Magnetic pickup - amplitude or frequency

[arup]

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]

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.