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TDC1000-TDC7200EVM: dTOF zero-flow offset

Thibault Helle
Expert 2090 points

Part Number: TDC1000-TDC7200EVM

Hello,

I managed to get Audio Wells 1MHz transducers with plastic pipe for water flow metering. I am getting a good receive signal but the delta TOF value is pretty large at no flow. With the following settings I managed to get the best repeatable result at around 1,9ns with a stable stdev. Cables are exactly the same length and directly fed into the TDC1000-7200 EVM board. I know that impedance matching circuits(TS3A44159PWR) can help but not by nanoseconds, right?

I am not sure if it is some combinations of settings or some electronics that is wrong. The dTOF should be around 30ps if I'm not wrong. 

Thank you in advance!

Regards,
Thibault

  • 0
    TI__Mastermind 31655 points
    Hi Thibault,

    I would expect the zero flow drift to decrease around 4-500ps when using the sensor interfacing circuit. Your settings look good, but you may try experimenting a bit with the PGA gain and the threshold. The threshold won't affect anything, but you may need to adjust it if you decrease the PGA gain too much. At higher levels the PGA gain can have a very small effect on the shape of the waveform and move the zero-crossings out of place.

    It looks like the audiowell pipe is using laterally mounted transducers firing into reflectors. Try to keep the transducers pointing up (connectors facing down) so that air bubbles cannot accumulate in the path of the ultrasound.
  • 0 in reply to Scott Cummins
    Expert 2090 points

    Hi,

    Okay thanks for the info. I tried putting it vertically in a tank full of water without any effect. Any other suggestions? 

    Could replacing the capacitors C42 C43 or R41 R42 (AudioWell transducers at 1000pF, 110ohm) reduce dTOF? Do you have any good theoretical way of choosing the values for impedance matching?

    Thanks in advance.