only b and c Quetion 4. An excesive vibrations ae absepeere he pinde machine str

Question

only b and c

Quetion 4. An excesive vibrations ae absepeere he pinde machine structure determines the vibration levels. Therefore, an accelerometer is used to measure the vibrations where a fundamental frequency of about 7200 rpm is observed and the engineers believes that significant harmonics may be present up to the 4th harmonic. Data are acquired with a data acquisition system. (a) What is the minimum sampling frequency they should use to avoid aliasing? (b) They decide to sample data at fs 4000 Hz. They take 1024 data points (N 1024 pts) and plug the data into a computer program to calculate a DFT (or FFT). How many useful data points (frequencies) will appear on their frequency spectrum? (c) The results are good, but the frequency resolution is not as good as they had hoped. Mehmet and Ahmet argue about what they should do to improve the a. Mehmet suggests using the same N, but increasing the sampling frequency b. Ahmet suggests using the same fs, but increasing the number of data points frequency resolution: N. Which of these suggestions would improve the frequency resolution and why?

Explanation / Answer

B) Frequency resolution = (Sampling rate/No of data points)

Given, Sampling=4000 Hz

Number of Data points= 1024

SO frequency resolution = 4000/1024 = 3.09625

Useful data points= No of Data points/Frequency resolution

=1024/3.90625

=262 Useful data points

c) Option 2 .i.e. increasing the number of data points with same sampling frequency will increase the frequency resolution as increasing the sampling rate wil increase the range of frewuencies over which the fft is computed but does not increase the frequency resolution

Related Questions

Navigate

• Browse (All)
• Browse O
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.