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.

 






S.I. SYSTEM

The international (metric) system of units.

SAWTOOTH SHOCK PULSE (Terminal Peak)

An ideal shock pulse for which the acceleration-time curve has the shape of a triangular wave wherein the acceleration increases linearly to a maximum value and then drops instantaneously to zero.

SEALED (or SEALED GAGE) PRESSURE

Pressure measured with reference to the pressure in a sealed container; the container is usually within the sensor.

SELF-HEATING

Internal heating resulting from electrical energy dissipated within a current-carrying element.

SENSING ELEMENT

The part of the transducer which reacts directly in response to the measurand.

SENSITIVITY

The ratio of the change in transducer output to a change in the value of the measurand (e.g., mV/g).

SHEAR WAVE

A wave in an elastic medium that causes an element to change its shape without a change in volume, a result of shear stresses. Normally a transverse wave.

SHOCK (Mechanical Shock)

The application of a sudden change in force, position, velocity, or acceleration that excites transient disturbances in a system. Change is normally considered sudden if it takes place in a time that is short compared with natural periods of concern.

SHOCK PULSE

A form of shock excitation characterized by a rise and decay of acceleration in a relatively short period of time.

SHOCK RESPONSE SPECTRUM

A plot (amplitude vs. frequency) of the response of a number of single-degree-of-freedom systems to an applied shock.

SHOCK SPECTRUM, PRIMARY (INITIAL)

A shock spectrum derived from response measurement within the duration of a simple shock pulse.

SHOCK SPECTRUM, RESIDUAL

A shock spectrum derived from response measurements after a shock has ended.

SHUNT CALIBRATION

The change in electrical output caused by placing a fixed resistor between the appropriate transducer terminals. Used “in the field” for quick calibration.

SHUNT CALIBRATION RESISTOR

A shunt resistor which, when placed across a specified element of the electrical circuit of a transducer, will electrically simulate a specified percentage of the transducer full-scale output at room conditions.

SHUNTING RESISTANCE (Transducer Resistance) (Leakage Resistance)

The electrical resistance observed between the two terminals of a piezoelectric transducer or its integral cable.

SIMPLE HARMONIC MOTION

Periodic vibration that is a sinusoidal function of time.

SINGLE-DEGREE-OF-FREEDOM SYSTEM

A system requiring but one coordinate to completely define its configuration at any instant.

SINGLE-ENDED INPUT

An input circuit configured such that one of the input lines is electrically and directly connected to signal ground.

SKIRT (Rolloff)

The terminal slope of attenuation of the frequency response of a filter, usually expressed at 6 n dB/octave, where n is the order of the filter.

SLEW RATE

The maximum rate at which the output voltage of an instrument can be made to change understated load conditions.

SOURCE CAPACITANCE

The total external capacitance shunting the input terminals of an amplifier. Includes transducer and cable capacitance.

SOURCE RESISTANCE

The total of all dc resistive leakage paths shunting the input terminals of an amplifier.

SPAN

The algebraic difference between the limits of the Range.

SPECIFICATIONS

The group of error limits within which each device will operate.

STAGNATION PRESSURE

The sum of the static pressure and the impact pressure. It can be measured at a point where the velocity of the fluid is zero.

STANDARD DEVIATION (sigma)

A statistical term: the square root of the variance, i.e., the square root of the mean of the squares of the deviations from the mean value. If the mean is zero, standard deviation is equal to RMS.

STATIC PRESSURE

The pressure of a fluid, exerted normal to the direction along which the fluid flows.

STATIONARY PROCESS

An ensemble of time-histories such that their statistical properties are invariant with respect to translations in time.

STEADY STATE VIBRATION

Periodic vibration for which the statistical measurement properties (such as the peak, average, RMS and mean values) are constant.

STIFFNESS

The ratio of change of force (or torque) to the corresponding change in translational (or rotational) displacement of an elastic element. Usually expressed as: k = F/d = W/δ.

STRAIN GAGE

A measuring element for converting mechanical strain into an electrical signal.

SUPPLY VOLTAGE

See EXCITATION.