How to measure and calculate the phase angle of auto Auto Balancing Bridge?

Discussion in 'General Electronics Chat' started by PSIR, Nov 19, 2010.

Apr 23, 2008
29
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Hi everyone:

Please take a look at the attached schematic.

There is an Auto Balancing Bridge in sight. I have realized how to calculate the Z(DUT). DUT is so called Device Under Test.

But, how to measure and calculate the phase angle of Z(DUT)?
Is there any circuit can make it? Thank you.

Best Regards.

• Auto Balancing Bridge.jpg
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2. t06afre AAC Fanatic!

May 11, 2009
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Apr 23, 2008
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The LOAD→DUT(Device Under Test) is a R-C series circuit.

Generally speaking, How dose the LCR meter measure the phase angle?
Is it complex? I couldn't figure out the principle. So help me please.

Apr 23, 2008
29
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May I ask a question.What does the mean of Auto Balancing Bridge?

How does it makes Auto Balancing? Thank you.

5. t06afre AAC Fanatic!

May 11, 2009
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What exactly are you trying to create? I see you have posted many questions about skin measurements. But you do not seam to follow up.

Apr 23, 2008
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Hi, Actually, I have been researching skin measurements for many years.
I find that skin measurements is based on LCR meter's principle.

I have searched plenty of technical document that is related on impedance measurement by using Auto Blancing Bridge. But hardly mention to how to measure phase angle accross the load.

May any body tell me where I can search the data?

Thanks a lot.

7. t06afre AAC Fanatic!

May 11, 2009
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Why do want use such high frequency. The higher frequency you use the more of the deeper tissue you will measure. What you want is to measure is the skin, and not deeper layers. Can you also tell us more about your (planed) measurement setup?
I have looked through your postings and I see I have recommended you the 3-electrode system. At least at one occasion. But you seams to drop out of your threads. Then the asnswers are not as you planed or wanted them to be

8. t06afre AAC Fanatic!

May 11, 2009
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@PSIR
I have designed several commercial skin conductance applications. So I actually do know my way in this topic And I may help you but it is up to you.
And I have always used the Auto Balancing Bridge. But I prefer to call it a current to voltage conveyor.

PSIR likes this.

Apr 23, 2008
29
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Dear Sir.
I'd like to appreciate your timely help. May I konw what kind of commercial skin conductance products which you have developed. Actually, I am interested in the Bioelectrical Impedance Analysis (BIA) instrument and try to realize the methood of measurement. I find that it is related to LCR meter, which is consist of Auto Balancing Bridge.

So far, I still ccoudn't understand how to measure the phase angle accross the DUT(Load). It is hard to search the related data form the internet. Can you give me some advise about developing (BIA) instrument?

Sincerely

PSIR

10. t06afre AAC Fanatic!

May 11, 2009
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Sorry I forgot about this thread. I am sorry but I can not speak about who my contractor was. As I have signed on not to do so. But I am quite free to talk about technical details. As this is mostly public know material. But to go back to your needs. How will your measurement setup be. And how do you plan to measure. Will you do frequency sweeps, or use a constant frequency. What are your reason for using 10 KHz.

Apr 23, 2008
29
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Dear Sir.

I look forward to talking to you about technical details.

First, I am desired to understand the LCR Meter's measurement principle. I try to measure a R-C series circuit and separate its' Impedance, Phase Angle, Resistance, Reactance. In the beginning, I wll follow the general spec of LCR Meters. Measure it with 10 KHz / 1 Vrms sinewave signal.

Second, as soon as I could measure the four parameter I will change the test frequency up to 50 KHz. Then I will take the device to measure body and get the four parameter of body. I regard the equal model of skin to R-C circuit.

Finally, My goal is to build a BIA test device. Maybe I will take multi frequency to measure body. May I ask a question. What is the methood of BIA measurement which is used generally?

12. jt6245 Member

Feb 18, 2011
21
4
A lock-in amplifier or phase sensitive detector is used to extract real and imaginary part. 0 degree for real and 90 degree for imaginary part. All calculation is in complex form.The last step is to change impedance in complex form to polar form,and we get the phase angle between impedance voltage and current.
"Agilent impedance measurement handbook fourth edition"provides very good information.In this case ,especially 2.3.3 section of vector ratio detector,recommand
PSIR has a look.
http://cp.literature.agilent.com/litweb/pdf/5950-3000.pdf

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