# REW for capacitor measurement !



## lurch1 (Feb 2, 2011)

did you know it' possible to measure capacity and loss resistance ( in ohm) ? :bigsmile:

select "measure" > "impedance" > do like a speaker measurement , but with capacitor instead.

on the curve , move your cursor , and see at bottom left the C+Rserial value .
I tried and compare with a calibrated high end LCRmeter , measure accuracy is good at 1KHz ;10KHz and above ..
bad measure at 100Hz .? why ?
I'll try with a shorter measure band ( 50 - 500HZ , 1M resolution .)


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## JohnM (Apr 11, 2006)

Make sure you go through the impedance cal step first, as small gain differences in the soundcard inputs can otherwise cause large errors. 

At low frequencies the capacitive impedance becomes high and the shunt impedance of the soundcard inputs starts to significantly affect the measurement.


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## lurch1 (Feb 2, 2011)

ok .
I 'll also try with another sound card (actually behringer uca202 usb) .
calibration curve is OK , with a precision measured resistor .

for example , a MKL siemens 10uF measured with :

....................100Hz......1K............10KHz
lcr meter :......1.4Ω........0.25Ω......43mΩ
REW :............*70*Ω.......0.27Ω......52mΩ
.......................:coocoo:
capacity value is ok , total Z (left side graph) and phase (right side) too .


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## regiregi22 (Mar 13, 2014)

JohnM said:


> Make sure you go through the impedance cal step first, as small gain differences in the soundcard inputs can otherwise cause large errors.
> 
> At low frequencies the capacitive impedance becomes high and the shunt impedance of the soundcard inputs starts to significantly affect the measurement.



How much of a requirement is the precision of the resistor? Can I get a decent measure just using 1% tolerance resistor? I would have to make an order just for a pari of resistors and delivery rates may not worth it...


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## JohnM (Apr 11, 2006)

You'll get a measurement that has a 1% tolerance in its impedance values 

If you can make a more accurate measurement of the resistor and enter that you will get more accurate results.


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## regiregi22 (Mar 13, 2014)

Cool! That's enough for me. I thought maybe 1% could lead to, lets say, 20% deviation.

Thanks!


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