Piezo as a contact microphone

I would like to program a MCU to be able to detect water flowing through a pipe. The requirements are:

1.) No tapping into the piping system (it should be an external device only).
2.) It should use the principle of sound measuring (audio quality does not matter).
3.) It should only detect sound emitted from the object it is in contact with.

So - I was thinking of using a piezo from a buzzer. I need help in choosing the correct piezo, I am not sure whether I should be using an internal or external drive piezo. I want it to be very sensitive.

Are there any suggestions to what kind of piezo I should be looking for or specific parameters of the piezo I should be looking for?
I was looking at these, but I am so not sure whether I should take the Internal or External drive: http://za.rs-online.com/web/c/passi...o+buzzer#sort-by=P_breakPrice1&sort-order=asc

 

It will probably be galvanized iron.

 

A Piezo contact microphone is exactly the same thing as a Piezo buzzer. It refers to the same device, just used for a different purpose. I already know I want to use a Piezo as a microphone, but my original question is how to choose the correct one. This component is not just a standard device, there are different types of discs with Piezo material on them.

My question is however, should I use a Internal or External drive Piezo? Should I use a Piezo buzzer disc with a higher or lower audio volume level, in dB (this rating refers to sound emission - but remember I want to use it as a microphone)? There are many types of Piezo's. I would like to know for what parameters to look for to choose the best Piezo element?

 

A Piezo contact microphone is exactly the same thing as a Piezo buzzer. It refers to the same device, just used for a different purpose. I already know I want to use a Piezo as a microphone, but my original question is how to choose the correct one. This component is not just a standard device, there are different types of discs with Piezo material on them.

My question is however, should I use a Internal or External drive Piezo? Should I use a Piezo buzzer disc with a higher or lower audio volume level, in dB (this rating refers to sound emission - but remember I want to use it as a microphone)? There are many types of Piezo's. I would like to know for what parameters to look for to choose the best Piezo element?

Yes - but that's my question. How to choose the "optimal Piezo". I have searched on RS's website, and they don't list the Piezo's under contact microphones, they list it as a buzzer. So, obviously I need to choose the right Piezo to make a good microphone. This is what I need help on. How do I choose the correct one?

For a dynamic microphone, there is lots of info out there with minimal use of Google. But for Piezo's - someone like me who have never used them as a mic before, I certainly need advise on how to choose one. At this stage, amplification is no problem. Filtering ain't no problem either. For my project, accuracy is what matters. And defining accuracy for my project would mean I want to detect the loudness of a sound (between 1 to 4 kHz) with a very high precision. As you know, water emits a sound at this frequency when passing through a pipe, but the vibration it causes are way too small to be even felt by hand (in my case). So, I need help on choosing the right Piezo that has the highest sensitivity that will generate the largest output voltage.

Like I said, Google is not to friendly regarding this.