Paul Collins: I happy to say I enjoyed the video very much
Flapjackbatter: "How to measure a capacitor with an oscilloscope."
Look at the time. 46 minutes. You babble way too much about things that are
Round House: Reducing the lead on the resister will also help. Nice video.
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.
aaron medina: Great
Round House: If you overlap vs with vc, you will see that pass the 63% mark, the current
is slowing in transit.
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.
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
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.
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."
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.
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.
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
shy zullo: its a pop quiz like ""speed"" and measurments of velocity...craisens
Leticia Grantham: Capacitor is fully charged at 5RC?
jeremyhall420: Yes the capicitor is considered fully charged at 5 time constants.
John Miller: Persistence, very interesting video. Thanks
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.
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.
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
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.
bee Hive: Martin, Can you do video on How to measure ESR using a scope and signal
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.
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.
freeman67891011: I have the same oscilloscope and its possible. Once you turn on Track
function, look for the ΔX in the information box. That's the time
difference between the 2 cursors. ΔY is the Voltage difference.
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! :)
james b: No problem with video length. The alternative is to remove footage that
some of us findd
Yoram Stein: Hello Lorton - your dacade box inserts lots of noise just use a singel
resistor with a high accuracy in serie.
Ashwin Bhat: I would say you can consider the point where its fully charged and then
make an approximation of ' 5T=RC ' and work your way in finding C, this
works fairly good given then 1 to 10% tolerances of normal resistors :)
kaihua cheng: after watched ur video,i found my school lecture is a piece of crap. u have
patient,and good attitude. really like the way u speak. keep it up
mjlorton: Thanks for the post...I checked it several times to make sure and it is 1M
Wharpt: You might want to try your setup with no capacitor and see how much
capacitance is inherent in your setup I'll bet it's around 55 pf.
Chad Moore: Too long and drawn out
Kevin Cho: Very Impressive Video. Thanks. Actually I'm considering to buy LCR meter
these days. However it's really expensive but I used very rarely. Your
Great Video saved my money and teach me how to use my scope. Thank you
William Sledge: Thank you Martin. I enjoy your videos very much and find them very
enlightening. Above all you are extremely kind and sensitive to your
viewers and assume them to be with it, this is one of the reasons you
shine. As I view your presentations I sense a generous collaborative spirit
as you plunge into your latest ideas with your great toys.
Retsu Ichijouji: 30:23 Is that resistor 4th band green or is it yellow mixing with the blue
color giving a green impression? It looks green to me, maybe I'm wrong. but
if it was green the result capacitance will be 5.99 pF
THEDOGBOYS3: Martin, Welcome to the USA ! Hope all went well with your move. I am glade
you can get back down to business. I just purchased a function gen. and
want to see the different things that I can do with it. I bought it for
radio work but want to apply it to electronics. Keeping up with your site,
like to see more of this. Just ordered a stepper motor to see how generator
will control the motor. I think you did a vid on this? Keep the fate. TDB3
mjlorton: You are correct...the cheaper scopes can't do both at the same time...I
will highlight this in a future video. Cheers, Martin.