Chris Gonzales: This was a great exercise. Even with a very basic scope I got reasonable
results ( with practice ). If I had to identify a bag of small "mystery"
caps I would put a bunch in parallel to reduce the error.
Round House: If you overlap vs with vc, you will see that pass the 63% mark, the current
is slowing in transit.
Flapjackbatter: "How to measure a capacitor with an oscilloscope."
Look at the time. 46 minutes. You babble way too much about things that are
Martin Lorton: I go through a practical exercise myself to measure the value of a
capacitor with an oscilloscope. This it to prepare for a future tutorial
and reviews of LCR meters.
Round House: Reducing the lead on the resister will also help. Nice video.
movax20h: Instead of using 63.21% (t = rc), you can use 86.47% (t = 2rc), because
slope of voltage on capacitor is smaller there, so it is easier to find out
exact spot for it. After that you do the same, but devide result by two. c
= t/(2r). Also it is use as wide time division as possible.
Other value to try is 75.00% (t = 1.3863 * rc), or 80.00% (t = 1.6095 * rc)
which should be also easy to setup on a scope.
Another approach is to take data to computer, and fit exponential function
(or linear after taking logarithm). This should be much more accurate and
also give you estimation of error.
Leticia Grantham: Capacitor is fully charged at 5RC?
Matthew McAllister: I don't know if anyone mentioned this yet, but since you were using
multiple resistors you do have to add the values together. If the
resistors are in parallel you add the the resistors inversely
(1/R+1/R)^-1. If the resistors are in series you add the values like you
did in the video (R+R). This could dramatically change the number you get
in your calculations. For example you were using a one megohm resistor and
one kilohm resistor. If they were in series the number you would use for R
in your calculation would be 1,001,000 ohm. If your resistors were in
parallel it would be (1/1000000+1/1000)^-1, which equals approximately 999
ohms. I went back into your video and used 999 ohms in your calculations
and came up with 60 nanoFarads as the value of your capacitor. That is
actually pretty close to the 47 nanoFarad value they list on the package.
Hopefully this was helpful if someone didn't already mention this. Thanks
for the video. I'm trying to figure oscilloscopes out. I found this
Barry Moore: An alternative measurement method is to use a sine wave and a two channel
scope, Place the channel 2 across the cap, and the channel 1 across the
resistor (R) and capacitor (C) in series. Adjust the frequency (F)
until channel 2 is 0.707 of the input (channel 1 value), At this frequency
the capacitive reactance is equal to the resistance of the resistor i.e.
R=1/(2*pi*F*C). As we know R and F we can calculate C. A digital storage
oscilloscope will display accurate peak voltages of the channels. The phase
angle could also be measured as it is exactly 45degrees.
constance washington: their crazy ...i gave a craisen
Bartolomeo Cianciatella: So when the square wave is down to 0, the capacitor is discharging itself
through the resistor and INSIDE the function generator ? Is that ok ? What
would be happen with higher voltages/currents ?
I suppose you could put a diode in series, and take its voltage drop into
Just asking because I'm pretty new to these things.
supershwa: An impressive arsenal of tools on your workbench, and lots of know-how! I
think a 5 minute version based on the [title] of the video would be
helpful, but the long version does show you're qualified as a
ducklandwikeno: Earn Some more biscuit Money what are you taking about
Selim Okutan: thanks for usefull recomandations
sanjursan: Well, it was instructive, but it should have been titled: "How jto measure
a capacitor with an oscilloscope AND a lot of other expensive equipment."
kimarchergy: Just a suggestion, measure the stray capacitance of the leads just as you
have them position on the bench without the Capacitor .Then insert the
Capacitor and test to get the total capacitance and subtract the stray
capacitance value to get the value of the Capacitor under test.
Marcos Ramirez: thank you so much, electronics is amazing!!
Aaron Hayes: The capacitance of the cables leads and breadboard may well higher than
that 4.7pF capacitor.
niceguy60: I know the goal of this video was to use a scope to solve for the capacitor
value but ohms law could have also been used to solve for capacitance by
measuring the voltage drop across the resistor you would have the data to
solve for power which would have given you the current. With series current
and the know voltage drop across the cap you then could have figured out
the reactance and then its just more simple math from there using the
Anthony Stewart: Dear MjL,
The probe capacitance must be observed when measuring capacitance <
100pF. Probe settings for 10:1 will give a higher impedance than 1:1 and
thus lower capacitance.
Harish Kumar: nice one! thank u
zinou sid: thank you so much (good job) (y)
logicsystems paddy: GREAT . VERY NICE WAY EXPLAINED
jeremyhall420: Yes the capicitor is considered fully charged at 5 time constants.
Thijs de Bont: The basic concept is sound, but a few comments though:
- you swapped 63.2 and 62.3 percent at some point.
- you have to take the output impedance of the signal generator into account
- the error margin of the measurement cursors is way to big at the given
- 4.7pF will be swamped by the capacitance of the cables and passive
probes. That's why this method with the given equipment doesn't work on
small value capacitors.
COUZINITROCKS: Another way to do this is to get the wave to fill up 8 divisions on the
scope then just count 5 divisions and read voltage at 5 divisions thats
your one time constant it works because 5/8 is about 62.5 percent and
is an oldschool trick from analog scope days
constance washington: It sounds a little weird--that's just based on the specifications already
existing--why do you have to do the measurement to a specification that
already exists if you can gather the % rate of loss through
electricity...its simple = of transmitting electricity and loss over *_*
metal...wire and transduction**Transduction can refer to: Signal
transduction, any process by which a **_____** converts one kind of signal
or stimulus into another. Here is what I am trying to say.....mmm....that
is specifications and so is = gains --circuit breakers...and
loss---connector-wire-gage-type of metals conductive to energy
transfer...complete circuit...so your calculation would have been already a
specification in the =....im not sure if I said that right ?.......so
physics--mechanical--signals--amplification--are all measurements in the
specifications already included--even in thought**.
constance washington: its a pop quiz like ""speed"" and measurments of velocity...craisens
Chakir El yattafti: Thank you very much. I do believe that the problem you have with 4.7 pF is
due to the reactance of the capacitor become significant big due to this
formula reactance is Xc=1/W.C the reason you did not have a problem with
47nF is because the reactance was low. your Circuit Impedance is
Z=sqrt(R^2+1/W^2*C^2), in order to compensate for the reactance of the
capacitor try to increase the frequency until the term 1/W^2*C^2 in Z
equation get smaller in order to get the impedance as pure resistive as
possible. I hope that helps.You do really great job.
Mark Cummins: I suggest The reason for the noise is because the test circuit has such a
high total impedance and there is no shielding. I suggest that the value of
the resistor and the impedance of the capacitor need to be approximately
the same to get a readable slop. In this case the resistor is about one
meg-ohm then the total circuit impedance will be more than 2 meg-ohms which
was much higher than the clean waveform test circuit impedance. You will
need shielding to get a noise free waveform. You would need to make sure to
decade resistor box was shielded as well. Or you could implement a bandpass
filter on the scope to remove the line power frequency noise and the higher
frequency noise. A much cleaner waveform could be derived if you raised the
testing frequency. This would allow a lower resistor value and because the
capacitor value would be lower in impedance the total circuit impedance
would be lower. This would load down the noise that is induced more and
thus clean up the waveform. But you would have then to be worried that the
capacitance would not be linear. That is to say the capacitance may not be
the same at 1 kHz as it is at 100 kHz. Linearity of the capacitance is
sometimes encountered with old or defective capacitors.
John Miller: Persistence, very interesting video. Thanks
Greg Cunns: Very good. I'm curious, did the probe cable capacitance affect the accuracy
the 47pF test?
As some one else also asked, can you do a ESR tutorial with a scope and
bee Hive: Martin, Can you do video on How to measure ESR using a scope and signal
spectrum1844: Thanks for explaining - how to measure capacitor using scope.Are there
scopes with built in function generators too? What would benefit people
more is if you could present a simple block diagram on paper and show how u
connect the wires for doing the measurements.
TheDkjayjay: hey, u are cooler than cool
got myself a Tektronix TBS 1022 and i love it.
Frank Berry From Upstate NY: Think about adding some "adsorbing dark materials" in your videos...you're
awash in white illumination Bro!
mjlorton: Thanks very much for the feedback.
alongkorn859082: Very nice lab .I like to have it at my home.
mjlorton: Good question! Let me add that to the list.
Retsu Ichijouji: have you checked the total resistance with a meter? maybe that noisy signal
had something to do with end result!
tindelsurf: I made a response to your video on my channel, hopefully it clears up some
of your questions... Good work! I think they removed the video response
cynikalX: glad i'm not the only one who feels this way, i found myself
frustrated/getting impatient hearing the same thing over and over repeated
and everything recounted several times.. and i'm a bit of a beginner myself
so it feels unnecessary :P this 46 minute video could have fit into 15-20
minutes of content easily methinks.. appreciate the effort that went into
making the video as i learned a bit, but might want to work on editing the
content down to just the meat and potatoes please
mjlorton: Thanks...noted and annotation added to your video. Cheers, Martin.
Nerdy Neddy: 47.6 nF assuming a function generator impedance of 50 ohms. Damn close. The
output impedance is in series with the 1 k ohm. cheers
Jeff Blount: My favorite Calculator for electronics work is the Casio 115MS it has short
cut buttons for working with metric prefixes from femto to Tera and it the
correct mode it will give you the result with a prefix instead of
scientific notation. Its also cheep at less than $20 but watch out for the
very similarly named Casio 115ES it trades the metric prefixes for Built in
Conversions for Metric units and US units and built in constants
mjlorton: Thanks for the post William...appreciated. Cheers, Martin.
1madscientist4u: Martin, I just purchased a Rigol DS1102E Scope. I tried to replicate your
method used in this video, but can not seem to place "X" and "Y" cursors on
the screen at the same time. It appears that either "Y" or "X" can be
selected, but not both. Is this correct or am I possibly missing something?
My scope does have a Track function, which does allow both an "X" and "Y"
cursor to perform tracking functions. Any wisdom you could provide would be
greatly appreciated! Thank you in advance! :)
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