### Author Topic: B&K 879B LCR meter Problem  (Read 18966 times)

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#### saturation

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##### Re: B&K 879B LCR meter Problem
« Reply #25 on: January 28, 2012, 11:01:17 pm »
I hope this helps.  The bode plots of interest is just amplitude vs frequency.  For practical work, you don't need to truly plot an entire curve just sample key points to insure its following the ideal slope, then jump to the frequency of your interest.

A quick way is make a simple [ i.e., "first" order ] RL or RC high pass filter such as:

Amplitude is proportionate to reactance, X, of the L or C under test, and if R is constant, then Z ~ X.

For inductors,  the working equation is:

and its X is :

What you want to find is any deviation from the ideal caused by manufacturing issues or parasitics, or when ESR in capacitors that cause the curve to flatten out, and the resonance point, were reactance rises with higher frequency in capacitors, or drops with inductors.

Impedance for audio transformers was described by The Electrician.

Accuracy depends mostly on the vertical accuracy of your scope and the parasitics in your setup.  Most scopes ~ 4%.   Its helpful to keep working frequency low, << 100kHz to avoid parasitics, except when you need to know impedance at your circuits working frequency, or checking capacitor ESR values reported in spec sheets at 100 kHz.

At higher frequencies, and smaller values of C or L, parasitics to watch out for come from interconnection capacitance in breadboards, inductance of test leads, and the load effects by the scope probes.

I think in your OP you used a function generator ?? or similar to spot check the HH.  You can do this for most all measurements too and do what both a HH LCR meter and an expensive impedance meter can do without spending more.  The problem is the set up and the cables to make it convenient; on the Rigol 1052e you can set up a pass-fail waveform to make it easier.  In high frequencies, the clamps, cables, and other fixing hardware used have intrinsic capacitance and inductance which now matter more, and have to be taken into account.

I guess I need some more info on how to set this up. Can you help me?
I do have a DS1052E and a DG1022, and also an HP 8903 so this is more than I need to make these plots I suppose. But I am not sure how to do it.

Best Wishes,

Saturation

#### bsgd

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##### Re: B&K 879B LCR meter Problem
« Reply #26 on: January 29, 2012, 03:58:15 pm »
@Saturation,
Thank you very much. I suppose I will have a lot to do and study now before I setup my transformer test jig.
I dont know how but I missed that other thread about the 879B wich I also intend to read.

#### saturation

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##### Re: B&K 879B LCR meter Problem
« Reply #27 on: January 31, 2012, 09:14:45 pm »
You're welcome.  If you have a quiet moment and some downtime, its an experiment that will help you know your parts better.  The technique is essentially the basic function of an impedance analyzer, just done all manually.

@Saturation,
Thank you very much. I suppose I will have a lot to do and study now before I setup my transformer test jig.
I dont know how but I missed that other thread about the 879B wich I also intend to read.
Best Wishes,

Saturation

#### grenert

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##### Re: B&K 879B LCR meter Problem
« Reply #28 on: February 13, 2012, 01:36:43 am »
I just read about a DIY LCR meter that appears to be able to handle large inductances (in the H range):
http://members.upc.hu/lethanh.hung/LCFESRmero/en/index.htm

The designer includes his email address there, so you can confirm with him that it would work for your application.

Smf