Author Topic: What frequency to use  (Read 2524 times)

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Offline Jane

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What frequency to use
« on: June 02, 2015, 08:03:09 am »
What frequency should I use to measure capacitors properly? I use LCR meter DEER DE-5000, where I can choose the measuring frequency. I checked an electrolytic  capacitor that is marked 4700uF.
I tried
100Hz measuring frequency and measured only 4400uF (ESR 0.089)
120Hz measuring frequency and measured only 3360uF (ESR 0.09)
1kHz measuring frequency and measured no measured value
Higher frequencies did not measure good values either

Is that capacitor bad?

When I used a smaller capacitor ( 1uF), it provided acceptable values for  higher frequencies.
 

Offline Simon

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Re: What frequency to use
« Reply #1 on: June 02, 2015, 08:35:03 am »
How long is a peice of string ........ ?

I think the frequency depends on the capacitor and it is probably more important to measure it with a frequency like the one you wish to use it with. All components values are specified under "certain" values.
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Online tautech

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Re: What frequency to use
« Reply #2 on: June 02, 2015, 08:40:38 am »
One must consider manufacturers intended use: coupling, linear PSU, SMPS etc.
Datasheets usually have a spec'ed ESR value @ 100 or 120 Hz and 10 or 20 KHz.

So depending on the actual usage of a cap you wish to check, you need to set the test frequency accordingly.

You haven't disclosed if the cap you tested was new, NOS or used.
If it is NOS then after re-forming it will probably test OK for capacitive value.
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Online tautech

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Re: What frequency to use
« Reply #3 on: June 02, 2015, 09:13:51 am »
Thought I'd better check the test frequencies in my Smart Tweezers, they are all I have ever used or needed for cap checks:
100 Hz
120
1 KHz
10 KHz
Or Auto

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Offline Jane

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Re: What frequency to use
« Reply #4 on: June 02, 2015, 11:46:08 am »
Thanks for the feedback. I use the capacitors in power supplies (in SMPS). What frequencies shall I use?
 

Offline retrolefty

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Re: What frequency to use
« Reply #5 on: June 02, 2015, 11:59:18 am »
Thanks for the feedback. I use the capacitors in power supplies (in SMPS). What frequencies shall I use?

 Check the datasheet of the active controller chip used in your SMPS. This might also require a schematic of your SMPS.

 

Offline macboy

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Re: What frequency to use
« Reply #6 on: June 02, 2015, 01:11:07 pm »
What frequency should I use to measure capacitors properly? I use LCR meter DEER DE-5000, where I can choose the measuring frequency. I checked an electrolytic  capacitor that is marked 4700uF.
I tried
100Hz measuring frequency and measured only 4400uF (ESR 0.089)
120Hz measuring frequency and measured only 3360uF (ESR 0.09)
1kHz measuring frequency and measured no measured value
Higher frequencies did not measure good values either

Is that capacitor bad?

When I used a smaller capacitor ( 1uF), it provided acceptable values for  higher frequencies.
There is an upper limit to the capacitance at the higher frequencies, check the manual. 4700 uF is definitely above the limit. You can still measure ESR of any capacitor at any frequency, just select the Rs function instead of Cs or Cp. Rs measures AC resistance at the test frequency. The DCR function is DC resistance and is used to measure resistors or resistance of inductor windings.

Also, make sure to run the Cal function every so often to ensure accuracy.
 

Offline tggzzz

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Re: What frequency to use
« Reply #7 on: June 02, 2015, 04:52:30 pm »
What frequency should I use to measure capacitors properly?

What is the purpose of the test? Acceptance/rejection test, binning components, correct circuit operation...?

Extreme example of why purpose is important...

Back in ~1980 phone calls were sent between telephone exchanges using 2Mb/s PCM over twisted pair cables. The cable was spec'ed and measured at 1.6kHz, and that was absolutely fixed and could not be varied. Why? Because even if the manufacturers didn't change the cable, changing the test would have allowed them to raise the price - and the GPO didn't want that!
There are lies, damned lies, statistics - and ADC/DAC specs.
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