# How to measure Capactive's ESR value with 10KHZ signal?

Discussion in 'General Electronics Chat' started by PSIR, Nov 11, 2010.

1. ### PSIR Thread Starter Member

Apr 23, 2008
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Hello everyone:

How to measure Capactive's ESR vaule with 10KHZ signal?
Is there any method or datasheet which I can refer to?

Best regard

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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Jul 7, 2009
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Hmm, lightning hits twice... I just posted a method for someone else here.

4. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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This is one I use most

I also have an LCR meter, but I reach for this one about 70% of the time. The values on LCR and Blue ESR Meter have always been very close when I tried out several good and bad on both. It also can can tell how charged/dead a battery is by showing you the internal resistance!

5. ### The Electrician AAC Fanatic!

Oct 9, 2007
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Why do you want to measure ESR? Are you trying to locate bad electrolytic capacitors on a computer motherboard? Or do you have another reason?

I don't think this is going to work. You have created a voltage divider, but the output isn't loaded down by just the capacitors ESR; it's loaded by the series combination of the capacitor reactance plus the ESR. This method assumes that the reactance of the capacitor is much less than the ESR so that the loading effect is due only to the ESR.

If you use a frequency of 60 Hz, even a large electrolytic (that is not defective) will have a reactance much larger than its typical ESR. The disparity will be even worse for small capacitors such as a typical film capacitor.

For example, a 10,000 uF capacitor from my parts bin has a measured ESR of 25 mΩ but has a reactance of 265 mΩ.

Jul 7, 2009
1,585
141
Dang, you're right, Electrician. I've used the method at 10-100 kHz and it works fine, but it could have a problem at 60 Hz or so. Still, if the ESR is an order of magnitude or more higher than the reactance, you'll see little voltage drop and it might be a clue that the cap is bad.

7. ### PSIR Thread Starter Member

Apr 23, 2008
29
0
Hi, I just want to know how does the LCR Meter measure ESR?
I try to figure out the principle of it.
How do I search the related data from the internet?

Thank you!

8. ### PSIR Thread Starter Member

Apr 23, 2008
29
0
It's a good idea. But I wonder if I could measured the ESR.
Would you please tell me how do I calculate the capacitor (C)?
Thanks!

9. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,377
355
The principle is easy to describe. This type of meter:

http://www.waynekerrtest.com/global/html/products/LCR/6430 6440.htm

and this type:

http://www.bkprecision.com/products/sub_categories/49/lcr-meters.html

use the following technique:

The meter applies a sinusoidal current (at 10 kHz or some other frequency also can be used) to the capacitor and then measures the voltage across the capacitor. The ratio of voltage to current (E/I) gives you the magnitude of the capacitor impedance (Z=E/I). The phase angle between the voltage and current allows you to calculate the ESR. If θ is the phase angle, then the ESR is given by ESR = Z*cos(θ).

This type:

http://www.bkprecision.com/products/model/881/in-circuit-esr-tester.html

and:

http://www.howardelectronics.com/ieinc/cwinfo.html

don't use 10 kHz. They use a 100 kHz frequency sinusoidal test signal and rely on the fact that at such a high frequency the capacitor's reactance is essentially zero and the ESR is the dominant component of the impedance.

This meter:

http://www.anatekcorp.com/blueesr.htm

and several others use the technique described here:

http://ludens.cl/Electron/esr/esr.html

which is to use a square wave or rectangular pulse technique.

PSIR likes this.
10. ### PSIR Thread Starter Member

Apr 23, 2008
29
0
Dear Electrician.

Thank you for your description. Now I have realized the principle of ESR measurment. According to the description. To get the ESR. First, you should measure the impedance by (Z=E/I). Second, measure the phase angle of capacitor. Finally, calculate the ESR by formula ESR = Z*cos(θ).

I tried the method and make it successfully.
Please take a look at the attached schmatic.
There is a capacitor with 10Ω ESR.
I can get the impedance of capacitor by (Z=E/I).
But, What kind of circuit can measure the phase angle between A and B?