capacitance meter?

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allmighty1

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Joined 2013
#1
I an planning to build an active cross over, specificly the ESP 09, and I recon a capacitance meter would be a good idea. I have seen come quite cheap meters on Ebay, some seem to be Arduino based. Are these any use? They seem pretty cheap which is great but would they be a waste of time?
I have no experience in these things so I'm hoping someone can advise.
Thanks Guys!
Chris.
 
#2
I have been wanting to build one of the PIC based ones for some time.
I have all of the parts but it is one of many projects that I have going.

Knowing how it works I don't question its accuracy at all.
Finding a LCD or even a LED display in my pile of stuff was the one thing holding me up.

I am just now learning use my computer as a display so I won't need any LCD's now. 😉

I also have a Capacitance function built in to my cheapo DMM's and they work good as well.
I have used them to check against some software based measuring systems such a Visual Analyzer and RLC that use a sound card and they work great as well and can be very accurate if care is taken that you learn to properly calibrate the system when you use it.

Here are links that will help get you started,

http://www.diyaudio.com/forums/software-tools/212908-exploring-visual-analyser-va-3.html#post3383659

WB6DHW

In this thread I also show a very good buffer to drive the DUT as well,

http://www.diyaudio.com/forums/soft...re-capacitor-impedance-graph.html#post3816243

This is the link to VA,
Visual Analyser

I hope this helps you.

jer 🙂
 
#3
Get the specs on it. See what the range(of capacitance) of measurement is and how accurate it is. Also look into what frequency it does the measurement at. I think most of them are audio frequency range. But if it does the measurement at like 1MHz, it'll give you false measurements, as many poly caps and audiophile-grade caps only act as pure caps out to a few hundred KHz.
 
#5
Fluke and I are like this, *imagine me crossing my fingers*

Cheap? Hardly. Awesome? Yes. It does so much that I don't have to use an O-scope or anything 99.99% of the time. I wish it could measure lower capacitance, 0.01nf isn't bad! For speakers etc, it's plenty. Frequency includes the entire audio band and AM. The temp measurement is very handy, too. You can check your chips and their consistency of heat dissipation!
 
#10
I would go for this one: Backlight Control LCR RCL Inductance Capacitance Resistance Meter Tester 4070L | eBay
Not only is it a complete, cased instrument, but much more important, it will be calibrated on all ranges. This is very important, because if you buy a µController board, you'll have to find a number of "standards" as well.

The accuracy of the DMM style one may not be great, but you can be sure that fresh from the factory, it does better than 1% provided you use the ranges sensibly.
 
#11
I have a meter similar to the 4070L eBay I bought 2 years ago for a similar price.

The absolute accuracy seems reasonable when I checked the value of some know parts, but I have no way to check it with calibrated standards.

It certainly is most useful for matching up capacitors and coils, for which I have mostly used it.

Amazing value for its low cost.
 
#12
Thanks Elvee, I'm hoping that even if the accuracy of these cheap meters is not great (although 1% is probably good enough for most things I am building) that the results would be repeatable. For the crossovers I think the most important thing is to match values so in that respect they should be fine for the job.
I recon if I measure a selection of caps several times and get the same result for each one then I can trust the meter for matching values?
Any thoughts on that?
 
#13
Thanks Cornelis too! Your post came up while I was writing. I will order one now.
I thought a LC meter would be way out of my budget but these things are amazingly cheap. I sort of assumed they would be rubbish.
Thanks to everyone who replied.
Chris.
 
#14
If you are comparing capacitance values, then even cheap high tolerance (low accuracy) meters (and free add ons to DMMs) are very good.

Absolute tolerance/accuracy is completely different.
Many capacitance meters are abominable for absolute accuracy.
Few good meters claim better than +-1%
 
#16
I don't have any absolute standards to go by, But, Even my cheap Cen-Tech P37772 shows exactly what is printed on the caps I have even down to 6-12pf and less with a 1pf resolution.

This is very surprising considering one or two of its other voltage and resistance ranges are way out of tolerance and accuracy spec between its ranges.

It almost seems to be more accurate than the Sperry DM-6450 that I just got for capacitance!!!
Hmmmmm......Go figure.

jer 🙂
 
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#17
In particular, for electrolytic capacitors, the Capacitance function in most multimeters is pretty inaccurate, NOT because it is inherently off but because it doesn't tell you the information you need to know. The capacitance meter on most DMMs tells you the DC capacitance or something close to it (at most a few Hz of AC). This value can be significantly (several % minimum) different from the value even at 120Hz. The larger the capacitance, the more it seems this becomes an issue.

Here is a test I did using a multimeter (UT61E, which is known for having a solid cap meter) and my Der EE DE-5000 LCR meter (.

The first capacitor is a United Chemicon LXZ 100uF electrolytic.
DC (on the UT61E): 103.90uF
100Hz (on the DE-5k): 101.84uF
120Hz (on the DE-5k): 101.69uF *this is the freq at which most caps are spec'd*
1kHz (on the DE-5k): 99.80uF
10kHz (on the DE-5k): 93.4uF
I attempted on the 100kHz range but it said out of limits (the upper range is 20uF)

The second is a Panasonic 560uF electrolytic
DC (on the UT61E): 549.30uF
100Hz (on the DE-5k): 525.60uF
120Hz (on the DE-5k): 524.2uF *this is the freq at which most caps are spec'd*
1kHz (on the DE-5k): 499uF
It was out of limits on the 10k and 100k ranges.

The third is an NKL electrolytic
DC (on the UT61E): 1031.1uF
100Hz (on the DE-5k): 975.0uF
120Hz (on the DE-5k): 968.4uF *this is the freq at which most caps are spec'd*
1kHz (on the DE-5k): 883uF
It was out of limits on the 10k and 100k ranges.

If you want to design proper crossovers, it would be ideal to get all of the values at a frquency as near to your crossover point as possible (1kHz or 10kHz depending). With a real LCR you can select this value, then you can also get Q, ESR, Rp, Theta, D, etc. Allowing you to much more accurately spec the capacitor and as a result the performance characteristics of the crossover.

Addressing the budget meters on ebay, some are better than others. The PIC/Arduino based ones tend to be OK at best but way better than the others at that price range. Definitely better than a multimeter in that you can get more information out of them but their are questions about the reliability of their reads. That being said, even within them, some are better than others. Many have a problem with the output frequency drifting under load which then affects the reads. Additionally, while their precision is decent to very good, their absolute accuracy tends to be VERY lack luster unless you can provide some better quality capacitor references and calibrate from those. For a hobbyist making cross-overs, these basic meters are may be enough.

For other uses, like checking capacitor health. These are nowhere near enough. Most people like to check ESR but ESR is at best an estimate at capacitor health. A much better way is tan delta (aka tan d or D). This value can easily be found in all capacitor datasheets and is done at a specified frequency (usually 10 or 100kHz). Having a meter that can hit these frequencies and measure what you need is indispensable. The best value this time is still the Der EE DE-5000 which is very easy to get one ebay for around $100 shipped (with three optional accessories). It basically meets or beats Agilent (now known as Keysight) best $400 handheld LCR U1733C. If you want to see more on it, read my review here. THis meter gives you 0.3% absolute accuracy, 0.25% tolerance binning, multiple frequencies, plus loads of measured values. If you can afford it, then you won't regret paying more for this one. It's highy highly thought of over at EEVBlog and is the exact same as the IET Labs DE-5000 and DE-6000(a marketing gimmick).


TL;DR version: Multimeter capacitance functions are usually at least several % off due to providing DC capacitance, not 120Hz capacitance. PIC/Arduino versions on ebay CAN be a bit better, with better precision but accuracy is still typically off by a few %. Best value option is the DER-EE DE-5000 at around $100.
 
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#18
There should be little or none of this effect(at audio frequencies) on poly caps, which is what you should be using anyways for crossover applications. Or at least something with a stable dielectric, like class I ceramics for example. If a cap truly changes its capacitance, as many do, at different voltages and frequencies then it's likely to add distortion when used as a filter.
 
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#19
Dave2 said:
There should be little or none of this effect(at audio frequencies) on poly caps, which is what you should be using anyways for crossover applications. Or at least something with a stable dielectric, like class I ceramics for example. If a cap truly changes its capacitance, as many do, at different voltages and frequencies then it's likely to add distortion when used as a filter.
Click to expand...

Yeah that's true, I forgot that electro's aren't really used in crossovers. In the case, you are ONLY going to be using it for crossovers and nothing else then any of them should be good enough. If you want a device with more than one use, I'd still recommend the DE-5000. Considering it occasionally goes on sale at the $85 or less price point (with the three optional accessories) it's a lot of value for not a LOT of money.
 
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