Article: Measuring Frequency Response

Tim Wescott wrote:

--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

Yes, your 'stupid mistake' was....

I don't know what the fuck you think you're on about.

Now, is that my problem?

DNA

holy shit!  have we caught another troll?

(geez i hope not.  my spray can of Troll-Away is almost empty.)

in article g201e.8099$ME3.575@newsfe1-gui.ntli.net, Genome at
ilike_spam@yahoo.co.uk wrote on 03/25/2005 17:13:


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r b-j                  rbj@audioimagination.com

"Imagination is more important than knowledge."

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
http://www.wescottdesign.com

I have a partially full suit with underware, you are naked.

DNA

in article 1148ve9mlhq6uf4@corp.supernews.com, Tim Wescott at
tim@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                  rbj@audioimagination.com

"Imagination is more important than knowledge."

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
http://www.wescottdesign.com

On Fri, 25 Mar 2005 13:08:25 -0800, Tim Wescott


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

Tim Wescott wrote:

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

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.

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.



--
--
kensmith@rahul.net   forging knowledge

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.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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
http://www.wescottdesign.com

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:

On 28 Mar 2005 18:00:04 -0800, wt70707@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.

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.

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.

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
Central Florida

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