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AFE4300: Ro and Ri

Esther Lee
Prodigy 50 points
Other Parts Discussed in Thread: AFE4300

Hello,


I want to calculate Ro_ohms and Ri_ohms values in I/Q mode from AFE4300 GUI results.
I know that Ro_ohms and Ri_ohms are corresponding to R0 and Rinf. Moreover, these values are Cole-cole model parameters.
But I am confused with these parameters calculation.

Maybe, should I draw the circle using Zx_mag and Zx_phase in 4 freqencies? But I can't calculate this circule.

How do I calculate Ro_ohms and Ri_ohms?

And, Why need I values in 4 freqencies? I think I can draw circle using values in just 3 freqencies..Am I right?

  • 0
    TI__Mastermind 18275 points
    Esther,

    I have deleted all other posts except this one. In the future, please edit your original post or continue on the same thread to reduce the number of posts.
  • 0 in reply to Amy Schnoor
    TI__Mastermind 49176 points
    Hello Esther,

    Below is the set of equations to calculate Ro and Ri.



    % retreive I Q data calibrated with units of ohms
    p=p*pi/180;
    [I,Q]=pol2cart(p,m);

    % take 3 pair of points of the 4 IQ data: 8, 16, 32 and 64
    x1= I(1);
    y1=-Q(1);
    x2= I(2);
    y2=-Q(2);
    x3= I(3);
    y3=-Q(3);

    %%%%%%%%%
    ma=(y2-y1)/(x2-x1);
    mb=(y3-y2)/(x3-x2);
    xc=(ma*mb*(y1-y3)+mb*(x1+x2)-ma*(x2+x3))/(2*(mb-ma));
    yc=-1/ma*(xc-(x1+x2)/2)+(y1+y2)/2;
    r=sqrt((x1-xc)^2+(y1-yc)^2);

    % parameters: ro: resistance at dc, ri resistance at infinity
    ro=xc+sqrt(r^2+yc^2);
    ri=xc-sqrt(r^2+yc^2);
  • 0 in reply to Amy Schnoor
    Prodigy 50 points

    Oh, I'm very sorry.

    I don't know that I uploaded many posts. Maybe my computer has a problem..

  • 0 in reply to Praveen Aroul
    Prodigy 80 points
    In which formula we can use Ro and Ri value to calculate FFM , %FM, TBW
  • 0 in reply to IMRAN SHAIKH
    TI__Genius 12555 points
    Hi Imran,

    Ro and Rinf are Cole parameters to estimate Total Body Water (TBW) and Extracellular Water (ECW).
    www.journals.uio.no/.../239

    Regards,
    Prabin
  • 0 in reply to Prabin Yadav
    Prodigy 80 points

    Thanks for the reply Prabin i saw the attachment pdf but in that they won't give us exact formula some parameter like alpha, tau are unknown, do we take standard value of alpha and Tau and what are they.

  • 0 in reply to IMRAN SHAIKH
    Prodigy 80 points
    Hello Sir,
    I have some problem while reading Q value from output register for lean body we get high impedance so that we got raw steps above 0x8000(32768) but for obese body we got maximum raw steps near about 0xFFFF (65535).
    in my project i am taking raw steps and make it negative force fully
    e.g. if i got raw steps 34210
    i am going to subtract 0x8000 from raw steps
    34210 - 32768 = 1442
    we take it -1442 for and using this value we calculate Magnitude.
    my calculation disturbed when raw steps exceed upto 64210 for obese or fat body pls guide me what should i do to calculate angle for Ro and Ri for all type of body.
  • 0 in reply to IMRAN SHAIKH
    TI__Genius 12555 points
    Hi Imran,

    The equations used for BCM parameters are empirical equations and there usage depends on the application. Since we are no expert in those fields, we can't really comment on the equations/parameters to be used.

    Regarding the sign conversion of the ADC output, you can follow the steps given below.

    If (ADC_OUT >= (2^15))
    Output = ADC_OUT - (2^16)
    else
    Output = ADC_OUT

    where, "ADC_OUT" is the output of the AFE4300. "Output" is the data after sign conversion.

    Regards,
    Prabin
  • 0 in reply to Prabin Yadav
    Prodigy 80 points

    Respected Sir ,

                             I am stuck on this section how can we achieve the below output , after setting 64Khz DAC frequency and sampling rate 64sps using double ended output A1- A2, after all this i got phase value of reference resistor R1 948ohm is 31955adc steps and RC network where R =515ohm , c=120pf i got 32650 adc steps   how can we achieve below phase I channel and Q channel output.

    SBAA202–October 2013 Impedance Measurement with the AFE4300

    For example, the two reference resistors remain the same. Injecting a 64-kHz frequency current and
    setting the data rate of the ADC to 64 SPS , the ADC code for I channel of reference resistor Rx was
    7625, ADC code for Q channel for reference resistor Rx was –4096. With Equation 2, the magnitude code
    is 8655 and the phase is –28.24°. Considering the same series RC network mentioned in Section 2.1, the
    ADC code for I channel was 6153 and the ADC code for Q channel was –3649 and based on Section 2.1,
    the magnitude code was 7154 or 0.07697 × 7154 – 0.026 = 550.62 Ω and the phase was –30.68°. The
    compensated phase of the sample series RC network becomes –30.68 – (–28.24°) = –2.44°. The
    theoretical magnitude and phase of the sample RC network is 549.96 and –2.33°. Hence the % error for
    the magnitude is –0.12 % and the relative error for the phase is –0.11°error.

  • 0 in reply to IMRAN SHAIKH
    Prodigy 80 points

    Respected Sir,

    from above query i am expecting complete AFE4300 register config setting. i just want to know how negative value of Q channel is come.

    I am waiting for your reply.