FAQs for RLTOOL, 1.2.

Following are some tips and tricks to get the most out of your RLTOOL package.
These are arranged in the following broad types

  1. Type of plants,  entering transfer functions etc
  2. Trouble with rootlocus
  3. Trouble with frequency plots (Nyquist, Bode etc)
  4. Can't Undo changes
  5. Dynamic responses (impulse, step, ramp, arbitrary input)
  6. More on arbitrary input
  7. Error/ Warnings/ Bugs
  8. i would like to contribute!


Q. What sort of plants does RLTOOL handle?
A. RLTOOL, ver 1.2 handles real valued SISO continuous time plants (proper scalar transfer functions).


Q. How do I enter transfer functions for RLTOOL?
A. The default value is 1/s. You can change this by editing the numerator and denominator. You should enter these as polynomials in 's'. For example, 3s^2+2s+5 should be entered as 3*s^2+2*s+5.

Q. My rootlocus plot shows "hanging" incomplete lines, what should I do?
A. You need to increase the maximum allowable gain. To do this, write the appropriate value in Settings->Rootlocus.

Q. I can't make out details on my rootlocus plot, what should I do?
A. Use the zoom utility for a bigger picture. Alternately, reduce the maximum allowed gain and you would get a more detailed plot.

Q. Though I don't click on a open loop pole/zero, the mouse handler reads the click as a open loop pole/zero, what should I do?
A. This happens because of tolerances set in RLTOOL. You can change the tolerances in Limits() macro. Alternately, ZOOM the region before selecting the point.

Q. Why is open loop frequency response (gain AND phase) not provided in the Design->Frequency menu?
A. There is a bug in Scilab graphics that doesn't recognize mouse coordinates in subplots. If you can figure out a way to read the mouse coordinates in magnitude as well as phase plots, please let me know..

Q. Why is my Nyquist plot drawn only for positive frequencies? Why is it coarse?
A. This is the default. You can put the lower limit of frequency as -1000 Hz for instance and you would get a symmetric Nyquist plot. If it is too coarse, reduce the step size. This can be found in Settings->Nyquist plot.

Q. I can't UNDO changes to my plant, what should I do?
A. RLTOOL requires to save your configuration details in a file called .rltoolcfg.sci. This is located in your present working directory. If you don't have write permissions in your present working directory, a warning message is displayed and you can't use the UNDO feature.

Q. Which dynamic responses can I see?
A. You can view the following CLOSED LOOP UNITY FEEDBACK responses: IMPULSE, STEP, RAMP, ARBITRARY INPUT. Click on Response->Dynamic to select the "operating point" on the rootlocus. You will then see a pop-up window which will prompt you to select the desired plot.

Q. Can I simulate with any arbitrary inputs?
A. No! At present you can simulate with inputs that are (1) piece-wise linear (2) continuous (3) single-valued. You will receive an error message if your input is not of this type.

Q. Can I change the size of the plotting frame in defining the arbitrary input?
A. Yes, click on Edit->size in the plotting frame. Enter the required x and y co-ordinates. The default is  x=[0,1], y=[0,1]. You may change these as required.

Q. My step/ramp/impulse response is incomplete/coarse, what should I do?
A. You need to set parameters for maximum time for incomplete response. For a finer resolution, decrease the step size. These settings are located at Settings-> dynamic response.

Q. Sometimes I see an error message while plotting the step response/ frequency response why is this? What should I do about it?
A. This happens when the pole and zero are too close by and the mouse handler can't distinguish between the two points. When pole and zero are close by, zoom the region by the ZOOM utility before selecting a point (gain).

Q. What should I do if I get a warning/error message?
A. Look up the quick reference on errors or warnings in RLTOOL. It will probably help you remove your error.

Q. I think I have found a bug, what should I do?
A. Please mail the bug report to ishan[AT]iitbombay.org. I would appreciate if you also let me know the remedy. It will help improve RLTOOL.

Q. My RLTOOL crashes , what should I do?
A. Mail your "plant" along with the explicit details to the author. It will help improve RLTOOL.

Q. I would like the feature XYZ to be in RLTOOL, what should I do?
A. Code it into RLTOOL and submit a fresh update. Alternately, let me know about it by e-mail. I shall try to add that feature sometime...

END OF FAQ.
author: Ishan Pendharkar