Detecting water flow in pipe with Ultrasonic Motion Detector

Im trying to detect when water stops flowing in a 1" iron pipe.... from the outside of the pipe. I see ultrasonic flow meters on-line, they look like Doppler effect instruments, but they are very expensive. So Im thinking to modify an off-the-shelf home security device for the job.

To start, Im thinking to put the transmitting ultrasonic device on the pipe, then put the receiving device some length away along the pipe.

Any input/ideas how to approach this and what to watch out for are greatly appreciated !

If you think sensing for lack of sound using a piezo transducer would work better, I want to hear your ideas on that, too.

Thank you !

You could just have a little propellor in the pipe that connects to a small generator. When water flows a small amount of electricity will be generated which you can detect with a voltmeter. If there is no water flowing, the propellor won't turn and therefore neither will the shaft of the generator. Thus, you have no electricity.

Why go for ultrasonic when there are cheaper alternatives? 2 wires in the pipe to a 2 transistor astable multivibrator will indicate water IF AND ONLY IF water doesnt stay in the pipe after pumping. If its a ground pipe, then water will stay always, so a vibration detector or a tiny generator as suggested above or an IR Tx-Rx will do.

If it is ultrasonic you need, modify the attachment ckt. And yes, you can use a piezo transducer, provided, you dont keep the waves just bouncing in the pipe and get false triggers.

Yes, using a mechanical flow switch would be totally simple, but would require hiring a plumber and "cutting it in". Simple water detection via conductance also requires taking the pipes apart, but in this case the water is always present, never goes dry... just flowing or not flowing. This is the domestic water main to apartment building.

Well then how are you gonna get those transducers in there??

Here is an example flow meter using the doppler effect with ultrasonic . Apparently if the water is too pure, it doesnt work well.

http://www.globalw.com/products/FM500.html

Have you considered heating tape and a thermistor? When the water is still, you will reach one steady state. When the water is moving, the steady state should be lower, or at least different. Probably can't measure flow too well that way, but you could tell on from off.

John

That's an interesting approach, John. I will think on it.