How to measure the value of a capacitor with an oscilloscope

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How to measure the value of a capacitor with an oscilloscope

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7 жыл бұрын

How to measure the value of a capacitor with an oscilloscope
In this video we demonstrate how to measure the value of a capacitor using an arbitrary waveform generator and an oscilloscope. In order to do this you will will need to be able to generate a square wave pulse between 100Hz & about 1KHz. Also your 'scope will have to be able to display both voltage and time cursors at once.
We will measure the time it takes to charge the capacitor to 63.2% of it's value (en.wikipedia.org/wiki/E_(math...) that number in either micro or nano seconds(delta X) will be the value of the capacitor in pF, nF,or uF.
If you would like more information on the theory behind this, Mike Lorton has an excellent video on the topic( • How to measure a capac... )\
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Please watch: "Diodes: The basic building block of all digital circuits"
• Diodes: The basic buil...
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Пікірлер: 59

@ericmartos8400 3 жыл бұрын

The time constant of an electronic circuit that contains resistive and capacitive elements is represented by the Greek letter tau (τ). This time constant in seconds is equal to the circuit resistance in ohms times the circuit capacitance in farads, τ = RC. Tau is the time required to charge a capacitor that is in series with a resistor to a level of 63.2% or 0.632 of the initial value, typically 0 V.

@ericmartos8400 3 жыл бұрын

C= τ /R, if you want to determine the capacitance

@tonycarboni2002 2 жыл бұрын

This stuff is starting to make sense. I like these simple demos. They explain a lot. Ty.

@w8lvradio 7 жыл бұрын

Wow Wow Wow! GREAT Demo! Lots of videos on KZfaq shows NUMEROUS "First Step" Scope-connect-it-to-Waveform Generator Videos, but THEN, after that... Diddly on what to do next! Please make more Videos! All the Best!

@learnelectronics 7 жыл бұрын

William Pietschman thanks. New videos every day

@Aemannin 5 жыл бұрын

Hi Paul, greetings from the Isle of Man, Really liked the video, great explanation of the charge/discharge of a capacitor and the easy way to measure it’s capacitance, it has improved my basic knowledge of electronic components. Many thanks, Regards, Les. R.

@learnelectronics 5 жыл бұрын

Thank you Les

@bogdanresume 4 жыл бұрын

His name (Euler) is pronounced “Oiler”, great video.

@CLGPerformance 3 жыл бұрын

You could have turned your voltage scale to 200mv/div and got your 632mv cursor also but its close enough for basic electronics. I use this method to test SMD unmarked capacitors for a short or degraded SMD Caps

@robertcalkjr.8325 5 жыл бұрын

Pretty cool. Thanks Paul!

@ElTexMexAlex 5 жыл бұрын

Thank you, this makes much more since.

@Braz1956 4 ай бұрын

Excellent video! I'm going to my bench shortly and try it.

@michaelpadovani9566 7 жыл бұрын

Another cool concept, keep it up!

@learnelectronics 7 жыл бұрын

thank you

@mikeoliver3254 7 жыл бұрын

You know what that was cool. You just changed my mind about eventually getting a scope. I live on a fixed income and be don't have much to spend on my hobby so I had decided that a scope was just out of my budget. But now I am beginning to see the utility of having one. So I guess I am going to have to put half of my $40 dollar spending money budget away each month untill I can afford one. I would try a USB scope but my computer is pretty horrendous so I am going to save for that hantek.

@learnelectronics 7 жыл бұрын

Mike oliver Thank you. I'm glad you enjoyed it. A scope is a great piece of gear. The Hantek is really nice for only $240 bucks. You don't have to have a great pc for a USB scope to work well. Most of the heavy lifting is done in the device. But whatever you do, don't get one of the little pocket scopes like the dso138 as your only scope. Did you see the video I did a couple weeks ago on the Eone ET201 scope/meter? That unit is only $50 Sund is both a digital meter and a 20KHz scope.

@1pcfred 6 жыл бұрын

I have a DSO 150 and for what it is it's not bad. It is a DSO 138 with some bugs ironed out of it.

@mickadams4471 3 жыл бұрын

I hope you managed to get your scope, Mike?

@mikeoliver3254 3 жыл бұрын

@@mickadams4471 yes I did it took awhile but it was definitely worth it.

@artemt1987ify 9 ай бұрын

Why do we put oscilloscope probe after the resistor? Why not next to function generator clips?

@user-uv4xe3cq2y Жыл бұрын

Hold on a second. How did you get from 67.48 nF to 68 usec?? A little slight of hand, maybe? ...then I read earlier comments covering this mystery. Nice video, very helpful

@imun1ty 3 жыл бұрын

I am not seeing a square wave in my rigol DS1054z. I am using a 1000uf cap do I need to change the settings on the frequency generator? It looks like multiple waves spiking no nice square wave?

@milaanpatel4997 3 жыл бұрын

If we ignore the fact that a DMM is the first thing you own before a scope and fn. gen., this is an interesting way to measure capacitance.

@gregjohnson5194 4 жыл бұрын

Didn’t you forget the the math “C=T/R”. Your number doesn’t match the capacitance Nano farad vs 68 usec. Instead 68u/1k=68nano.

@ApexMark2002 4 жыл бұрын

Yes I was scratching my head wondering why he made (resulting capacitance therefore = scope seconds). It only happened to work because of the resistance he used.

@gregjohnson5194 4 жыл бұрын

mlerch2002 yea right, but it really didn’t work, the scope showed 68 micro seconds and then he measured the capacitor on a capacitor tester and it came to 68 nano farad! So he looks up at the scope and says what did the scope say and he’s said “ 68 Nano “. He forgot the second part of the equation he needed to divide the time 68 micro by the resistance value 1 k ohm to take the resistance out of the measurement and that would leave him with the capacitor value as I’m sure you probably already know. But I just typed it out for the other people who aren’t getting you can’t just use the scope measurement as the value of the capacitor. Like you said, have him change the value of the resistor to 680 ohm and see what the scope reads.... Ok cool have a great one.

@ApexMark2002 4 жыл бұрын

@@gregjohnson5194 Yup! Thanks for clarifying my comment for others. What I intended to write was "the number only happened to match out of coincidence."

@michaelcloud9230 Жыл бұрын

can I use the function gen, that on my scope? Ive been trying to learn how to use my Oscope but falling short. I just or have bought the Rigol MSO5074

@3dtexan890 Ай бұрын

Can I use the arbitrary waveform generator that is in my oscilloscope to do this test or do I need an external arbitrary waveform generator?

@tonypoloney8721 7 ай бұрын

I followed your breadboard circuit to a T, but my scope displays a clean square wave. No cap discharge curve. Please help? Banging my head on the desk 😢

@qua7771 2 жыл бұрын

I would like to measure a 22000uf cap. will this work on a value that high?

@tonycarboni2002 2 жыл бұрын

I enjoyed this demo so much that I watched it a second time. I found a mistake. At 7:21. you look at the scope screen and declared that the capacitance is 68 nF. But you are looking at the Delta X value on the scope, and it says 68 microseconds not 68 nF. This was an odd coincidence that caused you to temporarily get confused and make an error. Plus, there must be a division step somewhere here. I learned all this from your videos anyway, so if I'm wrong, it is your fault. :-)

@tompullings6418 2 жыл бұрын

You are right. The OP lucked out because he used a resistor value of 1K. Without doing the math how does one know if 68uS corresponds to microfarads, nanofarads, picofarads, etc? Using: tau = RC we have 68E-6 = 1000 x C. Rearranging: C = 68E-6 / 1000 = 68E-9 or 68nF. Also it would have been better if he had blown it up in both axes as the trace is quite fat compared to the cursors. Initially it looked like he was measuring from the bottom of the trace at the lower voltage and the top of the trace at the higher voltage. Should use bottom in both cases or top in both cases. But it was a good experiment overall.

@sdrtech 5 ай бұрын

Im using the owen hand held ocilliscope for the generator the only way im geting a curve is by turning the generator on and off😮 is it because the generator doesnt have a duty cycle? Thanks for any info

@velimattiollilainen 6 күн бұрын

6:36 min: delta T / R = 68x10^-6 s / 1000 ohm = 6.8 x 10^-8 F ( Farad = seconds/ohms) = 68nF

@SlowfingerJC 4 ай бұрын

I guess it would have been possible to increase the resolution of the measurement by filling the screen with the area to be measured instead of making the measurement on a small part of the screen.

@jimle22 4 жыл бұрын

Hey Paul, I have one of the newer Hantek scopes it has a 1Khz signal built in. Can I tap that to provide the signal source? I don't have a function generator.

@learnelectronics 4 жыл бұрын

yes you can

@jacoblieberman5138 3 жыл бұрын

Same here, thank goodness!

@XtianApi 4 ай бұрын

Does the value of the resistor need to be exact?

@muhammedsons2675 5 жыл бұрын

hi there would you tell me please why the cap curve hasn't shown up on my scope even though I applied 1khz 1vpp on the cap???? thanks

@learnelectronics 5 жыл бұрын

I have no idea what your circuit looks like.

@muhammedsons2675 5 жыл бұрын

Thanks for your reply I have already found the reason anyway thanks again

@danedewaard8215 2 жыл бұрын

You are measuring the time constant not the charge capacity. Still, it is a fun video to watch!!!

@georgejames3868 4 жыл бұрын

My oscilloscope only shows a straight line

@etch4 6 жыл бұрын

no metal film resistor ? , 632mV -> 0:55 I like it.

@Ibelieve218 3 жыл бұрын

why 630mv?

@fredlllll 7 жыл бұрын

measure a super capacitor with it ;)

@learnelectronics 7 жыл бұрын

fredlllll soon...yes... very soon he he he (evil laugh) 💣💥💨

@fredlllll 7 жыл бұрын

i smell explosions... and ozone?

@learnelectronics 7 жыл бұрын

and burning dielectric

@sdrtech 5 ай бұрын

Try it with a 10uf capacitor you will only get a triangle wave

@ady_k 3 жыл бұрын

Nice experiment. the math is the 1000 Hz and that 1K resistor

@markday3145 3 жыл бұрын

The math is 𝛕 = RC where 𝛕 is in seconds, R is in Ohms (1KΩ), C is in Farads (68 nF). The frequency needs to be low enough that the capacitor fully charges and discharges. It will get to 99.3% after 5𝛕, so you want a period of at least 10𝛕 (5𝛕 each for charge and discharge). Therefore, a frequency of 1/(10𝛕) or lower. Since you don't know C in advance, you might have to keep lowering the frequency until you see the a full charge and discharge.

@ady_k 3 жыл бұрын

you should really try this experiment, full charge (5rc) in a practical cap is not happening