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Original question:

PGA460-Q1: How to drive the high frequency probe？

PGA460-Q1: PGA460: Why is this point judged as a goal?

user5901926
Prodigy 60 points
Part Number: PGA460-Q1
Other Parts Discussed in Thread: PGA460

Hi, I'm using PGA460 to measure the distance and I had a problem while measuring two target.

I set the target number to 2 : target 1 as aftershock target, target 2 as real target which I need.

Now the problem is that,Only one echo is shown in the envelope, but PGA460 give me the ToF datas of target is not " 00 27 1B ff ff ff ff ff ", but “00 27 1b ff 00 98 07 D0”. "00 98 07 D0" is just a point that doesn't go below the threshold line.

Here is the envelop diagram:

blue: echo data

red:threshold

yellow:gain

green circle :the wrong target 2

And this is the 128 bytes echo data-dump I got:

Why is this point judged as the target 2 ? How to avoid this misjudgment？

Hope to hear from you soon. Thank you so much.

  • 0
    TI__Mastermind 27940 points

    user5901926,

    The reason the burst and decay is being recognized as an object is because the threshold is allowing a low-to-high transition of the burst signal near ~0ms. The PGA460 FAQ # 5.2 How can I detect more than eight objects? Can I set the threshold to ignore ringing decay ripple or objects for a given time after bursting? How can the Threshold Offset be used? ( http://www.ti.com/lit/an/slaa733/slaa733.pdf ). This FAQ describes how to set the threshold level+offset and/or the time varying gain level to ignore the false positive created by the burst signal.