How To Measure A Capacitor With An Oscilloscope.




What do you think about this video?

AlainHubert: To marbleshark: FYI Martin is making a living out of his YouTube videos full time. So he's not donating anything. He's sharing knowledge and information in exchange for money.

Samuel Esther: Oh my god, 46mins just to explain how to measure a capacitor value with an oscilloscope!.. it could be explained in 4 times less, which would be 4 times more interesting. You've made a simple and passionate subject heavy and complicated to understand. Keep it simple and short please.

Andre Sant'Anna: Great video. Like many people have said, when you are measuring such a tiny tiny value capacitor, then there are a ton of other stray capacitances that confound the measurement - the probe, the wiring, the breadboard, they all have values in the pF range so you are actually trying to do something pretty difficult. These stray values don't affect the measurement of the bigger capacitors much because the stray values are so much smaller in comparison. When measuring something small like this, you might want to connect a bunch of them in parallel (the capacitances will add) and then divide by the number of capacitors you used to get the answer for a single one of them.

Curvian Vynes: Hey, 5.99E^-11 is not 5.99^-11. It's 5.99*10^-11. Anyway, great video! Thanks!

marbleshark: I love this guy - thanks so much Martin for generously donating your time to educating others with your excellent tutorial videos... I've learnt a lot and it's set me well on the way :) Cheers

magicman33069: Consider if you will, the capacitance of the probe, as well as the loading effect of test equipment used, which will of course, effect your results.

Najim MOUADILI: How to mesure permittivity of materials using osiloscope 

GardeningZ: Nice measurement. Now can we use a current mode square wave generator to measure capacitance? Say if I have a programmable power supply?

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.

Mike O'Neill: Could the error be caused by the noise induced? Noise is just another wave form placed over the one you are looking at. So, you should be taking your voltage readings either from the top of the noise, or the bottom. Not the top and bottom of the entire wave form.

John Elliott: Thanks for trick and hint and maths : 0 ) 

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.

a11457exp: awesome ..

Dustin Lewis: I've tried to watch a few of your videos, but you talk so much, its difficult to string the important bits together between the babbling.

The Lightning Stalker: Stray inductances are going to affect your measurement, particularly with small value capactiors. This should be taken into account. Oscilloscope probes also have a capacitance which will also affect the reading. Your breadboard also has a capacitance.

TheThore: So you need a calculator for dividing by 1000? ;)

Totardo Tobing: Too slow :(

tim master: How large of capacitors could you use this technique with?

Rod Dormido: the possible source of error is that you forgot to factor in the capacitance of the oscilloscope probe.

Phil Brown: You explained that very well ... Subscribed

charles bell: Just Great !!

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

tim master: I wonder if a cage would help reduce the noise.

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.

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

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.

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

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

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.

Ahmed Abdalsalam: thanks for your effort.

Harish Kumar: nice one! thank u

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.

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.

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

Anonymous News: what is all the noise on the scope

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

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

logicsystems paddy: GREAT . VERY NICE WAY EXPLAINED 

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

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.

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

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

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.

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

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

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

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."

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.

Rating:
How to measure a capacitor with an oscilloscope. 4.7 out of 5

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How to measure a capacitor with an oscilloscope.