| Author |
Message |
gmv
Guest
|
 Posted:
Sun Feb 06, 2005 10:39 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
The attention should be focused on
measuring the C of an electrolytic capacitor.
Can you tell me how to be sure within 1%
the true value of a 10Uf or 100uf cap
when your meter will give you different readings
at different frequencies.
at 80Hz I might get 10u and at 8Hz
I get 11u so which one do I trust ?
I have found the best way to be sure
is to make a filter ring and see if it
rings at the designed center frequency.
I lack the proper test equipment so I got be
imaginative.
"Fred Abse" <excretatauris@cerebrumconfus.it> wrote in message news:pan.2005.02.05.19.01.32.904972@cerebrumconfus.it...
| Quote: | On Sat, 05 Feb 2005 09:21:02 -0800, Watson A.Name - "Watt Sun, the Dark
Remover" wrote:
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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|
 |
Watson A.Name - \"Watt Su
Guest
|
| Posted:
Mon Feb 07, 2005 12:13 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"gmv" <noemail@please.123> wrote in message
news:jJdNd.21541$C24.9629@attbi_s52...
| Quote: | Interesting,
I always thought the opamp buffered the output
so you could hook it to anything between 2K
and infinity.
I will keep in mind what you have said.
I have noticed a terrible ringing effect at Q
5 and above.
Maybe that is what you are talking about.
In any case I really need to see things between .5Hz
and 2Hz. It is only the noise in my local area that
keeps me from doing this as far as I can tell.
http://home.mchsi.com/~gmvoeth/index.html
will show a bit more of what I am doing.
|
Buy the RS printed circuit board that has the same layout as the
breadoard. Build the circuit on that board, and put it inside of a
metal enclosure, so that most of the noise is kept out of the circuit.
All preamplification should be done as close as possible to the
geophone, to get the signal well above the noise _before_ it goes any
distance.
Filtering should be done at the other end, to get rid of noise in the
long transmission line between the sensor and the PC.
One other important point. The outside can of the electrolytic is at
signal level, and is a large capacitance to the outside world. Just
shielding these from outside noise should help. You might consider
putting some aluminum foil over the ones at the input, and grounding the
foil to common. Just to see how much it will help to put the whole
thing in an enclosure.
| Quote: | "Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in message news:1109v26sjt1i70c@corp.supernews.com...
"gmv" <noemail@please.123> wrote in message
news:EJ1Nd.51210$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)
|
|
|
| Back to top |
|
|
Watson A.Name - \"Watt Su
Guest
|
| Posted:
Mon Feb 07, 2005 12:18 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"Fred Abse" <excretatauris@cerebrumconfus.it> wrote in message
news:pan.2005.02.05.19.01.32.904972@cerebrumconfus.it...
| Quote: | On Sat, 05 Feb 2005 09:21:02 -0800, Watson A.Name - "Watt Sun, the
Dark
Remover" wrote:
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?
--
|
Or more like when does the variation of the current become slow enough
to allow the chemicals time to react, and change the capacitor?
|
|
| Back to top |
|
|
Fred Abse
Guest
|
| Posted:
Mon Feb 07, 2005 2:20 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
On Sun, 06 Feb 2005 16:39:34 +0000, gmv wrote:
| Quote: | The attention should be focused on
measuring the C of an electrolytic capacitor. Can you tell me how to be
sure within 1% the true value of a 10Uf or 100uf cap when your meter will
give you different readings at different frequencies.
at 80Hz I might get 10u and at 8Hz
I get 11u so which one do I trust ?
|
Both, if your measuring instrument is any good. The capacitance of
electrolytics *does* vary with applied frequency, though usually not as
much as 10% over a decade. What sort of instrument is it? Does it polarize
the capacitor?
| Quote: | I have found the best way to be sure
is to make a filter ring and see if it rings at the designed center
frequency. I lack the proper test equipment so I got be imaginative.
|
That's a sensible approach.
--
Then there's duct tape ...
(Garrison Keillor) |
|
| Back to top |
|
|
gmv
Guest
|
| Posted:
Mon Feb 07, 2005 9:51 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote in message news:110cnbn267cd7fe@corp.supernews.com...
| Quote: |
"gmv" <noemail@please.123> wrote in message
news:jJdNd.21541$C24.9629@attbi_s52...
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.
Buy the RS printed circuit board that has the same layout as the
breadoard. Build the circuit on that board, and put it inside of a
metal enclosure, so that most of the noise is kept out of the circuit.
|
What is "RS printed circuit board " ?
I have settled on using only a single filter
as is now posted to my web site. This will
limit one to only seeing P waves but in
this noisy environment it is the best I can do.
I agree with everything you say except I can not
put a preamp outside with the Geophone.
There is a circuit I have included not on the
schematic and it is a 567 tone decoder on the back
end to decode WWV calibration marks.
Thanks for your advice, I can see a lot of
common sense to it. But I still do not
know how to buy a circuit board that already
has my layout on it. I figure I will have
to do the layout and etching etc... myself.
| Quote: |
All preamplification should be done as close as possible to the
geophone, to get the signal well above the noise _before_ it goes any
distance.
Filtering should be done at the other end, to get rid of noise in the
long transmission line between the sensor and the PC.
One other important point. The outside can of the electrolytic is at
signal level, and is a large capacitance to the outside world. Just
shielding these from outside noise should help. You might consider
putting some aluminum foil over the ones at the input, and grounding the
foil to common. Just to see how much it will help to put the whole
thing in an enclosure.
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in message news:1109v26sjt1i70c@corp.supernews.com...
"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)
|
|
|
| Back to top |
|
|
Jamie
Guest
|
| Posted:
Tue Feb 08, 2005 3:06 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
gmv wrote:
| Quote: | 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.
have you thought of looking into doing some FFT (DFT) code? |
i don't know exactly what your doing but, its also possible to
to mix your input signal to generate a much higher signal.
something like the use of a LM1496 comes to mind. |
|
| Back to top |
|
|
loedown
Guest
|
| Posted:
Tue Feb 08, 2005 4:22 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
Hi All,
I know very little about radio and the like, but could some form
of superheterodyning be done in this instance, the idea of AM, or FM to
combine the slow signal with much higher frequency?
Paul |
|
| Back to top |
|
|
gmv
Guest
|
| Posted:
Tue Feb 08, 2005 6:45 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
Yes I think I understand what you mean
but i want to remain baseband at the moment.
The FFT will do no good for my purposes
except to identify the noise I am
fighting. I already know the noise is betweeen
2.5 Hz and 15 Hz that is causing my troubles.
But you got to realize a geophone is
most sensitive above its resonant freq
and that is the whole root of my troubles.
What Im trying to do is make a circuit that will
squish the noise down from the sensor so i can boost
those freqs I really want to see.
This noise is overwhelming it will jam all else
I am trying to look at. It is caused by human
activity and short of driving off most the people but me
in this town there is little i can do to stop it.
The high freqs will drive my amplifier into
saturation and cutoff so when that happens
it is no good for seeing anything but the harmonics
of the noise.
This time of year is the worst because all
the tourists are in town and it swells our
population to more than twice its normal size.
I find this problem interesting and have decided
to use a narrow band filter with a Q about 1 and
centered about 1/1.5Hz and at the moment that is
the very best I can do. I have found using more than
one filter in parallel only serves to complicate
the grams I am trying to achieve.
Thanks for your input.
"Jamie" <jamie_5_not_valid_after_5_Please@charter.net> wrote in message news:iJNNd.33372$3m.15296@fe06.lga...
| Quote: | gmv wrote:
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.
have you thought of looking into doing some FFT (DFT) code?
i don't know exactly what your doing but, its also possible to
to mix your input signal to generate a much higher signal.
something like the use of a LM1496 comes to mind.
|
|
|
| Back to top |
|
|
gmv
Guest
|
| Posted:
Tue Feb 08, 2005 6:51 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
I call that frequency translation but it will not work here
because the problem lies in the sensitivity profile of the sensor
itself.
I need to squish down the normal operating range
of the geophone so I can look at the signals
riding underneath the resonant point.
What I call equalization seems to work which is using
a LPF with a CF under the range you want to view
It serves to push down everything over the rolloff
including the noise you want to squish.
Then the range between the rolloff and resonance becomes
somewhat flat in response.
Thanks for your input.
"loedown" <zero242@internode.on.net> wrote in message news:4207ea40$1@duster.adelaide.on.net...
| Quote: | Hi All,
I know very little about radio and the like, but could some form of superheterodyning be done in this instance, the
idea of AM, or FM to combine the slow signal with much higher frequency?
Paul
|
|
|
| Back to top |
|
|
Watson A.Name - \"Watt Su
Guest
|
| Posted:
Tue Feb 08, 2005 4:28 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"gmv" <noemail@please.123> wrote in message
news:J7MNd.24453$C24.9065@attbi_s52...
| Quote: |
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in message news:110cnbn267cd7fe@corp.supernews.com...
"gmv" <noemail@please.123> wrote in message
news:jJdNd.21541$C24.9629@attbi_s52...
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.
Buy the RS printed circuit board that has the same layout as the
breadoard. Build the circuit on that board, and put it inside of a
metal enclosure, so that most of the noise is kept out of the
circuit.
What is "RS printed circuit board " ?
|
RS = Radio Shack AKA Radio Scrap, etc. They sell a PC board that has
the same layout as the breadboard. Makes it easy to transfer the
circuit to a permanent circuit board.
| Quote: | I have settled on using only a single filter
as is now posted to my web site. This will
limit one to only seeing P waves but in
this noisy environment it is the best I can do.
I agree with everything you say except I can not
put a preamp outside with the Geophone.
|
Well, that's probably the reason why you are getting so much noise!
| Quote: | There is a circuit I have included not on the
schematic and it is a 567 tone decoder on the back
end to decode WWV calibration marks.
Thanks for your advice, I can see a lot of
common sense to it. But I still do not
know how to buy a circuit board that already
has my layout on it. I figure I will have
to do the layout and etching etc... myself.
|
I'm not sure you understand. The hole patterns match those on the
breadboard.
Here it is, it's catalog # 276-170 and costs a bit over $3.
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fnam
e=CTLG%5F011%5F002%5F002%5F000&product%5Fid=276%2D170&MSCSProfile=745D84
CBF04D14A48AA6FF9C89D722C0BA68C1B04FE384678A5285FCD6E056B17AF21627FDABE3
16B90B3C038D68EBD6B7F9F3BD1712EAA9951ACB2590A05C6517EFE46941FEFDD1985D4E
FD6321F5E70B4DE9B6C1D45512DCD9FB3DBCACB9479D26760FAF1D7B193B4FEA078B5E09
80BDD61634ABB7D328B012D36915420A2B457BE162481F674B
| Quote: | All preamplification should be done as close as possible to the
geophone, to get the signal well above the noise _before_ it goes
any
distance.
Filtering should be done at the other end, to get rid of noise in
the
long transmission line between the sensor and the PC.
One other important point. The outside can of the electrolytic is
at
signal level, and is a large capacitance to the outside world. Just
shielding these from outside noise should help. You might consider
putting some aluminum foil over the ones at the input, and grounding
the
foil to common. Just to see how much it will help to put the whole
thing in an enclosure.
|
[snip] |
|
| Back to top |
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|
Watson A.Name - \"Watt Su
Guest
|
| Posted:
Tue Feb 08, 2005 4:31 pm Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
"loedown" <zero242@internode.on.net> wrote in message
news:4207ea40$1@duster.adelaide.on.net...
| Quote: | Hi All,
I know very little about radio and the like,
|
Yeah. I guess not.
| Quote: | but could some form
of superheterodyning be done in this instance, the idea of AM, or FM
to
combine the slow signal with much higher frequency?
|
If you mix the signal with a much higher freq, then the bandwidth of the
filter has to be much, much narrower. Which then makes filtering that
much more difficult.
> Paul |
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| Back to top |
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gmv
Guest
|
| Posted:
Wed Feb 09, 2005 12:15 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
I think this is the link you mean:
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F011%5F002%5F002%5F000&product%5Fid=276%2D170
The one you gave me would not function.
Yes, I will eventually do this.
I am still debating whether or not to use
what I call equalization in my circuit.
Thanks for your input.
--
Regards;
gmv
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote in message news:110h4qnsbpb3rf2@corp.supernews.com...
| Quote: |
"gmv" <noemail@please.123> wrote in message
news:J7MNd.24453$C24.9065@attbi_s52...
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in message news:110cnbn267cd7fe@corp.supernews.com...
"gmv" <noemail@please.123> wrote in message
news:jJdNd.21541$C24.9629@attbi_s52...
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.
Buy the RS printed circuit board that has the same layout as the
breadoard. Build the circuit on that board, and put it inside of a
metal enclosure, so that most of the noise is kept out of the
circuit.
What is "RS printed circuit board " ?
RS = Radio Shack AKA Radio Scrap, etc. They sell a PC board that has
the same layout as the breadboard. Makes it easy to transfer the
circuit to a permanent circuit board.
I have settled on using only a single filter
as is now posted to my web site. This will
limit one to only seeing P waves but in
this noisy environment it is the best I can do.
I agree with everything you say except I can not
put a preamp outside with the Geophone.
Well, that's probably the reason why you are getting so much noise!
There is a circuit I have included not on the
schematic and it is a 567 tone decoder on the back
end to decode WWV calibration marks.
Thanks for your advice, I can see a lot of
common sense to it. But I still do not
know how to buy a circuit board that already
has my layout on it. I figure I will have
to do the layout and etching etc... myself.
I'm not sure you understand. The hole patterns match those on the
breadboard.
Here it is, it's catalog # 276-170 and costs a bit over $3.
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fnam
e=CTLG%5F011%5F002%5F002%5F000&product%5Fid=276%2D170&MSCSProfile=745D84
CBF04D14A48AA6FF9C89D722C0BA68C1B04FE384678A5285FCD6E056B17AF21627FDABE3
16B90B3C038D68EBD6B7F9F3BD1712EAA9951ACB2590A05C6517EFE46941FEFDD1985D4E
FD6321F5E70B4DE9B6C1D45512DCD9FB3DBCACB9479D26760FAF1D7B193B4FEA078B5E09
80BDD61634ABB7D328B012D36915420A2B457BE162481F674B
All preamplification should be done as close as possible to the
geophone, to get the signal well above the noise _before_ it goes
any
distance.
Filtering should be done at the other end, to get rid of noise in
the
long transmission line between the sensor and the PC.
One other important point. The outside can of the electrolytic is
at
signal level, and is a large capacitance to the outside world. Just
shielding these from outside noise should help. You might consider
putting some aluminum foil over the ones at the input, and grounding
the
foil to common. Just to see how much it will help to put the whole
thing in an enclosure.
[snip]
|
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| Back to top |
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Rich Grise
Guest
|
| Posted:
Wed Mar 02, 2005 2:38 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
On Sat, 05 Feb 2005 09:06:45 -0800, Watson A.Name - "Watt Sun, the Dark
| Quote: | "gmv" <noemail@please.123> wrote in message
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
"gmv" <noemail@please.123> wrote in message
....
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.
|
They are not. They are oil-filled paper. I don't understand the
"too high power", unless you mean simply that they're big fat
things. But they _do_ capacitate!
Aren't there digital filters that you can tailor the response
with smaller caps?
Good Luck!
Rich |
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Rich Grise
Guest
|
| Posted:
Wed Mar 02, 2005 2:45 am Post subject:
Re: Accurately measure C of electrolytic capacitors ? |
|
|
On Sat, 05 Feb 2005 10:41:43 +0000, gmv wrote:
| Quote: | "Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote in message news:11094u4911pj497@corp.supernews.com...
....
Anyway, what you need to do is use a mechanical filter, instead of
trying to make an electronic filter. One thought comes to mind. Use a
speaker and microphone coupled by a mechanical link, and add weight to
that link so that it would only respond to freqs below some low value,
such as 1 Hz. This also makes it a bandpass filter.
That sounds quite a bit more complex to me
then what I am already doing quite successfully.
|
Why not add some mass to the geophone itself? Do you have any pictures
of it, or design notes or anything?
Thanks,
Rich |
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