Design, Test and Reliability Glossary of Terms and Definitions

This Glossary is compiled from the Terms and Definitions listed in IEST Recommended Practices published by the Design, Test, and Evaluation/Product Reliability Divisions. 

Jump to a section:

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

---

A

accelerance
The ratio of acceleration to force (also called inertance). The reciprocal of accelerance is dynamic mass.

acceleration
The rate of change of velocity with respect to time. For vibration testing, acceleration is usually expressed in gravitational units (g).

acceleration spectral density (ASD)
A description of the amplitude and frequency content of given random vibration spectrum, expressed in units of g2/Hertz. This can also be referred to as Power Spectral Density (PSD).

accelerometer
A sensor for converting acceleration into an electrical signal; a transducer whose instantaneous output is proportional to the instantaneous acceleration input.

acoustic field
Fluctuating pressure field generated either during an acoustic test or by the service environment; the service environment includes both the sound fields produced by acoustic sources, such as rocket motors, and the fluctuating pressure fields produced by aerodynamic sources, such as turbulent boundary layers; although these two types of pressure fields have different propagation velocities and spatial correlation characteristics, they are both commonly simulated by reverberant acoustic noise.

acoustic sensitivity
The rated output produced by a non-acoustic transducer in the presence of a specified acoustic field.

aeronautics systems
Systems designed to operate solely in the Earth’s atmosphere, e.g., jet aircraft, helicopters, tactical missiles, etc.

aerospace systems
Systems designed to operate in space as well as during launch and possible entry through the Earth’s atmosphere, e.g., Earth-orbiting satellites, deep space vehicles, and ballistic missiles.

ambient environment
Room conditions with no special environmental control imposed except for worker comfort.

amplitude
The magnitude of variation of a signal from its zero value. Amplitude should be used with a clarifying adjective such as peak, rms, or average. Amplitude may refer to displacement, velocity, acceleration, voltage, current, or other quantity.

armature
That part of an electrodynamic shaker that moves with the payload. The armature consists of a mounting table, a driver coil, and the structure that connects the mounting table to the driver coil.

assembly level
The product level of assembly at which a screen is applied, i.e., PCB, Module, Unit, or System.

audit
A test which is applied to a meaningful portion of a production lot to determine the acceptability of the manufacturing process associated with that lot.

axial resonance
The first mode of vibration of an armature that has the mounting table moving out-of-phase with the driver coil.

---

B

back-to-back comparison method
A method of performing a sensitivity/frequency response calibration of an accelerometer by mounting the unit under test to the “back” of a reference standard and comparing the outputs of the two devices.

base strain sensitivity
The rated output produced by an accelerometer in the presence of a specified amount of strain input induced by the bending motion at the mounting interface.

bias voltage
The DC voltage that appears at the output of the transducer in quiescent state (its level is determined and preset by the manufacturer); generally interferes with receiving recording devices and normally decoupled by a high value capacitor in series.

burn-in
A form of product conditioning that subjects a product to a constant temperature or applied power, or both, for a specified period of time. The intent of burn-in is to stabilize the product characteristics and identify failures. In the context of this document burn-in is not a form of ESS.

---

C

charge amplifier (converter)
A preamplifier designed for use with high-impedance piezoelectric transducers, commonly referred to as a “charge amp”; consists of an operational amplifier with a capacitor in its feedback loop; output voltage of the amplifier is proportional to the input charge generated by the transducer and independent of the cable capacitance.

charge sensitivity
The rated output produced by a high-impedance piezoelectric transducer per unit of acceleration or force input (e.g., pC/g).

circuit card assembly (cca)
An assembly containing individual components which are interconnected and mounted on a single (possibly multilayer) printed circuit board. Also referred to as printed circuit board assembly.

closed-loop accelerometer
An accelerometer in which the output generated by deflection in the mass-spring system is used as feedback in a circuit that closes the loop by physically driving the deflected mass back to its equilibrium position. NOTE: Some manufacturers claim that closed-loop accelerometer designs offer better amplitude linearity than open-loop designs.

commercial
A product (manufacturer) that is governed by the demands of the non-government market place.

compensation resistor
A resistor placed in parallel or in series with any of the legs of a piezoresistive accelerometer to correct for the imbalance in the bridge circuit and/or sensitivity errors at temperature.

compliance
The ratio of displacement to force. The reciprocal of compliance is dynamic stiffness.

compliance voltage
The DC supply voltage available to the integral electronics piezoelectric (IEPE) transducer circuitry; usually lower than the power supply voltage due to the voltage drop in the constant current device(s).

component
A nonrepairable throwaway item (i.e., integrated circuit, resistor, capacitor, diode, transistor, transformer, hybrid). Also referred to as a part or piece part.

corrective action
Step or steps taken to eliminate the root cause(s) of systematic defects in the overall product population. Corrective actions include changes in parts or materials sources, product design, or the production process.

cost effectiveness
The dollar difference between the cost of screening and the cost of benefits derived.

---

D

damping
The dissipation of oscillatory or vibratory energy with time.

damping ratio
For a system with viscous damping, the ratio of the actual damping coefficient to the critical damping coefficient or the fraction of critical damping. ? = c/cc is the symbol typically used.

dB
A decibel for acceleration or an acceleration-based shock response spectrum (SRS) in this case is defined as: 20 log10(new level/nominal level). The nominal level for acceleration is almost always 1 g.

dB/octave
A slope used for an acceleration-based SRS. An octave is a doubling in frequency. A pyroshock slope is 9 to 12 dB/octave or 1.5 to 2 decades in amplitude to one decade in frequency

decibel
The ratios of identical quantities are expressed in decibel or deciBel or dB units. The number of dB is given a ratio against some standard or reference value in terms of the base 10 logarithm of that ratio. In measuring acoustic or vibration power (as in PSD or ASD of random vibration), the number of dB = 10 log10 P/P0. P0, the reference level, equals 0 dB. In measuring the more common voltage-like quantities such as acceleration, the number of dB = 20 log10 E/E0. E0, the reference level, equals 0 dB.

defect (latent defect)
A flaw in a product that would eventually prevent it from meeting its functional requirements when operating within its specified environment and within its expected lifetime.

component defect
A flaw which could result in the failure of a component to meet its design specification.

design defect
A defect caused by inadequate design of a product or the design of the processes used to manufacture the product.

manufacturing defect
A defect caused by manufacturing process errors or uncontrolled conditions during assembly, test, inspection, or handling of the product.

workmanship defects
Defects caused by human error during manufacturing, fabrication and assembly.

degrees of freedom
In mechanics, the total number of directions of motion (of all the points being considered) on a structure. In statistics, the number of independent variables used in constructing a mathematical model representing a collection of random variables.

design characterization
Application of forcing function(s) to a product for the primary purpose of defining the environmental operating limits of the product.

design limit
For any given forcing function, the true capability of the product to withstand an applied forcing function without permanent damage. The design limit is typically in excess of the design requirement and operating limit.

design margin
The self-imposed restriction on a design more severe than either the specified or operational use requirements.

design requirement
The environmental conditions for which the product is required (or specified) to operate in and deliver full performance and reliability. Also referred to as the specification limit.

diaphragm mode
The first mode of vibration of an armature that has significant variations in vibration amplitude across the surface of the mounting table.

discharge time constant
The RC time constant determined by the design of a transducer’s circuit topology; time required for the signal level to reduce to 37% of its original value.

displacement
The distance or change of position of an object.

driver coil
The part of an armature that converts electrical energy to mechanical motion.

duration
The elapsed time of an event.

dynamic mass
The ratio of force to acceleration. The reciprocal of dynamic mass is accelerance or inertance.

dynamic range
The ratio of the highest level to the lowest level of signal to be measured, expressed in dB.

dynamic stiffness
The ratio of force to displacement. The reciprocal of dynamic stiffness is compliance.

---

E

E-D
An abbreviation for electrodynamic (which see).

electrical isolation
A condition in which the output and ground leads of the transducer are electrically isolated from the mounting surface

electrodynamic
A type of shaker that uses electrical energy to create dynamic motion. In physics, the technology used is called the voice coil principal.

electromagnetic rebalancing
A type of closed-loop accelerometer that uses electromagnetic mechanism to rebalance the deflected mass.

electromagnetic sensitivity
The rated output produced by an accelerometer in the presence of a specified electromagnetic field.

electrostatic rebalancing
A type of closed-loop accelerometer that uses electrostatic mechanism to rebalance the deflected mass.

environmental stress testing
Application of forcing function to a product for the purpose of characterizing the environmental performance of the product.

exciter
Another word for shaker.

---

F

failure
The termination of the ability of an item to perform its required function.

hard failure
A failure which exists during any condition.

infant failure
Failures which occur early in the operating life of a product.

soft failure
A failure which does not occur during operations in an ambient environment but does occur when subjected to one or more forcing function(s).

ferroelectric
A subset in the piezoelectric family of materials that typically has high dielectric constant. Example: Lead Zirconate Titanate (PZT)

fixed-reference transducer
A two-terminal transducer in which one terminal is fixed at a point in space as reference and the other terminal is attached to the object in motion.

force transducer
A transducer whose output is proportional to the force input.

forcing function
An environmental load which when imposed upon a product causes stress concentrations which accelerate the precipitation of the latent defects of the product.

Fourier transform; discrete Fourier transform (DFT)
The representation of a time-history by a harmonically related series of sines and cosines. The digitally sampled time-history is represented by the DFT.

frequency
The reciprocal of the period T in seconds. Usually given in hertz (Hz), expressing cycles per second (cps).

forcing frequencies
In sinusoidal vibration testing, the frequencies at which a shaker vibrates.

frequency spectrum
A description of the resolution of an electrical signal into its frequency components, giving the amplitude of each component.

fundamental frequency
The lowest frequency at which a system resonance occurs.

natural frequency
The frequency of an undamped system’s free vibration.

---

G

g
The acceleration of gravity: 9.8 m/sec (386 in./sec, or 32.2 ft/sec).

g
The acceleration produced by earth’s gravity. One international standard g is 9.80665 m/s2 or 386.087 in/sec2 or 32.1739 ft/sec2.

g
The quantity g is the acceleration produced by the force of gravity, which varies with the latitude and elevation of the point of observation. The value of 980.665 cm/sec2 (or 32.1739 ft/sec2) has been chosen as the standard acceleration due to gravity.

gauge factor
An indicator of efficiency for strain gauges, which is the ratio of the resistance change to the length change.

g-level
Acceleration time-history amplitude of a pyroshock as measured by an accelerometer calibrated in g’s.

gravitational units
A way to express acceleration in terms of a ratio with the gravitational constant. Divide a given acceleration by the appropriate value (9.80665 m/sec2 or 386.087 in/sec2 or 32.1739 ft/sec2).

---

H

hermetically sealed
A sealing method used in transducer design; usually accompanied by a welded construction and a glass-to-metal seal in the connector.

high-intensity acoustic test (HIAT)
Test that simulates an acoustic environment with an overall sound pressure level equal or higher than 120 dB.

hydraulic
A shortened form of the phrase servo-hydraulic.

---

I

inertance
The ratio of acceleration to force (also called accelerance). The reciprocal of inertance is dynamic mass.

input
The mechanical motion force or energy applied to a mechanical system to generate an output response.

input control signal
The signal that originates in a control sensor and is used to regulate shaker output intensity and profile.

in-service environment
airborne and structurally transmitted disturbances experienced during the operational life of aeronautical and aerospace systems.

in-service environment
The environment that exists where the product is used by the customer. In addition to operating environments, the transport and storage environments are also included.

integral electronics piezoelectric (IEPE)
A piezoelectric transducer with a built-in preamplifier to convert the high-impedance input into a low-impedance voltage output.

integral mechanical isolator
An accelerometer with a built-in mechanical isolator in one single package; considered superior to an external mechanical isolator because the transfer characteristics of the system can be clearly defined.

intensity
The severity of a vibration or shock event.

isolation
A reduction in motion severity, usually due to attenuation by a resilient structural member.

---

K

knee frequency
The dominant frequency in a pyroshock SRS, at which the slope for the SRS changes from an approximate +9 dB/octave slope to an approximately horizontal slope with peaks at the major local structural frequencies. All pyroshock SRS have a knee frequency, even if not properly measured or quantified.

---

L

laser Doppler velocity transducer
An instrument that uses the Doppler shift of laser light that has been backscattered from a vibrating object to produce a real-time analog signal proportional to instantaneous velocity.

laser interferometric displacement transducer
An instrument that uses an interferometric fringe counting technique for vibration-displacement measurement in low-frequency ranges.

linear variable differential transformer (LVDT)
A variable inductance transducer that provides an AC voltage output proportional to the displacement of a core passing through its internal windings.

linearity (nonlinearity)
The constant (or non-constant) behavior of the ratio of the electrical output of a transducer to the mechanical input; typically stated as a percentage of full scale based on a best-fit straight line, or as a percentage of reading.

lot
A quantity of the same product which is manufactured or processed under substantially similar conditions.

---

M

mass
Physical property: dynamically computed as acceleration divided by force, statically computed as weight divided by the acceleration due to gravity.

mass-loading error
An error in the structural response induced by the added mass of the accelerometer. Rule-of-thumb: The accelerometer should weigh less than one-tenth of the test object.

mass-spring (relative motion) transducer
A transducer that has only one terminal attached to its base and is attached to the object in motion; the motion of the device is inferred from the motion of the mass (of the mass-spring system) relative to the base.

maximax SRS
The maximum of the positive and negative primary and of the positive and negative residual.

mean time between failure (MTBF)
An established method of calculating and predicting the service life of an instrument.

mechanical impedance
The ratio of force to velocity, where the velocity is a result of that force only. The reciprocal of mechanical impedance is referred to as mobility.

micro electro-mechanical systems (MEMS)
A sensor that uses etching and micromachine fabrication techniques in forming its components; typically less than 1 mm square. NOTE: MEMS technology can be applied to piezoelectric, piezoresistive, variable capacitance, or other types of design.

micromachining
A manufacturing process that produces the entire sensing mechanism from a single piece of silicon by using anisotropic etching technique.

mission success
Systematic integration of design, reliability, availability, maintainability, quality, safety, system engineering, test, and human engineering disciplines to ensure that all products and services, including those of suppliers, fulfill their intended functions.

mobility
The ratio of velocity to force. The reciprocal of mobility is mechanical impedance.

mode
A characteristic pattern in a vibrating system, corresponding with a system resonance. All points reach their maximum displacements at the same instant.

module
An assembly of parts designed to function in conjunction with similar or different modules when assembled into a unit (i.e., CCA, power supply module, memory module).

mounting table
The part of an E-D shaker’s armature to which the payload is attached.

moving element
Another word for armature.

---

N

noise monitor
A dummy transducer that possesses all of the electrical and physical characteristics of a real transducer except for dynamic response, usually produced by replacing or desensitizing the sensing element(s); useful in assessing the quality of the output signal in the presence of environmental noise.

noise-treated cable
A type of cable designed to minimize triboelectric noise in a high-impedance piezoelectric transducer system; also known as low-noise cable.

notch
The deliberate reducing of a portion of a test spectrum.

notching
The intentional removal of a frequency band from a vibration spectrum.

Nyquist frequency
The highest frequency identified in a DFT, equal to one-half of the sample rate.

---

O

octave
The interval between two frequencies having a ratio of exactly 2:1.

on-off power cycling
Switching of product input power on and off at specified intervals.

open-loop accelerometer
An accelerometer in which the output generated by the deflection in the mass-spring system is used directly to indicate acceleration (cf. closed-loop accelerometer).

operating limit
The operational limit for a product is the maximum stress that the product can experience before specification degradation occurs. The operational limit can be viewed as the outer bound of the capability of the product – well beyond the capability required during normal service life.

overrange capability
The ability of a transducer to withstand excessive mechanical input beyond its stated full-scale range without sustaining permanent damage.

---

P

part
Same as component.

payload
Everything that is attached to the mounting table of a shaker.

peak
The extreme value of a varying quantity measured from the zero or mean value. Also, a maximum spectral value.

peak-to-peak value
The algebraic difference between extreme values above and below the zero or mean value.

period
The interval of time over which a cyclic motion repeats itself.

phase
The fractional part of a period between two motions or electrical signals having the same fundamental frequency (usually measured in degrees).

picoCoulomb (pC)
A common unit of charge from a PE transducer; 1012 Coulomb.

piezoelectric (PE) transducer
A transducer that utilizes piezoelectric elements as the spring in its mass-spring system and produces an electric charge proportional to the applied input.

piezoelectric coefficients
The measure of the amount of charge produced per unit of input force; unit is in picoCoulomb per Newton.

piezoresistive (PR) transducer
A transducer that utilizes piezoresistive elements as the spring in its mass-spring system, resulting in a change in resistance proportional to the applied input.

piston
That part of a servo-hydraulic shaker that moves with the payload.

pneumatic impactor
A type of shaker that uses compressed air to create motion.

power spectral density (PSD)
A measure of random vibration level that yields consistent results regardless of measurement bandwidth, usually expressed in units of g2/Hertz. This is also referred to as Acceleration Spectral Density (ASD).

power spectral density (PSD)
The power of random vibration intensity, in mean-square acceleration per frequency unit as g2/Hz or m2/sec3. This is the same term as acceleration spectral density (ASD) which is commonly used internationally.

printed circuit board (PCB)
An insulating base material (i.e., epoxy glass or polyimide) with necessary dielectric, electric, and mechanical properties which interconnects components when they are mounted to the circuit board.

product
An item that is fabricated by an individual or a company. A device which can be sold as a stand-alone item or needs to be integrated with other goods to form a finished good.

product ruggedization
The process of determining through analysis or test, or both, the ability of a product to withstand defined environmental conditions and the improvement of that ability through design changes.

pseudo-velocity
A widely used approximation for a relative velocity SRS is given by the relative displacement SRS multiplied by 2πfn. For hard impact and pyroshock transients, a relative velocity or pseudo-velocity SRS generally covers a much narrower dynamic range than either an absolute acceleration or a relative displacement SRS.

pyroelectric effect
The phenomenon in which an electric charge is produced when a transducer is subjected to a thermal transient input; relates primarily to piezoelectric transducers.

pyroshock
The response of a structure to a high-frequency, high-magnitude shock wave as a result of an explosive event; also known as pyrotechnic shock.

pyroshock (also called pyrotechnic shock)
The result of an explosive event, such as an explosive charge to separate two stages in a multi-stage rocket, and the resulting high-frequency (as high as 1 MHz), high-magnitude material stress phenomenon that propagates throughout the structure.

pyroshock, far-field
Pyroshock sufficiently distant from the pyrotechnic source that significant energy has transferred into the lower frequency structural response. Far-field pyroshock contains lower frequency and lower g-level energy than mid-field pyroshock; most of the energy is usually concentrated at one or a few frequencies at 3 kHz or less that corre¬spond to dominant structural mode(s). Additionally, some energy is dissipated by friction, material deformation, and heating and is not manifested in the lower structural frequency response.

pyroshock, mid-field
Pyroshock at a distance from the pyrotechnic source where significant energy is still contained in material stress-wave propagation, but some energy has transferred into the lower frequency structural response. Mid-field pyroshock contains lower frequency and lower g-level energy than near-field pyroshock; most of the energy is usually concentrated at frequencies between 3kHz and 10 kHz.

pyroshock, near-field
Pyroshock close to the pyrotechnic source, at a point before significant energy is transferred to the modal structural response. This type of pyroshock is dominated by material stress-wave propagation from the source, and contains very high frequency and very high g-level energy, which is distributed over a wide frequency range and is not generally dominated by a few selected frequencies.

---

Q

Q
The quality factor, 1/2ζ. Typically, Q = 10 for an acceleration-based pyroshock SRS.

---

R

RAD rating
An indicator used by the nuclear industry to represent the level of integrated gamma radiation.

reciprocity method
A primary vibration calibration method that uses a shaker designed with two coils, one to provide motion, one to measure the motion; the shaker is a reciprocal transducer, able to sense or drive, with a sensitivity factor relating the ratio of the drive current to force, to the ratio of pickup voltage to velocity.

resolution
The lowest level of signal that can be measured by a transducer, usually stated in terms of equivalent engineering unit; other terms, such as residual noise and threshold, are also used to represent the same parameter.

resonance
A frequency at which a structure amplifies vibration input.

resonance
The state in which a system experiences a peak of greater than 1 in the ratio of response motion to input motion.

resonance frequency
The frequency for which the response of a system undergoing forced, steady-state vibration is a maximum. NOTE: The mounted resonance frequency is usually higher than the unmounted resonance (the natural frequency of the device). When a transducer is mounted to a rigid structure, the stiffness of the system increases as a result.

resonance search
Exposing a product to vibration over a range of frequencies while monitoring the product response with the purpose of identifying resonances.

resonant frequency
Frequency or narrow frequency band in a product that, when excited by vibration, can result in damage to good product, or consume a significant amount of useful life, or do both.

response
The vibratory motion or force that results from mechanical input.

response signal
The signal from a response sensor measuring the test item reaction to an input vibration or shock stimulation.

reverberant chamber
Hard-wall chamber shaped in such a way that the sound field generated is reverberant.

reverberant sound field
Diffuse field in which the sound waves travel with equal probabilities in all directions.

root-mean-square (rms)
The square root of the time-averaged squares of a series of measurements. In the exclusive case of a sine-wave, the rms value is 0.707 times the peak value.

---

S

screen
The process of forcing defects to identifiable levels. A successful screen will uncover defects so that subsequent testing or operation is failure-free.

screening
A process or combination of processes applied to 100% of a lot or to an entire group of like products, this is an audit, to identify and eliminate defects.

environmental stress screening (ESS)
A process for uncovering defects in a product. This process involves the application to a product of one or more specific types of forcing functions. The forcing function may be applied either in combination or in sequence on an accelerated basis but within product design limits. The product is stressed to precipitate to hard failure, latent or incipient defects or flaws which, if not corrected will cause product failure during customer usage.

screen validation
A test performed to verify that a significant portion of the useful life of the product has not been consumed by the forcing function.

seeded samples
A test sample that is known to have a defect that is used to verify the effectiveness of a test. The sample may be a field return or a piece that is purposely weakened by the tester.

self-generating
A term referring to transducers that use only piezoelectric element(s) as the sensing mechanism, thus producing an electrical output without the need for an external power source.

sensing element
An element used in a transducer that is responsible for the sensing mechanism; in a piezoelectric transducer it is the piezoelectric crystal.

servo-hydraulic
A type of shaker that uses high pressure oil (i.e. hydraulics) and a servo valve to create motion.

shaker
A device that creates the motion that shakes payloads (some shakers can also shock payloads).

shaker table
Another word for shaker.

shock pulse
The transmission of kinetic energy into a system in a short event interval compared to the system’s natural period.

shock response spectrum (SRS)
The maximum response of a single-degree-of-freedom system to a shock input, plotted as a function of the natural frequency of the system with a constant damping value. The response and the input may be acceleration, velocity, or displacement. The damping value used for an SRS specification may affect the ability to meet that specification. Typically the maximum of the positive and negative SRS (maximax) is plotted, but many specifications require the positive SRS and negative SRS to be calculated separately and shown on the same log-log plot. In all cases, the SRS should be calculated according to ISO 18431-4.

shock response spectrum (SRS)
The plot of the maximum response experienced by a single degree-of-freedom system, as a function of its own undamped natural frequency, in response to an applied shock; may be expressed in terms of acceleration, velocity, or displacement.

single degree of freedom
Motion described by a single coordinate.

slew limiting
The output distortion (nonlinearity errors) resulting from a limit on the rate at which the output voltage can change; occurs when a load requires more current than the finite supply at the last stage of an amplifier, causing the output to adjust to draw only the available current; also known as slew rate limiting.

slew rate
The maximum slope or rate of change of a sinusoidal wave form.

sound pressure level (SPL)
amplitude of sound waves expressed in logarithmic unit dB; the SPL = 20 log (p/pref)

step stress testing
An experimental process of sequentially increasing forcing function levels, for periods of equal duration, incrementally so that the effects of each forcing function level may be evaluated.

stiffness
The ratio of force to deflection of a structure.

strain gauge
A small measurement device consisting of a piece of very thin foil, fine wire, or semiconductor that exhibits a change in resistance proportional to the mechanical strain imposed on it.

stress screening
The production inspection tool for precipitating manufacturing defects.

survivability
The ability of a transducer to withstand environmental inputs, such as shock and high temperature, without sustaining any damage.

system
A group of units interconnected or assembled to perform some overall electronic function (i.e., computer workstation, electronic flight control system, communications system).

electrodynamic (ED) vibration system
A system that converts electrical current into a mechanical force. This system can control both the shape and amplitude of the input spectrum.

repetitive shock (RS) system
A system in which the vibration table is excited with repeated shock pulses.

---

T

tailoring
The process of selecting an initial environmental stress screening program and then making subsequent changes to the methods and severity of the screen(s) to achieve maximum effectiveness.

temperature cycling
A screen that subjects a product to varying temperatures for specified periods of time. Also referred to as thermal cycling.

temperature response
An indication of output behavior of the transducer over a specified temperature range; also referred to as temperature coefficient. NOTE: Some manufacturers give a curve showing sensitivity versus temperature, others state it as a number (coefficient) in the specification, assuming a linear relationship. Temperature response should not be confused with thermal transient sensitivity.

temperature shock
Subjecting a product (component, PCB, module, unit, system) to high and low temperature limits. The transition between temperature limits is at a high rate of change (i.e., greater than or equal to 30°C per minute minimum). Also referred to as thermal shock.

temperature stabilization period
The amount of time required to reach thermal equilibrium.

test
A process of subjecting a product to conditions designed to determine whether or not the product meets specified performance requirements.

accelerated test
The application of exaggerated (relative to typical service conditions) forcing functions or the increase in rate of occurrence of service loading events to accelerate the rate of flaw growth in a product or structure.

acceptance test
A test used to demonstrate compliance of a product to specified criteria as a condition of acceptability for “next” usage (i.e., next higher assembly, customer use).

functional test
A test which measures a limited number of critical parameters to assure that the product is operating within specification limits.

life test
A test performed on a product which is continued until a specified percentage of the product fails or until some other predetermined criteria for end of life has been satisfied.

sample test
A test performed on a limited number of product during the manufacturing process.

test article
Another word for unit under test.

test platform
The table of a shaker or the carriage of a shock test machine.

test process
Set of activities that begins in the pre-proposal phase and ends with the delivery of a product that has been shown to satisfy all of its specifications and design requirements and to be suitable for its intended mission.

thermal survey
The measurement of the thermal response of various elements in the product in order to identify the slowest and fastest responding elements.

thermal transient sensitivity
The output response of a transducer when exposed to a defined temperature gradient (transient); usually stated in terms of equivalent engineering unit per degree centigrade.

time-to-failure
Elapsed time to precipitate a product defect.

tracking filter
A narrow band-pass filter with a center frequency that follows an external synchronizing signal.

transducer
A device which converts a mechanical phenomenon to an electrical signal; also called a pickup or sensor.

piezoelectric transducer
A transducer with an electrical signal output that depends on deformation of the transducer’s sensitive crystal or ceramic element to generate electrical charge and voltage.

piezoresistive transducer
A transducer with an electrical signal output that depends upon deformation of the trans-ducer’s semiconductor resistive element, offering greater resistive change than the wire of a strain gage transducer, for a given deformation.

transducer electronic data sheet (TEDS)
Transducer information stored inside a digital memory chip defined by IEEE 1451.4; typically located inside the transducer, the digital ID chip contains permanent information (model number, serial number) and temporary information (sensitivity, date of calibration) provided by the manufacturer or calibration facilities.

transducer (sensor)
A device that converts shock or vibration into an electrical signal that is proportional to the parameter of the experienced motion or force. NOTE: The term “transducer” is used inter¬changeably with the term “sensor” in industry. The term “sensing element” is used to describe the sensing mechanism inside the transducer or sensor.

transmissibility
The non-dimensional ratio of response signal to input signal.

transmissibility
The nondimensional ratio of the response amplitude of a system in steady-state forced vibration to the excitation amplitude; ratio may be one of forces, displacements, velocities, or accelerations.

transverse sensitivity
The output response of a transducer when excited by a transverse motion or force perpendicular to its sensitive axis; stated in percent of the nominal output.

triboelectric noise
The output generated by a coaxial cable in motion due to the momentary separation of its dielectric material from its shield.

---

U

unit
A self-contained collection of components or assemblies, or both, within one chassis performing a specific function or group of functions, and removable as a single chassis from a system (e.g., automobile computer, VHF communications transmitter, disc drive, etc.).

unit under test (UUT)
That which is being tested.

---

V

---

W

Wheatstone bridge
A four-element circuit arrangement that is one of the most precise methods for measuring change in resistance; widely applied in transducer design.

---

Z

zero measurand output (ZMO)
In the bridge circuit of a piezoresistive transducer, the small offset or residual DC voltage at the output due to slight differences in resistance between each arm; expressed in millivolts at full rated excitation; also known as zero balance.

zeroshift
The apparent shift from the zero-reference line of an accelerometer output due to an intense shock from mechanical, electrical, or thermal causes; all accelerometer types exhibit some degree of zeroshift under high shock load.