EEVblog 1465 - Your Multimeter Can Measure Inductors

Handy tip on how you can use your multimeters capacitance range to measure inductors, using the reciprocal method.
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#ElectronicsCreators #Multimeter #Measurement

[@colingale]

I love tool tricks like this, please do more.

[@ipr724]

Next year.

[@Boffin55]

Dave does a great tool trick like this once a year

[@colingale]

@@Boffin55 yup, i was so tired when i made this comment I "Should" have checked the date first then made my comment. Well played Dave, well played.

[@josephlunderville3195]

Almost got me, I'm just on the other side of the date line and queued it up on the 31st...

[@ipr724]

@@josephlunderville3195 Got it on 31st too.

[@asserslab]

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

[@Volcanoelectricity]

Problem is the accuracy is so piss poor you could never really properly calibrate it. That's a big problem if anyone ever wanted to use this meter at work, where equipment needs to be regularly and fully calibrated.

[@brainndamage]

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.

[@EricAdamsonMI]

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

[@oeckel10]

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

[@seanet1310]

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

[@JanCiger]

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). 👍

[@tejonBiker]

If you read about the saturation of magnetic cores in the forums on internet you will get the same conclusions, the values on inductors are more fuzzy than R or C.

[@envisionelectronics]

April fools.

[@tejonBiker]

@@envisionelectronics It's a shame that here in Mexico this video shows at 31 of March, hahahaha, well, this video give me some ideas.

[@hanedoggy]

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

[@slypig24]

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

[@ingolfmuller566]

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

[@dennissloatman3971]

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!

[@pnjunction5689]

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

[@horiamorariu]

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!

[@andycristea]

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.

[@teresacodilan7809]

At least one electrical engineer has read your comment.

[@kissingfrogs]

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

[@EEVblog]

A really old school trick.

[@miklov]

Had no idea about that. Mine will show internal temperature with no probe connected instead.

[@ryanb8302]

Why would you want the internal temperature of your multimeter?

[@kissingfrogs]

@@ryanb8302 Cause it would be closely related to ambient room temperature if you wanted to measure that. I often do.

[@ryanb8302]

@@kissingfrogs I see

[@insoft_uk]

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

[@godsinbox]

this video hasnt aged well. the date has been lost and its in the general pool of misinformation on the web. is this what we want for future generations?

[@mcpoogle9058]

@@godsinbox what do you mean

[@fase144]

Pretty neat trick, thanks Dave!

[@sharkbaitsurfer]

Absolute champion!

[@barry2718]

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.

[@denny9931]

He practically got me on this one until i read your comment and started thinking about it in another way.

[@robingalipeau5642]

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

[@danmoos3635]

Been waiting all year for this video.

[@demoncloud6147]

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.

[@Galileocrafter]

I've soldered and programmed a kit with the same principle for my programming class at uni. Pretty neat!

[@mrstijntje]

Measuring at 1 times RC would yield a better accuracy. The curve is steeper so every error in reference voltage amounts to a smaller error in calculated capacitance. This acutually works with inductors too.

[@adamadamhoney]

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 😜)

[@kaziq]

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.

[@dinushkam2444]

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

[@ki4dbk]

Awesome sauce.

[@tl1024]

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

[@Seiskid]

Thanks dave. This is helpful.

[@50Hz]

didnt think of that, thats awesome

[@rodrigomaero]

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

[@moristo]

Nice measurements tools.

[@odindimartino597]

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

[@BrianG61UK]

That's what I've done in the past. Make parallel tuned circuit and use a little negative dynamic resistance circuit to make it oscillate and then measure the frequency.

[@sunuk1915]

Wow great episode 👏 👌 Thank you very much 💝

[@raymondcourtois67]

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).

[@urugulu1656]

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

[@mikeadler434]

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

[@hannescamitz8575]

This is a must test when I get home.

[@inspectormills3290]

Thanks! I'll give this a try

[@inspectormills3290]

Well, I tried it with my Crenova multimeter and the capacitance displayed was always OL.

[@kenarf3332]

nice tip. thanks

[@vgamesx1]

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.

[@greywolf271]

You know you can make your own measurement test set with better accuracy ? Just use a kelvin bridge.

[@andreavergani7414]

Fascinating

[@Zardox-The-Heretic-Slayer]

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

[@EEVblog]

What accuracy did you get?

[@Zardox-The-Heretic-Slayer]

@@EEVblog it was pretty much the same as yours with a hair of a difference either way - I have the same inductor test box as you so I just tried it with that

[@EEVblog]

@@Zardox-The-Heretic-Slayer Nice! It's a handy box. Had a bit of a hard time with the SMD inductor though, tricky to probe those little suckers.

[@Zardox-The-Heretic-Slayer]

@@EEVblog I use an offcut of an old gold plated PCB (from old RAM sticks so the pitch is perfect for general components) to measure SMD stuff like that. using 4-wire measurement on that seems to be pretty accurate; good enough for England!

[@Palmit_]

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

[@JKnight89]

Very interesting trick.

[@groovejet33]

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

[@worroSfOretsevraH]

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...

[@MAA567000]

Very useful trick.. Thank you

[@landspide]

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

[@tvelektron]

Nice trick for sure 😊

[@greywolf271]

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 !

[@hjhhhjhjh9474]

nice tip.

[@SirBunghole]

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

[@R2D2internet]

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

[@ludzinc]

*Golf clap* Bravo Sir, Bravo.

[@KD0CAC]

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

[@johnsonlam]

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

[@Bipolarvideos]

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

[@bhu1334]

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

[@movation]

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

[@lebenitj]

Can you measure shorten rotor windings?

[@JumpingSpiderDesign]

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

[@jakenbaked87]

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

[@dfgaJK]

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. :(

[@bobdavelisafrank_4850]

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!

[@vincei4252]

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.

[@EEVblog]

I heard something about the jacks? Don't know the details.

[@p_mouse8676]

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.

[@jamesttol]

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.

[@EEVblog]

You can get the same functionality for under $100 these days though.

[@jamesttol]

@@EEVblog oh I agree completely. I was just pointing out the value of the lcr meter you used. But yeah, rotor influence check please :)

[@africantwin173]

I need one that can measure 15v zener diodes ?

[@synchro-dentally1965]

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.

[@marcus_w0]

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

[@ElTwOJaY]

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!

[@rocketman221projects]

Mouser has 10 TΩ resistors in stock, they're not cheap though.

[@ElTwOJaY]

@@rocketman221projects What would the purpose be of such large resistors?

[@rocketman221projects]

@@ElTwOJaY The one that Mouser has is rated for 30 KV, so it's probably intended for high voltage measurement. It would only have a 3 nA load at 30 KV.

[@uwezimmermann5427]

@@ElTwOJaY they can be used in transimpedance amplifier configurations to measure very small currents (fA - nA). I have some resistors which are contained in quartz tubes and labelled with powers of ten It literally says 10¹² Ω on the part.

[@ElTwOJaY]

@@uwezimmermann5427 hmm interesting, I am not much of an RF guy.

[@JoshuaNorton]

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.

[@EEVblog]

Yeah, well, that's just, like, your opinion, man.

[@der.Schtefan]

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

[@extremgear]

yes we do in France , at least at school

[@uwezimmermann5427]

yes, it is common use in electronics and electrical engineering - both in Europe and the US. We teach it here in Sweden and I know it from German and American text books as well.

[@cerulyse]

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 👍

[@user-ke7bi4mo2p]

Youre hilarious 😂😂 thx for the vid.

[@ThomasHaberkorn]

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

[@cowasakiElectronics]

Was that fluke with the weird measurement the one you upgraded to rms?

[@steventhomas5865]

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.

[@xplore7359]

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 🤣

[@EEVblog]

The 786 is a great meter, don't worry about it.

[@PlasmaHH]

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

[@SeanBZA]

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.

[@WojciechMajstrzyk]

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

[@sbrun8600]

good one :D

[@kkathulgangadharan2262]

Great 👍

[@gonzalomeabe5256]

Why do most multimeters don't include an inductance measuring function? It would be very useful

[@SnabbKassa]

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.

[@vgamesx1]

The simplified answer is an inductor is a lot like a capacitor, just replace voltage with current and capacitance with magnetic fields, you put current though it, it charges up a magnetic field which restricts current flow until it's full then it becomes just a wire, afterwards it does the opposite when current flow stops feeding its charge, thus it smooths out changes in current, similar to how a capacitor smooths changes in voltage.

[@nevaznozabil]

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

[@gfcwfzkm]

Neato!

[@Robotech010]

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

[@iamdarkyoshi]

Since it's mostly just a bit of maths.... 121GW firmware update to add an inductor measurement mode utilizing the hardware on the capacitor range?

[@EEVblog]

Will have the look into it!

[@hansibull]

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

[@marijndegezelle3819]

Hey, is there a github for the box your using? seems very cool to tinker and find the right value for stuff

[@EEVblog]

Website: www.ak-modul-bus.de/cgi-bin/iboshop.cgi?showd1010!0,849115999257891,RLC-Box2

[@xxycom8963]

@EEVBlog sorry your link is not working. It brings one to a German page, where the content of the displayed page is blank.

[@ferrumignis]

@@xxycom8963 Working fine for me, maybe you have an adblocker or similar interfering?

[@xxycom8963]

@@ferrumignis My bad. I did not wait long enough. That is like one minute waiting time. It brought up the description.

[@OneBiOzZ]

where did the screws go on just the multimeter measurements dave? :P

[@Jnglfvr]

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.

[@frosty129]

This video left me somewhat confused. Are you suggesting the capacitance mode on a multimeter will always read the inverse of inductance? How does it depend on the test frequency?

[@EEVblog]

It should do, neat trick huh. Give it a try.

[@wthornton7346]

Dave answered that in the video. You need to consider the equations for impedance, they show the relationship of frequency to capacitance and inductance.

[@erikdenhouter]

Don't forget to convert the value on the display to mF first, and then the inverse answer will be in mH.

[@frosty129]

@@EEVblog thanks, I’ll try this

[@halatiseifeddine7652]

شكرا

[@gustavodinosaurio]

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

[@cremvustila]

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

[@Actinuon]

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.

[@remontlive]

Fantastic, but i did not get, why we need to multiply by 1000. Where the 1000 come from?