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EVM430-FR6047: absolute ToF measurement

Maik Bruhn
Prodigy 170 points
Part Number: EVM430-FR6047

Hi.

I have some questions regarding the calculation of the absToF.  Is the maxLobe mentioned in https://www.ti.com/lit/an/slaa889/slaa889.pdf?ts=1610816769623&ref_url=https%253A%252F%252Fwww.google.com%252F  calculated for every peak in the ADC capture or just till the max. value for the peak is reached? 


I'm wondering because i did some measurements under zero flow conditions and measure the signal in parallel with a oscilloscope with 8 GSa/s and the ToF calculated by the EVM is smaller compared the ToF measured with the Oscilloscope. I set the threshold for the Oscilloscop to 0.1 and the 'Envelope Crossing Threshold' parameter is set to 10. That means 10% of the max, right?

The difference between both ToF's is in the range of 1 µs. In the USS all offset parameters are set to 0. Target of this test was to determine the delays and offset times for my setup.


Maik

  • 0
    TI__Genius 12615 points

    Hi Maik,

    The peak should be calculated for every lobe and the 10% threshold should correspond to 10% of the max peak.  The threshold will determine which lobe to lock on to in order to calculate the absolute time of flight.  When you are comparing timing with your scope, you should be looking at the time to the peak of the lobe that can be found after the 10% threshold.

    BR,
    Leo

  • 0 in reply to Leonardo Estevez
    Prodigy 170 points

    Hi Leo,

    Does that mean the AbsToF is equal to the first lobe after the threshold is crossed?
    There does no interpolation takes place to find the excat crossing point?

  • 0 in reply to Maik Bruhn
    TI__Genius 12615 points

    Hi Maik,

    There are two different algorithms which can be used, the Lobe algorithm locks onto a lobe based on the threshold. The Hilbert algorithm computes the Hilbert envelope of the signal and interpolates to find the exact threshold crossing with the envelope. The Lobe algorithm is the most commonly used algorithm for water.  The Hilbert algorithm is most commonly used for gas.

    BR,

    Leo

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