How To Measure A Capacitor With An Oscilloscope.




What do you think about this video?

Jeff Burris: I have o-scopes but I don't have a dedicated function generator per say (as a test instrument made for the purpose). Until I do (like tonight, now, in a pinch ) perhaps this video can get me testing capacitance nonetheless, using something on hand, like maybe a receiver or transmitter receiving or transmitting a plain carrier or consistent signal (not Beethoven's 5th) :) I'm not trying to calibrate instruments, rather, I just need to get approximate readings on hand-made air capacitors for value. I want to make a rotary but instead of flat vanes use concave soda can bottoms (novelty, for antenna tuning with a coil)... can bottoms for both stator & rotor vanes (I know I can't offset them but spindle through the middle should be fine :) :) o man I can maybe measure inductance of the coil, too, without buying an LCR meter this week (my multi has neither) THANK YOU (subscribing). Between you and Ray Heffer I'm in high cotton.

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

Gabriele Barbaraci: finally I have seen someone explaining the things how must be done!!!!

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.

Nouman tajik: Thanks for tutorials, It is Really Helpful, Good Luck :)

Ahmed Abdalsalam: thanks for your effort.

Harish Kumar: nice one! thank u

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.

Paul Collins: I happy to say I enjoyed the video very much

zinou sid: thank you so much (good job) (y)

Marcos Ramirez: thank you so much, electronics is amazing!!

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.

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: Reducing the lead on the resister will also help. Nice video.

logicsystems paddy: GREAT . VERY NICE WAY EXPLAINED 

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 account. Just asking because I'm pretty new to these things.

Aaron Hayes: The capacitance of the cables leads and breadboard may well higher than that 4.7pF capacitor. 

Round House: If you overlap vs with vc, you will see that pass the 63% mark, the current is slowing in transit.

aaron medina: Great

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.

TheDkjayjay: hey, u are cooler than cool got myself a Tektronix TBS 1022 and i love it.

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.

John Miller: Persistence, very interesting video. Thanks

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."

constance washington: its a pop quiz like ""speed"" and measurments of velocity...craisens

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.

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.

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

constance washington: their crazy ...i gave a craisen

James Holmes: lekker

ducklandwikeno: Earn Some more biscuit Money what are you taking about 

ช่างตั้มมือถือ รับซ่อม iPad iPhone 0846726028, 0832735824, 0895010100: good

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**. 

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.

Selim Okutan: thanks for usefull recomandations

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.

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

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.

Leticia Grantham: Capacitor is fully charged at 5RC?

jeremyhall420: Yes the capicitor is considered fully charged at 5 time constants.

Frank Berry From Upstate NY: Think about adding some "adsorbing dark materials" in your videos...you're awash in white illumination Bro!

bee Hive: Martin, Can you do video on How to measure ESR using a scope and signal generator? 

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.

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

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

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How to measure a capacitor with an oscilloscope.