Actually, now that I think about it again, I believe there are at least two methods in use for ultrasonic fluid flow measurement. One is the Doppler effect, since the faster the fluid is flowing, the higher the ultrasonic pitch at the downstream sensor. Another is acoustic transit time (http://www.ore.com/theory/ttime1.htm), where the time for a signal to pass from transmitter to downstream sensor decreases as flow speed increases. Both these methods will also detect and measure reverse flow. Once you know the flow speed, you can determine the volume/time value from the cross sectional area of the pipe or tube. Incidentally, on thinking about it a little, I realized the acoustic transit time method is depended on dimensional stability between the sensors, whereas the Doppler method is not. This site has a really good picture of a clamp on flowmeter in use: http://freespace.virgin.net/pt.rydin-orwin/flotec.htm CIAO - Martin R. Green elimar@bigfoot.com ---------- From: Leon Heller[SMTP:leon@LFHELLER.DEMON.CO.UK] Sent: Friday, September 26, 1997 7:41 AM To: PICLIST@mitvma.mit.edu Subject: Re: ?: fluid measurement In message , Pasi T Mustalahti writes >On Fri, 26 Sep 1997, Steve Smith wrote: > >> 1. Consider a car with a fuel computer fitted and use the information >> supplied. >> 2. As above but disconnect the fuel computer thus giving a raw transducer >> output and reinvent the wheel. >> >PTM: I'm looking for a new method. Not only for a car because there is >many comparable situations, where some fluid flow should be measured. >For example in hospitals and chemical laboratories. I was at a process control and instrumentation show a couple of weeks ago, and saw some ultrasonic doppler flow meters on a stand. They should do what you want, but looked very expensive. Leon -- Leon Heller: leon@lfheller.demon.co.uk http://www.lfheller.demon.co.uk Amateur Radio Callsign G1HSM Tel: +44 (0) 118 947 1424 See http://www.lfheller.demon.co.uk/rcm.htm for details of a low-cost reconfigurable computing module using the XC6216 FPGA