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.

 






RANDOM VIBRATION

(See Probabilistic Vibration). One whose in°stantaneous magnitudes cannot be predicted. Adjective "Gaussian" applies if they follow the Gaussian distribution. May be broad-band, covering a wide, continuous frequency range, or narrow-band, covering a relatively narrow frequency range. Random vibration contains no periodic or deterministic components.

RANGE

The measurand values, over which a transducer is intended to measure, specified by their upper and lower limits.

REFERENCE SENSITIVITY

The ratio of the change in charge or voltage generated by a transducer to the change in value of measurand that is measured under a set of defined conditions. For accelerometers, it is typically measured at 100 Hz (in the USA) and standard room conditions (q.v.).

REFLECTED OVERPRESSURE

The total pressure that results at the interface when a shock wave traveling in a medium encounters a discontinuity such as a rigid surface or another shock wave.

RELATIVE HUMIDITY. R.H.

The ratio, expressed as a percentage, of the amount of water in a given volume of air at a given temperature to the amount required to saturate the air at that temperature. RELIABILITY: The characteristic of an item expressed by the probability that it will perform a required function under given conditions for a specific period of time.

REPEATABILITY

The maximum deviation from the mean of corresponding data points taken under identical conditions. (2) The maximum difference in output for identically-repeated stimuli (no change in other test conditions). The maximum difference in outputs, at the same input, with the input changing in the same direction. Do not confuse with Accuracy.

RESIDUAL NOISE

The RMS noise measured at the output of an accelerometer over a specified bandwidth. The bandwidth can be broadband with noise expressed in ng or μg RMS or a series of narrow band specifications expressed in ng or μg/√Hz

RESOLUTION

The resolution is the smallest change of measurand, i.e., displacement, velocity, or acceleration, for which a change in output is discernible.

RESONANCE

Resonance of a system in forced oscillation exists when any change, however small, in the frequency of excitation causes a decrease in the response of the system.

RESPONSE

The vibratory motion or force that results from some mechanical input. In general, the output of a system that results from some input.

RESPONSE SIGNAL

The signal from a "response sensor" measuring the mechanical response of a mechanical system to an input vibration or shock. RISE TIME: The length of time required for the output of an instrument to rise from a small percentage of its final value to a large percentage of its final value as a result of a step change of input measurand. Usually assumed to be between 10% and 90% of the final value.

RESPONSE TIME

The time required for the output of a transducer to increase from zero to some specified percentage of its final value when excited by a step change in measurand.

RISE TIME

The length of time required for the output of an instrument to rise from a small percentage of its final value to a large percentage of its final value as a result of a step change of input measurand. Usually assumed to be between 10% and 90% of the final value.

RMS or ROOT-MEAN-SQUARE value

The square root of the time-averaged squares of a series of measurements. Refer to a textbook on electrical engineering. In the exclusive case of a sine wave, the RMS value is 0.707 X the peak value.

ROOM CONDITIONS (ISA S37.1(1969)

Ambient environmental conditions, which have been established as follows: a) Temperature: 25 ±10° C (77 ±18° F) b) Relative Humidity: 90% or less c) Barometric Pressure: 26 to 32 inches Hg (880 to 1083 mbar).

RSS or ROOT-SUM-Square

The square root of the sum of the squares of a series of measurements. Most often used to statistically sum independent errors.