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Disappointed of ceramic capacitor ESR value, does these values appear valid?

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David_

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Hello.

I just bought the following:
ceramic 1µF 100V 10% X7S 0805.
ceramic 0.1µF 100V 10% X7R 0805.
ceramic 10nF 100V X7R 0805.
polymer 12µF 80V 20% 50mΩ ESR.

And some more but it is these four that I have measured, which gave these results.
the first pair of values are at 100Hz, second is 1kHz, then 10kHz and 100kHz using my mastech MS5308 LCR Meter:

1µF cer:
960nF/21Ω 936nF/2.2Ω 900nF/0.16Ω 905nF/0.01Ω

0.1µF cer:
94nF/186Ω 92.3nF/20.6Ω 90.5nF/2.2Ω 87.9nF/0.2Ω

10nF cer:
10.2nF/1.5kΩ 10.07nF/194Ω 9.83nF/30Ω 9.52nF/4.95Ω

12µF poly:
13.2µF/1.6Ω 12.95µF/0.25Ω 12.63µF/0.08Ω 14.65µF/0.04Ω

Now the polymer electrolytic checks out, my meter shows ESR when calculating as a series model and if I choose parallel on 100kHz it shows near 12µF.

But what about the ceramic, I guess the 1µF is not bad since it is for higher frequency's as the a mainly if not only for decoupling.
But the 10nF at 100kHz shows 4.95Ω!!! That aint low...
Nor is 200mΩ for the 0.1µF, but then again this is the first ones that I have bought and they are better than the ones I have de-soldered for the most part.

Is this normal values?
What is good values?
How do you separate a bad/low quality ceramic from a good/high quality one?

Regards
 

pjmelect

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Ceramic capacitors have very low ESR, You are measuring the reactance of the capacitor.
 

David_

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Wait, what?
The meter as a few things it can measure, why would it say ESR and be reactance?
This answer confuses me somewhat, could you explain anything more about this?
 

pjmelect

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The reactance of a capacitor is very much higher than the readings that you are getting, your meter is not correctly subtracting this from the ESR, which I would expect to be a small percentage of an ohm.
 

The Electrician

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It looks like your measurements are ok. Here's a sweep of the impedance (green) and ESR (yellow) of a 10 nF ceramic cap. Unfortunately, it's a Z5U dielectric, but you get the idea of how ESR varies with frequency in a ceramic. The sweep goes from 100 Hz to 1 MHz. Bottom of the Y axis is .001 ohm, and the top is 1 K ohm. The ESR decreases about an order of magnitude for each order of magnitude increase in frequency. My numbers are close to yours, except at 100 kHz I get about .9 ohms while you get 4.95 ohms, but your meter seems to see .01 ohms ok with the 1 uF cap. I suspect your meter's reading is correct; I assume you did the open/short compensation before measuring. The impedance is off scale below about 20 kHz.



Here we see impedance and dissipation factor for the same capacitor. D is about a constant .005 from 100 Hz to 100 kHz, which is reasonably good.



And, finally, here is a sweep of a 22 uF polymer electrolytic (OSCON):

 

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The measured ESR values are well in accordance to manufacturer specifications for X7R capacitors.

The low frequency numbers can be best described by a constant disspation factor D.F. = ESR/Xc which translates to a constant distance between Z and ESR curve in the logarithmic impedance plot. Typical X7R D.F. is in a low percent range at ambient temperatures. Besides type variations, a strong temperature dependency is characteristic for it, so measurements are expected to differ.

 

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