Question

Suppose a signal from a vibrating motor is to be sampled discretely with a digital data acquisition system to determine the RPM of the motor. It is known that the maximum possible RPM is 1800. What is the minimum sampling frequency (in Hz) with which the signal can be sampled in order to measure the RPM of the motor

Answer 1

f > 60 Hz

Step-by-step explanation:

• According to Nyquist's Sampling Theorem, to be fully reconstructed without any aliasing, the signal must be sampled at least more than twice during the period of the maximum frequency of the signal.
• In this case, the signal to be sampled has only one frequency.
• However, as we have the information in RPM, we need to convert this to cycles/sec (Hz) first, as follows:

`f = (1800 rev)/(min) * (1 min)/(60 sec) = 30 Hz`

• Per Nyquist, fs > 2*30 Hz

⇒ fs > 60 Hz