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PGA970EVM: PGA970EVM frequency error

Bene_S
Prodigy 80 points

Part Number: PGA970EVM

Hi,
using a PGA970EVM (and USB2ANY) with PGA970GUI for an test application with LVDT.
I can config the PGA970EVM with the GUI, but i dont get the correct waveform at generator ouput.
Following the introductions in the datasheet or users guide did not succeed.

In case of 1kHz there are about 150Hz, 5kHz => 700Hz,  10kHz => 1.5kHz at waveform generator output.

All necessary options are enabled, i populate the waveform table and write it to the device before generating the sine wave.

I dont know whats going wrong, would you give me some support?

Thanks!

  • 0
    TI__Mastermind 31655 points
    Hello,

    Do you have any scope captures of the waveforms that are being generated? Do the sine waves look like sine waves or are they distorted in any way?

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 80 points

    The sine waves looks OK, just frequency is wrong.  Measuring on Pin P1 without external amplifier.

    GUI settings:

    Regards.

  • 0 in reply to Bene_S
    Prodigy 80 points

    Hello,

    we ordered a new PGA970EVM board, configured it with GUI and we got the correct waveform at primary side (3V amplitude, 10 kHz).

    After connecting and disconnecting a 3-wire LVDT to the primary and secondary side, we got a frequency error again.

    Again the sine wave looks ok, but frequency is lower than it should be (10 kHz => only 6 kHz at output).

    We used the diagram demonstrating how to connect the sensor to the PGA970 (posted in another thread).

    Is this the right diagram?

    It looks like the PGA970 has been damaged. Is there a possibility to check if the PGA970 is still ok?

    There should be any protection at input pins S1x and S2x?

    Do you know whats going wrong?

    Regards

  • 0 in reply to Bene_S
    TI__Mastermind 31655 points
    Hi Benedikt,

    So after, testing the waveform generator with the LVDT sensor attached, the frequency was shifted, and now it is still incorrect even with the LVDT disconnected from the board?

    The diagram you have posted is correct, so I don't believe this an issue with incorrect connections to the EVM.

    Can you please post the model of the LVDT you are using? Or a link to the datasheet?

    Do you have J1 and J6 installed on your board?

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 80 points

    Hi Scott,

    Yes that`s right. It is still incorrect even with the LVDT disconnected from the board.

    - LVDT: Solartron AX/1/SH:

    - J1 and J6 are installed

    Regards.

  • 0 in reply to Bene_S
    Prodigy 80 points
    Hi,

    Any ideas?
    We are grateful for every suggestion or tip!

    Regards