Thoughts on a non-invasive water flowrate tester?

[fastline]

I need to obtain the flowrate of water in a pipe. I am just going to throw this wild card out and see if anyone has any ideas on ways to test this WITHOUT cutting the pipe? I realize the common and tried method of a spinning impeller in the pipe works well, but I got to wondering if there is enough charge in the water that we might be able to "inductively" test it? Absolute accuracy is not critical.

Obviously we would be looking for velocity here and the pipe diam would need to be calculated to determine actual flowrate.

 

[MikeMl]

Doppler shift in a transverse acoustic wave?

 

[cowboybob]

... might be able to "inductively" test it?...

This would require conductivity, which, in a general sense, is lacking in potable water. Thus, not a viable method for monitoring flow rate.

Doppler shift in a transverse acoustic wave?

Only practical, reliable and accurate method (generally referred to an "ultrasonic transit time" concept). Not easy, therefore not cheap and requires fairly complex circuits driven by a uC.

 

[Reloadron]

Along the thinking of cowboybob and what mike mentions you may want to start here.
The link reads in part:

The Ultrasonic doppler flowmeter incorporates a technology offering an increased range of applications. Because of its non-invasive nature, no pressure drop is created, and this type of flowmeter can be used to measure the flow of fluids and slurries which ordinarily cause damage to conventional sensors. The basic principle of operation employs the frequency shift (Doppler Effect) of an ultrasonic signal when it is reflected by suspended particles or gas bubbles (discontinuities) in motion. This metering technique utilizes the physical phenomenon of a sound wave that changes frequency when it is reflected by moving discontinuities in a flowing liquid. Ultrasonic sound is transmitted into a pipe with flowing liquids, and the discontinuities reflect the ultrasonic wave with a slightly different frequency that is directly proportional to the rate of flow of the liquid (Figure 1). Current technology requires that the liquid contain at least 100 parts per million (PPM) of 100 micron or larger suspended particles or bubbles.

You eventually need to consider Clean Liquids, Liquids with Solids and exactly what you wish to measure the flow rate of? Things can also get pricey depending on what exactly you want.

Ron

 

[JimW]

An interesting trial and error approach might be a heating element on the pipe and monitoring the temperature on either side of the heating element. Higher flow rate would affect the heat transfer along the pipe. I doubt you could get any accuracy, but I suspect you could differentiate between no flow, low flow and high flow rates.

-Jim