Vibration calibrators , sometimes also called reference shakers, are electromechanical instruments which enable
calibration
In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known ...
of vibration sensors and measuring instruments to
traceable standards. They produce sinusoidal mechanical vibration signals with known
amplitude
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...
s and
frequencies. The vibrating part of the instrument is usually a cylindrical steel stud with an internal thread for attachment of the test object. An
electrodynamic or
piezoelectric
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied stress (mechanics), mechanical s ...
actuator system is used to produce the vibrations. With older instruments it was necessary to adjust the vibration amplitude according to the weight of the test object. However, modern instruments contain a built-in reference
accelerometer
An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change (mathematics), rate of change of velocity) of the object relative to an observer who is in free fall (tha ...
and
closed-loop control, with which the amplitude is kept constant up to a maximum specified weight of test object. Older models can be used to calibrate objects weighing up to a maximum of approximately 100 g, whereas the latest instruments can work stably with test objects weighing over 500 g.
Vibration calibrators are most often used for testing and checking vibration sensors and measuring instruments at the site of their operation and are, therefore, usually transportable and battery operated.
The most commonly occurring vibration frequency of calibrators is 159.2 Hz, which is equivalent to a
radian frequency of 1000 rad/s. The vibration displacement, velocity and acceleration of sinusoidal signals are connected with each other through the factor of the radian frequency. Advantageously, at 1000 rad/s the numerical values of the amplitudes for all three vibration quantities are the same. For example, a vibration acceleration of 10 m/s² at 159.2 Hz is equivalent to a vibration velocity of 10 mm/s and a vibration displacement of 10 μm.
With some instruments it is possible to choose between several frequencies or to finely tune a specific frequency range. Frequencies between 16 Hz and 10 kHz are common on the market.
Occasionally, vibration calibrators also contain a signal conditioner for connection to various types of vibration sensors, and additionally a display for reading the sensitivity.
A procedure for the calibration of vibration calibrators is described in the international standard ISO 10816-44.
References
* T. Usuda, A.O. Oota, H. Nozato, Y. Hino. (2009) "Transportable Vibration Calibration System Employing E-trace Scheme", Proceedings of the IMAC-XXVII
External links
Vibration Calibrators, Brüel & Kjær{Dead link, date=June 2022 , bot=InternetArchiveBot , fix-attempted=yes
Portable Vibration Calibrator, The Modal ShopPortable Vibration Calibrators, Agate Technology Measurement