Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Measuring absolute capacitance.

Status
Not open for further replies.
I have been reading this thread with interest since Mr RB referred me to it, but I am a bit confused regarding the need to measure absolute capacitance?

Unless the test capacitance is significantly large regards to the parasitic capacitance and inherent errors in the test equipment, how useful is this absolute capacitance reading?

Obviously I am missing something as the best people I know on this forum have answered with a lot of enthusiasm, so I am genuinely curious!

Also - how many of you would be interested in a project that involved making your own LRC meter with ESR testing capibility?

I have been reading a lot of similar projects online and did not see anything good and open.

Ones that seem to be useful are unfortunately in Russian - that I cannot read.

The design would be based on a PIC18F series - perhaps starting off with the Rice LC meter, unless there is specific reason to use something else.
 
Last edited:
The only other choice is to measure relative capacitance. Relative to what? To a standard. How many of us have standard capacitors?
 
Alas its true. Everything requires some form of calibration, and yes, parasitic capacitances will vary, but those can be zeroed out for a short period of time. The reason I started the thread was to gather idea's about methods (well used, or new/exotic) where-by one can trade the need for a 'standard capacitor' for other, more available 'standards'. In my case, a high accuracy voltmeter, and some precision (0.1% 15ppm) resistors.

About ESR, one of the links I posted does a pretty good job of measuring ESR. Uncalibrated (built only using 10% caps, and zero'd) it claims to get 5% accuracy for L, C, and ESR. My build seems to be pretty much spot on regarding ESR, with ceramic SMT caps soldered to leads getting <2mohm. With 1206 100n having a lower ESR than the 0805's (which in theory should be right). Many SMT lowesr caps from laptop motherboards also seemed to agree with the datasheets more of less (ESR varies considerably).

As far s 'what micro to use', any really :) AVR's are quick, and have plenty of beefy peripherals, PIC18's (even PIC16's) will do a similar job. I think for this application, it is much more a case of 'what ever you are acustomed to' as opposed to 'which one can handle things better'.

Apologies for leaving this thread for so long, a got a pretty good contract, its eaten up much of my time.

As a small side issue, I also started a thread about measuring absolute inductance (asking you clever folks all sorts of awkward questions!), along with saturation current - mainly for power magnetics. Which is really the inductance version of a cap/ESR meter. I have not forgotten about either of these projects, and hopefully when work calms down, can collate more information, and come up with a prototype of each or perhaps both in one unit. Lord knows theres enough DIY LCR meter's on the web, but an L meter specifically for SMPS inductors/transformers (L, Isat, DCr) isn't so popular, and I would definately find it handy for dirty custom wound magnetics, or salvaged parts.

I will try to be more active in the forums, I owe it to the many who have shared their knowledge/experiences.
 
About ESR, one of the links I posted does a pretty good job of measuring ESR. Uncalibrated (built only using 10% caps, and zero'd) it claims to get 5% accuracy for L, C, and ESR. My build seems to be pretty much spot on regarding ESR, with ceramic SMT caps soldered to leads getting <2mohm. With 1206 100n having a lower ESR than the 0805's (which in theory should be right). Many SMT lowesr caps from laptop motherboards also seemed to agree with the datasheets more of less (ESR varies considerably).

As a small side issue, I also started a thread about measuring absolute inductance (asking you clever folks all sorts of awkward questions!), along with saturation current - mainly for power magnetics. Which is really the inductance version of a cap/ESR meter. I have not forgotten about either of these projects, and hopefully when work calms down, can collate more information, and come up with a prototype of each or perhaps both in one unit. Lord knows theres enough DIY LCR meter's on the web, but an L meter specifically for SMPS inductors/transformers (L, Isat, DCr) isn't so popular, and I would definately find it handy for dirty custom wound magnetics, or salvaged parts.

I completely agree with your last sentence! If I could be of any help in sharing some load, let me know.

About the ESR meter, were you talking about the LCFesR 3.06 meter?

I would also like to read your thread about measuring absolute inductance - could not find it using forum search.
 
I completely agree with your last sentence! If I could be of any help in sharing some load, let me know.

Will do! Its always good to have other peoples input on such things, be they technical aspects, or just what folks think would be useful. I hope I'm not the only one who doesn't throw anything 'electronic' away without taking a heatgun to its PCB first... promising myself 'they'll come in useful one day!'

About the ESR meter, were you talking about the LCFesR 3.06 meter?

I am indeed. Although perhaps the documentation isn't 'spot on' English, its readable, and convinced me it was worth the hassle of etching a PCB for it (my own design using some SMT, simply because I'm crap at drilling PCB holes accurately). I can't say I've really put it through its paces, but appears to do pretty much what the designer said it would, and rather well I might add.

I would also like to read your thread about measuring absolute inductance - could not find it using forum search.

Ahh, sorry about that. I believe I started a thread on a specific part of a specific way of measuring inductance, which I had already decided on, rather than as general 'what ways do we measure it'. It was mainly to avoid lots of folk saying 'buy an L meter', or 'just use a frequency sweep' :)

Here's the link:
https://www.electro-tech-online.com...-high-current-pulse-generator-l-meter.117836/

As you can see, it starts off mainly as a 'convenient' method for creating a short-duration, high current source using a capacitor, which is for measuring saturation currents on inductors. Sure, we have bench supplies capable of 10A+, but if we're testing say, a 22uH inductor, the current rises so quickly the pulse is very short. That made me think of a small hand held meter, because the average power required to measure saturation current is tiny. Plus if you've ever shorted out a 30A 12V supply accidently, you know its just more hassle (my pliers have scars...).

I should resurect that post really, because I'm still unsure if its a viable and accurate idea. But the basic L=(V/I)*t shouldn't be affected by interwinding capacitance on transformers, and work with all magnetics at the cost of accuracy.
I did start a prototype which I'll have to dig out if you wish.

Blueteeth
 
I am indeed. Although perhaps the documentation isn't 'spot on' English, its readable, and convinced me it was worth the hassle of etching a PCB for it (my own design using some SMT, simply because I'm crap at drilling PCB holes accurately). I can't say I've really put it through its paces, but appears to do pretty much what the designer said it would, and rather well I might add.

Did the author make his firmware open?

I saw this about 3 years ago and noticed that the firmware was closed.

That did not interest me as he uses the same LC oscillation technique as the Rice meter and thus suffers from not being able to measure low Q/high ESR devices that distort the sine waves due to loading.
 
AFAIK the firmware isn't open source. He just provides a hex file which 'timesout' after a minute or so, but you just need to reset the chip (I flip the on/off switch on my box).

LC oscillation, as you rightly pointed out, can lead to erronous readings with low Q, and high ESR. Similar properties affect measuring inductance - in my case coupled inductors (or a transformer). That lead this thread, and the other :)
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top