I know acoustic displacement sensor can be used to measure gas flow rate accurately. who can give me some ideas about how? what kind sensor should I use?
thanks

 

I am not sure what you mean by "acoustic".
Ultrasonic meters are used for fiscal gas measurement in large pipe flow situations and i suggest a web earch as "ultrasonic Gas flow meters".
If you are interested in domestic meters then Schlumberger and Siemens have meters with no moving parts.
One principal i know was being investigated is a fluidic device based on the coander pricipal. I don't know if it made it as a gas meter but you can see the principal demonstrated at the Fusion meters web site (it is used for water meters) www.fusionmeters.co.uk.