# Glossary

The vibration monitoring industry has specialized jargon that is commonly used when talking about vibration sensors, accelerometers and associated applications. It's important that you understand common terminology to communicate effectively with vibration monitoring, reliability, condition monitoring and process automation professionals. We hope you find our glossary useful to find specialized terms and definitions used across vibration, condition monitoring and predictive maintenance.

FAST FOURIER TRANSFORM (FFT)

A shortcut method implemented in computers and digital measurement instrumentation to quickly create a frequency domain spectrum, often in real-time.

FIGURE OF MERIT (ACCELEROMETER)

The measure of the efficiency of an accelerometer’s design. F of M = Charge Sensitivity X Fn 2.

FILTER

A device to pass certain frequencies (pass band) but block other frequencies (stop band). Classified as low-pass (high-stop), high-pass(low-stop), band-pass or band-stop. Filters may be mechanical, electrical, or optical.

FLUSH DIAPHRAGM

Sensing element is located on the very tip of the transducer (No pressure port).

FORCED VIBRATION

The vibratory motion of a system caused by some mechanical excitation. If excitation is periodic and continuous, motion eventually becomes steady-state.

FOURIER SERIES

A series which expresses the values of a periodic function in terms of discrete frequency components that are harmonically related to each other

FREE FIELD (Sound)

The field in a homogeneous, isotropic medium free from acoustically reflecting boundaries. Usually a field in which the effects of the boundaries are negligible over the region of interest.

FREE VIBRATION

Free vibration occurs without force, as after a reed is plucked.

FREQUENCY

The reciprocal of the period in seconds (of a periodic function) (1/T). Usually given in hertz (Hz), meaning cycles per second (cps).

FREQUENCY RESPONSE

The change, with frequency, of the sensitivity with respect to the reference sensitivity of a transducer, for sinusoidally varying applied measurand within a stated range of frequencies. The output signal expressed as a function of the frequency of the input signal.

FREQUENCY SPECTRUM

A description of the resolution into frequency components, giving the amplitude (sometimes also phase) of each component.

FREQUENCY, NATURAL

The frequency of free oscillations of the sensing element of a fully assembled transducer. The frequency of a sinusoidally applied measurand at which the transducer output lags the measurand by 90 degrees.

FULL-SCALE OUTPUT

The algebraic difference between the end points of the range. Usually expressed as plus or minus one-half of the algebraic difference.

FUNDAMENTAL FREQUENCY

The number of cycles per second of the lowest-frequency component of a complex, cyclic motion. (See also Harmonic and Subharmonic). g: The acceleration produced by Earth's gravity. By international agreement, the value for 1 gravitational unit is 9.80665 m/s2 = 386.087 in/sec 2 = 32.1739 ft/sec2. g UNITS or GRAVITATIONAL UNITS: A way to express acceleration in terms of the gravitational constant, is equal to in/sec 22/ 386.087 in/sec2 or to m/s2 / 9.80665 m/s2 . GAGE FACTOR: The ratio of the relative change of resistance to the relative change in length of a Resistive Strain Transducer. GF = ΔR/R ΔL/L