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AD5933 GainFactor and impedance calculation problem

Question asked by umapathi on Mar 12, 2012
Latest reply on Mar 12, 2012 by AndyR

Hi,

I am using AD5933 and ATmega 128 controller for my project to find the impedance.

In AD5933  i used the below  formula to find the gain factor and  Impedance.

 

gain factor =1/(Impedance*Magnitude)

 

Note: I used the  reference impedance RFB = 100 kOhms. and Zunknown==>(Rcalibaration) =100KOhms.

 

and to find the impedance,

 

impedance = 1/(Gain factor*Magnitude)

 

 

 

The gain factor is changes is very small for all resistance measurements.. so the magnitude changes it will be small. so when i am reading the impedance it shows only constant values which is showing at the time of calibration time(always shows  like 100000.00000 respective of any changes in Calcode(Magnitude) values)  not the original impedance value. But Magnitude value changed largely.... how to i change that both of the line to measure original impedance value from AD5933 .

 

Here i have written my source code which is connected with atmel Atmega128 controller.

 

source code:

 

Calcode=sqrt(R*R+I*I);

 

code=1/(100000*Calcode);

 

impedance =  1/( code * Calcode);

 

here i have attached my circuit configurations also. What is the change i should make to read the correct value impedance from AD5933.

 

  Please give me suggestions.. Thanks...

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