Capacitance measurement help

Dear All,

I just bought my first LCR meter Applent AT825 and faced issue when testing it. I measured capacitance of 22 uf Panasonic NHG series aluminium electrolytic capacitor with this meter and same thing with Agilent U1252B multimeter. Well Applent is 4 wire meter and dedicated measure this but Agilent tells it has error max. 1%. Look at the differences, I don't understand why is there so big differences:



Applent is measuring with 100Hz but I don't find from Agilent manual what frequency it is using. It only says display update rate 4 times/sec so is it 4Hz? Which one is showing the right thing, please could someone explain?

btw. there was test report included with the Applent telling there is only 0.0016uF error on 10uF range.

Thank you in advance. Your help is greatly appreciated.

the applent is a true lcr meter, so it is probably closer to the real value
you can even measure the capacity in DC (measuring the charging time)
and also the measured value can change with the frequency a lot
these different values are not impossible
you should trust the applent more when dealing with L C or R measurments.

Hi,

here you see: just a value form a measurement tool is only half of the information.

you additinally need to know how the measurement is done.

* Different frequencies
* including/excluding ESR
* different AC voltage levels
* different DC bias voltage
* different cable length (and wiring: 2W or 4W)
* different waveform
* different measurement methods (fixed frequency sine; constant current slope measurement...)

Both values may be true and precise.

Klaus

Both values may be true and precise.

Click to expand...

Yes. It's pretty useless to compare different measurements of a lossy and frequency dependent capacitor like aluminium electrolytic without knowing the exact conditions.

It is difficult to compare capacitance values of electrolytic capacitors because the capacitor is formed by an electrolyte and a metal foil. If you could give us the reported values for a film capacitor (or a mica capacitor) we can definitely comment. The double layer capacitance is a diffuse concept and the capacitance values are usually have wide margins (and there is a reason for that).

Tantalum capacitors are somewhat better because they use a solid electrolyte. The diffuseness is still there but far more reproducible.

Try measuring a good quality film capacitor instead of an electrolytic.
The measurements should be much closer.

Try measuring that same capacitor at 1 kHz and 10 kHz.

Confirmed that the value seems to be quite much different with different frequencies. Eg. Higher the frequency lower the capacintace. Didn't figure out how to measure capacity with that applent in DC.

I had some tantalum caps and they seem to vary much less on frequency like mentioned. I had 1.0183uF by Applent and 1.05 by Agilent. Probably both meters are correct like KlausST said.

I expect that the difference between the two readings for a good film capacitors will be less than 1%, perhaps within 0.5%.

I am surprised to see the difference for a Ta cap is more than 3%- it should have been around 1-2% max.

Veketti said:

Confirmed that the value seems to be quite much different with different frequencies. Eg. Higher the frequency lower the capacintace. Didn't figure out how to measure capacity with that applent in DC.

I had some tantalum caps and they seem to vary much less on frequency like mentioned. I had 1.0183uF by Applent and 1.05 by Agilent. Probably both meters are correct like KlausST said.

Click to expand...

;

See this thread for discussion of the reason why the measured capacitance of electrolytics (including tantalums) varies with measurement frequency, and why DMMs get different results:

https://www.eevblog.com/forum/testgear/about-capacitance-measurement-with-dvms/msg489690/#msg489690