EEVblog 1465 - Your Multimeter Can Measure Inductors 

I love tool tricks like this, please do more.

What you need now is a firmware update so that the multimeter calculates the reciprocal for you and handles the units properly ;)

Two other useful methods: create a parallel LC circuit with a known C, feed it with a signal generator through a series resistor, find the resonant peak and calculate L from it (if L is sufficiently large, you can use your phone as a signal gen). You can also measure the Q by measuring where the voltage falls to 1/sqrt(2). The other method is to feed the L through a small current sense resistor (in the GND side) with pulses starting from 0 duty cycle, increasing very slowly. Look at the rate of increase of current through the sense resistor, calculate L from it. If your pulser can provide enough current you can even measure the saturation current. You can build a pulser circuit with just a 555, mosfet, catch diode, and a handful of passives.

Thanks for sharing -- I've known this "trick" for decades, but it's still worth pointing out!

This would be a good test for a late first or early second year engineering student. Htey would know the theory but can they put it into practice. It is obvious when you think about it that the capacitance measurement must be using non DV waveform so from first principals, you can get the conversion as an inverse from impedance. I've only ever used this a couple of times, normally a check to make sure the inductor is still good rather than looking for a value but it is a good trick to know if your short an LCR but there are some decent very budget options for these measurements in the hobbyist and student space

EE here in "the States." Excellent tip, Dave! I have never considered this - good tip for field work (which I do for a living). Love your videos - keep up the excellent work!

Great video, as usual. A couple of years ago, I did this experiment, but did not make the step forward - I simply didn't see the utility of this, at the time. But yes, as presented by you, is really useful. You are a Genius, as usual. Cheers!

Great tip, Dave, didn't think of using a multimeter like that. Not very accurate but plenty good to get a ballpark value which is often enough (and the inductors are rarely precise components anyway). 👍

You really got a lot of people this year... I'll admit you had me thinking for a while.

I has no idea what you were talking about, but I liked the way you presented it.

"That's good enough for Australia." Love it... Great video!

I love this stuff Dave, cheers. It'd be great if you could do a vid series on basic field service noob tips for CAN, voltage drops, traps for young players. I know this has been covered before, back in the day but there's a lot of young blokes on the tools that can benefit from your knowledge. Speaking from a guy who's leveled up from you're years of content. Love your work, always a big thumbs up,!!! (Edit: read what I typed 😜)

Pretty neat trick, thanks Dave!

Absolute champion!

Nice trick. It tooks me almost 7 long minutes to understand the deeper meaning. 🙈 Congratulations!! You put in big effort!! 👍👍

Nice one, Dave! I had to think about it for a minute 🙂

@EEVblog, hats off. You are really good at this 😉

i liked the "short the temperature leads" trick to get the internal temperature but this is the first time I have heard of using capacitance four measuring inductance

Dave is so good at April Fool videos, I decided to see what this year’s is and comes over as very convincing as usual 👍, some of the other channels first 30sec to 1min April Fool tho not Daves

Been waiting all year for this video.

April fool to you too. The capacitor measurement uses a relaxation oscillator and measures the frequency that is proportional 1/C. I.e. Smaller C gives higher frequency. The relaxation oscillator can be as simple as a built in Schmitt trigger inverter and the dmm measures the period for a direct conversion to capacitance. Putting any inductor in place of the capacitor with a dmm set to capacitance is just a short circuit. The relaxation oscillator just won't oscillate. It was good to see the 10G ohm resistor I sent to you in mailbag in use too. Great joke video.

Great video Dave, Your tool tips are great 👍. This would have been very useful and save lots of money. I'm definitely waiting for next video.... I subscribe this channel 10 years back for these kind of videos. Not mail bag or fundamental Fridays

This is actually very very useful! I always wanted an LCR meter but couldn’t really justify the expense

That was a really good trick! I never would have figured that out myself.

I have made a Big Capacitance measurement device with Cypress PSoC 4 using the build in Current Source and ADC, not very accurate but it can measure FAST and thousands of uF in a blink. The idea is to charge up the capacitor with current and measure 5RC time constant, which is the time required to reach Vcc voltage.

I love how the 121GW was actually almost bang-on with the 150mH inductor - it has shown 161mH, which you have commented as "not too far off", but then the LCR meter at 7:46 showed almost exactly the same, so 121GW was not off that much :D. It has more error for smaller inductors though.

well since you essentially need a scope to pull this off anyway (for probing the meter) you can just aswell use the test signal gen for probe compensation for that purpose. some scopes can generate a variable frequency on that output which is quite handy too

I measure large inductances by sticking the coils on my tongue. Based on what AM radio station I pick up in my head, I can tell the inductance +/- 10%. It's a good technique but takes years to master.

It's interesting that for some of the meters the frequency changed with the capacitance. I wonder if those use the capacitor in an oscillator and then measure the resulting frequency to calculate the capacitance value (as opposed to measuring the time it takes to charge the capacitor which is how I had assumed it measured them).

that was *way* more complicated than i thought it was going to be

This is a must test when I get home.

Thanks dave. This is helpful.

Nice measurements tools.

The method I use (make a LC circuit with a reference capacitor and measure the resonance frequency ) work mostly for small values so it cans be useful

Fascinating

Wow great episode 👏 👌 Thank you very much 💝

didnt think of that, thats awesome

Wow! I was always wondering what could be the inductance of the high voltage lines on those poles near my house. Now I can climb right up and find out! brb...

fantastic video, works a treat! (I have the 87V though so it was pretty much guaranteed to work)

Awesome sauce.

Before I had sufficient money to buy an impedence analyser, I did my own pen and paper calculations with a cheap oscilloscope and a kenwood audio spectrum generator. Dave makes the point that you need to understand basic science before you take the next leap. Tedious - maybe. A whole lotta fun ? - definitely !

Cool trick thanks, I sometimes forget about it but those ~$15 component testers also do a decent job at testing inductors and they can test the lower values too, I can't verify its accuracy, but now I could compare it to my meter at least.

Thanks! I'll give this a try

nice tip.

You got a lot of them this year, Dave! haha... Good on ya.

Here I was about to build a variable frequency signal generator... This is much easier. Thanks!

I love it!, now I'm going to have to try it! 🙂

Nice trick for sure 😊

Not getting a result with an old Fluke 83 original! By the manuals I can find all the old Fluke 80's work by charging with a fixed current and testing voltage -- updating only once a second -- rather than testing at frequency. They walk you through though how to estimate large capacitances quick by using the ohm-meter though since it's also a constant current source, so I still got a useful tool added to my belt today!

Very useful trick.. Thank you

Very interesting trick.

*Golf clap* Bravo Sir, Bravo.

Very cool. Makes me wonder if it would be advantageous/convenient to have multimeters perform a mathematical operation (in real time) on a measurement. Basically, integrating the calculator into the device.

I have a set of yumcha LCR tweezers it's surprisingly accurate

great tip.Thnaks Dave. Also, quick question as i might have missed it... can this be used in (unpowered) circuit?

With these typical values I just use my audio interface. Plenty of software programs that are able or function as a RLC meter. I have seen also smartphone apps.

Hey Dave great video as always. I believe the keysight (old agilent) LCR meter is somewhat affordable. roughly $450 if i remember correctly. Id love to see a video on conducting a loop impedance check or rotor influence check on a brushless motor.

nice tip. thanks

Fun video. Oh! Dave your finger hurts, wish you recover soon.

Neet. I'm trying to tune an electronic speed controller, this would be great for a close enough measurement of phase inductance.... a shame my meter doesn't even do capacitance. :(

Well that's cool, unfortunately my Fluke 117 isn't good at it at all. It can't even be used on larger ones. The only one I got read reliably was a 100mH coil. I looked at it at the scope and it sends the pulse super random. Had to capture it, and it's a 120mV pulse, lasting 1.2ms, whenever it wants to. Surprisingly though, it reads capacitance great, down to the 10nF level.

Actually ive got a brand new electric shower i fitted but it let out the majic smoke after 1st power up. I found 2 inline inductors on the power to the control pcb. Aqualisa Lumi 10.5KW, a pretty expensive shower. Its a touch sensitive front panel on/off. So im wondering if the inductors are really needed? As i linked them both out, but havent tested it yet. I think i blew it when i had power going to shower when i connected molex connector for panel pcb. Which blew the inductors. I wouldnt mind getting it working

Multimeters which measure capacitance are a fairly newfangled thing for me I was assuming it was slightly more clever than just seeing how long it took to charge 👍

Probably not something I'll need to use in my tool set, but thanks for sharing! On the subject of metres I was in the market for an upgrade the last few days and really wanted the 121gw but there's not really been a comprehensive review on the final build with latest firmware? I ended up going for the bm786 instead but kind of kicking myself now after watching this and seeing you pull the 121 out 🤣

This got burried beyond all recognition. Thanks for all your efforts. Being australian, makes you come a couple hours to early for such jokes.

I don't think that's supposed to be a triangle wave at 2:23 with the fluke. Looks more like the charge/discharge cycle of a cap subjected to a square wave. I think that it's basically using a DC measure of capacitance using time constants.

Yes! Protek 505/506 can do it. :-)

Neato!

I'm more impressed by that 10 GOhm resistor! I didn't know they made such high resistor values. I remember one of my professors scoff at the idea of 1 GOhm!

Wonder how good this will be to find those inductors with a short. Must go grab a meter, grab inductor and a wire to make a shorted turn around the core, and see how it changes.

Why the hell did RU-vid feel the need to give me 7 notifications in a row that you uploaded this video?

Dave, they don't output a triangle wave but rather a pulse. The priciple is called a charge balance. It's what you likely learned in high school about capacitors: Switch on a voltage in a RC circuit and you get an exponential charging function. Do a little bit of maths and you can calculate the C, provided you knew the R. Some of these do it exactly like that and this is where you don't get the triangle wave and others use a constant current source which results in the triangle. The idea behind the triangle wave is that you can easily calculate the slope by doing a linear fit which then leads to easy calculation of the C.

Good one; I'd have to measure my multimeter's cap-meter frequency some time

What typical frequency is used for capacitor and inductor 'printed' value references? From the video it sounds like 1Khz.

Great video as always! Anyone knows what is that switchable L-C-R blue box that says OpenSource on the corner?

I'm sort of confused because what I think is happening is that some DMMs dont measure impedance, but they measure the time constant repeatedly on each update. Hence the frequency sort of increases with the capacitance values and ranges I might be wrong tho Atleast when I did this on my meter it didn't even measure the inductor

I still don't understand inductive loads. A good idea for a video would be a summary of the best free online electrical engineering courses and channels. I love the content from Big Clive, and Fran and you, but I don't have the understanding to properly appreciate them.

Hmm, my meter keeps reading 0.104nF. Must be that time of year to replace the battery!

Oh Dave! Excellent tip on 1st of April! Who knew? DMMs on steroids!!

man... forget about the "one day difference" in Mexico this day comes in December!

Dave , or if someone knows , more info on the " open source " board used in video ? Thanks again

Hi Dave, did you catch wind of the Fluke 87 recall? I got an email from Amazon saying there's a recall of the one I bought in 2021 and to test and ship it back to Fluke at their expense.

Great 👍

Thats basically what a lot of multimeters with inductance built in do internally, with some calibration....

I have 2 very old multimeters (over 20 years) and one has no capacitance measure and the other has slots to measure both on through hole components.

Youre hilarious 😂😂 thx for the vid.

That’s a whole lot easier than busting out the VNA in lieu of an LCR meter.

Please note that it is not always easier to probe on the bottom.

@eevblog: Confusor gave result of 161.7 uH, The RCL 161.23 I think more of "bang on"

Shouldn't the capacitive reactance be negative? Maybe that could explain some effects.

Hi Dave, Great video, never thought of that. Your variable L C R box on the left looks useful and well made, would you post some details please? Thanks ct1igu

What a useful impedance box. Was it a mailbag item maybe?

شكرا

good one :D

Hey Dave, very interesting video. If you know a trick, could you make a short video about measuring extremely small inductors as well ? I'm trying to reverse engineer the components between a balun and a printed antenna on a small 2.4GHz transmitter and I have no Idea on how to measure them. Many Thanks !

Can you measure shorten rotor windings?

Hey, what an awesome idea, loving it! Takes some calculation but opens up new possibilities. Well, I've got a vintage Meratronik E316 analog RLC bridge here, and can assess inductances, but the thing will surely need some verification and calibration before I'm comfortable with it :) I just hooked up my UT890D+ to a scope, got a triangle wave like 2.7 cm period at 100µs/cm, which would calculate to 3.7kHz, and that should be in the audible range. Checked that with an AF signal tracer, heard nothing. No 3.4kHz here... Measured the frequency with a meter - got 60kHz. So, it looks like the scope was wrong. Test gear sheenanigans all the time, LOL. Will take the meter to our local hackerspace to measure the frequency more accurately. "Let's check again to see if it was not a Fluke..."

I got to the 5:40 mark before it hit me. Damnit!

Isn't the Reactance formula at 3:14 only valid for sine voltage?

Do other countries also use lower case omega ( ω ) as short for 2 pi f?