EEVblog 1473 - How Your LCR Meter Works

How an LCR meter works.

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#ElectronicsCreators #LCR #Tutorial

[mortenhattesen]

A little correction.
At the bottom right on the whiteboard, you have ...
D = |Rs| / Xs
... it should be ...
D = Rs / |Xs|
... as Xs is the value that can be negative.

[Sahko]

Gotta love it when you're designing an lcr meter and this just so happens to come out ❤️

[carlosanvito]

Great stuff Dave. I worked a full career in power generation and now I'm an adjunct prof. I can't stress how important fundamentals like these are for engineering students. Sadly, I'm finding that these foundational concepts are not being stressed as they were when I was a student. I hope that students are watching your videos. Keep up the great work!

[galileo_rs]

A suggestion for a video: how to use an LCR meter and what all those Cp, Cs, Lp etc mean.

[zedcarr]

I'll be honest, I'm a bit crap at maths, but videos like this inspire me to make the effort and try to expand my knowledge. I'll have to watch this and the other videos you mentioned several times before the penny drops, but I'm sure I'll get there.
Years ago, when I was in college, I remember being fascinated that we could calculate the dynamic impedance of a diode using Pythagoras Theorem.
I've been a service engineer for over 30 years, and I've NEVER had a practical use for that knowledge, but I'm glad I learned it because I found it very interesting. 😊
For me at my repair bench. Diode working, correct voltage drop across forward biased PN junction. Diode short circuit. Diode open

[jimreineri]

I ♥️ these tutorials. I always learn new stuff or at least reinforce previous knowledge. Cannot get enough.

[Cmensailing]

You timed this one for the overseas markets Dave! Midnight now I'll watch it in the morning mate!

[packratswhatif.]

Damn it Dave, why couldnt you have been my college electronics teacher (for everything) back in my younger times ! Good stuff …thanks….

[Proudbmodest]

The measurement doesn't have to be in phase with the source signal, it's only important that the two measurements be 90 degrees apart in phase at exactly the source frequency. This is what the fast Fourier transform does and outputs two vectors 90 degrees apart. Although the phase of the two vectors is random with respect to the source phase, the calculations are exactly the same because it is the ratio of the real and imaginary amplitudes and the relative phase between them that is important.
This simplifies the hardware because there is no need to synchronize with the source as long as the frequency is precise. The A/D sampling has to be frequency precise with regard to the source and then an FFT can use the sampled data to extract the vectors and then calculate component values.
A primitive LCR meter can be made using an Arduino to generate a square wave source with the A/D triggered at four times the square wave frequency to give the proper phasing with half the samples the sine value and the other half the cosine. This is the hardware equivalent of doing an FFT. The first sample is sine +, the second cosine +, the third sine - and the fourth cosine -. The - samples are multiplied by -1 and added to the + samples and averaged to get the amplitude of the vector. The cosine value is the real part of the vector and the sine is the imaginary part.
For higher precision the source voltage should also be measured using the same technique. If this is done, the source voltage value is not important as long as it is stable. The LCR measurement depends only on the ratio of the DUT impedance to the reference resistor impedance and if the same A/D reference is used for all measurements a fairly accurate measurement can be made.
A PC sound card can also be used as the basis of an LCR meter because it can easily source and measure and only requires a simple op-amp input buffering and guarding stage.

[TradieTrev]

You put the fun into phasor diagrams mate!

[rafaelestevam]

oh, you have no idea how this video came out in a perfect timing!!! Thanks Dave!

[bain]

Excellent. This was needed for persons whom don't understand impedance.

[groovejet]

Dave, your a Freak of Nature my mate! ha ha ha.
I LOVE how you believe that for all of us to be able to use a LCR Meter competently, we need to understand 'How a LCR Meter fundamentally works'.
Just GENIOUS, my Aussie matey.
Side note- A thumbnail to the right just showed a video from 13 years ago, Rigol DS1052E Oscilloscope review Crazy dont you think?
13 years WOW

[HaseebElectronics]

Sir
I salute to your valuable knowledge. thanks for sharing
God Bless You

[KingLoopie]

Thanks for explaining q and how my old lcr meter works! I'm not sure that all stuck, but the overview really helps me a lot! 👍

[scottholmes]

I still reference your 2010 video about an LCR meter you built for marine exploration. This is a healthy update.

[Derlis_Jara]

I'll try and design one myself.. that'd be a very interesting proyect. Nice video..
Greetings from Argentina.

[JoshuaNorton]

I wish you had gone into into the series and parallel model a bit more as that's actually important understand when doing measurements with an LCR meter. I see people bungling it up all the time. What's the difference between Cp and Cs? Why switching between these give you vastly different values? Some LCR meter don't let you switch between these at certain values, what gives? And so on. Lots to talk about imho. Again, some people I work with have very little experience with LCR meters and like once I year I stumble over someone having measured and documented the wrong one and it being undetected for months. So, you'd do the industry a favor clearing this up.

[puffinjuice]

Just bought a Hantek LCR meter. This helps a lot. Thabks ^^

[KeritechElectronics]

Nice :)
It goes pretty well with the one about measuring inductance with a multimeter set to capacitance measurement.

BTW, back in 2004 my high school was having some serious remodeling and the labs were to be packed up, so lots of old gear had to go; a few electronics geeks (including me) who were on good terms with the physics and chemistry teachers got some cool stuff. Mine included a vintage '80s analog RLC bridge (Meratronik E316 for those interested) that can measure on DC, 50Hz and 1kHz. I rarely used it, but it's there in case I need to measure a choke.