Page 27 - Shock and Vibration Overview

Equipment Setup

Environmental Concerns
The largest environmental concern is temperature. All sensors will have some
temperature dependence, especially piezoelectric accelerometers and strain gauges.
Therefore temperature compensation will be needed to offset these effects. Some

sensors will have the necessary hardware to compensate the output integrated into the
sensor package; but in some instances the engineer may need to add a temperature
sensor and perform their own compensation. In addition there are some other sensor
concerns, especially for accelerometers.

1) Base Strains

Many piezoelectric accelerometers are using a piezoelectric element with a tip mass
mounted to the base and measuring shear. Therefore when the surface the
accelerometer is mounted to experiences strain, this can often appear as
“acceleration” in your data. Accelerometer manufacturers are aware of this and
design their sensors to minimize the effect; but base strains can still result in
erroneous data.

2) Acoustic Noise
As we’ve mentioned, noise is simply pressure waves that can excite the
accelerometer and your structure. Normally though these induced vibrations are
much less than the actual inherent structural vibrations but it is something to
consider.

3) Transverse Vibrations
Accelerometers are sensitive to vibrations acting in directions perpendicular or
orthogonal to the main axis of interest. This transverse sensitivity is typically less than
5% for single axis accelerometers; triaxial accelerometers typically have a little higher

transverse sensitivity.

4) Magnetic Fields
The magnetic sensitivity of accelerometers is very low, but should be considered in
especially extreme environments like naval ships.

5) Humidity
Most accelerometers are sealed to ensure reliable operation in humid environments;
but this humidity can cause issues at the cable connections especially. Especially
humid environments may require special accelerometers that come pre-wired to

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