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LCR Meter using Sound Card - revisited
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RobertMacy
Jan 23, 2014, 9:26:50 AM1/23/14
to
I just set up one of my soundcards to do LCR measurements. I took an old
radial lead cap from bench marked 1100 uF, 35Vdc, and I mean old. I
purposely measured using too large a series resistor, 10k, which became
immediately apparent from the 'ratty' results. Toned it back down to 220
ohm, still too large, but the results were 'cleaner'.
Did not verify the methodology a lot, easier to ask this knowledgeable
group about the results. The results were somewhat as expected.
Cap measured, approx 890uF, with Resr approx 90 milliohms.
with age and never having voltage previously applied, the low value seemed
appropriate (maybe)
the Resr was disappointly high, but as expected. too
But what I saw regarding characteristics vs freq I don't know are true, or
are these artifacts of what I did.
The plot of C vs log(f) produced a rather linear straight line descending
down as freq went up.
The plot of log(Resr-offset) vs log(f) also had a similar straight line.
with offset slightly less that 84 milliohms
QUESTION:
Are these relationships real, or artifacts of technqiue and/or accuracy?
For example, the Q of this cap at 20 Hz is around 25, so it didn't seem
reasonable that the soundcard couldn't pick up the phase well enough to
discern the Resr there, but Resr had increased at the lower frequency to
around 100-200 milliohms [forgot which now!]
Also, C droppoed to around 830uF going up infreq and looked like it was
asymptotically approaching 900+uF going down to '0' freq. But again, the
Xc is very small compared to the Resr as you go up, so the values could be
in question.
My point is, are the values about right or should I comb through the
measurement technique?
PS: Earlier I said you needed a good VTVM to measure voltage and
resistance. WRONG! Using soundcard for measuring C you only need a pure
resistance of known value. You don't need to know ANYTHING else. assuming
your soundcard's frequency is accurate :) Should be able to get better
than 0.1% accuracy, too.
radial lead cap from bench marked 1100 uF, 35Vdc, and I mean old. I
purposely measured using too large a series resistor, 10k, which became
immediately apparent from the 'ratty' results. Toned it back down to 220
ohm, still too large, but the results were 'cleaner'.
Did not verify the methodology a lot, easier to ask this knowledgeable
group about the results. The results were somewhat as expected.
Cap measured, approx 890uF, with Resr approx 90 milliohms.
with age and never having voltage previously applied, the low value seemed
appropriate (maybe)
the Resr was disappointly high, but as expected. too
But what I saw regarding characteristics vs freq I don't know are true, or
are these artifacts of what I did.
The plot of C vs log(f) produced a rather linear straight line descending
down as freq went up.
The plot of log(Resr-offset) vs log(f) also had a similar straight line.
with offset slightly less that 84 milliohms
QUESTION:
Are these relationships real, or artifacts of technqiue and/or accuracy?
For example, the Q of this cap at 20 Hz is around 25, so it didn't seem
reasonable that the soundcard couldn't pick up the phase well enough to
discern the Resr there, but Resr had increased at the lower frequency to
around 100-200 milliohms [forgot which now!]
Also, C droppoed to around 830uF going up infreq and looked like it was
asymptotically approaching 900+uF going down to '0' freq. But again, the
Xc is very small compared to the Resr as you go up, so the values could be
in question.
My point is, are the values about right or should I comb through the
measurement technique?
PS: Earlier I said you needed a good VTVM to measure voltage and
resistance. WRONG! Using soundcard for measuring C you only need a pure
resistance of known value. You don't need to know ANYTHING else. assuming
your soundcard's frequency is accurate :) Should be able to get better
than 0.1% accuracy, too.
Maynard A. Philbrook Jr.
Jan 23, 2014, 7:37:13 PM1/23/14
to
In article <op.w94820fg2cx0wh@ajm>, robert...@gmail.com says...
Jamie
> My point is, are the values about right or should I comb through the
> measurement technique?
>
>
> PS: Earlier I said you needed a good VTVM to measure voltage and
> resistance. WRONG! Using soundcard for measuring C you only need a pure
> resistance of known value. You don't need to know ANYTHING else. assuming
> your soundcard's frequency is accurate :) Should be able to get better
> than 0.1% accuracy, too.
>
>
>
Did you consider induction ?
> measurement technique?
>
>
> PS: Earlier I said you needed a good VTVM to measure voltage and
> resistance. WRONG! Using soundcard for measuring C you only need a pure
> resistance of known value. You don't need to know ANYTHING else. assuming
> your soundcard's frequency is accurate :) Should be able to get better
> than 0.1% accuracy, too.
>
>
>
Jamie
whit3rd
Jan 23, 2014, 7:47:04 PM1/23/14
to
On Thursday, January 23, 2014 6:26:50 AM UTC-8, Robert Macy wrote:
> I just set up one of my soundcards to do LCR measurements. I took an old
> radial lead cap from bench marked 1100 uF, 35Vdc, and I mean old. I
> purposely measured using too large a series resistor, 10k, which became
> immediately apparent from the 'ratty' results. Toned it back down to 220
> ohm,...
> I just set up one of my soundcards to do LCR measurements. I took an old
> radial lead cap from bench marked 1100 uF, 35Vdc, and I mean old. I
> purposely measured using too large a series resistor, 10k, which became
> immediately apparent from the 'ratty' results. Toned it back down to 220
> Cap measured, approx 890uF, with Resr approx 90 milliohms.
> The plot of C vs log(f) produced a rather linear straight line descending
> down as freq went up.
Probably the capacitor is intended for power supply filtering (120 Hz),
> down as freq went up.
and you are seeing inductive impedance. Mostly, such capacitors are spiral
wrapped (though stacked-foil is available for higher frequency applications).
Your measurement, if it includes phase shift as well as 'C value' should
deviate from the lagging-by-90-degrees phase shift of a capacitor, for the
higher frequency values, if this is the case.
"Müller, Frank-Stefan (MRT)"
Jan 24, 2014, 5:34:49 AM1/24/14
to
Hi,
I missed the original posting of this thread, so I missed the reference
to the software used. I tried a similar approach from "ELEKTOR"
magazine, but the program (written in Java script) didn´t run proberly
on my PC. I think the idea of using a soundcard for impedance
measuremenrt is VERY clever and would like to use it.
Can anybody send me the original posting or a link to it?
Frank
I missed the original posting of this thread, so I missed the reference
to the software used. I tried a similar approach from "ELEKTOR"
magazine, but the program (written in Java script) didn´t run proberly
on my PC. I think the idea of using a soundcard for impedance
measuremenrt is VERY clever and would like to use it.
Can anybody send me the original posting or a link to it?
Frank
RobertMacy
Jan 24, 2014, 9:27:04 AM1/24/14
to
On Fri, 24 Jan 2014 03:34:49 -0700, Müller, Frank-Stefan (MRT)
<mue...@mrt.uka.de> wrote:
> Hi,
> I missed the original posting of this thread, so I missed the reference
> to the software used. I tried a similar approach from "ELEKTOR"
> magazine, but the program (written in Java script) didn?t run proberly
<mue...@mrt.uka.de> wrote:
> Hi,
> I missed the original posting of this thread, so I missed the reference
> to the software used. I tried a similar approach from "ELEKTOR"
> on my PC. I think the idea of using a soundcard for impedance
> measuremenrt is VERY clever and would like to use it.
> Can anybody send me the original posting or a link to it?
>
> Frank
Frank, feel free to contact me offline to discuss in detail. You're in
> measuremenrt is VERY clever and would like to use it.
> Can anybody send me the original posting or a link to it?
>
> Frank
Germany! I use the streaming audio interface from Steinberg, called ASIO.
Well done package. I then wrote C/C++ code to exercise that interface and
control my soundcard directly, make it do EXACTLY what I need, and then
provide back the resulting values.
For other posters I was planning on measuring 'equivalent' inductance in
future testing expecting less than 100nH. Usually, inductance rears its
ugly head as a rise in impedance as you go up in frequency, but just
didn't seem to show up here. So ignored it partially to 'simplify' the
resulting model,which just made last night.
Over freq range of 20 to 1000 Hz, using 220 ohm resistor:
The best curve fit to the data for this antique part using a series Resr
and C:
Resr = 80 milliohm + 5/f, I'm NOT kidding! where did THIS come from? It's
like my measuring technique got drug into it.
C = 1e6*(888.34 - 34.8*log10(f/20)), again could be due to the accuracy
going away as you go up in frequency.
For those who don't undertand how to use their sound card to measure an
unknown impedance:
[Note: the system has higher range, and rejects AC mains better when used
as a 'balanced' system; it's far easier to work with if you set up the
card in 'unbalanced' mode. requires only a single resistor, not two,
'absolutely' equal resistors. Smaller range, just easier to work with.]
Find a great broadband resistor of KNOWN value, 0.01%, or 0.05% if you got
it, or measure a 1% one and note its R
Then use the output of one channel to drive, provide the signal source
Now using the two input channels perform the following:
connect L & R to the output to calibrate the two channels
connect L to the drive and then resistor to R to calibrate the input
impedance of R, knowing the value of R
connect the unknown component across R's input
The first calibrates L channel and R channel to be identical voltmeters.
The second calculates the input impedance of the R channel so you can
remove that value later.
[for my soundcard a close fitting model was around 10.094k with a parallel
capacitance of around 0.002384uF in series with 132.2 ohm resistor (fit
within 0.04% window over the range of interest), which closely matched the
manual's desc. of 10k in parallel with 0.0025uF
The third step provides the data to then be manipulated to find what
impedance was added.
Simple.
You can store the values in a fileand reload for continually running Step
3, or Initialize once and continually run Step 3. I recommend running Step
1 and then Step 2 each time you have turned on your system, let it warm up
[about an hour], and then want to take measurements. The accuarcy is high,
you can still see drift in the ppm after letting sit there for a couple
hours. But is ok, because if you touch your sense resistor, its tempco
will swamp that out. I even see the change caused by holding my fingers
within a 1/4 inch of the setup during measurements. Don't even get me
started on the effect of using your fingers to hold the cap under test! I
digress.
But I wonder if somewhere during all this process. I missed something that
injects a frequency dependent term erroneously in there. Any help
appreciated.
For example, removing the frequency sensitive term from Resr and assuming
80 milliohms, and moving that term over to the C, makes C become sensitive
to frequncy instead of log(frequency), kind of.
QUESTION:
Does anybody KNOW what values I should be obtaining?
Jan Panteltje
Jan 24, 2014, 10:07:25 AM1/24/14
to
On a sunny day (Fri, 24 Jan 2014 07:27:04 -0700) it happened RobertMacy
<robert...@gmail.com> wrote in <op.w963regy2cx0wh@ajm>:
>future testing expecting less than 100nH. Usually, inductance rears its
>ugly head as a rise in impedance as you go up in frequency, but just
>didn't seem to show up here. So ignored it partially to 'simplify' the
>resulting model,which just made last night.
>
>Over freq range of 20 to 1000 Hz, using 220 ohm resistor:
>
>The best curve fit to the data for this antique part using a series Resr
>and C:
>
>Resr = 80 milliohm + 5/f, I'm NOT kidding! where did THIS come from? It's
>like my measuring technique got drug into it.
>C = 1e6*(888.34 - 34.8*log10(f/20)), again could be due to the accuracy
>going away as you go up in frequency.
>
>For those who don't undertand how to use their sound card to measure an
>unknown impedance:
Circuit diagram would help...
<robert...@gmail.com> wrote in <op.w963regy2cx0wh@ajm>:
>future testing expecting less than 100nH. Usually, inductance rears its
>ugly head as a rise in impedance as you go up in frequency, but just
>didn't seem to show up here. So ignored it partially to 'simplify' the
>resulting model,which just made last night.
>
>Over freq range of 20 to 1000 Hz, using 220 ohm resistor:
>
>The best curve fit to the data for this antique part using a series Resr
>and C:
>
>Resr = 80 milliohm + 5/f, I'm NOT kidding! where did THIS come from? It's
>like my measuring technique got drug into it.
>C = 1e6*(888.34 - 34.8*log10(f/20)), again could be due to the accuracy
>going away as you go up in frequency.
>
>For those who don't undertand how to use their sound card to measure an
>unknown impedance:
RobertMacy
Jan 24, 2014, 10:39:25 AM1/24/14
to
On Fri, 24 Jan 2014 08:07:25 -0700, Jan Panteltje
<pNaonSt...@yahoo.com> wrote:
>> ...snip...
> Circuit diagram would help...
Thought word description was enough.
I can't post a picture onto a 'service' website. Often can't even retrieve
pics from them.
so here is the ascii stuff: Rsens is added known resistor, DL is drive
FROM soundcard, L & R are the input channels TO the soundcard.
Step 1, Calibrate L & R channels
DL --+--+
| |
L R
Step 2. Find Input Impedance of R soundcard
Rsens
DL --+--/\/\/\---+
| |
L R
Step 3. Measure capacitor
Rsens
DL --+--/\/\/\---+----+
| | |
| | === Cmeas
| | |
L R GND
The equivalent input impedance of the R channel is
----+-------------+
| |
| |
| |
| === 0.0025uF
| |
/ |
\ |
/ 10k /
\ \
/ / 130
| \
| /
| |
| |
| |
| |
GND GND
and the model for C
||
-------||-----/\/\/\-------
||
C Resr
hope this helps, but sure thought the verbal description was sufficient.
<pNaonSt...@yahoo.com> wrote:
>> ...snip...
> Circuit diagram would help...
Thought word description was enough.
I can't post a picture onto a 'service' website. Often can't even retrieve
pics from them.
so here is the ascii stuff: Rsens is added known resistor, DL is drive
FROM soundcard, L & R are the input channels TO the soundcard.
Step 1, Calibrate L & R channels
DL --+--+
| |
L R
Step 2. Find Input Impedance of R soundcard
Rsens
DL --+--/\/\/\---+
| |
L R
Step 3. Measure capacitor
Rsens
DL --+--/\/\/\---+----+
| | |
| | === Cmeas
| | |
L R GND
The equivalent input impedance of the R channel is
----+-------------+
| |
| |
| |
| === 0.0025uF
| |
/ |
\ |
/ 10k /
\ \
/ / 130
| \
| /
| |
| |
| |
| |
GND GND
and the model for C
||
-------||-----/\/\/\-------
||
C Resr
hope this helps, but sure thought the verbal description was sufficient.
Jan Panteltje
Jan 24, 2014, 11:09:59 AM1/24/14
to
On a sunny day (Fri, 24 Jan 2014 08:39:25 -0700) it happened RobertMacy
<robert...@gmail.com> wrote in <op.w9663zko2cx0wh@ajm>:
I understand this so far,
you measure the current in the series RC at some frequency,
and from that calculate losses in C?
My test is always differential scope probe on each side of C,
if you see fast edges then C is kaput ;-)
Can be done in circuit, live.
I do not usually give a ... what the exact 'ESR' is, or whatever,
it can take many forms,
I have seen electrolytics go inductive if the foil
on the edge was not making good contact, what not.
The important point is that a C should be a C only, and at the value written on it.
This aloso works for a C out of circuit:
scope 1V calibration square wave output ---->------->-- ch 1 input
|
---
--- C under test (elco)
|
///
If you see fast edges than C is kaput...
For smaller Ls and Cs I build this LC meter, very good actually:
http://panteltje.com/panteltje/pic/lc_pic/
<robert...@gmail.com> wrote in <op.w9663zko2cx0wh@ajm>:
you measure the current in the series RC at some frequency,
and from that calculate losses in C?
My test is always differential scope probe on each side of C,
if you see fast edges then C is kaput ;-)
Can be done in circuit, live.
I do not usually give a ... what the exact 'ESR' is, or whatever,
it can take many forms,
I have seen electrolytics go inductive if the foil
on the edge was not making good contact, what not.
The important point is that a C should be a C only, and at the value written on it.
This aloso works for a C out of circuit:
scope 1V calibration square wave output ---->------->-- ch 1 input
|
---
--- C under test (elco)
|
///
If you see fast edges than C is kaput...
For smaller Ls and Cs I build this LC meter, very good actually:
http://panteltje.com/panteltje/pic/lc_pic/
RobertMacy
Jan 24, 2014, 1:37:26 PM1/24/14
to
On Fri, 24 Jan 2014 09:09:59 -0700, Jan Panteltje
<pNaonSt...@yahoo.com> wrote:
>> ...snip...
C, Resr, R dielctric loss, L
> ...snip....
It's just in my old age, I'm getting lazy about building hardware! Plus,
the soundcard can get you beyond 0.005% relative accuracy comparing parts
and with a good R can get to 0.01%, even finding the Capacitance value, or
inductor value.
range of C from 100,000 uF down to less than 100 pF To do with one machine
is handy.
<pNaonSt...@yahoo.com> wrote:
>> ...snip...
> I understand this so far,
> you measure the current in the series RC at some frequency,
> and from that calculate losses in C?
>
Yes, including FULL characterization over the whole spectrum.
> you measure the current in the series RC at some frequency,
> and from that calculate losses in C?
>
C, Resr, R dielctric loss, L
> ...snip....
>
> If you see fast edges than C is kaput...
>
>
> For smaller Ls and Cs I build this LC meter, very good actually:
> http://panteltje.com/panteltje/pic/lc_pic/
>
Neat circuit and construction, thanks for sharing!
> If you see fast edges than C is kaput...
>
>
> For smaller Ls and Cs I build this LC meter, very good actually:
> http://panteltje.com/panteltje/pic/lc_pic/
>
It's just in my old age, I'm getting lazy about building hardware! Plus,
the soundcard can get you beyond 0.005% relative accuracy comparing parts
and with a good R can get to 0.01%, even finding the Capacitance value, or
inductor value.
range of C from 100,000 uF down to less than 100 pF To do with one machine
is handy.
Jan Panteltje
Jan 24, 2014, 5:10:16 PM1/24/14
to
On a sunny day (Fri, 24 Jan 2014 11:37:26 -0700) it happened RobertMacy
<robert...@gmail.com> wrote in <op.w97fcpq82cx0wh@ajm>:
Yes that is a huge range, I do not think I have 100,000 uF in the box...
<robert...@gmail.com> wrote in <op.w97fcpq82cx0wh@ajm>:
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