I've got an inground swimming pool, and was inspired by an ill-formed question that was recently posted. I would like to non-invasively measure the volume of water my pump is circulating through the pool over a given period of time. By non-invasively, I mean I would rather not have to hack into the plumbing and embed a sensor into the stream, but rather I'd like to measure it inferentially somehow (e.g. perhaps the water current actually has an electrical current that can be measured through the PVC pipe with a hall effect sensor an an instrumentation-amp — not to bias the answers or anything).
For the sake of bounding the problem with some requirements, I'd be happy with an accuracy of ±1 gallon/min and a component cost of less than $100. To be clear though, these are artificial requirements, since I just want to build something like this for myself.
Best Answer
A quick google search turned up a website with a variety of flow measurement techniques and even full products for sale (albeit, quite expensive).
Some of these are invasive while others are not.
The most promising non-invasive ones I've noticed:
Using ultrasound waves.. Takes advantage of the Doppler effect to measure fluid velocity, which can be used to calculate volume flow rate.
Using magnetic induction.. Takes advantage of Faraday's law generate a voltage from moving ions through an electric field.