I am trying to make an ultrasonic flowmeter. The device has two ultrasonic tranducers (resonance frequency of about 200kHz) that sample one ultrasonic signal in the upstream directon and then immediately after one signal in the downstream direction. I know a correlation between the upstream and downstream signals might be enough but the problem is that we don't have a lot of processing power available. We have signals that are 1024 samples long each and a full cross correlation would take too long to process. The maximum sampling Rate is about 6MHz if that helps.
Since I don't come from an audio background, I am also finding it hard to figure out at what point the signal really 'arrives' and how to detect it at the resolution that I need. With the SNR that I have, it seems like the exact startng point would be lost in the noise?
No matter what I try, I seem to end up with too many wrong measurements where the time measured is exactly one wave period away from the correct value.
I know this question is far too vague but I would really appreciate any ideas on how I could understand the problem better!
- What is the exact time of arrival of these two signals at the ultrasonic transducer?
- What is the differential time of arrival between both the signals?