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.
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
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.
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.
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.
Wow Wow Wow! GREAT Demo! Lots of videos on TH-cam 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!
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.
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.
@@gregjohnson5194 Yup! Thanks for clarifying my comment for others. What I intended to write was "the number only happened to match out of coincidence."
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
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
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. :-)
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.
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?
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 😢
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.
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.
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.
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.
C= τ /R, if you want to determine the capacitance
This stuff is starting to make sense. I like these simple demos. They explain a lot. Ty.
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
Excellent video! I'm going to my bench shortly and try it.
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.
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.
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.
I hope you managed to get your scope, Mike?
@@mickadams4471 yes I did it took awhile but it was definitely worth it.
His name (Euler) is pronounced “Oiler”, great video.
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.
Thank you Les
Wow Wow Wow! GREAT Demo! Lots of videos on TH-cam 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!
William Pietschman thanks. New videos every day
6:36 min: delta T / R = 68x10^-6 s / 1000 ohm = 6.8 x 10^-8 F ( Farad = seconds/ohms) = 68nF
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.
Why do we put oscilloscope probe after the resistor? Why not next to function generator clips?
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.
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.
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.
@@gregjohnson5194 Yup! Thanks for clarifying my comment for others. What I intended to write was "the number only happened to match out of coincidence."
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?
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
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
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
Does the value of the resistor need to be exact?
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. :-)
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.
Thank you, this makes much more since.
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?
Another cool concept, keep it up!
thank you
I would like to measure a 22000uf cap. will this work on a value that high?
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 😢
Pretty cool. Thanks Paul!
You are measuring the time constant not the charge capacity. Still, it is a fun video to watch!!!
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.
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.
yes you can
Same here, thank goodness!
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
I have no idea what your circuit looks like.
Thanks for your reply I have already found the reason anyway thanks again
no metal film resistor ? , 632mV -> 0:55
I like it.
Nice experiment. the math is the 1000 Hz and that 1K resistor
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.
you should really try this experiment, full charge (5rc) in a practical cap is not happening
My oscilloscope only shows a straight line
Try it with a 10uf capacitor you will only get a triangle wave
measure a super capacitor with it ;)
fredlllll soon...yes... very soon he he he (evil laugh) 💣💥💨
i smell explosions... and ozone?
and burning dielectric
No explanation how to calculate the cap value. That doesn't teach anything. The scope reads 68us, ok....
why 630mv?
Oiler and Youclid. Not Youler and Oiclid!
What is the meter you're using in the video?
You only refer to it as "one of these"... 🤦
I've got some huge 100v 100000uF nichicon gold tune high-end capacitors that I need to check