Article: Measuring Frequency Response

T

Tim Wescott

Guest
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
http://www.wescottdesign.com
 
Tim Wescott wrote:
For embedded closed-loop control systems.

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Comments welcome (particularly if I made some stupid mistake).
Click to expand...

Hi Tim,

Yummy, thanks.



--
_______________________________________________________________________
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.
 
"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:1148ve9mlhq6uf4@corp.supernews.com...
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
http://www.wescottdesign.com
Click to expand...
Yes, your 'stupid mistake' was....

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

Now, is that my problem?

DNA
 
in article 1148ve9mlhq6uf4@corp.supernews.com, Tim Wescott at
tim@wescottnospamdesign.com wrote on 03/25/2005 16:08:

For embedded closed-loop control systems.

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Comments welcome (particularly if I made some stupid mistake).
Click to expand...
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."
 
On Fri, 25 Mar 2005 13:08:25 -0800, Tim Wescott
<tim@wescottnospamdesign.com> wrote:

For embedded closed-loop control systems.

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Comments welcome (particularly if I made some stupid mistake).
Click to expand...
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
 
robert bristow-johnson wrote:

in article 1148ve9mlhq6uf4@corp.supernews.com, Tim Wescott at
tim@wescottnospamdesign.com wrote on 03/25/2005 16:08:


For embedded closed-loop control systems.

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Comments welcome (particularly if I made some stupid mistake).


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

The sweep is exponential, and some extremely vague handwaving in there
Click to expand...
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
 
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:

"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:1148ve9mlhq6uf4@corp.supernews.com...
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
http://www.wescottdesign.com

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

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

Now, is that my problem?

DNA
Click to expand...
--

r b-j rbj@audioimagination.com

"Imagination is more important than knowledge."
 
"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:1148ve9mlhq6uf4@corp.supernews.com...
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
http://www.wescottdesign.com
Click to expand...
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.
 
In article <1148ve9mlhq6uf4@corp.supernews.com>,
Tim Wescott <tim@wescottnospamdesign.com> wrote:
For embedded closed-loop control systems.

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Comments welcome (particularly if I made some stupid mistake).
Click to expand...
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:
For embedded closed-loop control systems.

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Comments welcome (particularly if I made some stupid mistake).
Click to expand...
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.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
 
robert bristow-johnson wrote:
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:


"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:1148ve9mlhq6uf4@corp.supernews.com...

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
http://www.wescottdesign.com

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

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

Now, is that my problem?

DNA

My bad, for crossposting to sci.electronics.offtopic. Genome actually
Click to expand...
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
 
Jerry Avins wrote:

Tim Wescott wrote:

For embedded closed-loop control systems.

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Comments welcome (particularly if I made some stupid mistake).


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
Click to expand...
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
 
"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:114bajud8691r13@corp.supernews.com...
robert bristow-johnson wrote:
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:


"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:1148ve9mlhq6uf4@corp.supernews.com...

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
http://www.wescottdesign.com

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

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

Now, is that my problem?

DNA

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

DNA
 
On 28 Mar 2005 18:00:04 -0800, wt70707@yahoo.com wrote:

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:
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
http://www.wescottdesign.com
Click to expand...
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.
 
On Tue, 29 Mar 2005 02:13:40 GMT, xray <notreally@hotmail.invalid>
wrote:

Great to share this stuff, Tim, but a link to printable format like pdf
or doc would be nice.
Click to expand...
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 03:43:56 +0000, xray wrote:

On Tue, 29 Mar 2005 02:13:40 GMT, xray <notreally@hotmail.invalid
wrote:

Great to share this stuff, Tim, but a link to printable format like pdf
or doc would be nice.

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.
Click to expand...
Feh.

If you have a graphic, and aren't on a binaries newsgroup, then proper
netiquette is to find a website somewhere to put it up, and post a link
in the NG.

In binaries newsgroups, just attach the image. Whether it's gif, jpeg,
acrobat, or hooptifratz, let the viewers figure out how to interpret
it. Since it's a binaries group, you can post anything in the world,
and the only ones who can complain are your ISP. Or Homeland Security,
if you post pictures of naked underage children. Images of people
enjoying Love are verboten in the puritanical countries, while images
of pain, suffering, death, destruction, mayhem, and torture seem to
be de rigeur amongst the neo-nazis.

Good Luck!
Rich
 
On Tue, 29 Mar 2005 06:08:26 GMT, Richard the Dreaded Libertarian
<eatmyshorts@doubleclick.net> wrote:

On Tue, 29 Mar 2005 03:43:56 +0000, xray wrote:

On Tue, 29 Mar 2005 02:13:40 GMT, xray <notreally@hotmail.invalid
wrote:

Great to share this stuff, Tim, but a link to printable format like pdf
or doc would be nice.

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.

Feh.

If you have a graphic, and aren't on a binaries newsgroup, then proper
netiquette is to find a website somewhere to put it up, and post a link
in the NG.

In binaries newsgroups, just attach the image.
[snip stuff that doesn't matter]
Click to expand...

Good Luck!
Rich
Click to expand...
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" <notreally@hotmail.invalid> wrote in message
news:0jjh41pvulmkov9h4js3fbbgoniumjftgn@4ax.com...
On Tue, 29 Mar 2005 02:13:40 GMT, xray <notreally@hotmail.invalid
wrote:

Great to share this stuff, Tim, but a link to printable format like
pdf
or doc would be nice.

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.
Click to expand...
Burp!!!!!!!!!!!!!

If you are using MicroWank Intersnuff Expunger then go to....

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Click File, Save As, Web Page Complete and save it somewhere. I think
you might have done so.....

Then, go to.....

http://www.openoffice.org/

and download a nice bit of the soft.

You might also need the Java runtime engine.....

http://java.com/en/

Having installed your balls then you will be able to do a File Open in
Open Office thing from the bit that Tim wrote and you saved as a
complete webfile.

Spukely.

Then you click on the PDF icon in the Open Office toolbar and it saves
it as a PDF file.......

And I have to say that the translation is Mother Beautiful!

If you don't want to go through such huge downloads..... I dunno, you
got ghostscript..... go the whole hog, then it's posted in ABSE....

Err, if it turns up.

DNA
 
"xray" <notreally@hotmail.invalid> wrote in message
news:0jjh41pvulmkov9h4js3fbbgoniumjftgn@4ax.com...
On Tue, 29 Mar 2005 02:13:40 GMT, xray <notreally@hotmail.invalid
wrote:

Great to share this stuff, Tim, but a link to printable format like
pdf
or doc would be nice.

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.
Click to expand...
Burp!!!!!!!!!!!!!

If you are using MicroWank Intersnuff Expunger then go to....

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Click File, Save As, Web Page Complete and save it somewhere. I think
you might have done so.....

Then, go to.....

http://www.openoffice.org/

and download a nice bit of the soft.

You might also need the Java runtime engine.....

http://java.com/en/

Having installed your balls then you will be able to do a File Open in
Open Office thing from the bit that Tim wrote and you saved as a
complete webfile.

Spukely.

Then you click on the PDF icon in the Open Office toolbar and it saves
it as a PDF file.......

And I have to say that the translation is Mother Beautiful!

If you don't want to go through such huge downloads..... I dunno, you
got ghostscript..... go the whole hog, then it's posted in ABSE....

Err, if it turns up.

DNA
 
"Genome" <ilike_spam@yahoo.co.uk> wrote in message
news:XlC2e.703$ua5.136@newsfe2-gui.ntli.net...
"xray" <notreally@hotmail.invalid> wrote in message
news:0jjh41pvulmkov9h4js3fbbgoniumjftgn@4ax.com...
On Tue, 29 Mar 2005 02:13:40 GMT, xray <notreally@hotmail.invalid
wrote:

Great to share this stuff, Tim, but a link to printable format
like
pdf
or doc would be nice.

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.


Burp!!!!!!!!!!!!!

If you are using MicroWank Intersnuff Expunger then go to....

http://www.wescottdesign.com/articles/FreqMeas/freq_meas.html

Click File, Save As, Web Page Complete and save it somewhere. I
think
you might have done so.....

Then, go to.....

http://www.openoffice.org/

and download a nice bit of the soft.

You might also need the Java runtime engine.....

http://java.com/en/

Having installed your balls then you will be able to do a File Open
in
Open Office thing from the bit that Tim wrote and you saved as a
complete webfile.

Spukely.

Then you click on the PDF icon in the Open Office toolbar and it
saves
it as a PDF file.......

And I have to say that the translation is Mother Beautiful!

If you don't want to go through such huge downloads..... I dunno,
you
got ghostscript..... go the whole hog, then it's posted in ABSE....

Err, if it turns up.

DNA
Click to expand...
Oh shit, you wanted proper page breaks.

Pass me my pistol.

DNA
 
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