Measuring inductance with an oscilloscope and signal generator 

This video and the link with the formulas helped me a lot to get back into the topic, I had forgotten almost all the formulas and the calculations and after this I feel like I am ready to continue!

What a fantastic video! Didn't realise measuring inductance can be so easy.

The great truth, I know other methods with AWG and oscilloscope, but this is the fastest to measure an inductance, thank you very much for your contribution.

Another way that I like to use is one that works well if your function generator is crappy and doesn't necessarily have a nice linear output impedance (e.g. the FG-100 DDS generator). You connect up the resistor (in your case the 178.2 ohm resistor) as a shunt resistor, and use a 2-channel scope to measure voltage across the inductor, and voltage across the (known) resistor - from which you can infer the inductor current. Note that you would want a low ESL resistor, or at least ESL orders of magnitude above what you're measuring. You also measure the delay between the "current" & voltage waveforms, from which you calculate phase shift (along with freq.). From there you can use Ohm's law to calculate the magnitude of the impedance, and with the phase shift you can calculate the complex impedance. Take a few different data points and plot them in Excel, and compare with the theoretical calculated impedance :) An interesting thing you can see with this method, is the ESR of an inductor shows up as a linear offset to the calculated theoretical impedance!

Awesome!!! thank you for the extra link in the description.

This is fascinating! The simplest method I’ve seen for using a function generator and a scope to determine inductance. Saved & noted.

Thank you soooo much for this. This was the first video I found on youtube where you SHOW the wiring setup. cheers

This is a really practical method, well explained.Thanks for the link to Ronald's page, it's well worth reading. Y

If you have an oscilloscope and a known size of capacitor you can deternine the inductance in a perhaps more straightforward fashion. The idea is to constuct a series LC circuit and find the resonant frequency. Then use that frequency to calculate the inductance from the formula for series LC resonance. Put the inductor and capacitor in series, add a resistor (e.g 50 ohms) to stop the function generator from shorting out at low frequencies. Find the value of frequency which minimizes the p-p voltage,. Use this frequency you found, the known capacitance, to calcuate the inductance using the formula for resonant frequency of an LC circuit.

Nice and concise explanation. Thanks for the effort :)

Your method works perfectly. But, I usually test the resonant frequency. Place a known capacitor (measured value, not just from the specs) and connect it to any voltage source. Disconnect the voltage and look at the resonant frequency. You only need an oscilloscope (and a good tester to measure the actual capacitor value). Also, voltage measurements are usually not very accurate with regular oscilloscopes, but frequency/time measurement are spot on, even for cheap oscilloscopes.

If you adjust the frequency until the voltage is 0.71 x generator voltage (in this case 2.2V), then the coil impedance XL is the same as the generator output impedance. Hereby the inductance is calculated as: XL=2pi*f*L=50.5 Ohm and L=50.5/(2pi*f)

Measuring inductance with ordinary meters can be deceiving unless it is air core inductor. This video did great job on inductances measurement

Excellent tutorial thanks chap

Thank you for the video. It helped me confirming my LCR meter was crappy with higher inductance. I did had some problem with my Uni-t 962 Function Generator set to 50 ohm, i changed to HighZ (scope was on M as well) and everything was fine.

S11 Smith chart can be set to indicate the combination of resistance and inductance (capacitance) of a component as a direct reading. The impedance of a component may widely vary as a function of frequency and also with excitation level (volt seconds that is, flux density, gauss or tesla) The VNA is a great tool to plot the component impedance as a function of frequency. - for the case in this video, a 10 fold change in the capacitor value likely computes a different inductance value

I'm not the best with maths but you explained this so clearly, I followed easily. Thank-you. I like your calm and clear presentation style.

Very nice, neat explanation and video.👍

Thanks Scott, that's brilliant. I tested two inductors I wound on two T50-6, they were wound per the toroid specs to give me 3.98uH on one and .13uH for the second. Using your method the first came out at 3.95uH. The second was too small for my scope & FG upper limits. I then modified the formula per your comments to 1/4 & sqrt(1/15) to try to estimate the smaller inductor value. The 1/4 volts was right on the limit of my gear and the math came out at .09uH. This has given me confidence that my winding calcs have created inductors pretty darn close to my target. Until I found your video I was progressing with fingers crossed, now I'm progressing with a lot more confidence. Cheers!

Now I andestent how you do))LC filter))Nice metod)

Thank you so much for this. As a newbie Radio Homebrewer this has helped me greatly. Much appreciated. Liked subbed and rang your bell too!

Very clever metod

Neglecting the wire resistance of the inductor can introduce some error, I would prefer to adjust the scope time scale to look at the charge time of the inductor (or capacitor) and use that to calculate the value of the component.

Superb, thanks.

Good tutorial, I was looking for a way to use my new oscilloscope and signal generator to measure inductors. You helped me do this plus also determine the output impedance of my signal generator. Does this work for capacitance too?

Thanks for the video. Btw, if you search for the frequency where the voltage is down to 1/3, the equation ends in L = 1/f within 1%. Having said so, a scope plus functiongenerator is a bit out of scope for me. I use an oscillator setup with a series LC circuit. In that, the Rinductor disappears. I measure the frequency with a soundcard on the PC. For an occasional measurement, it does the job.

Fantastic. How easy is that!!

Thanks Scott for the video. Could you please provide me the link where to purchase the M Tester the same as on your video? Have you done any modification on it?

if u increse frequency without geving load then amplitude remains same when frequency 1khz sine wave?

Hi Scott A really fascinating video. I am trying to use your method to measure a large unmarked smoothing choke. The FG calc works out perfectly at just under 50 ohms but I get no p/p drop whatsoever with the choke in parallel and reducing the frequency as instructed. The DC resistance of the choke is 418 ohms. Is it possible this method only works for small inductors? I expect the choke to measure 10 -15 Henrys. Keep up the great work!

1 khz to 600khz output amplitude at no load position does amplitude remain same?

Sir . 2.4Volt (connected with resistor) , how about 3.06 volt ? sorry sir , poor english i have ... Your method quite useful ...

thank you very much. so, is it possible to measure the inductance with square waves instead of sine waves?

NICE ONE

I think to be more accurate in measuring , we should measure resistance of inductor first and do our calculations based on (resistance of function generator and resistance of inductor)

I think I am missing something! I take the unloaded voltage and it was 3v peak to peak. I connect the inductor but still get the same voltage value of unloaded generator

I must watch again

Would you happen to know how many uH the chines MDS-60 metal detector kit might be?

I just wanted to double check. A 0.5 mH inductor at 9300 Hz (from the video) would have a resistance of 29.2 ohms (L * F * 6.28). I think I understand the voltage divider part of the measurement, but therefor it would make more sense to me if the found frequency would result in the same resistance of the output impedance (50 ohms). To get 50 ohms at 9300 Hz you would need 0.86 mH. I'm sure your formula is correct and I simply don't understand how it works. It would be nice if you can elaborate.

At 4:17 you said it was 3.06Vpp but later in your calculations at 9:30 it became 3.08Vpp. Did you manually adjust it to get an output impedance closer to 50Ohm?

Hi, I tried a large inductor that I have and it wouldn't drop the voltage at all. I have the same signal generator as you have and dialed all the way up to ~10Mhz to get to 3V. It only drops down to about 2.7V in the low frequencies. How can I measure it seeing as the voltage doesn't drop by half?

Great tips! I tried out this method on my Voltcraft DSO-1084F (rebranded Hantek DSO4084C) scope with builtin function generator and guess the measurement worked out. I measured the output impedance of the generator to be 390 Ohms. Alternative to your calculation of the output impedance of the generator, you could also measure it with a pot, aiming to achieve half of the peak voltage compared to the unloaded state.

sir which frequency will be best to use

As I understand it, RO is output resistance not output impedance, as impedance is always frequency dependant, which is why it is used as a constant in the formular ie not as a frequency dependant value.

my function generator metravi make is bad. its amplitude going smaller when increasing frequency other OHM tech indian make is good upto 1.4Mhz its amplitude remain constant as per set point. i have tested with multisim also, One problem shows that multisim inbuilt function generator or inbuilt agilent function generator shows 50 ohm impedence but when connecting any resistance like 132 ohm its voltage accross 132 ohm does not fall. so my test as per ur methode(finding impedence) is not functioning. then i add additional 50.49 ohm to output and measure as per ur video , it is perfectly working.thanks for ur video,

can we measure low wattage line 1/4 Watt inductance value using on DSO

Could you just wire a resistor in series in front of inductor, put a probe before the resistor, and after the resistor, and adjust the frequency until the voltage on the probe after the resistor is half that of the first?

Im guessing this method is most accurate for higher inductor values. While for lower inductances, since you need to fairly large frequency, the parasitic in the circuit might be relatively big and give a erroneous result

my function generator says its 50 ohm output impedance but I found it 400 ohms based on this video. is this not strange?

How to get the Vo & Vl value . Thx

Really enjoyed using this method which was only hampered by my rusty maths. But works perfectly and simplified to 4.614/f for a sig gen impedance of 50.25 ohms

Shout out to the Chinese multitesters for having a decent crack at it.

Where is the 3.08 V PP coming from? I think it is 3.00 V PP everywhere?

how to measure low wattage value inductance(1/4 w,1/2 W) measurement using CRO and Function generator

sir in formula why 0.5 used for V out by V in

👍

triple checked. pk->pk 5.08V -> 4.32v 271.5 r so aim for 2.54v 17.490Mhz Getting 2.7 mH - INductor is a 5.6mH. Any clue what I am screwing up? signal generator is new rigol. Oscilloscope is a new 2ga sample siglent. dvm is old HP that passed certs recently. I should be measuring closer to 8Mhz. Just a software engineer trying tolearn to measure toroids he needs to wind.

m or n?

I have got a headache

doesn't work

Disappointed that you completely punted on explaining the math… I didn’t really need to watch 11 minutes of hooking stuff up to measurement devices; I can figure that out myself. The key thing to know is how to derive the inductance from the measurements, and you skipped that entirely.