A presentation about vibration signal filtering

1. MECHANICAL VIBRATION TASK
VIBRATION SIGNAL FILTERING
Member :
1. Ibrahim Faqih M
2. M. Nur Ardian
3. Arief Zulfauzi S
4. Petricius Ginting

2. INTRODUCTION
Fig.1 Fast Fourier Transform used to convert spectrum
from time domain into frequecy domain.
Filtering is a tool for resolving signals. Filtering can be
performed on either analog or digital signals. Furthermore,
filtering can be used for a number of purposes.
For example, analog signals are typically routed through a
lowpass filter prior to analog-to digital conversion. The
lowpass filter in this case is designed to prevent an aliasing
error. This is an error whereby high frequency spectral
components are added to lower frequencies
Another purpose of filtering is to clarify resonant behavior
by attenuating the energy at frequencies away from
resonance

3. INTRODUCTION
With today’s digital technology, there are two methods that
are primarily used: the Fast Fourier Transform (FFT), and
digital filtering. Both make use of digitized measurement
values.
Ideally, filters would block unwanted frequencies and
provide a clean cutoff and keep out of unwanted signals.
However this is not the case. In reality, there is a transition
region where some frequencies will be attenuated, but not
blocked. The actual filter designs are shown in Figures. It
can be concluded that it’s very important to understand
filter types to enable us to look at the data that we are only
interested in.
Fig.2 Conversion from time domain to
frequency domain using FFT

4. THE TYPES OF VIBRATION
SIGNAL FILTERING
The vibration signal filtering have several types, there are :
a) Low pass filter
b)High pass filter
c) Band pass filter
d)Band stop filter

5. a) Low Pass Filters
Antialiasing filtering is also known as low-pass filtering, where the
frequency components above the Nyquist frequency in the signal are
simply filtered out during data collection. However, depending on the
requirements, signals can be low-pass filtered at any other frequency
lower than the Nyquist frequency for the collected data during signal
processing.
THE TYPES OF VIBRATION
SIGNAL FILTERING

6. a) Low Pass Filters (Continued)
The characteristic of low pass filter are :
 Allow the low frequencies to pass through, but block the
high frequencies
 Low pass filter set at 100Hz will remove the frequency
content above 100Hz, but not below 100Hz
 It follows that a sinewave with a fundamental frequency of 10Hz
would not be affected by a 100Hz low pass filter
 sinewave of 200Hz would be heavily affected by a low pass 100Hz
filter as the frequency content above 100Hz would be removed
THE TYPES OF VIBRATION
SIGNAL FILTERING

7. a) Low Pass Filters (Continuous)
THE TYPES OF VIBRATION
SIGNAL FILTERING

8. b) High Pass Filters
A HP filter typically removes the frequency content from a signal at and
below any particular frequency fHigh. A typical high-pass filter at fHigh
= 10 Hz for a signal is shown in Figure 6.4. In many cases, it is required
to filter out low-frequency noise, DC components, etc., from the
recorded/measured signals
THE TYPES OF VIBRATION
SIGNAL FILTERING

9. b) High Pass Filters (Continued)
The characteristic of high pass filter are :
 The opposite to low pass filters
 Remove the frequency content below the cut off
Frequency.
THE TYPES OF VIBRATION
SIGNAL FILTERING

10. THE TYPES OF VIBRATION
SIGNAL FILTERING
c) Band Pass Filter
This is a combination of both HP and LP filters. For example, a time signal
with a sampling rate ( fs) of 1000 samples/s (Hz) can be band-pass filtered
in a frequency band of fHigh= 10 Hz to fLow = 200 Hz, as shown in Figure
6.5. This simply means the frequency components below 10 Hz and above
200 Hz will be filtered out from the signal.
Typical examples of the above three filters are illustrated through measured
data from a rotating machine in Figure 6.6.
The characteristic of band pass filter is :
 Have a low and high cut off and will pass frequencies that fall
between these two limits.

11. THE TYPES OF VIBRATION
SIGNAL FILTERING
c) Band Pass Filter (Continued)
d) Band Stop filter
 Block the frequency content between the lower cut off and the
higher cut off.

12. THE SPECTRUM
Fig. 3 Different filters influence on a noise
signal’s frequency spectrum when
the signal passes through them:
(i) Low pass filter (ii) High pass filter (iii)
Band pass filter (iv) Band stop filter
(Source: Brüel & Kjær, course material.)

13. REFERENCES
http://www.xyobalancer.com/xyo-balancer-blog/filters-in-the-field-of-vibration
http://blog.prosig.com/2011/10/04/understanding-filter-characteristics/
http://nptel.ac.in/courses/112107088/module1/lecture40/lecture40.pdf
Jyoti Kumar Sinha. Vibration Analysis, Instrument, and Signal Processing. Boca Raton. 2015

14. THANK YOU