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Magnetic pickup - amplitude or frequency

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arup

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Hi,
I would like to measure speed of generator using magnetic pickup. Range of speed is 300 rpm to 3500 rpm and min AC voltage would be 0.5V.Hence I have to interface magnetic pickup sensor with microcontroller. In this regard I require few i/ps :

a) As the speed changes does the o/p of magnetic pickup changes in amplitude or in frequency.To find out the rpm should I count the pulse or measure the amplitude of the signal.
To my understanding it should be function of frequency.Correct if it’s wrong.

Speed = 60 X Hz (to be measured) / No of Rotor Teeth


b) The signal o/p of mag pickup sensor would be sinusoidal with 50 % duty cycle ??

c) suggest a interfacing circuit with micro.

Regds,
 

FvM

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As the speed changes does the o/p of magnetic pickup changes in amplitude or in frequency
Both. As you said, frequency measurement will be better (more exact).
The signal o/p of mag pickup sensor would be sinusoidal with 50 % duty cycle ??
A good guess, I presume. An oscillscope can tell you more.
suggest a interfacing circuit with micro.
E.g. a comparator with a small hysteresis. If the signal magnitude is sufficient, a standard schmitt-trigger gate (e.g. 74HC14) with capacitive coupling and suitable DC bias can do.
 

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