A proximity sensor will be used to sense the teeth on a rotating gear. The outpu

Question

A proximity sensor will be used to sense the teeth on a rotating gear. The output of the sensor will be used to measure the rotational speed of the gear. Select a sensor from Table 7.1 for each of the following condition sets. A 20-tooth gear is operating at 1000 rpm with a minimum sensing range of 4 mm. A 10-tooth gear is operating at 300 rpm with a minimum sensing range of 8 mm. A 50-tooth gear is operating at 4200 rpm with a minimum sensing range of 0.8 mm. A 30-tooth gear is operating at 1800 rpm with a minimum sensing range of 1.6 mm. A 10-tooth gear is operating at 180 rpm with a minimum sensing range of 16 mm.

Explanation / Answer

There are number of ways to do it.

Measure the period T between two consecutive sensed pulses at high resolution (using a gated fast clock) and then numerically compute the frequency as 1/T or 1/(n*T) if there are n teeth for sensing.

60/T or 60/(n*T) will be RPM measured in just one pulse period.

RPM=f * t/n. n is the total teeth number of the gear

So according to me correct anser would be C

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