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phase extractor question

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Achu:
Could you explain how the op amp section work?

Thank you

pwlps:

--- Quote from: Achu on December 31, 2019, 01:43:52 pm ---Could you explain how the op amp section work?

Thank you

--- End quote ---

There is nothing special about the opamp section: U7 is a high impedance buffer and U1 an inverter. U3 and U6 select either a direct or inverted voltage depending on the sign of reference signals (square waves) Vrefc and Vrefs (see my explanations posted on June 24).

If you were asking about U2 and U8 these are comparators, not opamps. U2 generates a square signal following the voltage across C1 and U8 generates a square signal following the voltage across R1. Since R1 and C1 are in series the voltage across R1 is proportional to the current through C1, therefore the two generated square signals are in quadrature. The U8 signal Vrefc is in phase with the current through Z (because Z is in series with R1) and the U2 signal Vrefs is in quadrature with it.   R8 and R11 are just to provide a DC polarisation of the comparator inputs.
 

Achu:
Ok thanks for explaining.
Now, if I were to use it as an LCR meter, when measuring a capacitor one of the output voltage will be negative and could you tell me how would I measure it using a standard Microcontroller ADC say,Arduino or PIC.?

I know I'm going off topic but I could really use the knowledge.

Thank You

pwlps:

--- Quote from: Achu on January 01, 2020, 01:15:07 pm ---Ok thanks for explaining.
Now, if I were to use it as an LCR meter, when measuring a capacitor one of the output voltage will be negative and could you tell me how would I measure it using a standard Microcontroller ADC say,Arduino or PIC.?

I know I'm going off topic but I could really use the knowledge.

Thank You

--- End quote ---

Happy New Year!
You can map any voltage range to the 0-5V range, e.g.
https://electronics.stackexchange.com/questions/378301/circuit-for-mesure-positive-negative-voltage-vref-resolution
https://krakkus.com/measuring-negative-voltage-arduino/"

This needs a careful and stable calibration, therefore to correctly measure very small phase shifts (signal close to zero) I would add here an auto-zero feature using a micro reed relay like D31A3100 or equivalent.
 

Achu:
Happy new year to you too!!

So it is possible to use the same circuit??
I used an SPST switch ti mix non shifted input and shifted reference and sampling gave same results I think, is that wrong?
Also if I were to remove the coupling transformer, how should I modify it?
And could I use an op amp current source to drive the impedance?
One more question, don't we need two readings for current and voltage?


Thanks

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