Is there a sensor which located away from source (like an electric motor or an automotive engine) can measure the motor's frequency or identify that a motor exists in a 100m radius?
Dear Mr. Kashyap, you will need an electro-acoustic sensor (e.g. a piezoelectric one) and a suitable amplifier. A motor operates at 50Hz (i.e. 60Hz), while a combustion engine usually at 3000rpm = 50Hz. Higher harmonics regularly apparent are the 3d and the 5th i.e 150Hz (180Hz), 250Hz (300Hz). Electric motors with more than 2 pole pairs are rotated at lower speeds i.e 3000/p (3600/p), p = 1, 2, 3, 4, 5, 6...(p>6 are rear and only for big motors)
therefore speeds such as 1500rpm, (1800), 750 (900), ... are produced. For p =6 (12pole machine) the speed will be 500rpm (600) i.e 8,33Hz (10Hz). Proposed frequency range should be 8-300Hz, i.e in the sonic (acoustic) frequency area. Perhaps a simple acoustic amplifier would be sufficient.
Dear Mr. Kashyap, you will need an electro-acoustic sensor (e.g. a piezoelectric one) and a suitable amplifier. A motor operates at 50Hz (i.e. 60Hz), while a combustion engine usually at 3000rpm = 50Hz. Higher harmonics regularly apparent are the 3d and the 5th i.e 150Hz (180Hz), 250Hz (300Hz). Electric motors with more than 2 pole pairs are rotated at lower speeds i.e 3000/p (3600/p), p = 1, 2, 3, 4, 5, 6...(p>6 are rear and only for big motors)
therefore speeds such as 1500rpm, (1800), 750 (900), ... are produced. For p =6 (12pole machine) the speed will be 500rpm (600) i.e 8,33Hz (10Hz). Proposed frequency range should be 8-300Hz, i.e in the sonic (acoustic) frequency area. Perhaps a simple acoustic amplifier would be sufficient.
Krishna,
A few questions.
Are the motors presumed to be in hermetic enclosures?
Are they induction motors or brushed (if electric)?
Are they acoustically baffled in some way?
I know of no technology that can detect *all* kW class motors at that range - even narrow-beam doppler radar will have a hard time seeing a crank shaft if that is buried in 1cm of steel. Pulsed neutrino spectroscopy has a chance - except you might as well ask for magic.
An acoustic approach with a single detector suffers from poor angular resolution and the rotation speeds (not stated) might be low. Furthermore, subsonic transducers aren't off the shelf - you may want (instead) to look at very high bandwidth pressure transducers (MEMS, possibly dielectrics) or even optical methods.
Are you asking for an acoustic radar system?
You could mount a high gain cardioid (highly directional) microphone on a rotating table, then use a statistical averaging technique to extract acoustic signatures emitted by the vehicle or device you want to detect as outlined by Dr Paraskevopoulos. As well as Fast Fourier analysis, you could try Kalman filtering. http://en.wikipedia.org/wiki/Kalman_filter.
Also look at http://en.wikipedia.org/wiki/Kurtosis. Kurtosis is the derivative of acceleration and usually occurs in rotating devices such as bearings.
A high gain mic. will easily pick up the signal 100m away as long as you have good noise reduction as mentioned above.
Hope this helps
Regards
Paul
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