Using the Right-Click Menu in the LTI Viewer

Overview of the Right-Click Menu

The quickest way to manipulate views in the LTI Viewer is use the right-click menu. You can access several LTI Viewer controls and options, including:

  • Plot Type — Changes the plot type

  • Systems — Selects or deselects any of the models loaded in the LTI Viewer

  • Characteristics — Displays key response characteristics and parameters

  • Grid — Adds grids to your plot

  • Properties — Opens the Property Editor, where you can customize plot attributes

  • Design Requirements — Opens the New Design Requirement window for adding step response design requirements to your plot (available only for LTI Viewers linked to the Graphical Tuning window of the SISO Design Tool)

In addition to right-click menus, all response plots include data markers. These allow you to scan the plot data, identify key data, and determine the source system for a given plot.

Setting Characteristics of Response Plots

The Characteristics menu changes for each plot response type. Characteristics refers to response plot information, such as peak response, or, in some cases, rise time and settling time.

The next sections describe the menu items for each of the eight plot types.

Step Response

Step plots the model's response to a step input.

You can display the following information in the step response:

  • Peak Response — The largest deviation from the steady-state value of the step response

  • Settling Time — The time required for the step response to decline and stay at 5% of its final value

  • Rise Time — The time require for the step response to rise from 10% to 90% of its final value

  • Steady-State — The final value for the step response

Impulse Response

Impulse Response plots the model's response to an impulse.

The LTI Viewer can display the following information in the impulse response:

  • Peak Response — The maximum positive deviation from the steady-state value of the impulse response

  • Settling Time — The time required for the step response to decline and stay at 5% of its final value

Bode Diagram

Bode plots the open-loop Bode phase and magnitude diagrams for the model.

The LTI Viewer can display the following information in the Bode diagram:

  • Peak Response — The maximum value of the Bode magnitude plot over the specified region

  • Stability Margins (Minimum Crossing) — The minimum phase and gain margins. The gain margin is defined to the gain (in dB) when the phase first crosses -180°. The phase margin is the distance, in degrees, of the phase from -180° when the gain magnitude is 0 dB.

  • Stability Margins (All Crossings) — Display all stability margins

Bode Magnitude

Bode Magnitude plots the Bode magnitude diagram for the model.

The LTI Viewer can display the following information in the Bode magnitude diagram:

  • Peak Response, which is the maximum value of the Bode magnitude in decibels (dB), over the specified range of the diagram.

  • Stability (Minimum Crossing) — The minimum gain margins. The gain margin is defined to the gain (in dB) when the phase first crosses -180°.

  • Stability (All Crossings) — Display all gain stability margins

Nyquist Diagrams

Nyquist plots the Nyquist diagram for the model.

The LTI Viewer can display the following types of information in the Nyquist diagram:

  • Peak Response — The maximum value of the Nyquist diagram over the specified region

  • Stability (Minimum Crossing) — The minimum gain and phase margins for the Nyquist diagram. The gain margin is the distance from the origin to the phase crossover of the Nyquist curve. The phase crossover is where the curve meets the real axis. The phase margin is the angle subtended by the real axis and the gain crossover on the circle of radius 1.

  • Stability (All Crossings) — Display all gain stability margins

Nichols Charts

Nichols plots the Nichols Chart for the model.

The LTI Viewer can display the following types of information in the Nichols chart:

  • Peak Response — The maximum value of the Nichols chart in the plotted region.

  • Stability (Minimum Crossing) — The minimum gain and phase margins for the Nichols chart.

  • Stability (All Crossings) — Display all gain stability margins

Singular Values

Singular Values plots the singular values for the model.

The LTI Viewer can display the Peak Response, which is the largest magnitude of the Singular Values curve over the plotted region.

Pole/Zero and I/O Pole/Zero

Pole/Zero plots the poles and zeros of the model with `x' for poles and `o' for zeros. I/O Pole/Zero plots the poles and zeros of I/O pairs.

There are no Characteristics available for pole-zero plots.

Adding Design Requirements

If you open an LTI Viewer for the Graphical Tuning window, you have plots linked to your compensator design. In this environment, the LTI Viewer provides access to design requirements, a set of graphical tools for creating constraints in your design plots.

In addition to all the design requirements available in the Graphical Tuning window, the LTI Viewer has the step response design requirements described in Choosing Step Response Specifications.

For more information on adding design requirements to LTI Viewer plots, see LTI Viewer for SISO Design Task Design Requirements.

    Note   Design requirements are not available from an LTI Viewer that is opened using the ltiview command.

Choosing Step Response Specifications

To specify step response characteristics select Design Requirements > New in the right-click menu. This action opens the New Design Requirements editor. Select step response bounds from the Design requirement type pull down menu to display the step response specifications as shown below.

The top three options specify the details of the step input:

  • Initial value: input level before the step occurs. This option is grayed out because LTI systems always have intial value equal to 0.

  • Step time: time at which the step takes place. This option is grayed out since LTI systems always have an initial time equal to 0.

  • Final value: input level after the step occurs

The remaining options specify the characteristics of the response signal. Each of the step response characteristics is described in the figure below.

  • Rise time: The time taken for the response signal to reach a specified percentage of the step's range. The step's range is the difference between the final and initial values.

  • % Rise: The percentage used in the rise time.

  • Settling time: The time taken until the response signal settles within a specified region around the final value. This settling region is defined as the final step value plus or minus the specified percentage of the final value.

  • % Settling: The percentage used in the settling time.

  • % Overshoot: The amount by which the response signal can exceed the final value. This amount is specified as a percentage of the step's range. The step's range is the difference between the final and initial values.

  • % Undershoot: The amount by which the response signal can undershoot the initial value. This amount is specified as a percentage of the step's range. The step's range is the difference between the final and initial values.

Enter values for the response specifications in the Design Requirements editor, based on the requirements of your model, and then click OK. The constraint edges will now reflect the constraints specified.

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