Page 12 - Shock and Vibration Overview

Sensor Selection

Figure 4: Laser displacement sensors (and capacitive sensors) offer a sensor option that allows
direct measurement of displacement without contacting or interfering with your test article.

Laser displacement sensors (KEYENCE is the leader) and capacitive displacement sensors
would be the two main sensor types that would be useful for vibration testing. These
systems will typically be upwards of $5,000 and lead times over 4 weeks.

Microphones
Sound is not often thought of as a way to measure vibration; but it should be! After all
sound, by definition, is a vibration that travels through the air in the form of pressure
waves. Microphones offer a cost effective means of measuring high frequency vibration
and is especially useful to determine how a system’s vibration changes with time. Health

monitoring applications can greatly benefit from using a microphone on cost and
simplicity.

Microphones aren’t limited to applications where cost is a concern; some acoustics
applications will use high end microphones for vibration testing and analysis. You’ll
notice a lot of the accelerometer companies also offering high end microphones, like
PCB Piezotronics. Microphones and acoustic analysis can be a great option for some
applications; but if you need absolute shock and vibration data, not relative change,
then microphones probably won’t work. They also won’t be able to analyze modal
shapes and specific/discrete points along your structure. But again, they are very

effective for overall frequency analysis.

Strain Gauges

Often times the end goal of vibration testing is determining the stress and strain in your
structure. Strain gauges can be an effective sensor type to directly measure the strain of
your test article. A change in capacitance, inductance or resistance is proportional to the
strain experienced by a strain gauge so that mechanical energy can be converted to an
electrical signal. Strain gauges do present some challenges though; they can be very

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