Article: Measuring Frequency Response

For embedded closed-loop control systems.
http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html
Comments welcome (particularly if I made some stupid mistake).

--

Tim Wescott
Wescott Design Services
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Tim Wescott wrote:

Hi Tim,
Yummy, thanks.
--
_______________________________________________________________________
Christopher R. Carlen
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes, your 'stupid mistake' was....
I don't know what the fuck you think you're on about.
Now, is that my problem?
DNA
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
holy shit! have we caught another troll?
(geez i hope not. my spray can of Troll-Away is almost empty.)
in article g201e.8099$ snipped-for-privacy@newsfe1-gui.ntli.net, Genome at ilike snipped-for-privacy@yahoo.co.uk wrote on 03/25/2005 17:13:

--

r b-j snipped-for-privacy@audioimagination.com

"Imagination is more important than knowledge."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
robert bristow-johnson wrote:

My bad, for crossposting to sci.electronics.offtopic. Genome actually participates in that group with positive content, but he tends to average it out with this kind of stuff.
--

Tim Wescott
Wescott Design Services
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

actually
I have a partially full suit with underware, you are naked.
DNA
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
in article snipped-for-privacy@corp.supernews.com, Tim Wescott at snipped-for-privacy@wescottnospamdesign.com wrote on 03/25/2005 16:08:

just a first impression, i can't tell from the body of the article, but it appears in the code that you are doing swept frequency measurements. are you, or am i reading the code wrong ("startF", "stopF").
if you are doing *linearly* swept frequency measurements and your sweep rate is not slow enough, you might want to review:
http://groups-beta.google.com/group/comp.dsp/msg/0763020cf20587c3
it's just to show what the apparent frequency response is and then how to correct for any deterministic error.
--

r b-j snipped-for-privacy@audioimagination.com

"Imagination is more important than knowledge."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
robert bristow-johnson wrote:

Note to self: make sure that it's clear that I'm doing swept-sine measurements.

The sweep is exponential, and some extremely vague handwaving in there about making it slow enough -- I should think about how to clarify that.
Generally the method as I use it, with the exponential sweep, moves things slowly enough that the transient response doesn't cause a great deal of difficulty -- particularly if you have the system operating in closed-loop, which generally causes the transient to settle out much faster than the initial sine wave.
--

Tim Wescott
Wescott Design Services
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 25 Mar 2005 13:08:25 -0800, Tim Wescott

Tim,
I just did a quick read and it looks like you've covered the topic pretty well. Not much I'd add, actually.
Well organized, stated pretty simply, well explained. I think you could expect a red or blue ribbon at the science fair. ;)
Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Tim Wescott wrote:

Hi,
you may want to consider adding a brief discussion about interpreting the results. For example the amount and location of peaking in the closed loop response can give a rough idea of the loop bandwidth and the stability margin ( From the closed loop peaking, can you tell the gain and phase margin separately or not??). Also I'm sure you are familiar with Venabale which uses some similar techniques. http://www.venable.biz /
Mark
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I think you may have a typo in your discussion of eq. 7. You refer to a "Pi/2 term" which I don't see.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Figure 5 etc would be better if the Right hand scale showed the 45, 90 and 180 degree points directly.
The font on the equations is a bit small.
--
--
snipped-for-privacy@rahul.net forging knowledge


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Tim Wescott wrote:

A nice discussion, Tim. You put it in terms of z-domain transfer function, but surely s-domain would be at least as appropriate for most of the paper. Is there a z-domain Bode plot?
Jerry
--
Engineering is the art of making what you want from things you can get.

  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jerry Avins wrote:

It works for any stability problem that can be made into ratios of polynomials with contiguous regions of stability -- so it works for z, s, w = (z-1)/(z+1), etc.
I have a mission to make software engineers comfortable with control theory, so I cast it entirely in terms of the z transform -- I should probably note that it'll work in the s domain, but then I'd have to explain how to do sampled-time measurements and convert them to continuous-time conclusions.
When I'm doing design for discrete-time control I _always_ do the analysis in the z domain, and if frequency response measurements are appropriate I nearly always do them in the context of the controller, rather than trying to make continuous-time measurements and translate.
Well, _I_ call it a Bode plot when I do it in the z domain. You can't construct it with a pencil and a ruler like you can in the s domain, but you interpret it exactly the same way so it seems appropriate.
--

Tim Wescott
Wescott Design Services
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi,Tim
Your article makes clear many things for me. I think it very good except its long line which is bad for printing.
Thomas Atmel ShangHai
Tim Wescott wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 28 Mar 2005 18:00:04 -0800, snipped-for-privacy@yahoo.com wrote:

Not top-posting in this reply...
What kind of browser are you using? When I do a print preview with Firefox, the page fills nicely but getting page breaks not to split images is another issue.
Great to share this stuff, Tim, but a link to printable format like pdf or doc would be nice.
I know... looking the gift horse, etc. But if you could find a way to present in a printable format that you like, even better.
Thanks for sharing either way.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

For what it's worth, I converted your pages into a doc file and tried to use that with GhostView to create a pdf. Apparently my old veraion of Word is inadequate. Seems the pictures were not imbedded and I haven't found a setting to change that. Dang!
I tried.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 29 Mar 2005 06:08:26 GMT, Richard the Dreaded Libertarian

[snip stuff that doesn't matter]

Thanks, but this is a web page with figures interspersed. The web page is fine but hard to print nicely. A formatted version with imbedded images would be the solution. I tried to convert it but I was reporting on my failure to generate one with free or available tools.
Maybe someone else has better success. Otherwise, the web page has all the information, and I found a way to locally print the content. I just tried (and failed) to make an easily printable version for download.
Thanks, again, to Tim for writing and sharing the web page.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
xray wrote:

Did you try printing the web page with something like PDF995? Not always pretty, but it will print the pictures along with the text. Its a shell for ghostscript.
http://www.pdf995.com /
--
Former professional electron wrangler.

Michael A. Terrell
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You missed this thread a couple of weeks back about virtual print drivers (3 options): http://groups-beta.google.com/group/sci.electronics.design/browse_frm/thread/373cbd5dabdf1e13/ce7079b0b870f7c1?q=PDF995+PDFCreator+print-driver-com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.