How To Measure A Capacitor With An Oscilloscope.

What do you think about this video?

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 not interesting.

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.

ช่างตั้มมือถือ รับซ่อม iPad iPhone 0846726028: good

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 cyber-teacher. +Awesome

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 formula inversely.

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 timebase. - 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 function gen

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 generator? 

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 recently.

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 :) Good Video!!

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 Ohm.

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 again.

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.

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How to measure a capacitor with an oscilloscope. 4.8 out of 5

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