when you set Model type to Discrete and set Estimation method to Indirect.
Zero-Pole cancellation toleranceDetermines zero-pole cancellations. If the difference between the location of a pole and a zero is within the tolerance, this VI removes the zero-pole pair. This option is available only when you set Model type to Discrete and set Estimation method to Indirect.
System DiagramDisplays the system diagram of the closed-loop system.
Estimated ModelDisplays the mathematical equation and sampling rate of the estimated transfer function model.

Block Diagram Inputs

ParameterDescription
stimulus signalSpecifies the input waveform or array of a stimulus signal.
reference signalSpecifies the input waveform or array of a reference signal.
response signalSpecifies the input waveform or array of a response signal.
sampling rateSpecifies the sampling frequency in hertz. For discrete models, sampling rate (Hz) is the system sampling rate. For continuous models, sampling rate is used to convert the continuous model to a discrete model before simulating the output.
error in (no error)Describes error conditions that occur before this node runs.

Block Diagram Outputs

ParameterDescription
system model outsystem model out returns information about the model structure, nominal or estimated parameters, identification result, and so on. Use the Model Management VIs to retrieve the information system model out contains.
Note  You can use a customized system model probe to view model information that flows through system model wires when you debug a block diagram created with the System Identification VIs. Right-click a system model wire and select Custom Probe»SI System Model from the shortcut menu to use the system model probe.
coefficientsReturns the coefficients of the transfer function (TF) model. Contains the following elements:
  • numerator—returns the estimated numerator coefficients of the transfer function.
  • denominator—returns the estimated denominator coefficients of the transfer function.
continuous delayReturns the estimated delay of the continuous system in seconds.
error outContains error information. This output provides standard error out functionality.

This Express VI operates similarly to the following VIs and functions:

SI Estimate Transfer Function Model

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