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.

 






PARTIAL PRESSURE

The pressure which would be exerted by one constituent of a mixture of gases, if it alone were to occupy the same volume as the mixture. See also TOTAL PRESSURE.

PASCAL

Pressure of one Newton (force) per square meter.

PEAK-TO-PEAK VALUE

For an oscillating quantity, the algebraic difference between the extreme values of the quantity. (Same as double amplitude.)

PERIODIC VIBRATION (See also Deterministic Vibration)

An oscillation whose waveform regularly repeats. Compare with Probabilistic Vibration.

PHASE SHIFT

The amount of time by which the output of an instrument lags a sinusoidally varying input. Usually expressed as a fraction of a cycle of the frequency, in degrees.

PIEZOELECTRICITY

That property of asymmetric crystalline materials that develop electric polarization proportional to strain.

PIEZORESISTIVE TRANSDUCER

A transducer that relies on deformation of its sensitive element to change the resistance of the element. Some semi-conductors give greater resistance change for a given deformation than metals.

POLARITY

The relationship between the transducer output and direction of applied measurand; taken as "standard" or "positive" when a positive charge or voltage appears on the "high" side of the transducer output for an acceleration directed from the mounting surface into the body of the accelerometer.

POWER SPECTRAL DENSITY, G(f), PSD

The mean square measurand at a specified frequency divided by the bandwidth used to measure it, as the bandwidth approaches zero. In vibration measurement it is usually expressed as g2/Hz.

PRECISION

The relative closeness of the distribution of measurements of a quantity about their mean value. A high precision implies that the measurement has small random errors such as: a) Errors of judgment b) Fluctuating conditions (temperature, pressure, line voltage) c) Small disturbances (vibration, spurious electrical pickup, etc.)

PRESSURE HEAD

The height of a liquid column at the base of which a given pressure would be developed due to gravity acting on the fluid mass.

PROBABILISTIC VIBRATION

(As compared to Deterministic Vibration), one whose magnitude at any future time can only be predicted statistically. See also Random Vibration.

PSI

Pounds per square inch.

PSIA

Pounds per square inch absolute.

PSID

Pounds per square inch differential.

PSIG

Pounds per square inch gage.

PULSE DURATION

The time during which the faired magnitude of the pulse is above 10% of its maximum value.

PYROELECTRIC OUTPUT

Electrical signal (charge) which appears on the surfaces of a piezoelectric crystal when temperature gradients occur across the crystal.