Mechanical Engineering - 22.302 ME Lab I
ME 22.302
Mechanical Lab I
Aspects of Filtering
Dr. Peter Avitabile
University of Massachusetts Lowell
Filtering Effects 122601 - 1
Copyright © 2001
Mechanical Engineering - 22.302 ME Lab I
Filtering is performed for a variety of reasons. All types of
filtering occurs around you everyday that you may not be aware of
Dr. Peter Avitabile
Low Pass Filter
High Pass Filter
Band Pass Filter
Band Stop Filter
University of Massachusetts Lowell
Filtering Effects 122601 - 2
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Mechanical Engineering - 22.302 ME Lab I
The aspects of filtering closest to you everyday involve hearing.
Another important filtering example involves music - whether it be
on the web, in your car or at home.
A few examples are presented which are related to the
measurements that are made in the mechanical enegineering lab
entitled “Quantifying Electrical Energy”
Dr. Peter Avitabile
University of Massachusetts Lowell
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Copyright © 2001
Mechanical Engineering - 22.302 ME Lab I
Let’s start with an example involving music
Dr. Peter Avitabile
University of Massachusetts Lowell
Filtering Effects 122601 - 4
Copyright © 2001
Mechanical Engineering - 22.302 ME Lab I
Basically, the equalizer in your stereo is nothing more than a set
of band pass filters in parallel. Each filter has a different
frequency band that it controls. The equalizer is used to balance
the signal over different frequencies to “shape” the noise (music)
Dr. Peter Avitabile
University of Massachusetts Lowell
Filtering Effects 122601 - 5
Copyright © 2001
Mechanical Engineering - 22.302 ME Lab I
The instrument that is used to make measurements will have some
very definite frequency characteristics. This defines the “usable”
frequency range of the instrument. As part of the lab and
measurements taken, there was a different usable frequency
range for the oscilloscope and the digital multimeter
Oscilloscope
Dr. Peter Avitabile
University of Massachusetts Lowell
Multimeter
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Mechanical Engineering - 22.302 ME Lab I
The “usable” frequency range is also affected by the signal
coupling used for the measurement. If AC coupling is used then
an additional high pass filter is applied to the measurement.
Oscilloscope
Dr. Peter Avitabile
University of Massachusetts Lowell
Multimeter
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Mechanical Engineering - 22.302 ME Lab I
If we consider the hearing ability of a human and a dog, then we
also see that there is some usable (or hearable) frequency range.
Basically, a dog can hear much higher frequencies than a human.
Human
Dr. Peter Avitabile
University of Massachusetts Lowell
Dog
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Mechanical Engineering - 22.302 ME Lab I
If fact, not only instruments have frequency characteristics. The
actual transducers used to make measurements also have useful
frequency ranges. For instance, a strain gage accelerometer and
a peizoelectric accelerometer have different useful frequency
ranges
Piezoelectric
Accelerometer
Dr. Peter Avitabile
University of Massachusetts Lowell
Strain Gage
Accelerometer
Filtering Effects 122601 - 9
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Mechanical Engineering - 22.302 ME Lab I
So filtering can be seen in a variety of ways in the analog
instrumentation and measuring devices that are used to acquire
data. Filtering can also be performed digitally once the digital
data is collected and stored in memory or on disk
Dr. Peter Avitabile
University of Massachusetts Lowell
Filtering Effects 122601 - 10
Copyright © 2001