I am looking to investigate ways of creating a non contact flow sensor for a diesel fuel pipe. I have seen some on the market but they are real expensive, but are based around an ultrasonic sensor. In my eyes these are pretty cheap so I assume the cost is in the methodologies behind processing the information.
I dont need terribly accurate flow level values, even sensing whether a liquid is in the pipe or not would be sufficient (for now) to see whether it is economically possible.
Other than ultrasonic is there another way??