Guitar Contact Microphone or Ultrasonic Transducer to Detect Flow In Pipes?

Water companies do, in order to detect and locate leaks.

They use accelerometers rather than microphones, usually magnetically fastened onto iron pipes in the road.

There are basically two systems.

1) Use multiple sensors at specific points, set to record audio signals at a specific time and period. You then collect the sensors, put them back in their case and download the data later. By analysing the recorded data you can tell if there's a leak, and get an indication of the area it's in.

2) Correlation - you fit two sensors on either end of a metal pipe, this transmits audio wirelessly to a control unit which you set for the type of pipe (cast iron etc.). The control unit compares the time difference between the two signals, and because you entered the type of pipe (sound travels at different speeds down different types of pipe) it calculates the distance from each sensor to where the leak is (between them). This allows you to get a fairly accurate estimation of where the underground leak is, so you can dig in the correct spot (hopefully).

It costs a LOT of money to dig a hole so it makes sense to try and dig it in the right place.

You could try a contact mike, and see what you can hear - but I suspect that slight leaks will make very little noise.

Incidentally, leak noises are basically white noise, funnily enough I copied a test cassette (used to test correlators after repair) only last night, as we wanted a backup (as MP3's) in case the cassette chews up

Here's a picture of the cassette box.

Are you trying to make a device to sell? It might be interesting to try. If you just want to check your own toilets, you can try putting a bunch of blue food coloring in the bottom of your tank (don't mix with the whole volume of the tank) and checking if it leaks to the bowl.

Why I like forums:

Guy #1: I just had an idea. <idea> Has anyone here done anything like this?

Me: Hmmm - That might maybe sorta kinda could work. I should write something.

Guy #2: That's my day job. <spew of information>

Thanks for the comments Nigel.

Detecting leaks isn't my goal here – I simply want to know if water is flowing. Fortunately, I don't have leaks to track down, but (as example) sometimes a toilet flapper valve doesn't seal because the linkage hangs up, or a flapper needs to be replaced, causing the toilet to periodically flow.

For the navy, I have done AVLD (Acoustic Valve Leak Detection) in a past life. In many shipboard systems, there are large primary valves paralleled by small bypass valves. If a leak past those valves is detected, the question is whether it's the small, quickly repaired bypass valve that's leaking or the large primary valve, which could require significant time and money to disassemble and repair.

AVLD uses an accelerometer as you described to listen for ultrasonic noise and heterodynes it down to the audible range. A leak sounds just like you think it would

I expect the flow noise of water flowing through a pipe would be primarily in the audio range rather than the ultrasonic.

AnalogKid said:

Guy #2: That's my day job. <spew of information>

Click to expand...

Well, somewhat related to my day job in a past life, but not quite as noted above. I suppose it could be similar to submarine sonar [REDACTED].