When conducting a vibration test, not only does an engineer need to have a quality controller to process the data but also the appropriate transducers to collect the data. A transducer is an electronic piece of equipment that converts energy (or, more precisely, the signal carried in a particular form of energy) to another form of energy. Broadly speaking, microphones, speaker systems, Geiger counters, strain gauges, and pressure sensors are examples of transducers. A handy reference manual on a variety of transducers is Henry Norton’s Handbook of Transducers (Prentice-Hall, 1989).
Advantages/Disadvantages of Select Transducers
In the vibration testing industry, the three most common transducers are the acceleration sensor, the velocity sensor, and the displacement sensor. An examination of the advantages/disadvantages of each of these is described below.
Displacement sensors measure the relative position and change in position of an object. They are very effective and accurate at the low frequencies that are often found in hydraulic shaker systems. However, at higher frequencies, the displacements are small and the displacement sensors are ineffective at detecting the change in position.
Good at low frequencies
Measures relative position, not absolute position
Ineffective at high frequency due to small displacements
Velocity sensors measure the relative linear speed or angular speed of an object. A velocity sensor is effective for mid-range frequencies. Similar to an accelerometer, a velocity sensor is not effective for frequencies below 10Hz. It is also unable to give effective data for frequencies of vibrations above 2kHz. Although there may be situations where a velocity sensor may be helpful, in most circumstances the accelerometer (for mid and high frequencies) or a displacement sensor (for low frequencies) would be a better choice.
Good at middle frequency
Laser sensors don’t add mass
Not effective below 10Hz
Not effective above 2000Hz
Accelerometers are the most commonly used and best option for most vibration tests. They are effective over a wide range of frequencies (3Hz to 20kHz). Accelerometers tend to be small instruments with rigid construction, which permits them to be useful in the most hostile of environments. Velocity and displacement data can easily be obtained from the acceleration data through integration processes. In addition, accelerometers have a large dynamic range, which allows test engineers to identify large resonances for a specific device under test (DUT). The main disadvantage of an accelerometer is its limitations at low frequencies (below 3Hz).
Good at middle frequency
Good at high frequency
Can produce velocity and displacement data via integration functions
Small, rugged construction: useful in a variety of environments
If you found this blog post useful, download our handy checklist to run an efficient vibration test every time!
National Instruments. “Vibration Signals and Transducers” (obtained on-line June 7, 2016 at https://zone.ni.com/reference/en-XX/help/372416A-01/svtconcepts/vbr_sig/).
Norton, Henry. Handbook of Transducers. Prentice-Hall, 1989. (obtained on-line June 8, 2016 at https://www.scribd.com/doc/39878089/Handbook-of-Transducers-Harry-N-Norton).
Phuc, Duong. Vibration Sensors 2012. Published June 11, 2015. (obtained on-line June 8, 2016 at https://www.slideshare.net/phucduong397/vibration-sensors-2012 ).
Tustin, Wayne. Random Vibration & Shock Testing. Equipment Reliability Institute, 2005.