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Original question:

Regarding PGA970

PGA970: What 's the role of the PGA970's phase information

Sherry Liang
Genius 10255 points
Part Number: PGA970

Dear team,

When the voltage of the secondary side of PGA970-LVDT is obtained, A-B/A+B, it should be able to get the position. So what is the role of phase information at this time? 

Could you help answer this question?

Thanks & Best Regards,

Sherry

  • 0
    TI__Mastermind 31655 points
    Hi Sherry,

    The phase angle of the output is used to determine where the core passes the null point in the LVDT sensor, which is where the mutual inductance is equal between the primary and both secondaries. The phase of the output shifts 180 degrees when crossing the null point, which can be used to determine if the core is on the left or the right side of the center. The magnitude of the output is the same regardless of which side of the null point the core is on, so the phase is needed to determine this.

    Regards,
  • 0 in reply to Scott Cummins
    TI__Genius 10255 points
    Hi Scott,

    Thanks for you reply!

    Best Regards,
    Sherry
  • 0 in reply to Scott Cummins
    TI__Genius 10255 points

    Hi Scott,

    Base your reply, the customer has new questions.

    If he uses the 4-wire connection, how to judge whether it is on the left or right side of the zero point?

    In addition, he did not know how to get the sinusoidal waveform of the excitation. Is it necessary to load a sine table into the address 0x9FF memory area with SPI? The PAGE1 memory area is byte-aligned. Starting from 0X9FF, the waveform data is 16 bits? If aligned, is the high byte first or the low byte first? Is there a complete example of sinusoidal waveform output via SPI configuration?

    Thank you!

    Sherry

  • 0 in reply to Sherry Liang
    TI__Mastermind 31655 points
    Hi Sherry,

    They will have to check the phase of the output when the LVDT core is at the left and right positions to tell which side it is on.

    You can generate a waveform table using the EVM GUI even if you do not plan to use the EVM to program the device. You can save the waveform to a txt file from the GUI for use elsewhere. www.ti.com/.../PGA970EVM

    Regards,