The Illustrated Dictionary of Electronics - Loscha

underload relay • unequal alternation 707underload relay A relay actuated when circuit currentdrops below a predetermined value. CompareOVERLOAD RELAY.undermodulation Incomplete modulation of a carrierwave. Compare COMPLETE MODULATIONand OVERMODULATION.underpass The crossing of two conductors on asemiconductor wafer, without an electrical connection.underpower relay A relay actuated when powerdrops below a predetermined level. CompareOVERPOWER RELAY.underrate To assign a rating (e.g., current orpower) lower than the quantity of the rating anequipment can handle, or tolerate. For safety orreliability, apparatus sometimes is deliberatelyunderrated—especially in power output and maximumcurrent or voltage.undershoot On an oscilloscope screen or graph, amomentary swing of a current or voltage belowthe reference axis. Compare OVERSHOOT.Relative amplitude+−undershootUndershootTimeundershoot distortion Distortion caused by reductionof the maximum amplitude of a signalwavefront below the steady-state amplitude thatwould be reached by a prolonged signal wave.understudy See BACKUP.underthrow A form of signal distortion that occurswhen the modulating-waveform frequency is toohigh in proportion to the frequency of the wave itself.undervoltage A voltage of lower than specifiedvalue. Compare OVERVOLTAGE.undervoltage protection The automatic disconnectionof a load device from its driving sourcewhen the driving voltage falls below a predetermined(threshold) level. This action is sometimesaccomplished with a Zener diode (whose breakdownvoltage is equal to the threshold voltage) inseries with a disconnect relay.undervoltage relay A relay actuated when voltagedrops below a predetermined level. CompareOVERVOLTAGE RELAY.underwater antenna A transmitting or receivingantenna normally operated in a body of water. Itis usually associated with a submarine.underwater sound projector A hydroacoustictransducer that converts audio-frequency powerinto sound waves, which it radiates through abody of water to a receiver.Underwriters Code The advisory National ElectricalCode adopted by the National Fire ProtectionAssociation; it is often enforced by courts of lawand inspection agencies.Underwriters Laboratories Abbreviation, UL. Aprivate corporation that issues standards ofsafety for electrical components and equipment,and for their operation.undistorted power output For active amplifier devices,a specified maximum audio power outputlevel at which the total distortion does not exceeda specified low value (i.e., at which operation ispractically distortionless).undistorted wave 1. A sine wave that contains essentiallyno harmonic energy. 2. A nonsinusoidalwave whose shape corresponds exactly to theequation for the wave.undisturbed-one output In digital-memory operations,the one-output of a magnetic cell or othermemory unit that has received a full, rather thanpartial, read pulse. Compare UNDISTURBEDOUTPUT SIGNAL.undisturbed output signal In digital-memory operations,the output of a magnetic cell or othermemory unit previously set to one or zero, andthat has received a full, rather than partial, readpulse. Also called undisturbed response voltage.undisturbed response voltage See UNDIS-TURBED OUTPUT SIGNAL.undisturbed-zero output In digital-memory operations,the zero-output of a magnetic cell or othermemory unit that has received a full, rather thanpartial, read pulse. Compare UNDISTURBEDOUTPUT SIGNAL.Universal Truth Machine (UTM) A hypotheticalcomputer capable of proving any logically truestatement. According to the Incompleteness Theoremproved in 1930, such a machine cannot existfor a first-order logical system.undoped Pertaining to a pure semiconductor material(i.e., one containing no lattice-altering additives).undulating current A current, such as an alternatingor composite current, whose value oscillatesin the manner of a wave.undulation A wavelike alternation.undulatory theory The theory that light is transmittedby means of an undulating (wavelike) movementbetween the luminous object and the eye.unequal alternation In an alternating-currentwaveform, a form of asymmetry in which the positiveand negative half-cycles are not exact mirrorimages; they might vary in peak amplitude, duration,shape, etc.