The maximum rate at which an instrument’s output can be changed by some stated amount.

Standard deviation

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.

Steady state vibration

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

Step Stress Test

A test consisting of several stress levels applied sequentially for periods of equal duration to a sample. During each period a stated stress level is applied and the stress level is increased from one step to the next.

Stress screening

A modern electronics production tool for precipitating latent defects such as poorly soldered connections. Utilizes random vibration and temperature shock.

Sub harmonic

A sinusoidal quantity having a frequency that is an integral sub multiple(X1/2,X1/3) of a fundamental (X1) frequency.

Tailoring

Selecting or altering test procedures, condition, values, tolerance. etc., to simulate or exaggerate the environmental effects of one or more forcing functions.

Transducer (or pickup or sensor)

A device which converts some mechanical quantity into an electrical signal.

Transmissibility

In steady state vibration, Tr is the non dimensional ratio of response motion/ input motion. two displacements, two velocities or two accelerations. The maximum Tr value is the mechanical ‘Q’ of a system. At resonance, Tr is maximum.

Vibration

Mechanical oscillation or motion about a reference point of equilibrium.

Vibration machine (or exiter or shaker)

One which produces controlled and reproducible mechanical vibration for vibration testing mechanical systems, components, or structures.

Vibration meter

An apparatus ( usually an electronic amplifier, detector and readout meter) for measuring electrical signals from vibration sensors. May read \ displacement velocity and /or acceleration.

Wear-out Failure period

That period during which the failure rate of some items is rapidly increasing due to the deterioration processes.