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PGA970: Phase detection with PGA970 evaluation board

Maurizio Gosmar
Prodigy 90 points
Part Number: PGA970


Hello,

We have a PGA970 demo board connected to a 3 wire LVDT.

All is working OK and the ADC is showing correctly the value of the amplitude of signals.

The problem is the phase ........ if we try to show the phase value on the graph ( the only place where is possible to read it on demo software ) the phase is always a value around 45° ..... also if the received signal from LVDT has the classic phase inversion ( 180* ) after and before the central core position . 

Where is possible to see on the demo software the value stored in DEMODX_PHXDATA and DEMODX_DATA registers ?

Why the calculation of phase is apparently wrong on the demo software ?

Thank You

Maurizio

  • 0
    TI__Mastermind 31655 points

    Hello Maurizio,

    So to clarify, the phase is always 45 degrees even after the LVDT moves from one side of the central position to the other? You don't see the phase inversion?

    You can read the raw DEMODX_PHXDATA and DEMODX_DATA registers directly from the "Low Level Configuration Page" to monitor the values.

    Regards,

  • 0 in reply to Scott Cummins
    Prodigy 90 points

    Hello Scott,

    Thank you for your collaboration.

    Yes, the calculated phase in the demo software is always 45 degrees also if the core is going from one side to the opposide side.

    Instead the ADC voltage value, and the relative voltage graph, is always present the passage of the core from one side to the other ..... is only the phase value is always fixed around 45 degrees.

    In other words we can see the position of the core but not the side relative to the zero.

    With oscilloscope we see the phase changing and the correct modulation ....... on one side is phased correctly and on the other side is in phase opposition, like must be.

    Can be a wrong setup of some parameters ? 

    Maurizio

  • 0 in reply to Maurizio Gosmar
    Prodigy 90 points

    Hello Scott,

    Do you have any suggestions ?

    Thank you.

    Maurizio

  • 0 in reply to Maurizio Gosmar
    TI__Mastermind 31655 points

    Hi Maurizio,

    Can you please share a screen capture of the ADC capture window and the register map for your PGA970 in its current state?

    I have a PGA970EVM setup in the lab that I will have to go try myself to test if the phase measurement is working correctly for me. It may take another few days before I can make my way into the lab to confirm this.

    Regards,