How to calculate RPM from a square wave signal Voltage-Time graph

Question

I'm struggling to understand how to show the relationship between the input and output of a hall effect sensor used as a wheel speed sensor through mathematical expression. How can I calculate the RPM if the input gives me a square wave signal? I understand it may be through calculating the frequency, but I feel like I'm missing something.

Answer 1

1. Hook up a voltmeter to the sensor.
2. Turn the wheel by hand one full revolution while counting the number of positive-going pulses generated. Call that n.
3. Measure the periodic time of the squarewave from your graph. Call that t. (It's 10 ms in the graph in your question.)

$$ RPM = 60 \times rps = 60 \frac 1 t \frac 1 n $$ where rps = revolutions per second.

$$ RPM = \frac {60}{tn} $$