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Ultra High Frequency
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Ultra Large Scale Integration
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(ULSI) -
Refers to the number of logic gates in a device. By one convention, ultra-large-scale integration represents a device containing a million or more gates.
Source: Maxfield & Montrose Interactive Inc.
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Ultra Low Frequency
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Ultrasonic
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Signals that are just above the frequency range of human hearing of approximately 20 kHz.
Source: Twisted Pair
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Ultrasonic Spectroscopy
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Analysis of the frequency content of an acoustic wave generally performed using a Fast Fourier Transform.
Source: Sonoscan
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Ultraviolet
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The range of the electromagnetic spectrum from 10 to 400 nanometers.
Source: JML Optical
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Unasserted
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Uncertainty
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From a metrologist's standpoint, what appears in the manufacturer's specification sheet under accuracy is more properly deemed uncertainty with accuracy being reserved to indicate the probability of the reading being accurate. A specification of 1% uncertainty would have an accuracy of 99%. Common practice among instrument manufacturers is to use the term accuracy and for calibration labs to use uncertainty with both representing the same thing in real life.
Source: Tektronix
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An expression of the combined errors in a test measurement process. Stated as a range within which the subject quantity is expected to lie. Comprised of many components including: estimates of statistical distribution and results of measurement or engineering analysis. Uncertainty established with a suitable degree of confidence, may be used in assuring or determining product conformance and technical specifications.
Source: MIL-Std-883F at Defense Supply Center Columbus
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An uncertainty is a figure of merit associated with the actual measured value; the boundary limits within which the 'true' value lies. Contributors to this "potential for inaccuracy" include the performance of the equipment used to make the measurement, the test process or technique itself and environmental effects. Additional imprecision may result from behavior of the phenomenon or item being measured. A skilled metrologist will assess and combine these various components in an uncertainty budget. To prove that a product complies with specification (or doesn't), the uncertainty must be less than the unknown's specification.
Source: Agilent
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Uncertainty of a Certified Value
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1. Estimate attached to a certified value of a quantity which characterizes the range of values within which the true value is asserted to lie with a stated level of confidence.[ISO Guide 30:1992]
2. Parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand.[VIM:1993]
Source: National Institute of Standards and Technology
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Uncommitted Logic Array
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Undersampling
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The process of sampling at a frequency lower than the signal-of-interest and still achieving needed resolution.
Source: LogicVision
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Undetectable Failure
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A postulated failure mode in a FMEA for which there is no failure detection method by which the operator is made aware of the failure.
Source: Testability.com
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Undetectable Faults
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Faults for which no test exists (within the test environment used) that can conclude whether or not the item under test (circuit node, component, etc.) is faulty or not.
Source: A.T.E. Solutions, Inc.
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Undetected Faults
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Ungroup
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An operation performed on a circuit description (RTL- or gate-level netlist) that consists of removing levels of hierarchy. This operation can be performed by a synthesis or a layout tool.
Source: LogicVision
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Uniform Distribution
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A simple failure calculation algorithm where a random number is simply limited to a range.
Source: Testability.com
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Uniform Resource Locator
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(URL) -
The name (or string of characters) that uniquely identifies each Web site.
Source: A.T.E. Solutions, Inc.
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Uniform Theory of Diffraction
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(UTD) -
The UTD analysis technique is useful for direct rays, reflected rays, diffractions from edges and corners, and waves around curved surfaces. UTD uses modeling elements of flat plates, cylinders of elliptical cross-section, and the end caps of each cylinder that may be tilted.
Source: eEngineer
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Uninterruptible Power Supply
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(UPS) -
Array of switches, rectifiers, inverters and particularly batteries which ensures a continuos supply of power to the consumers in case of power failure and possibly improves energy quality.
Source: Schaffner EMC
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Unit Delay Simulation
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A simplified form of timing simulation where every digital gate is assumed to introduce one unit of delay to a signal. In reality, different gates have different speeds, but unit delay simulation trades off accuracy for simulation speed.
Source: EE Design
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