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Original question:

PGA970: LVDT sensors and PGA970

PGA970: PGA970 secondary side demod1 & demod 2 values

Özge Biçer
Prodigy 20 points
Part Number: PGA970

Tool/software:

The values ​​I read from demod1 and demod2 are not the same as the voltage coming to the IC between S1P S1N, S2P S2N. How can I find the amplitude of the voltage from the values ​​I read from demod1 and demod2?

  • 0
    TI__Intellectual 2055 points

    Hi Ozge,

    Welcome to E2E! The output of DEMOD1 is the amplitude of the S1/S2 input signals, and the output of DEMOD2 is the phase of the S1/S2 input signals. 

    The amplitude demodulation depends on the LPF and the BPF you've configured in the PGA970.

    The phase can be calculated with M0 software. 

    Thanks,

    Maggie

  • 0 in reply to Maggie Lee
    Prodigy 20 points

    Hello Maggie,

    thank you.

    I think demod1 is Va value, demod2 is Vb value. I understand demod1 is result of “s1/s2” but i am wondering how can I calculate Va-Vb/ Va+Vb ratiometric value? Which register?

    BR, 

    ozge

  • 0 in reply to Özge Biçer
    TI__Intellectual 2055 points

    Hi Ozge, 

    I apologize, I misspoke in my previous message. DEMOD1 is not literally the value of S1 divided by S2. From the datasheet: "The outputs of DEMOD1 and DEMOD2 are the amplitude and phase values of the S1 and S2 gain-stage input signals respectively. The amplitude and phase demodulation algorithm is described in the Digital Demodulation section."

    If you would like to calculate a ratiometric value from S1 and S2, you will have to write firmware to do so. PGA970 does not have a specific register to report the ratiometric value you want to read. 

    Thanks,

    Maggie