| Author |
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Watson A.Name - \"Watt Su
Guest
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 Posted:
Sat Feb 05, 2005 9:41 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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"Fred Abse" <excretatauris@cerebrumconfus.it> wrote in message
news:pan.2005.02.05.12.21.24.536446@cerebrumconfus.it...
| Quote: | On Fri, 04 Feb 2005 20:18:02 +0000, Jim Backus wrote:
I'm not sure reality allows measuring electrolytics to 1% :-)
Reality allows measuring electrolytics to better accuracy than that.
Unfortunately, however, it doesn't allow *making* them to such
tolerances.
Capacitance can also vary with polarizing voltage.
|
The thought occurred to me that at those very low freqs, the polarized
electrolytic may have a charge on it long enough during each cycle so
that the chemicals have time to do something that changes the
capacitance.
> --
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Charlie+
Guest
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| Posted:
Sat Feb 05, 2005 9:41 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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On Thu, 03 Feb 2005 21:37:45 GMT, "gmv" <noemail@please.123> wrote as
underneath my scribble :
Just a thaught on your original question if you are still going there!
- Have you thought of a Peak Atlas LCR Analyser? It uses DC transient
analysis to measure in the range 1uF upwards (10,000uF) at about 1V.
accuracy approaches what you want absolute. See www.peakelec.co.uk
but you can get pretty good repeatability which might be the key
I can take 10 readings off the same 100uF electrolytic and let you
know the variation if it wd help.? what voltage rating?
Charlie+.
| Quote: | Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.
I am trying to get a reading
within 1% of reality.
Help here is appreciated. |
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Watson A.Name - \"Watt Su
Guest
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| Posted:
Sat Feb 05, 2005 9:41 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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"gmv" <noemail@please.123> wrote in message
news:0F3Nd.50241$EG1.24027@attbi_s53...
| Quote: | Yes, that is the kind of thing I am looking for.
In case you are wondering the thing I want to
use them in is here:
As you can tell I am no expert but i can tell you
this will show Earthquakes in a relatively noisy area.
Just got a big one from the Philippines I think.
The big capacitors on the front end are just to
simulate the mass/housing relationship in the
geophone. They are not a reality as far as
capacitors go.
|
The last three filters are simple 6dB per octave rolloff filters, and
they claim to be different freqs, but their parts values are identical,
so something is wrong there. But they are preceded by three bandpass
filters in parallel, so there are some incongruities in thie circuit.
And there seems to be a lot of room for improvement.
| Quote: | "Boris Mohar" <borism_-void-_@sympatico.ca> wrote in message
news:75e9011tvdtt0kmg1202q713e35udgg5rh@4ax.com...
On Sat, 05 Feb 2005 11:03:00 GMT, "gmv" <noemail@please.123> wrote:
motor caps are too high power for my needs
I am just using small signal here.
NP caps are what i need.
I think the ceramic ones would be perfect.
I just want ones that will read consistant with my C meter.
At these values ceramic caps have very unstable dielectric. Your
filter
will be all over the place with respect to temperature. The voltage
coefficient does not look good either.
Try here:
http://www.electronicstalk.com/news/eas/eas123.html.
Regards,
Boris Mohar
Got Knock? - see:
Viatrack Printed Circuit Designs (among other things)
http://www.viatrack.ca
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Watson A.Name - \"Watt Su
Guest
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| Posted:
Sat Feb 05, 2005 9:41 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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"Charlie+" <charlie@xxx.net> wrote in message
news:395a01p8rbd7j5loadqvdqrjm8irpe4ojp@4ax.com...
| Quote: | On Thu, 03 Feb 2005 21:37:45 GMT, "gmv" <noemail@please.123> wrote as
underneath my scribble :
Just a thaught on your original question if you are still going there!
- Have you thought of a Peak Atlas LCR Analyser? It uses DC transient
analysis to measure in the range 1uF upwards (10,000uF) at about 1V.
accuracy approaches what you want absolute. See www.peakelec.co.uk
|
Probably pretty hard to get one in the U.S. But he could plug the cap
into a standard astable circuit using a 555, and if the values of the
resistors are accurate, he could get a fairly close value for the
capacitance.
| Quote: | but you can get pretty good repeatability which might be the key
I can take 10 readings off the same 100uF electrolytic and let you
know the variation if it wd help.? what voltage rating?
Charlie+.
Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.
I am trying to get a reading
within 1% of reality.
Help here is appreciated.
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Hal Murray
Guest
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| Posted:
Sun Feb 06, 2005 5:09 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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| Quote: | I must filter out the high stuff first because my sample rate
is only 65539.3 samples per hour and my dynamic range is only
8 bits. Like I told someone else my sensor has a non-linear
response in the frequency range of interest.
2Hz to 1/20 Hz.
It would be so wonderful to have a dead end at 2HZ kind
of filter then most of my troubles would evaporate.
|
What is your signal/noise ratio? (without the filter)
Can you get an A/D with enough bits so that you can see
the signal in the bottom bits when the gain is set so that
the noise doesn't saturate the A/D? If so, then consider
the DSP suggestion. It's easy to do the sort of filtering
you want in software, especially at such slow speeds.
--
The suespammers.org mail server is located in California. So are all my
other mailboxes. Please do not send unsolicited bulk e-mail or unsolicited
commercial e-mail to my suespammers.org address or any of my other addresses.
These are my opinions, not necessarily my employer's. I hate spam. |
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gmv
Guest
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| Posted:
Sun Feb 06, 2005 6:26 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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Look more closely and tell me what can be done
because I am at at a dead end.
The noise is horrible above 2Hz I really
need a filter that has a precipitous
dropoff between 2 and 3 Hz in order get the
gain to see anything worth watching.
The phase distortions are terrible too
but if I want to see a meaningful picture i have
no other choices I know of. I have tried just about
everything under the sun and these BP filters seem
the very best for me and my location.
The last three filters simply help to steepen
the high rolloff so i can get more gain at
the lower without being swamped by noise.
The Earthquake people want me to look at
..5 to 2Hz but that just is not possible for me
unless I can roll 3 Hzand above -24db from what i get at 2Hz.
I need a miracle filter that does not exist.
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote in message news:110a7kmdfs6d633@corp.supernews.com...
| Quote: |
"gmv" <noemail@please.123> wrote in message
news:0F3Nd.50241$EG1.24027@attbi_s53...
Yes, that is the kind of thing I am looking for.
In case you are wondering the thing I want to
use them in is here:
As you can tell I am no expert but i can tell you
this will show Earthquakes in a relatively noisy area.
Just got a big one from the Philippines I think.
The big capacitors on the front end are just to
simulate the mass/housing relationship in the
geophone. They are not a reality as far as
capacitors go.
The last three filters are simple 6dB per octave rolloff filters, and
they claim to be different freqs, but their parts values are identical,
so something is wrong there. But they are preceded by three bandpass
filters in parallel, so there are some incongruities in thie circuit.
And there seems to be a lot of room for improvement.
"Boris Mohar" <borism_-void-_@sympatico.ca> wrote in message
news:75e9011tvdtt0kmg1202q713e35udgg5rh@4ax.com...
On Sat, 05 Feb 2005 11:03:00 GMT, "gmv" <noemail@please.123> wrote:
motor caps are too high power for my needs
I am just using small signal here.
NP caps are what i need.
I think the ceramic ones would be perfect.
I just want ones that will read consistant with my C meter.
At these values ceramic caps have very unstable dielectric. Your
filter
will be all over the place with respect to temperature. The voltage
coefficient does not look good either.
Try here:
http://www.electronicstalk.com/news/eas/eas123.html.
Regards,
Boris Mohar
Got Knock? - see:
Viatrack Printed Circuit Designs (among other things)
http://www.viatrack.ca
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gmv
Guest
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| Posted:
Sun Feb 06, 2005 6:35 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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My meter says the reading will
change if the leakage resistance is low
and that seems to be true for just about
most Electrolytics i test.
Maybe what i need is a high quality Electrolytic
with fantastic high leakage resistance.
"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message news:5jh901tjbopm0mh3pvf6hr381mdvvddpqs@4ax.com...
| Quote: | On Sat, 05 Feb 2005 07:20:18 -0500, the renowned Boris Mohar
borism_-void-_@sympatico.ca> wrote:
On Sat, 05 Feb 2005 11:03:00 GMT, "gmv" <noemail@please.123> wrote:
motor caps are too high power for my needs
I am just using small signal here.
NP caps are what i need.
I think the ceramic ones would be perfect.
I just want ones that will read consistant with my C meter.
At these values ceramic caps have very unstable dielectric. Your filter
will be all over the place with respect to temperature. The voltage
coefficient does not look good either.
Try here:
http://www.electronicstalk.com/news/eas/eas123.html.
Electrolytics are actually pretty stable wrt temperature, time and
applied voltage- unlike those pesky hi-K ceramics. Less microphonics,
too. If your meter doesn't read them consistently, maybe it's time to
invest $50 or $60 in a new meter?
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com |
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gmv
Guest
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| Posted:
Sun Feb 06, 2005 6:41 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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Interesting,
I always thought the opamp buffered the output
so you could hook it to anything between 2K
and infinity.
I will keep in mind what you have said.
I have noticed a terrible ringing effect at Q
5 and above.
Maybe that is what you are talking about.
In any case I really need to see things between .5Hz
and 2Hz. It is only the noise in my local area that
keeps me from doing this as far as I can tell.
http://home.mchsi.com/~gmvoeth/index.html
will show a bit more of what I am doing.
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote in message news:1109v26sjt1i70c@corp.supernews.com...
| Quote: |
"gmv" <noemail@please.123> wrote in message
news:EJ1Nd.51210$eT5.4698@attbi_s51...
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in message news:11097hnlc4n3q25@corp.supernews.com...
"gmv" <noemail@please.123> wrote in message
news:f_QMd.49525$eT5.27123@attbi_s51...
Sorry, Do not know what a DSP/FIR is.
I am using only 8 bit data.
Surprising enough the filters work quite well
between 1Hz and DC just like they do between
1Hz and infinity. The only problem I have is
getting those capacitors in a non-electrolytic form.
I have found I can get pretty good matches in frequency
simply if I can know the true value of the capacitors.
The design matches the theory if only I can
match the capacitors.
I used to laugh at precision and accuracy but
I have found that is the only way to go when
dealing with filter circuits and possibly
oscillator circuits too.
The only way I will play with things like FIR or
DSP is if it will handle data from a non-linearI still think
kind of sensor that tends to overdrive the
preamp at high freqs making it impossible to
look at the low freqs also it got to be cheap.
I need to filter out
the upper freqs right off the bat or it is
impossible to get enough gain to look at the low.
I still think you need to raise the impedance of the circuits
up high enough so that the capacitors are much smaller.
That increases the noise.
Using FET input opamps and megohm resistors, you should be able
to get down to very low freqs with caps of a microfarad.
I think I need BJT types if I remember right
they are lower in noise. I have found chopper
amps to be out of the question.
I offered that Action Electronics web page with the motor
capacitors,
but I don't know if they are electrolytic or not. Maybe someone
could help. They also have tantalom caps, which are more stable
than 'lytics. http://www.action-electronics.com/capacitr.htm
motor caps are too high power for my needs
I am just using small signal here.
NP caps are what i need.
Well, the motor caps are non-polarized. That's what you want.
And they are not electrolytic, I believe, but I'm not certain.
And the power doesn't make any diff, but they are large, and
that might be a problem. As I already mentioned, there are
ceiling fan capacitors at the local hardware store that are
about 10 uF, and are not very large. ANd reasonably priced IIRC.
About noise, you decrease noise by reducing the bandwidth. You
reduce the bandwidth by reducing the load on the tuned circuit.
You do this by increasing the impedance of the load on the tuned
circuit, IOW use a higher resistance, and that means FETs or
other very high impedance amps.
I think you are getting more noise because you are decreasing
the bandwidth by keeping the load the same impedance, but
increasing the tuned circuit impedance. That's backwards
from what you should be doing.
I think the ceramic ones would be perfect.
I just want ones that will read consistant with my C meter.
Thanks to everyone for your answers
but like always I must seek a solution myself
because it is so rare I really find any answers
on these newsgroups.
It is as if the Engineers and Scientists
avoid this internet stuff like it is the plague.
I just tried building my own cap and a monster
size it was and only 3.3nf...they must be very
hard to make at 10uf or higher and be small.
You need to use the same technology that makes
ICs. Thin layer of metal, thin layer of insulator,
do this repeatedly until you get the right value.
Surely there must be a breakthrough in technology
to make decent high value caps.
Sort of like the movie THIS ISLAND EARTH
I need to find that engineers supplier of
interocitor parts.
Yes, a log amp is a possibility, I have already
considered that. But the signals I now receive
are good enough for myself and all I wish to do
is to bring closure to my circuit be acquiring what
I consider to be decent capacitors. These electrolytics
are seemingly only for one frequency because
funny things start happening if you read the
capacitance with different frequencies.
Like I get a lower capacitance at a higher frequency.
I have found no such problems with regular
caps that do not use an electrolytic form.
Your solution would be possible if I had a sensor
resonant at 20 seconds but the Geophone I am using
is resonant at something over 1 Hz.
Geospace has just the device I would like to have
they have a .5 Hz Geophone but they want about
$3000 for one and that is way too high for someone
living on Social Security.
"Rob Gaddi" <rgaddi@bcm.YUMMYSPAMtmc.edu> wrote in message
news:cu0elc$t4c@gazette.corp.bcm.tmc.edu...
While I hate to give my usual answer, have you considered just
digitizing the data and running it through a DSP? You're talking
about some massively slow filters to be trying to make with any
reliable tolerance in analog, and with component values that large
it's not going to be cheap. Plus you can use a linear FIR filter
and not have to worry about the phase distortion you were
mentioning.
If your noise is really swamping the signal, and dynamic range is
a
concern, at the low speeds you're talking about you could run
the signal through a log amp before you A/D it.
Lucky for me different phases of Earthquakes
seem to prefer different frequencies.
But my picture will never be as good as the
big boys.
Just too darn noisy at this location.
I get a terrible noise at maybe 15 Hz or so.
Need to filter like crazy to get rid of it.
It drowns out just about everything i try to do.
I suspect but can not prove that my geophone
is out of spec and not working at the 1Hz
it is supposed to.
The only adjustment I can make is to center the
mass in the housing. If there is a way to lower the
resonant freq I would sure like to know.
I am thinking of finding some weights to put on
the adjustment screw as much weight as can still be
centered.
But it is my experience that for a spring to
lower its frequency it needs to extend or compress
farther in distance. similar to a pendulums length.
T=2PiSqRt(length/gravity)
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gmv
Guest
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| Posted:
Sun Feb 06, 2005 6:43 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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The noise above 2Hz is so great it will clip before I can look at
my area of interest.
"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message news:36kbo6F52lcvnU1@individual.net...
| Quote: |
"gmv" <noemail@please.123> wrote in message
news:Y3RMd.19306$C24.13288@attbi_s52...
"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message
news:36htfrF5289nrU1@individual.net...
"gmv" <noemail@please.123> wrote in message
news:HgIMd.47990$EG1.27201@attbi_s53...
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in message news:1106d0pdpsb0i35@corp.supernews.com...
"gmv" <noemail@please.123> wrote in message
news:PczMd.46765$IV5.32350@attbi_s54...
snip
Run it through an A/D to get it into the digital domain where you can
handle
it sensibly without having to consider what temperature, sonics, etc
will
otherwise do to your filters if you need that sort of accuracy.
I must filter out the high stuff first because my sample rate
is only 65539.3 samples per hour and my dynamic range is only
8 bits. Like I told someone else my sensor has a non-linear
response in the frequency range of interest.
2Hz to 1/20 Hz.
It would be so wonderful to have a dead end at 2HZ kind
of filter then most of my troubles would evaporate.
In which case why not, as I said before, run it through an AtoD etc etc. and
do a proper job on it.
Simple enough to tailor exactly to your needs.
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gmv
Guest
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| Posted:
Sun Feb 06, 2005 6:54 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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All I can tell you is the noise is way way up there
and I need to filter most all of it out before I can see
anything of interest. You need to understand the nature
of a Geophone resonant at 1Hz to understand what I am dealing
with. The device acts like a high pass filter with a rolloff
at the resonant freq.
There are noises in the ground at about 15 Hz it seems that
swamp all else. All I can think of is there are some
very big motors working fast and furious all the time
in my town.
I can not evaluate the noise because my sample rate is only good
for up to 9Hz.
The area I need to look is between .5Hz and 2Hz so what I really
need is a .5Hz Geophone but it will be a cold day in hell
before I will pay $3000 to buy one.
I have been thinking of building a great little
pendulum sensor but that will be too large for me to
hide well in my back yard.
I have come to hate being forced to live
with the rat race kind of people because of all
the noise they generate.
"Hal Murray" <hmurray@suespammers.org> wrote in message news:jZKdndS0X8axz5jfRVn-vw@megapath.net...
| Quote: | I must filter out the high stuff first because my sample rate
is only 65539.3 samples per hour and my dynamic range is only
8 bits. Like I told someone else my sensor has a non-linear
response in the frequency range of interest.
2Hz to 1/20 Hz.
It would be so wonderful to have a dead end at 2HZ kind
of filter then most of my troubles would evaporate.
What is your signal/noise ratio? (without the filter)
Can you get an A/D with enough bits so that you can see
the signal in the bottom bits when the gain is set so that
the noise doesn't saturate the A/D? If so, then consider
the DSP suggestion. It's easy to do the sort of filtering
you want in software, especially at such slow speeds.
--
The suespammers.org mail server is located in California. So are all my
other mailboxes. Please do not send unsolicited bulk e-mail or unsolicited
commercial e-mail to my suespammers.org address or any of my other addresses.
These are my opinions, not necessarily my employer's. I hate spam.
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gmv
Guest
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| Posted:
Sun Feb 06, 2005 6:59 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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Exactly what I was considering.
Possibly a simple RC inverter oscillator.
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote in message news:110a7te1fihrmd9@corp.supernews.com...
| Quote: |
"Charlie+" <charlie@xxx.net> wrote in message
news:395a01p8rbd7j5loadqvdqrjm8irpe4ojp@4ax.com...
On Thu, 03 Feb 2005 21:37:45 GMT, "gmv" <noemail@please.123> wrote as
underneath my scribble :
Just a thaught on your original question if you are still going there!
- Have you thought of a Peak Atlas LCR Analyser? It uses DC transient
analysis to measure in the range 1uF upwards (10,000uF) at about 1V.
accuracy approaches what you want absolute. See www.peakelec.co.uk
Probably pretty hard to get one in the U.S. But he could plug the cap
into a standard astable circuit using a 555, and if the values of the
resistors are accurate, he could get a fairly close value for the
capacitance.
but you can get pretty good repeatability which might be the key
I can take 10 readings off the same 100uF electrolytic and let you
know the variation if it wd help.? what voltage rating?
Charlie+.
Is there anyway to accurately measure the
capacitance of an electrolytic capacitor
in the range of 10uf to 100uf.
I am trying to get a reading
within 1% of reality.
Help here is appreciated.
|
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gmv
Guest
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| Posted:
Sun Feb 06, 2005 7:01 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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You make an electrolytic capacitor sound like
it is a very large veractor diode.
"Fred Abse" <excretatauris@cerebrumconfus.it> wrote in message news:pan.2005.02.05.12.21.24.536446@cerebrumconfus.it...
| Quote: | On Fri, 04 Feb 2005 20:18:02 +0000, Jim Backus wrote:
I'm not sure reality allows measuring electrolytics to 1% :-)
Reality allows measuring electrolytics to better accuracy than that.
Unfortunately, however, it doesn't allow *making* them to such tolerances.
Capacitance can also vary with polarizing voltage.
--
Then there's duct tape ...
(Garrison Keillor)
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Fred Abse
Guest
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| Posted:
Sun Feb 06, 2005 4:24 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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On Sat, 05 Feb 2005 09:21:02 -0800, Watson A.Name - "Watt Sun, the Dark
Remover" wrote:
| Quote: | The thought occurred to me that at those very low freqs, the polarized
electrolytic may have a charge on it long enough during each cycle so that
the chemicals have time to do something that changes the capacitance.
|
Quite true.
Interesting question: When does low frequency AC become varying DC?
--
Then there's duct tape ...
(Garrison Keillor) |
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Charlie+
Guest
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| Posted:
Sun Feb 06, 2005 6:10 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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On Sun, 06 Feb 2005 00:59:10 GMT, "gmv" <noemail@please.123> wrote as
underneath my scribble :
Problem is getting your absolute value with a homemade solution unless
you have a calibrated standard to go from/compare with especially with
large caps as there are residual voltage issues.
I have an old homemade oscillator based L/C bridge measurer which has
very good repeatability and accuracy with small values but relies on
comparison in any range with calibrated standards - it is rough at
anything over 1 uF as far as repeatability goes especially with
electrolytics, over 5uF forget it! ; and this unit was not
particularly cheap or simple to make at the time!
Charlie+
| Quote: | Exactly what I was considering.
Possibly a simple RC inverter oscillator. |
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gmv
Guest
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| Posted:
Sun Feb 06, 2005 10:28 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
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I built a high Q filter circuit and could
get it to ring and when it did it rang
at the correct frequency so I guess my
meter is telling me the truth.
"Charlie+" <charlie@xxx.net> wrote in message news:7jpb01dj59j1lj61np1tjeq5454cqhcnks@4ax.com...
| Quote: | On Sun, 06 Feb 2005 00:59:10 GMT, "gmv" <noemail@please.123> wrote as
underneath my scribble :
Problem is getting your absolute value with a homemade solution unless
you have a calibrated standard to go from/compare with especially with
large caps as there are residual voltage issues.
I have an old homemade oscillator based L/C bridge measurer which has
very good repeatability and accuracy with small values but relies on
comparison in any range with calibrated standards - it is rough at
anything over 1 uF as far as repeatability goes especially with
electrolytics, over 5uF forget it! ; and this unit was not
particularly cheap or simple to make at the time!
Charlie+
Exactly what I was considering.
Possibly a simple RC inverter oscillator.
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