Condition Monitoring Systems

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T-V

TAAF

Test, analyze and fix. See Accelerated Life Testing.

Tailoring

Selecting or altering test procedures, conditions, values, tolerances, measures of failure, etc., to simulate or exaggerate the environmental effects of one or more forcing functions.

Test Type

The mode of measurement operation

Temperature coefficient

The amount of drift, in percent of full scale output, that might result from a 1[DEGREE]C change in ambient temperature.

Temperature range

The temperatures between which a sensor will operate accurately.

Total Harmonic Distortion (THD)

For a signal, the ratio of the sum of the powers of all harmonic frequencies above the fundamental frequency to the power of the fundamental frequency.

Thermal cycling

Subjecting a product to predetermined temperature changes, between hot and cold extremes.

Thermistor

An electrical device used for temperature measurement.

Thermocouple

An electrical device used for temperature measurement. Two dissimilar metals joined together, making a continuous loop.

Threshold

The smallest change in a measured variable that gives a measurable change in output signal.

Thrust position

Location in direction of a shaft centerline. See axial position.

Thump Signal

A “velocity and displacement compensated” half-sine pulse. This transient is a classic shock-test acceleration waveform.

Time Averaging

In a DSA, averaging of time records that results in reduction of asynchronous components.

Time Constant

The interval needed for an instrument’s output to move 63% of its ultimate shift as a result of a step change in its input.

Time constant

The interval needed for an instrument’s output to move 63% of its ultimate shift as a result of a step change in its input.

Time Record

In a DSA, the sampled time data converted to the frequency domain by the FFT. Most DSAs use a time record of 1024 samples.

Toggle

A switch that causes the opposite value. For example, a switch that is “on,” when toggled, becomes “off.”

Torsional Vibration

Amplitude modulation of torque measured in degrees peak-to-peak referenced to the axis of shaft rotation.

Tracking filter

A narrow band-pass filter whose center frequency follows an external synchronizing signal.

Tracking Filter

A low-pass or band-pass filter which automatically tracks the input signal. A tracking filter is usually required for aliasing protection when data sampling is controlled externally.

Transducer (or pickup or sensor)

A device which converts some mechanical quantity into an electrical signal. Less commonly, the reverse conversion./ A device for translating the magnitude of one quantity into another quantity./ An element or device which receives information in the form of one quantity and converts it to information in the same or an other quantity or form. Primary elements and transmitters are also referred to as transducers.

Transform

A mathematical operation that converts a function from one domain to another domain with no loss of information. For example, the Fourier transform converts a function of time into a function of frequency.

Transient

The behavior of a variable during transition between two steady-states.

Transient Vibration

Temporarily sustained vibration of a mechanical system. It may consist of forced or free vibration or both. Typically this is associated with changes in machine operating condition such as speed, load, etc. / Transient vibration Short-term vibration of a mechanical system.

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.

Transmitter

A transducer which responds to a measured variable by means of a sensing element, and converts it to a standardized transmission signal which is a function only of the values of the measured variable.

Transverse sensitivity

The unfortunate sensitivity of a sensor (or pickup or transducer) in a direction perpendicular to the advertised or stated sensitive axis. Also called cross-axis or lateral sensitivity.

Transverse Sensitivity

See Cross-Axis Sensitivity.

Trigger

Any event which can be used as a timing reference. In a DSA, a trigger can be used to initiate a measurement.

Time Span (Tspan)

The time duration (second) of each frame or capture window that is numerically equal to Block Size x dT.

Tuneable filter

A filter whose cut-off frequencies are adjustable, either manually or under remote electrical control.

Ultrasound

Ultrasound is sound with a frequency greater than the upper limit of human hearing, this limit being approximately 20 kilohertz (20,000 hertz). SignalCalc analyzers provide measurements will into the ultrasonic range, as high as 97 kHz.

Unit

Every measurement is expressed as a multiple or fraction of dome appropriate, well-defined unit quantity such as centimeter, volt, etc.

Unbalance (imbalance)

Unequal mass distribution on a rotor. The mass centerline does not coincide with the rotation or geometric centerline.

Undamped Natural Frequency

The same as the natural frequency of a structure.

Uniform Window

In a DSA, a window function with uniform weighting across the time record. This window does not protect against leakage, and should be used only with transient signals contained completely within the time record.

In the FFT Analyzer, the uniform, or rectangular, window does not modify the signal amplitude at all. It is also called rectangular weighting, or uniform weighting, and is selected when the signal to be Analyzed is a transient rather than a continuous signal.

Unit

Every measurement is expressed as a multiple or fraction of dome appropriate, well-defined unit quantity such as centimeter, volt, etc.

Upper range limit (URL)

The highest value of the measured variable that a device can be adjusted to measure. (This value corresponds to the top of the range.) Also Universal Resource Location on the web.

Upper range value (URV)

The highest value of the measured variable that a device is adjusted to measure. (This value corresponds to the top of the span.)

USB

Universal Serial Bus. USB data acquisition devices are ideal for a variety of applications from simple data logging to embedded OEM systems. The SignalCalc ACE powered by Quattro is an example of a USB data acquisition product.

UUT

Unit under test. See also DUT or device under test (being tested).

Variable

Any condition which is measured, controlled (directly or indirectly) or manipulated.

Vector

A quantity which has both magnitude and direction (phase).

Velocity

Rate of change of displacement with time, usually along a specified axis; it may refer to angular motion as well as to axial motion.

Rate of change of displacement with time. A vector quantity that specifies the time rate of change of displacement with respect to a reference frame. If the reference frame is not inertial, the velocity is often designated relative velocity

Velocity Transducer

An electrical/mechanical transducer who’s output is directly proportional to the velocity of the measured unit. A velocity transducer consists of a magnet suspended on a coil, surrounded by a conductive coil. Movement of the transducer induces movement in the suspended magnet. This movement inside the conductive coil generates an electrical current proportional to the velocity of the movement. A time waveform or a Fourier transform of the current will result in a velocity measurement. The signal can also be integrated to produce a displacement measurement.

Velocity limit

A limit on the rate of change, which a particular variable may not exceed.

Vibration

Mechanical oscillation or motion about a reference point of equilibrium. / A periodic motion or oscillation of an element, device, or system.

Any periodic process, especially a rapid linear motion of a body about an equilibrium position. SignalCalc analyzers and SignalStar controllers require transducers to convert the mechanical vibrations to electrical signals for analysis or control.

Vibration Analysis

The study of a continuing periodic change in the magnitude of a displacement with respect to a specified central reference. Various measurements for vibration analysis are provided as part of all SignalCalc systems.

Vibration machine (or exciter or shaker)

A device which produces controlled and reproducible mechanical vibration for the vibration testing of mechanical systems, components and structures.

Vibration meter

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

Vibrator

A device which produces controlled and reproducible mechanical vibration for the vibration testing of mechanical systems, components and structures.

Vibromyography

Also called mechanomyography or acoustic myography. The measurement of muscle vibration when a muscle contracts.

Viscous Damping

Damping that is proportional to velocity. Viscous damping is used largely for system modeling since it is linear.

Volt (V)

The electrical potential difference between two points in a circuit. One volt is the potential needed to move one coulomb of charge between two points while using one joule of energy.