| Interesting! I've not seen the 'sonic' method before but I presume the basis of this technique is to treat the belt (or section thereof) as a kind of guitar string. Thus, the frequency of the belt vibration (after being plucked) will be determined directly by the tension of the belt (assuming that belt to belt variation is not a complicating factor of course). The 'sound' of the belt will then be picked up by the microphone and then displayed on an oscilloscope (or a PC program doing the same thing). Any microphone with sensitivity to the relevant frequency should work though experimentation will be necessary to get a clean signal from the belt (ie other bits may also vibrate). Calibration of the microphone will not be necessary as you just count the oscillations per second and you can just set belt tension so you get 112 waves per sec. You would obviously also want to check against a correctly tensioned belt to confirm the quoted 112Hz! I should be able to knock something up so I might give it a go!
Keith  |