Page 16 - Shock and Vibration Overview
P. 16
Data Acquisition (DAQ) System Selection
Figure 6: Two 1g sine waves are plotted on each other with different resolutions.
When looking for a DAQ system they will typically have a resolution on the order of 16
or 24 bits. The lower quality shock and vibration data loggers however may only have a
resolution of 12 bits or less which may not be adequate for your application.
4) Filtering
Filtering can be used to remove unwanted frequency content and should be an
important part of your evaluation of different DAQ systems. High pass filters remove
lower frequency vibration and is inherent to all piezoelectric accelerometers (resistor
and capacitor in series) which gives these accelerometers the AC response. Low pass
filters are more important however to prevent aliasing which can’t be filtered out in
software. Aliasing causes a signal to become indistinguishable or to look like a
completely different signal as shown in Figure 7. It’s important to realize that an analog
lowpass filter is needed to prevent aliasing. Once a signal is aliased, it can’t be filtered
out digitally in software.
16 of 69
