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2  Detailed Help on usage

2.1  Starting RLTOOL

load the rltool library as per instructions in the README file. If the library loads properly the following message is displayed on Scilab prompt:
mode(-1);
rltool is loaded. Type "rlt()" to start rltool-1.5
Type ``rlt()'' to start this programme.

2.2  Using RLTOOL

It is intended to make RLTOOL very user friendly and as such most features should be obvious.

2.2.1  Rootlocus

On typing ``rlt()'', the you will be prompted to either select a new rltool session or load a previous saved file. If a new session is selected, the you will be prompted to enter the transfer function as numerator / denominator in the variable 's'. Rltool will automatically load the plant you were working with in the previous session of rltool. Click ``Ok'' to confirm this plant. You may wish to edit the plant, in that case type the new plant and click ``Ok''.

A Rootlocus plot of the transfer function is displayed. Open loop poles are shown by crosses and zeros by circles. Click on any point of the rootlocus plot to know the gain and whether the closed loop system is stable or unstable

A popup window displays the following ``subplots'' that can be used for preview:
  1. Closed loop pole(s) and zero(s)
  2. Closed loop unit step response.
  3. Closed loop bode plot.
  4. Sensitivity plot
Note that ``closed loop plant'' may include either ``gain in feedback'' or ``gain in forward path''. Please see the ``Settings'' section for how to do this. You can also set the units (hz or rad/sec) for bode and sensitivity plots. Please see the section on "Settings".

You can view the exact (numerical value) of closed loop poles, zeros and gain by clicking on ``Response ®Details''. A popup window displays this data. Click on "step response" button of the popup window to view data like damping factor, overshoot, rise time etc. The damping factor is computed for a dominant pole approximation.

If you want a grid on the rootlocus, select ``Grid ®On''. Likewise, to turn it off, select ``Grid ®Off''. If you want to draw constant damping ratio z and natural frequency wn lines, click on ``Grid ®Zeta/Wn''. You will be prompted to enter one z and one wn of your choice. If you want to do this for various values of z and wn try ``Grid ®sgrid''.

The rootlocus is plotted with a finite (maximum) gain. This is, by default set to 1000. You can change this by clicking on ``Settings ®Rootlocus''. You might want to increase/decrease the maximum possible gain if your rootlocus shows hanging/incomplete lines or is too cluttered. Keeping this gain more than 1× e10 may result in errors.

2.2.2  Frequency design

Rltool comes with two design modes... time domain (rootlocus) and frequency domain. You can select the frequency domain mode by clicking on ``Design ®Frequency''. You will see the frequency magnitude plot of the open loop transfer function. The magnitude is shown in decibel and frequency in rad/sec. Click on the plot to determine the magnitude and frequency. The frequency domain part is still under development. It will be a great idea to take up this aspect and design it further! You can ofcourse return to the rootlocus mode by clicking on ``Design ®Root Locus''.


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