Under high flow conditions, my mechanical household water meter makes a ticking sound that travels through the pipework and can be heard inside the house. The frequency range is approx 5 to 15 Hz.
I'm guessing that it's a nutating disk or similar type of meter that introduces a pressure pulse every time it rotates. I guess you could describe it as a low level water hammer that gently shakes the pipes.
The meter is owned by the water company and is used for billing purposes so obviously I cannot attach anything to it, but attaching something to the pipework inside the house would be OK.
I use the sound to check that my garden watering system is working ok. As the different watering zones activate the flow changes and the ticking sound speeds up or slows down. If a pipe springs a leak then the flow increases dramatically and I can hear that something is not right and needs investigating.
Has anyone done a project that listens acoustically using a microphone or strain gauge for this subtle type of water hammer and is able to pick out the pulse frequency. Ideally I would like something that is non-invasive and cheaper than cutting the pipework and installing a mains pressure rated (100 psi+) professional level electronic flow meter.
Sounds like a job for a contact microphone - I suspect the cheapest ones are piezo elements used for accoustic guitar pick-ups, or possibly just adding a bare piezo element on to a pipe or pipe-support could be used.
Add a microphone preamp module, start trying to record/recognize the ticks in software...
Your best bet is to buy a flow sensor that connects to 3/4 or 1/2 pipe and is very cheap will connect to Arduino. These can be found at the RobotShop web site under robot parts/sensors. Hook to 1/2 solenoid valve you have automated sprinkler system
If you are getting anything like water hammer from a water meter, then something is wrong. Water hammer is caused when something like a solenoid valve in a washing machine closes and shakes the pipework. Some newish "equilibrium" diaphragm cistern valves do the same. The solution is to fit a surge vessel to absorb the shock - something as simple as a closed vertical tube filled with air does the same - really big pumps use huge surge vessels to take the start-up shock out.
If you want to get pulses from the meter, it depends where it is and what type. Almost all domestic meters have some means of getting pulses without interfering with the meter itself. I have a 1/2" (15-mm) meter which is the company meter and the last rotating dial has a very small magnet. An omnipolar Hall effect switch easily picks up the magnet and feeds into a battery powered XBee. I do exactly the same with the gas meter. All low voltage, non-invasive, no problem. Just like a pukka "smart" meter, but better. The water meter sensor saved me from a flood by firstly picking up the unusual flow, then pin-pointing by isolating sections - it was under the boards.
The microphone idea is good and I have an electret mic on the contactor that changes over the tariffs (Economy 7 in the UK). I started with a Sparkfun sound detector based on an LM324 op am, but getting the gain right is hit and miss. To make it really selective, I got hold of the head of a stethoscope (Amazon) and piped the head to a minute electret. The stethoscope has a large area diaphragm and channels the sound straight into the mic. I tried piezos but never got any worthwhile signal.
MarkT:
Sounds like a job for a contact microphone - I suspect the cheapest ones are piezo elements used for accoustic guitar pick-ups, or possibly just adding a bare piezo element on to a pipe or pipe-support could be used.
Add a microphone preamp module, start trying to record/recognize the ticks in software...
I've ordered a piezo pickup for an acoustic guitar (complete with built in amp and 5 band eq) for the princely sum of $10. Hopefully this will do the job.
tigger:
If you are getting anything like water hammer from a water meter, then something is wrong. Water hammer is caused when something like a solenoid valve in a washing machine closes and shakes the pipework.
Nutating disk meters have a mechanical element that sweeps past the outlet once every revolution causing a change in pressure. The pipes don't rattle violently like when you suddenly turn off a tap. It's more like a subtle ticking sound that you would hear from a low rpm diesel engine. You have to actively listen for it otherwise you wouldn't notice it above the ambient background noise.