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PGA970: PGA970 ADC read Problem

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Replies: 13

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Part Number: PGA970

Hello,

Can anybody an help me in below issue. I am using PGA970EVM board.

How can I read ADC data from DEMOD1_DATA1, DEMOD1_DATA2, DEMOD1_DATA3, DEMOD1_DATA4 ?

Thanks and Regards

VAI

  • Hi Vai,

    The PGA970EVM GUI user's guide (http://www.ti.com/lit/ug/sldu023/sldu023.pdf) gives instructions for how to use the ADC Settings page.

    In short you have to enable the VREF buffer, turn on the Analog Power, enable DEMOD1, Test Mux Enable, and the Interfaces & Deci Clk, and finally make sure the Sigma Delta Modulators and the Modulator Clock are set to "Not Reset".

    Then you can click "Read ADC" below the ADCx data table and the values will populate in the table.


    Regards,

    ____________

    Scott Cummins

    Precision ADC Applications

  • In reply to Scott Cummins:

    Dear Scott,

    I am trying to generate the sine wave through firmware for 50Hz frequency.

    what are  the hex value should we pass to generate sine wave for accurate as well as stable primary excitation output.

    I only want the hex value table.

    Regards,

    VAI

  • In reply to Vai:

    Hi Vai,

    I'm not sure I understand. Your latest question seems unrelated to the original question of this post. Was your original question answered? If so, and this is a new question please let me know and I can split this off into its own thread.

    Regards,

    ____________

    Scott Cummins

    Precision ADC Applications

  • In reply to Scott Cummins:

    Dear Scott,

    My first question was not able to read ADC value through firmware not PGA970 GUI software.

    I am using PIC controller to read data through SPI of PGA970 .

    Please help me to how to read data through SPI also please answer the above query also.

    Reading through PGA970 GUI software has been done now current i am working on firmware.

    Kindly give solution as soon as possible,

    Regards,

    VAI

  • In reply to Vai:

    Hello Vai,

    In order to program a sine wave of 50 Hz you can use the procedure outlined in the "Turning on the Waveform Generator" section of the datasheet. The key portion is the equation used to generate the table values here:

    "Load the waveform RAM with quarter-waveform values. For example, to generate a sine wave of amplitude
    amp and frequency freq, calculate waveform table values using the formula: amp * sin(2*pi*freq * (0.5 us + n1
    us)), n = 0..N. N is the number of 1-us samples in a quarter-sine wave."

    To communicate through SPI please review the SPI section of the datasheet. The structure of each data transfer is described in detail, and there are several examples available in the "SPI Transfer Examples" table.

    Regards,

    ____________

    Scott Cummins

    Precision ADC Applications

  • In reply to Scott Cummins:

    Dear Scott,

    Thanks for the reply it has help to generate the sine wave for 50Hz,

    Currently i have another issue that is how to get stable ADC read value in PGA970 GUI

    As shown below image Reg 2  Value is stable but reg 3 and reg 4 value is varying but my input is stable.

    Atleast the value of reg 3 should be stable.

    Also I want the Value of ADC Should read in positive and negative value how to do this configuration. 

    Thanks and regards,

    VAI

  • In reply to Vai:

    How can increase amplitude of the primary as well as secondary waveform without changing my supply ??

    Currently my input supply is 3.3V and primary excitation Vpp is 2.3V. 

    and secondary maximum VPP is 0.75V.

  • In reply to Vai:

    Hello Vai,


    The demodulator output will always be positive since it only outputs the magnitude of the waveform. This is described in the Digital Demodulation section of the datasheet. To determine the phase of the secondary waveform with respect to the waveform generator output you will need to write firmware which extracts the phase information using the DEMODx_PH1/PH2 data.

    If your data seems unstable it could be that there is additional noise in the system. It could be electrical or mechanical. Is the LVDT on a still and stable surface? Small vibrations could move the core and cause your readings to fluctuate.

    The primary supply is limited by the waveform generator output. If you require a larger amplitude you will have to use an external amplifier to increase the waveform generator output voltage before it enters the LVDT.

    Regards,

     

    ____________

    Scott Cummins

    Precision ADC Applications

  • In reply to Scott Cummins:

    Dear Scott,

      I have seen the whole setup for stable operation.

    1) The Power Supply which i am supplying is constant i,e. i have used external Stable DC Source for supply.

    2) I have used LVDT vernier for measuring the LVDT probe measurement so it is also stable.

    So according to my side i am not able to rectify.

    is their any other option  like filter circuit or any other thing if Yes then please let me know,

    also with their values,

    Thanks and regards,

    VAI

  • In reply to Vai:

    Hello Vai,

    Have you experimented at all with the BPF and LPF available for ADC1 and ADC2? There are some example coefficients that can be written to the registers in the datasheet under the "ADC1 and ADC2 BPF Register Settings" section.

    For additional frequencies you are free to use the Matlab script provided in the following thread to generate coefficients for any center frequency and bandwidth that you are looking for: https://e2e.ti.com/support/sensors/f/1023/t/803535

    Regards,

    ____________

    Scott Cummins

    Precision ADC Applications

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