V
V 1. Letter symbol for volt. 2. Symbol for voltmeter. 3. Schematic symbol for vacuum tube.
VCC Symbol for the supply voltage to an integrated circuit with respect to ground.
VDD, VSS, VCC, VEE In an MOS circuit, the designation of the power-supply terminal serving the drain, source, collector, or emitter. The double subscript refers to the power-supply terminal, while a single subscript references the parameter at the element of a device. For example, VC is the voltage measured on the collector itself, while VCC is the (constant) voltage supplied to the collector circuit. Note: In CMOS, the term VDD has been adopted as a convention referring to the positive power-supply terminal, although it is actually applied to the source of a p-channel transistor.
VA Letter symbol for voltampere.
vaccine A program to detect the presence of a computer virus.
vacuum Abbreviated vac. Theoretically, an enclosed space from which all air and gases have been removed. However, since such a perfect vacuum is never attained, the term is taken to mean a condition whereby sufficient air has been removed so that any remaining gas will not affect the characteristics beyond an allowable amount.
vacuum capacitor A capacitor consisting usually of two concentric cylinders enclosed in a vacuum to raise the breakdown voltage.
vacuum deposition A process in which a substance is heated in a vacuum enclosure until the substance vaporizes and condenses (deposits) on the surface of another material in the enclosure. This process is used in the manufacture of resistors, capacitors, microcircuits, and semiconductor devices. The deposited material is called a thin film.
vacuum envelope The airtight envelope that contains the electrodes of an electron tube.
vacuum evaporation A process in which a material is vaporized and the vapor deposits itself, through openings in a mask, onto a substrate to form a thin film.
vacuum gage A device that indicates the absolute gas pressure in a vacuum system (e.g., in the evacuated parts of a mercury-arc rectifier).
vacuum impregnation Filling the spaces between electric parts or turns of a coil with an insulating compound while the coil or parts are in a vacuum.
vacuum level The degree of a vacuum, as determined by the pressure: rough vacuum (760 torr to 1 torr), medium vacuum (1 torr to 10–3 torr), high vacuum (10–3 torr to 10–6 torr), very high (hard) vacuum (10–6 torr to 10–9 torr), ultrahigh (ultrahard) vacuum (below 10–9 torr).
vacuum metalizing A process in which surfaces are given a thin coating of metal by exposing them to metallic vapor produced by evaporation under vacuum (one millionth of normal atmospheric pressure).
vacuum phototube 1. A phototube that is evacuated to such a degree that its electrical characteristics are essentially unaffected by gaseous ionization. 2. A phototube that functions within a vacuum and therefore eliminates the effect of gaseous ionization on its electrical properties.
vacuum pickup A handling instrument with a small vacuum cup on one end, used to pick up chip devices.
vacuum range For a communications system, the maximum range computed for an atmospheric attenuation of zero.
vacuum seal An airtight junction between component parts of an evacuated system.
vacuum switch A switch in which the contacts are enclosed in an evacuated bulb, usually to minimize sparking.
vacuum tank An airtight metal chamber that contains the electrodes and in which the rectifying action takes place in a mercury-arc rectifier.
vacuum tube An electron tube evacuated to such a degree that its electrical characteristics are essentially unaffected by the presence of residual gas or vapor.
vacuum-tube amplifier An amplifier in which electron tubes are used to control the power from the local source.
vacuum-tube characteristics Data that shows how a vacuum tube will operate under various electrical conditions.
vacuum-tube keying A code-transmitter keying system in which a vacuum tube is connected in series with the plate-supply lead going to the winding in the plate circuit of the final stage. The grid of the tube is connected to its filament through the transmitting key so that when the key is open, the tube is blocked, interrupting the plate supply to the output stage. Closing the key allows plate current once more through the keying tube and the output tubes.
vacuum-tube modulator A modulator in which a vacuum tube is the modulating element.
vacuum-tube oscillator A circuit in which a vacuum tube is used to convert dc power into ac power at the desired frequency.
vacuum-tube rectifier A tube that changes an alternating current to an unidirectional pulsating direct current.
vacuum-tube transmitter A radio transmitter in which electron tubes are utilized to convert the applied electric power into radio-frequency power.
vacuum-tube voltmeter Abbreviated VTVM. See electronic voltmeter.
valence A number representing the proportion in which an atom is able to combine with other atoms. It generally depends on the number and arrangement of electrons in the outermost shell of each type of atom.
valence band — 1. In the spectrum of a solid crystal, the range of energy states containing the energies of the valence electrons that bind the crystal together. In a semiconductor material, it is just below the conduction band, separated from it by the forbidden gap. 2. The band of atomic energy levels containing the valence electrons, i.e., those electrons in the outer shell of an atom. In an insulating or semiconductor material, the valence band energy level is below the conduction band. In a conducting material — for example, copper, aluminum, silver, gold, and lead — the valence-band energy level is above the conduction-band energy, thus allowing the electrons to be more free to move as an electric current.
valence bond Also called a bond. The bond formed between the electrons of two or more atoms.
valence electrons 1. The electrons of an atom in the outer shell that determine the chemical valency of the atom. 2. Electrons in the valence band of a semiconductor, where they are free to move under the influence of an electric field.
valence shell The electrons that form the outermost shell of an atom.
validate To ensure correctness of data that has been (previously) or is being entered by any of a number of means, including check digit, batch total, numeric only field, and verification.
validation The process of verifying that execution of a system in its specified environment causes no operational problems. Includes prevention, diagnosis, recovery, and correction of errors.
validity Correctness; specifically, how closely repeated approximations approach the desired (i.e., correct) result.
validity check 1. A check to determine that a code group actually represents a character in the particular code being used. 2. A computer input-data check based on known limits for variables in given fields.
valley A dip between two peaks in a curve.
valley current In a tunnel diode, the current measured at the positive voltage for which the current has a minimum value from which it will increase if the voltage is further increased.
valley point The point on the characteristic of a tunnel diode corresponding to the lowest voltage greater than the peak point voltage for which the differential conductance is zero.
valley-point current The current value at the valley point.
valley-point emitter current The current flowing in the emitter of a unijunction transistor when the device is biased to the valley point.
valley-point voltage The voltage value at the valley point.
valley voltage In a tunnel diode, the voltage corresponding to the valley current.
value 1. The magnitude of a physical quantity. 2. The quantitative measure of a signal or variable.
value analysis The systematic use of techniques that serve to identify a required function, establish a value for that function, and finally to provide that function at the lowest overall cost. This approach focuses on the functions of an item rather than the methods of producing the present product design.
value theory The assignment of numerical significance to the worths of alternative choices.
valve 1. A British term for a vacuum tube. 2. A device permitting current flow in one direction only (e.g., a rectifier). 3. A device or system that is capable of flow diversion, cutoff, or modulation.
Van Allen radiation belts Two doughnut-shaped belts of high-energy particles that surround the earth and are trapped in its magnetic field. They were first discovered by Dr. James A. Van Allen of Iowa State University.
Van Atta antenna A retrodirective array of antenna elements so interconnected that an incident wave produces a radiated beam from the array in the direction of the incident wave reversed over a significant range of angles of incidence, as in the case of an optical auto-collimator. Versions of the array may contain amplifiers, circulators, and mixers, and may direct the transmitted beam, with or without modifications, in a direction or directions other than that of the incident wave reversed.
Van Atta array An antenna array designed so that the received signal is reflected back toward its source in a narrow beam to provide signal enhancement without amplification. It consists of pairs of corner reflectors or other elements equidistant from the center of the array and connected together by means of low-loss transmission line.
Van de Graaff accelerator An electrostatic-generator type of particle accelerator from which the voltage is obtained by picking up static electricity at one end of the machine (on a rubber belt) and carrying it to the other end, where it is stored.
vane-anode magnetron A cavity magnetron in which the walls between adjacent cavities have parallel plane surfaces.
vane attenuator A waveguide device designed to preset attenuation in a circuit by sliding a resistive element from the side wall of the waveguide to the center for maximum attenuation. This method of attenuation is used in precision calibrated attenuation readings, and resetting must be made. Some of its countless applications are calibrations of other attenuators, directional couplers, filters, and other lossy components, in antenna-pattern measurements, noise-level measurements, and for setting power levels to desired values.
vane-type instrument A measuring instrument in which the pointer is moved by the force of repulsion between fixed and movable magnetized hon vanes, or by the force between a coil and a pivoted vane-shaped piece of soft iron.
vane-type magnetron A cavity magnetron in which the walls between adjacent cavities have plane surfaces.
V-antenna A V-shaped arrangement of conductors, the two branches being fed equally in opposite phase at the apex.
vapor pressure The pressure of the vapor accumulated above a confined liquid (e.g., in a mercury-vapor rectifier tube).
vaporware A jocular term for products or components that have been announced by a vendor that do not yet exist and may never exist.
var Letter symbol for voltampere reactive. The unit of reactive power, as opposed to real power in watts. One var is equal to one reactive voltampere.
VAR Abbreviation for visual-aural range.
varactor Also called varactor diode, silicon capacitor, voltage-controlled capacitor, and voltage-variable capacitor. 1. A two-terminal solid-state device that utilizes the voltage-variable capacitance of a pn junction. In the normal semiconductor diode, efforts are made to minimize inherent capacitance, while in the varactor, this capacitance is emphasized. Since the capacitance varies with the applied voltage, it is possible to amplify, multiply, and switch with this device. 2. Semiconductor diode that exhibits a change in capacitance with a change in applied voltage when operated in a reverse-biased condition. Varactors are used as voltage-variable capacitors in tuned circuits.
varactor diode A two-terminal semiconductor device in which use is made of the fact that its capacitance varies with the applied voltage. See also varactor.
varactor-tuned oscillator An oscillator in which a varactor diode is used in the frequency-determining networks that encompass the circuit’s active device(s).
varhour meter Also called a reactive voltamperehour meter. An electricity meter that measures and registers the integral (usually in kilovarhours) of the reactive power of the circuit into which the meter is connected.
variable 1. Any factor or condition that can be measured, altered, or controlled (e.g., temperature, pressure, flow, liquid level, humidity, weight, chemical composition, color). 2. A quantity that can take on any of a given set of values. 3. In a computer, a symbol whose numeric value changes from one iteration of a program to the next or within each iteration of a program.
variable-area track A sound track divided laterally into opaque and transparent areas. A sharp line of demarcation between these areas forms an oscillographic trace of the waveshape of the recorded signal.
variable-capacitance diode Abbreviated VCD. A semiconductor diode in which the junction capacitance present in all semiconductor diodes has been accentuated. An appreciable change in the thickness of the junction-depletion layer and a corresponding change in the capacitance occur when the dc voltage applied to the diode is changed.
variable-capacitance transducer A transducer that measures a parameter or a change in a parameter by means of a change in capacitance.
variable capacitor 1. A capacitor that can be changed in capacitance by varying the useful area of its plates, as in a rotary capacitor, or by altering the distance between them, as in some trimmer capacitors. 2. A capacitor whose capacitance can be varied by varying the separation between a pair of plates, or by varying the depth of insertion of interleaved plates. (Most widely used for tuning radio-frequency circuits.)
variable-carrier modulation See controlled-carrier modulation.
variable-compression capacitor A capacitor in which the capacitance can be varied by compressing a stack of electrode and dielectric layers.
variable concentric capacitor An air dielectric capacitor in which the capacitance can be varied by the axial movement of a rotor in a stator.
variable connector 1. A flowchart symbol representing a sequential connection that is not fixed, but which can be varied by the flowcharted procedure itself. 2. The device that inserts instructions in a program corresponding to the selection of paths appearing in a flowchart. 3. The computer instructions that cause a logical chain to take one of several alternative paths.
variable coupling Inductive coupling that can be varied by moving the windings.
variable-cycle operation Computer operation in which any cycle is started at the completion of the previous cycle, instead of at specified clock times.
variable-density track A sound track of constant width and usually, but not necessarily, of uniform light transmission on any instantaneous transverse axis. The average light transmission varies along the longitudinal axis in proportion to some characteristic of the applied signal.
variable-depth sonar A sensor that can be lowered by cable from a ship or helicopter, through the thermal layers, to detect submarines operating at deeper levels.
variable disc capacitor A solid-dielectric capacitor in which the capacitance can be varied by rotating a metal or metallized disc.
variable-erase recording The method of recording on magnetic tape by selective erasure of a prerecorded signal.
variable field A field in which the scalar (or vector) at any point changes during the time under consideration.
variable-frequency oscillator Abbreviated VFO. A stable oscillator whose frequency can be adjusted over a given range.
variable-frequency synthesizer An instrument that translates the stability of a single frequency, usually obtained from a frequency standard, to any one of many other possible frequencies. In common usage, such instruments are called simply frequency synthesizers.
variable inductance Also called variable inductor. A coil whose inductance can be varied.
variable-inductance pickup A phonograph pickup in which the movement of a stylus causes the inductance to vary accordingly.
variable-inductance transducer A transducer in which the output voltage is a function of the change in a variable-inductance element.
variable-length record In a computer, pertaining to a file in which there is no constraint on the record length. (Opposite of fixed-length record.)
variable monoergic A type of emission in which the magnitude of the homogeneous particle or radiation energy is continuously variable over broad limits; e.g., the proton energy from some types of accelerators can be controlled by varying the high voltage.
variable-mu pressure transducer A device that converts mechanical input pressure to a proportional electrical output based on the change of the mu of its magnetic circuit due to the applied pressure (Villari effect).
variable-mu tube See remote-cutoff tube.
variable point Pertaining to a system of numeration in which the position of the radix point is indicated by a special character at that position.
variable radio-frequency radiosonde A radiosonde whose carrier frequency is modulated by the magnitude of the meteorological variables being sensed.
variable reluctance Principle employed in certain phonograph pickups. Deflections of the stylus when playing a record make an armature vibrate between the poles of an electromagnet. The reluctance is the ratio of magnetic force to magnetic flux in a magnetic field. Variations due to stylus movement create variations in the current through the electromagnet.
variable-reluctance microphone Also called a magnetic microphone. A microphone that depends for its operation on the variations in reluctance of a magnetic circuit.
variable-reluctance pickup 1. A phonograph cartridge that derives its electrical output signal from change effected in a magnetic circuit by means of some mechanical device such as a moving coil or magnet. 2. A type of cartridge that generates its signal from the relative motions of a magnetic field and a coil or coils (either the field or the coils may move, depending on cartridge design). The output is proportional to the velocity of the stylus motion. This requires an equalization circuit in the preamplifier to restore proper frequency balance, since records are cut with more nearly constant-amplitude than constant-velocity characteristics. 3. A phonograph pickup that depends for its operation on the variation of a resistance.
variable-reluctance stepping motor A motor with a soft-iron rotor that is made to step by sequential excitation of stator coils. It requires complementary equipment to furnish the sequencing pulses.
variable-reluctance transducer Also called a magnetic transducer. A transducer that depends for its operation on the variations in reluctance of a magnetic circuit.
variable-resistance transducer A transducer in which the signal output depends on the change in a resistance element.
variable resistor A wire wound or composition resistor whose resistance may be changed. See also potentiometer, 1; rheostat.
variable-Speed motor A motor whose speed can be adjusted within certain limitations, regardless of load.
variable-speed scanning A scanning method whereby the optical density of the film being scanned determines the speed at which the scanning beam in the cathode-ray tube of a television camera is deflected.
variable transformer An iron-core transformer with provision for varying its output voltage over a limited range, or continuously from zero to maximum — generally by the movement of a contact arm along exposed turns of the secondary winding.
variable tubular capacitor A solid-dielectric capacitor in which the capacitance can be varied by the axial movement of an electrode within a tube.
variable vane capacitor A capacitor in which the capacitance can be varied by rotating the rotor vanes between the stator vanes.
Variac An autotransformer that contains a toroidal winding and a rotating carbon brush so that the output voltage is continuously adjustable from zero to line voltage plus 17 percent. Trade name of General Radio Company.
variance A measure of the fluctuations of data around the mean.
variants 1. Two or more cipher or code groups that have the same plain-language equivalent. 2. Two or more plaintext meanings that are represented by a single code group.
variate See random variable, 1.
variation The angular difference between a true and a magnetic bearing or heading.
varindor An inductor whose inductance varies markedly with the current in the winding.
variocoupler A radio transformer with windings that have an essentially constant self-impedance, but the mutual impedance between them is adjustable.
variolosser A device whose loss can be controlled by a voltage or current.
variometer A variable inductor consisting of a pair of series- or parallel-connected coils whose axes can be varied one with respect to the other. The change in mutual inductance causes a change in the total inductance.
varioplex A telegraph switching system that establishes connections on a circuit-sharing basis between a number of transmitters in one locality and corresponding receivers in another locality over one or more intervening channels. Maximum use of channel capacity is obtained by employing momentary storage of signals and allocating circuit time in rotation among the transmitters that have information in storage.
varistor From “variable resistor.” 1. A two-electrode semiconductor device with a voltage-dependent nonlinear resistance that drops markedly as the applied voltage is increased. 2. A passive resistorlike circuit element whose resistance is a function of the current through it. The current through it is a nonlinear function of the voltage across its terminals; hence, a self-varying resistance. See also voltage-dependent resistor. 3. A voltage-dependent symmetrical resistor with a high degree of nonlinearity (the resistance does not change linearly as a function of the applied voltage). The value of the resistance is very high at voltages lower than nominal and very quickly changes to an extremely low value of resistance as the applied voltage is increased above the nominal voltage. The device is used as a voltage-transient or voltage-surge suppressor to improve the reliability of a voltage-sensitive circuit. It provides instantaneous response to high voltage, with good temperature stability and excellent clamping characteristics. The device is normally connected across its input terminals or across the ac power source, providing protection with an effective low resistance somewhat above the normal input or line voltage values. One of the varistor’s main uses is to protect electronic equipment against lightning. It is also used to protect against sudden or transient surges of voltage in an ac power line. See also MOV.
Varley loop A type of Wheatstone-bridge circuit that gives, in one measurement, the difference in resistance between two wires of a loop.
varmeter Also called a reactive voltampere meter. An instrument for measuring reactive power in either vars, kilovars, or megavars. If the scale is graduated in kilovars or megavars, the instrument is sometimes designated a kilovarmeter or megavarmeter.
varnished cambric A linen or cotton fabric that has been impregnated with varnish or insulating oil and baked. It is used as insulation in coils and other radio parts.
varying duty A requirement of service that demands operation at loads and for intervals of time, both of which may be subject to wide variation.
varying-speed motor A motor that slows down as the load increases (e.g., a series motor, or an induction motor with a large amount of slip).
varying voltage control A form of armature-voltage control obtained by impressing, on the armature, a voltage that varies considerably with a change in load and consequently changes the speed of the motor (e.g., by using a differentially compound-wound generator or a resistance in the armature circuit).
V-beam system A radar system for measuring elevation. The antenna emits two fan-shaped beams, one vertical and the other inclined, which intersect at ground level. Each beam rotates continuously about a vertical axis, and the time elapsing between the two echoes from the target provides a measure of its elevation.
VCD Abbreviation for variable-capacitance diode.
v-chip A semiconductor that blocks the display of violent and/or pornographic material on a TV. Transmitters have to incorporate a signal for the system to function.
VCO Abbreviation for voltage-controlled oscillator.
VCR 1. Abbreviation for voltage-controlled resistor. 2. Abbreviation for videocassette recorder (or player).
V-cut A type of oscillator-crystal cut in which the major plane surfaces are not parallel to the X, Y, or Z planes.
VDR See voltage-dependent resistor.
VDT Abbreviation for video display terminal. A CRT or gas-plasma tube display screen terminal or keyboard console that allows keyed or stored text to be viewed for manipulation or editing.
VDU 1. See video display unit. 2. Abbreviation for visual display unit. A display of data for use by human operators. Data is usually displayed as several rows of alphanumeric characters.
vector A quantity that has both magnitude and direction. Vectors commonly are represented by a line segment with a length that represents the magnitude and an orientation in space that represents the direction. See vector quantity.
vector admittance The ratio for a single sinusoidal current and potential difference in a portion of a circuit of the corresponding complex harmonic current to the corresponding complex potential difference.
vector-ampere The unit of measurement of vector power.
vector cardiograph An instrument that measures both the magnitude and the direction of heart signals by displaying cardiograph signals on any desired set of axes, usually x, y, and z.
vector diagram An arrangement of vectors showing the relationships between alternating quantities having the same frequency.
vectored interrupt 1. An interrupt in a computer that carries its identity number or the address of its handler. 2. An interrupt scheme in which each interrupting device causes the operating system to branch to a different interrupt routine. This scheme is useful for a very fast interrupt response.
vector field In a given region of space, the total value of some vector quantity that has a definite value at each point of the region (e.g., the distribution of magnetic intensity in a region surrounding a current-carrying conductor).
vector function A function that has both magnitude and direction (e.g., the magnetic intensity at a point near an electric circuit is a vector function of the current in that circuit).
vector generator That part of the display controller which draws vectors on the screen. Control codes within the display list specify whether the vector generators will move the beam in a blanked or unblanked mode. If the beam is unblanked, the vector will be drawn in a specified texture.
vector impedance The ratio for a simple sinusoidal current and potential difference in a portion of a circuit of the corresponding complex harmonic potential difference to the corresponding complex current.
vector interrupt A term used to describe a microprocessor system in which each interrupt, both internal and external, has its own uniquely recognizable address. This enables the microprocessor to perform a set of specified operations that are preprogrammed by the user to handle each interrupt in a distinctively different manner.
vector power A vector quantity equal to the square root of the sum of the squares of the active and reactive powers. The unit is the vector-ampere.
vector power factor Ratio of the active power to the vector power. In sinusoidal quantities, it is the same as power factor.
vector processing A method for carrying out many repetitive mathematical operations with a single computer instruction.
vector quantity A quantity that has both magnitude and direction. Examples of quantities that are vectors are displacement, velocity, force, and magnetic intensity.
vector refresh display See calligraphic display.
vector scan Technique of displaying images on a screen, particularly suitable for precision drawings and animation. It is available only on special visual display units. Images are created by moving an electron beam in the CRT to any place on the screen, just as a pen is moved in any direction on paper. The positions are specified as x and y coordinates.
vectorscope 1. An oscilloscope with a circular time base of extreme stability (determined by the frequency of the color subcarrier). The instrument can be used to check the time delay between two signals because the phase difference at a particular frequency can be related to time difference. 2. Special synchroscope used in color TV camera and color encoder calibration. The vectorscope will graphically indicate on a CRT the absolute angles the different color signals describe in respect to a reference and to each other. These angles as read on the vectorscope represent the phase differences of the signals.
vector stroke display See calligraphic display.
velocimeter A continuous-wave reflection Doppler system used to measure the radial velocity of an object.
velocity A vector quantity that includes both magnitude (e.g., speed) and direction in relation to a given frame of reference.
velocity error The amount of angular displacement existing between the input and output shafts of a servomechanism when both are turning at the same speed.
velocity filter A storage-tube device that blanks all targets that do not move more than one resolution cell in less than a predetermined number of antenna scans.
velocity hydrophone A type of hydrophone in which the electric output is substantially proportional to the instantaneous particle velocity in the incident sound wave.
velocity-lag error A lag between the input and output of a device, proportional to the rate of variation of the input.
velocity level In decibels of a sound, 20 times the logarithm to the base 10 of the ratio of the particle velocity of the sound to the reference particle velocity. The latter must be stated explicitly.
velocity microphone A microphone in which the electric output corresponds substantially to the instantaneous particle velocity in the impressed sound wave. It is a gradient microphone of order one, and is inherently bidirectional.
velocity-modulated amplifier Also called a velocity-variation amplifier. An amplifier in which velocity modulation is employed for amplifying radio frequencies.
velocity-modulated oscillator Also called a velocity-variation oscillator. An electron-tube structure in which the velocity of an electron stream is varied (velocity-modulated) in passing through a resonant cavity called a buncher. Energy is extracted from the bunched electron stream at a higher level in passing through a second cavity resonator called the catcher. Oscillations are sustained by coupling energy from the catcher cavity back to the buncher cavity.
velocity modulation Also called velocity variation. 1. Modification of the velocity of an electron stream by the alternate acceleration and deceleration of the electrons with a period comparable to that of the transit time in the space concerned. 2. Modulation of an electron stream by alternately accelerating and decelerating the electrons, thus grouping them into bunches.
velocity of light A physical constant equal to 2.99796 × 1010 centimeters per second. (More conveniently expressed as 186,280 statute miles per second, or 161,750 nautical miles per second, or 328 yards per microsecond.)
velocity of propagation 1. The speed at which a disturbance (e.g., sound, radio, light waves) is radiated through a medium. 2. The ratio of the speed of the flow of an electric current in an insulated cable to the speed of light, expressed in percentage. In the case of coaxial cables, this ratio is 65 to 66 percent, where the insulation is polyethylene. 3. The speed of transmission of electrical energy through a cable compared with its speed through air, expressed as a percentage of the speed in free space. Radio-frequency signals are transmitted in free space at a speed of 1.86,280 statute miles per second (2.99796 × 108 m/s). Velocity of propagation is determined by the ratio of the dielectric constant of air to the square root of the dielectric constant of the insulation and is expressed in percent. 4. The speed with which a signal wave travels through a particular transmission.
velocity pickup A magnetic pickup whose output increase is a function of recorded velocity. (This differs from the ceramic pickup, whose output is a function of amplitude or deflection of the stylus.)
velocity resonance See phase resonance.
velocity sorting The selecting of electrons according to their velocity.
velocity spectrograph An apparatus for separating an emission of electrically charged particles into distinct streams in accordance with their speed, by means of magnetic or electric deflection.
velocity transducer A transducer that generates an output proportionate to the imparted velocities.
velocity variation See velocity modulation.
velocity-variation amplifier See velocity-modulated amplifier.
velocity-variation oscillator See velocity-modulated oscillator.
Venn diagrams Diagrams in which circles or ellipses are used to give a graphic representation of basic logic relations. Logic relations between classes, operations on classes, and the terms of the propositions are illustrated and defined by the inclusion, exclusion, or intersection of these figures. Shading indicates empty areas, crosses indicate areas that are not empty, and blank spaces indicate areas that may be either. Named for English logician John Venn, who devised them.
vent A controlled weakness somewhere in the enclosure of an aluminum electrolytic capacitor to permit pressure relief in case of failure due to shorting or improper installation of the capacitor.
vented baffle An enclosure designed to properly couple a speaker to the air.
ventilated transformer A dry-type transformer that is so constructed that the ambient air may circulate through its enclosure to cool the transformer core and windings.
venturi tube A short tube with flaring ends and a constricted throat. It is used for measuring flow velocity by measurement of the throat pressure, which decreases as the velocity increases.
verification The process of checking the results of one data transcription against those of another, both transcriptions usually involving manual operations. See also check.
verifier 1. Of computers, a device on which a record can be compared or tested for identity character by character with a retranscription or copy as it is being prepared. 2. A machine that is used to check the correctness of manually recorded data.
verify 1. To check, usually with an automatic machine, one recording of data against another in order to minimize the number of human errors in the data transcription. 2. To make certain that the information being prepared for a computer is correct.
vernier 1. An auxiliary scale comprising subdivisions of the main measuring scale and, thus, permitting more accurate measurements than are possible from the main scale alone. 2. An auxiliary device used for obtaining fine adjustments.
vernier capacitor A variable capacitor placed in parallel with a larger tuning capacitor and used to provide a finer adjustment after the larger one has been set to the approximate desired position.
vernier dial A type of tuning dial used chiefly for radio equipment. Each complete rotation of its control knob moves the main shaft only a fraction of a revolution and thereby permits fine adjustment.
vernitel A precision device that makes possible the transmission of data with high accuracy over standard frequency-modulated telemetering systems.
vertex plate A matching plate placed at the vertex of a reflector.
vertical In 45/45 recording, the signal produced by a sound arriving at the two microphones simultaneously and 180° out of phase, causing the cutting stylus to move vertically.
vertical amplification Signal gain in the circuits of an oscilloscope that produces vertical deflection on the screen.
vertical-amplitude controls See parabola controls.
vertical antenna A vertical metal tower, rod, or suspended wire that is used as a receiving and/or transmitting antenna.
vertical blanking Blanking of a television picture tube during the vertical retrace.
vertical-blanking interval The brief time between television fields required for the scanning electron gun to retrace from the bottom of the image to the top to begin scanning the next field. The interval occupies 16,667 milliseconds and occurs at the end of each 262.5 field scan lines. There are 21 usuable lines in this interval, which are devoted to 6 vertical synch pulses and 12 equalizing pulses, as well as additional horizontal pulse intervals.
vertical-blanking pulse In television, a pulse transmitted at the end of each field to cut off the cathode-ray beam while it returns to the start of the next field.
vertical-centering control A control provided in a television receiver or cathode-ray oscilloscope to shift the entire image up or down on the screen.
vertical compliance The ability of a reproducing stylus to move vertically while in the reproducing position on a record.
vertical-deflection electrodes The pair of electrodes that move the electron beam up and down on the screen of a cathode-ray tube employing electrostatic deflection.
vertical dynamic convergence Convergence of the three electron beams at the aperture mask of a color picture tube during the scanning of each point along a vertical line at the center of the tube.
vertical-field-blanking interval See vertical-blanking interval
vertical field-strength diagram A representation of the field strength at a constant distance from, and in a vertical plane passing through, an antenna.
vertical frame transfer A CCD configuration in which all charges accumulated during an integration period are rapidly moved out of the optically active area and to an identical optically shielded CCD area where the accumulation is read out at a slower pace during the next integration period.
vertical-frequency response In an oscilloscope, the band of frequencies passed, with amplification between specified limits, by the amplifiers that produce vertical deflection on the screen.
vertical-hold control See hold control.
vertical-incidence transmission The transmission of a radio wave vertically to the ionosphere and back. The transmission remains practically the same for a slight departure from the vertical (e.g., when the transmitter and receiver are a few kilometers apart).
vertical-lateral recording A technique of making stereo phonograph discs by recording one signal laterally, as in monophonic records, and the other vertically, as in hill-and-dale-transcriptions.
vertical linearity control A control that permits adjustment of the spacing of the horizontal lines on the upper portion of the picture to effect linear vertical reproduction of a television scene.
vertically polarized wave 1. An electromagnetic wave with a vertical electric vector. 2. A linearly polarized wave with a horizontal field vector.
vertical polarization 1. Transmission in which the transmitting and receiving antennas are placed in a vertical plane, so that the electrostatic field also varies in a vertical plane. 2. Transmission of radio waves whose undulations vary vertically with respect to the earth.
vertical quarter-wave stub An antenna with a vertical portion that is electrically one quarter-wavelength long. It is used generally with a ground plane at the base of the stub.
vertical radiator A transmitting antenna perpendicular to the earth’s surface.
vertical recording Also called hill-and-dale recording. Mechanical recording in which the groove modulation is perpendicular to the surface of the recording medium.
vertical redundance In a computer, an error condition that exists when a character fails a parity check, i.e., has an even number of bits in an odd-parity system or vice versa.
vertical resolution 1. On a television test pattern, the number of horizontal wedge lines that can be clearly discerned by the eye before they merge together. 2. The number of horizontal lines that can be seen in the reproduced image of a television pattern.
vertical retrace 1. The return of the electron beam from the bottom of the image to the top after each vertical sweep. 2. The return of the electron beam to the top of the picture tube screen or the pickup tube target at the completion of the field scan.
vertical scanning Scanning that proceeds in a series of vertical lines.
vertical scrolling The ability of a word processor to move vertically, a line at a time, up and down through a display page or more of text. This allows text that will not fit on a video display screen to be accessed for review or editing. Used in systems that have a display buffer (memory area) larger than the display screen capacity.
vertical speed transducer An instrument that furnishes an electrical output that is proportionate to the vertical speed of the aircraft or missile in which it is installed.
vertical structured metal-oxide silicon power field-effect transistor See VMOS power FET.
vertical stylus force See stylus force.
vertical sweep The downward movement of the scanning beam from top to bottom of the televised picture.
vertical sync The synchronizing pulses used to define the end of one television field and the start of the next, occurring at a rate of approximately 59.94 Hz (color) and 60 Hz (black and white).
vertical-synchronizing pulse Also called picture-synchronizing pulse. One of the six pulses transmitted at the end of each field in a television system. It maintains the receiver in field-by-field synchronism with the transmitter.
vertical tracking The phonograph pickup stylus motion path that is near vertical. Applies to hill-and-dale recordings on stereo discs.
vertical tracking force The minimum downward force at which a phonograph cartridge works without mistracking, i.e., a momentary hop by the stylus (making a raspy sound) or a jump into the next groove.
very high frequency Abbreviated VHF. Frequency hand: 30 to 300 MHz. Wavelength: 10 to 1 meters.
very large-scale integration See VLSI.
very long range A classification of ground radar sets by slant range, applied to those with a maximum range exceeding 250 miles (402 km).
very low frequency Abbreviated VLF. Frequency band: below 30 kHz. Wavelength: above 10,000 meters.
very short range Classification of ground radar sets by slant range, applied to those with a maximum range of less than 25 miles (40.2 km).
vestigial Pertaining to a remnant or remaining part.
vestigial sideband Amplitude-modulated transmission in which a portion of one sideband has been largely suppressed by a transducer having a gradual cutoff in the neighborhood of the carrier frequency.
vestigial-sideband filter A filter that is inserted between an AM transmitter and its transmitting antenna to suppress part of one of the sidebands.
vestigial-sideband transmission Also called asymmetric-sideband transmission. Signal transmission in which one normal sideband and the corresponding vestigial sideband are utilized.
vestigial-sideband transmitter A transmitter in which one sideband and only a portion of the other are transmitted.
v/f converter See voltage-to-frequency converter.
VFO Abbreviation for variable-frequency oscillator.
VGA Abbreviation for Video Graphics Array. A VGA monitor has a 480 × 640 display resolution and can display up to 256 colors simultaneously. A video standard for IBM PC and compatible computers.
V-groove metal-oxide silicon See VMOS.
VHF 1. Abbreviation for very high frequency. 2. In television, a term used to designate channels 2 through 13.
VHF omnirange Abbreviated VOR. A specific type of range operating at VHF and providing radial lines of position in a direction determined by the bearing selection within the receiving equipment. A nondirectional reference modulation is emitted, along with a rotation pattern that develops a variable modulation of the same frequency as the reference modulation. Lines of position are determined by comparing the phase of the variable with that of the reference.
VHLL Abbreviation for very high-level language. Usually a problem or requirements description language, ranging in form from the highly abstract to plain English.
VHSIC Abbreviation for very high-speed integrated circuits.
via 1. A vertical conductor or conductive path forming the interconnection between multilayer hybrid circuit layers. 2. Means of passing from one layer or side of a printed circuit board to the other.
via hole A plated-through hole that establishes electrical continuity but which is not intended for a component lead. See plated-through hole.
vibrating bell A bell having a mechanism designed to strike repeatedly and as long as it is actuated.
vibrating-reed meter Also called reed frequency meter. A frequency meter consisting of a row of steel reeds, each having a different natural frequency. All are excited by an electromagnet fed with the alternating current whose frequency is to be measured. The reed whose frequency corresponds most nearly with that of the current vibrates, and the frequency is read on a scale beside the row of reeds.
vibrating-reed relay 1. A type of relay in which an alternating or a self-interrupted voltage is applied to the driving coil so as to produce an alternating or pulsating magnetic field that causes a reed to vibrate. 2. A type of relay that is actuated by sound frequency. Can be triggered by an electrical resonant circuit, or simply by a mechanically induced sound vibration.
vibrating-wire tranducer A transducer that utilizes a thin wire suspended in a magnetic field; the change in tension of the wire reflects a frequency-modulating output.
vibration 1. A continuously reversing change in the magnitude of a given force. 2. A mechanical oscillation or motion about a reference point of equilibrium.
vibration analyzer A device used to analyze mechanical vibrations.
vibration-detection system An alarm system that employs one or more contact microphones or vibration sensors that are fastened to the surfaces of the area or object being protected to detect excessive levels of vibration. The contact microphone system consists of microphones, a control unit containing an amplifier and an accumulator, and a power supply. The unit’s sensitivity is adjustable so that ambient noises or normal vibrations will not initiate an alarm signal. In the vibration sensor system, the sensor responds to excessive vibration by opening a switch in a closed-circuit system.
vibration galvanometer An ac galvanometer in which a reading is obtained by making the natural oscillation frequency of the moving element equal to the frequency of the current being measured.
vibration isolator A resilient support that tends to isolate a system from steady-state excitation or vibration.
vibration meter Also called a vibrometer. An apparatus comprising a vibration pickup, calibrated amplifier, and output meter, for the measurement of displacement, velocity, and acceleration of a vibrating body.
vibration pickup A microphone that responds to mechanical vibrations rather than to sound waves. In one type, a piezoelectric unit is employed; the twisting or bending of a Rochelle-salt crystal generates a voltage that varies with the vibration being analyzed.
vibration sensitivity The peak instantaneous change in output at a given sinusoidal vibration level for any one stimulus value within the range of an instrument or equipment. It is usually expressed in percentage of full-scale output per vibratory “g” over a given frequency range. It may also be specified as a total error in percentage of full-scale output for a given vibratory acceleration level.
vibration sensor A sensor that responds to vibrations of the surface on which it is mounted. It has a normally closed switch that will momentarily open when it is subjected to a vibration with sufficiently large amplitude. Its sensitivity is adjustable to allow for the different levels of normal vibration, to which the sensor should not respond, at different locations. See also vibration-detection system.
vibration survey A method of determining the natural frequency of a transducer by observation of the output waveform upon the application of a shock or tapping of sufficient magnitude to initiate oscillation of the instrument.
vibration test A test to determine the ability of a device to withstand physical oscillations of specified frequency, duration, and magnitude.
vibration welding Method of fusing two plastic parts by vibrating (rubbing) the mating surfaces together at relatively low frequencies, 90 to 120 Hz.
vibrato 1. A musical embellishment that depends primarily on periodic variations of frequency, often accompanied by variations in amplitude and waveform. The quantitative description of vibrato is usually in terms of the corresponding modulation of frequency (typically 5 to 7 Hz), amplitude, or waveform, or all three. 2. Regular variation in the frequency of a sound, generally at a frequency between 2 and 15 times per second. This frequency modulation by a low-frequency oscillator is commonly used with guitars, organs, synthesizers, and the human voice.
vibrator 1. A vibrating reed that is driven like a buzzer and has contacts arranged to interrupt direct current to the winding(s) of a transformer, resulting in an alternating current being supplied from another winding to the load. 2. Electromagnetic device that is used to change a continuous steady current into a pulsating current. 3. An electromagnetic device for converting a direct voltage into an alternating voltage.
vibrator power supply A power supply incorporating a vibrator, step-up transformer, rectifier, and filters for changing a low dc voltage to a high dc voltage.
vibration A triode with an anode that can be moved or vibrated by an external force. Thus, the anode current will vary in proportion to the amplitude and frequency of the applied force.
vibrometer See vibration meter.
video 1. Pertaining to the bandwidth and spectrum position of the signal resulting from radar or television scanning. In current usage, video means a bandwidth on the order of several megahertz and a spectrum position that goes with a dc carrier. 2. A prefix to the name of television parts or circuits that carry picture signals. 3. Radar or television signals that actuate a cathode-ray tube. 4. Composite video contains color and luminance (brightness information) as well as horizontal and vertical synch pulses during the horizontal and vertical blanking intervals. One line of video, for instance, amounts to approximately 52 microseconds in visible horizontal scan time, and 63.5 microseconds for a complete line, including the color burst and horizontal synch.
video adapter An expansion board in a computer that provides enhanced display capabilities.
video amplifier 1. An amplifier that provides wideband operation in the frequency range of approximately 15 hertz to approximately 5 megahertz. 2. An amplifier designed for linear amplification over a wide range of frequencies from dc (zero) to over about 10 MHz. 3. A wideband amplifier used for passing picture signals.
video band The frequency band utilized to transmit a composite video signal.
video carrier 1. The television signal whose modulation sidebands contain the picture, sync, and blanking signals. 2. A frequency that is 1.25 MHz above the lower edge of the assigned 6-MHz frequency band of a TV channel. At channel 2, for instance, with a bandwidth of 54 to 60 MHz, the video carrier rests at 55.25 MHz.
videocassette A plastic shell containing two reels and a given length of videotape.
videocassette recorder Abbreviated VCR. A device for recording and playing video images on magnetic tapes that are contained in plastic cases.
videocast 1. To broadcast a program by means of television. 2. A program so broadcast.
VideoCipher I, II A trademark for a video/audio encryption system developed by M/A-COM LINKABIT, Inc. VCI uses digital video and audio encryption; VCII uses analog video and digital audio encryption.
video compression 1. The reduction of the number of bits needed to describe a video image. 2. A digital technique to compress several video channels into the bandwidth, normally required by one channel.
video correlator A radar circuit that enhances the capability for automatic target detection; supplies data for digital target plotting; and provides improved immunity to noise, interference, and jamming.
video data digital processing Digital processing of video signals for pictures transmitted by way of a television link. A computer is used to compare each scanned line with adjacent lines so that extreme changes resulting from electromagnetic interference can be eliminated.
video detector The demodulator circuit that extracts the picture information from the amplitude-modulated intermediate frequency in a television receiver.
video dialtone An FCC term for the new generation of home-distribution video systems that deliver compressed digital signals over switched networks to an interactive set-top box in the user premises.
video digitizing The process of capturing, converting, and storing video images for use by a computer.
video disc See optical video disc.
Video discrimination A radar circuit that reduces the frequency band of the video-amplifier stage in which it is used.
video display unit Abbreviated VDU. A device for visual presentation of information. A CRT is a typical video display unit.
video freeze A TV mode which makes it possible to “freeze” an image to study specific details at ease, e.g., to make notes of certain program information like phone numbers.
Video frequency 1. The frequency of the signal voltage containing the picture information that arises from the television scanning process. In the present United States television system, these frequencies are limited from approximately 30 Hz to 4 MHz. 2. A band of frequencies extending from less than 100 hertz to several megahertz.
video-frequency amplifier A device capable of amplifying those signals that comprise the periodic visual presentation.
video-gain control A control for adjusting the amplitude of a video signal. Two such controls are provided in the matrix section of some color television receivers so that the proper ratios between the amplitudes of the three color signals can be obtained.
video impedance Of a detector diode, the output impedance measured at the video frequency when the diode is operating under specified bias conditions.
video integration A method of improving the output signal-to-noise ratio by utilizing the redundancy of repetitive signals to sum the successive video signals.
video integrator A device that uses the redundance of repetitive signals to improve the output signal-to-noise ratio by summing the successive video signals.
video inversion A type of encoding or scrambling in which the transmitted downlink video signals are inverted.
video mapping The procedure whereby a chart of an area is electronically superimposed on a radar display.
video masking A method for the removal of chaff echoes and other extended clutter from radar displays.
video mixer A circuit or device used to combine the signals from two or more television cameras.
video monitor A high-quality television set (without rf circuits) that accepts video baseband inputs directly from a TV camera, VTR, or satellite TV receiver with no rf modulator required.
video pair cable A transmission cable containing low-loss pairs with an impedance of 125 ohms. Used for TV pickups, closed circuit TV, telephone carrier circuits, etc.
video recording (magnetic tape) The methods of recording data having a bandwidth in excess of 100 kHz on a single track.
video signal 1. The picture signal in a television system — generally applied to the signal itself and the required synchronizing and equalizing pulses. 2. In television, the signal that conveys all of the intelligence present in the image, together with the necessary synchronizing and equalizing pulses. 3. That portion of the composite video signal that varies in gray-scale levels between reference white and reference black. Also referred to as the picture signal, this is the portion that can be seen. 4. The picture signal. A signal containing visual information and horizontal and vertical blanking. See also composite video signal. 5. The output from a video graphics adapter incorporating the red (R), green (G), and blue (B) signals and the luminance signal, or combinations of these signals, that pass to the video input of a monitor.
video stretching In navigation, a procedure whereby the duration of a video pulse is increased.
video synthesizer A video analog computer that accepts standard video signals from a camera, film chain, videotape or graphics generator, which it then processes and applies a combination of effects to in order to reshape and add motions (animation) to fixed graphics or live scenes.
videotape A wide magnetic tape designed for recording and playing back a composite black and white or color television signal.
videotape recorder Abbreviated VTR. 1. A device that permits audio and video signals to be recorded on magnetic tape and then played back without any processing, as with films, on a CCTV monitor. 2. A device that translates the electrical signals of a VTR television camera into corresponding magnetic variations, which are recorded on magnetic tape; the original image can be displayed on a television receiver at a later time by reconversion of the magnetic variations, stored on the tape, into appropriate electrical signals.
videotape recording Abbreviated VTR. A method of recording television picture and sound signals on tape for reproduction at some later time.
videotex 1. A system that links TV screens to mass databases through television or telephone-based communication channels. 2. A generic term for interactive services delivered to personal computers or adapted television sets in the home or office. 3. Technology that connects computerized text and graphics to a television screen via telephone lines. 4. A terminal-oriented communication network that links users’ equipment to a computer that maintains a database of information services. Videotex services include shop-at-home catalogs, listings of community events, and message forwarding.
videotext system A system for the widespread dissemination of textual and graphic information by wholly electronic means for display on low-cost terminals (often suitably equipped television receivers) under the selective control of the recipient using control procedures easily understood by untrained users.
vidicon 1. A camera tube in which a charge-density pattern is formed by photoconduction and stored on that surface of the photoconductor which is scanned by an electron beam, usually of low-velocity electrons. 2. A vacuum tube capable of changing light images into electrical voltage variations corresponding to the brightness of those images; a particular type of cathode-ray pickup tube used in some video cameras.
viewer A software application that permits visual display of content. See also browser; player.
viewfinder An auxiliary optical or electronic device attached to a television camera so the operator can see the scene as the camera sees it.
viewfinder monitor See electronic viewfinder.
viewing angle The angle through which an LCD display has acceptable contrast.
viewing area The area of the CRT face that can be directly seen by the user. Its size is determined by the size of the CRT and the area covered by the face mask.
viewing area The area of the CRT face that can be directly seen by the user. Its size is determined by the size of the CRT and the area covered by the face mask.
viewing mirror A mirror used in some television receivers to reflect the image formed on the screen of the picture tube at an angle convenient to the viewer.
viewing screen The face of a cathode-ray tube on which the image is produced.
viewing time The time during which a storage tube presents a visible output that corresponds to the stored information.
Villari effect A phenomenon in which a change in magnetic induction occurs when a mechanical stress is applied along a specified direction to a magnetic material having magnetostrictive properties.
vinyl resin A soft plastic used for making phongraph records.
virtual address In a computer, an immediate, or real-time, address.
virtual cathode An electron cloud that forms around the outer grid in a thermionic vacuum tube when the inner grid is maintained slightly more positive than the cathode.
virtual circuit In packet switching, a network facility that gives the appearance to the user of an actual end-to-end circuit; a dynamically variable network connection in which sequential data packets may be routed differently during the course of a virtual connection. Virtual circuits enable transmission facilities to be shared by many users simultaneously.
virtual connection A packet-switched data path between two terminals that performs as if the two devices were linked by a switched circuit.
virtual height 1. The height of the equivalent reflection point that will cause a wave to travel to the ionosphere and back in the same time required for an actual reflection. In determining the virtual height, the wave is assumed to travel at uniform speed and the height is determined by the time required to go to the ionosphere and back at the assumed velocity of light. 2. The apparent height of a layer of the ionosphere. It is determined from the time interval between the transmitted signals and the ionospheric echo at vertical incidence (the radio wave penetrating the ionosphere perpendicular to it).
virtual image The optical counterpart of an object, formed at imaginary focuses by prolongations of light rays (e.g., the image that appears to be behind an ordinary mirror).
virtual memory 1. The use of techniques by which the computer programmer may use the memory as though the main memory and mass memory were available simultaneously. 2. A technique that permits the user to treat secondary (disk) storage as an extension of core memory, thus giving the virtual appearance of a larger core memory to the programmer. 3. A technique for managing a limited amount of high-speed memory and a (generally) much larger amount of lower-speed memory in such a way that the distinction is largely transparent to a computer user. The technique entails some means of swapping segments of program and data from the lower-speed memory (which would commonly be a drum or disk) into the high-speed memory, where it would be interpreted as instructions or operated on as data. The unit of program or data swapped back and forth is called a page. The high-speed memory from which instructions are executed is real memory, while the lower-speed memory (drums or disks) is called virtual memory. 4. Any of several schemes in which the user-visible address space is divided into several subspaces, so that each of the subspaces in use can be placed anywhere in main memory. In some schemes, parts of the virtual memory may be on a mass-storage device.
virtual PPI reflectoscope A device for superimposing a virtual image of a chart onto the PPI pattern. The chart is usually prepared with white lines on a black background to the scale of the PPI range scale.
virtual reality Abbreviated VR. 1. A technology that is computer generated and allows the user to interact with data that gives the appearance of a three-dimensional environment. The user can enter and navigate the 3D world portrayed as graphic images, and change viewpoints and interact with objects in that world as if inside that world. A virtual reality environment can be experienced using a headset and electronic gloves, or simply viewed on a monitor. 2. Sophisticated, multidimensional imaging systems and high-speed processing capabilities that create environments that users can interact with and manipulate directly.
virtual storage Storage space that may be viewed as addressable main storage, but is actually auxiliary storage (usually peripheral mass storage) mapped into read addresses; the amount of virtual storage is limited by the addressing scheme of the computer.
virus 1. A software program that attaches itself to another program in computer memory or on a disk, and spreads from one program to another. Viruses may damage data, cause the computer to crash, display messages, or lie dormant. 2. Any destructive self-replicating program. 3. A computer program written to secretly reproduce itself across many computer systems. Viruses can cause serious software damage.
viscometer Also called a viscosimeter. A device for measuring the degree to which a liquid resists a change in shape.
viscosity 1. The frictional resistance offered by one part or layer of a liquid as it moves past an adjacent part or layer of the same liquid. 2. The property of a liquid that resists internal flow; measured in units of poise or centipoise. Low-viscosity materials are usually thin, while high-viscosity materials are thick.
viscous and magnetic damping Damping by virtue of the viscosity of a fluid around the sensing element or of a magnetic field.
viscous-dampened arm A phonograph pickup arm mounted on a liquid cushion of oil, which provides high damping to eliminate arm resonances. It also protects the record groove and stylus; the arm does not fall on the record when dropped, but floats down gently.
visibility factor Also called display loss. Ratio of the minimum input-signal power detectable by ideal instruments connected to the output of a receiver to the minimum signal power detectable by a human operator through a display connected to the same receiver. The visibility factor may include the scanning loss.
visible emission Also called visible light. Radiation that is characterized by wavelengths of about 0.38 to 0.77 micrometer.
visible light Electromagnetic wavelengths that can be seen by the human eye, ranging from 380 to 770 nanometers.
visible radiation Radiation with wavelengths ranging from about 0.4 and 0.7 micrometer, corresponding to the visible spectrum of light.
visible spectrum That region of the electromagnetic spectrum to which the retina is sensitive and by which the eye sees. It extends from about 400 to about 750 nanometers in wavelengths of the radiation.
vision The series of processes in which luminous energy incident on the eye is perceived and evaluated.
visual-aural range Abbreviated VAR. A special type of VHF range providing a pair of radial lines of position that are reciprocal in bearing and are displayed to the pilot on a zero-center, left-right indicator. This facility also provides a pair of reciprocal radial lines of position located 90° from the above visually indicated lines. These are presented to the pilot as aural A-N radio-range signals, which provide a means for differentiating between the two visually indicated lines (and vice versa).
visual carrier frequency The frequency of the television carrier that is modulated by the picture information.
visual communication Communication by optical signs such as flags and lights.
visualization Graphic representation of abstract data usually relayed in text and numbers.
visual radio range Abbreviated VRR. A radio range whose course is fallowed by means of visual instruments.
visual scanner 1. A device that generates an analog or digital signal by optically scanning printed or ‘written data. 2. See scanner, 2.
visual signal device A pilot light, annunciator, or other device that provides a visual indication of the condition of the circuit or system being supervised.
visual storage tube An electron tube that stores and visually displays information by means of a cathode-ray beam scanning and charge storage mechanism.
visual telephony The transmission of picture information (television) by means of telephone lines.
visual transmitter Also called a picture transmitter. In television, the radio equipment for transmission of the picture signals only.
visual transmitter power The peak power output during transmission of a standard television signal.
vitreous 1. Having the nature of glass. 2. A term used in ceramic technology to indicate fired characteristics approaching being glassy, but not necessarily totally glassy.
vitreous binder A glassy material used in compounds to bind other particles together. This takes place after melting the glass and cooling.
vitrification 1. The progressive reduction in porosity of a ceramic material as a result of heat treatment or some other process. 2. The reduction of porosity in a ceramic product through the formation of a glassy bond.
VLF Abbreviation for very low frequency.
VLSI Abbreviation for very large-scale integration. Generally considered to be an IC with more than 1000 gates.
VLSI circuit Abbreviation for very large-scale integrated circuit. See gate array, 3.
VMOS 1. Abbreviation for V-groove metal-oxide silicon — a variation of MOS technology. A manufacturing process (called isotropically etched double-diffusion MOS process) based on the technique of using V-shaped grooves in the silicon wafer to provide a third-dimensional surface. This allows for a smaller chip geometry than the (older) process using a two-dimensional area technique of manufacture. With smaller geometry, the same diameter wafer can, theoretically, yield more chips (roughly 50 percent more) and thereby reduce the unit cost per chip considerably. The cost of processing a wafer generally remains constant no matter how many chips it contains. 2. Abbreviation for vertical MOS. A semiconductor device in which current travels vertically in the semiconductor chip. A cross section shows a four-layer diffusion consisting of n+ at the top (source), p as the channel, n– as the drift region, and n+ as the drain. The layers’ dimensions are precisely controlled by diffusion processes. Unlike conventional bipolar transistors, VMOS devices exhibit high density because of their short channel spacing: 1 μm compared with bipolar devices typical 5 μm.
VMOS power FET Abbreviation for vertical structured metal-oxide silicon power field-effect transistor. In these semiconductor devices, current flows vertically from source to drain. This structure results in high current densities, low saturation resistance, excellent heat dissipation and power handling capabilities, low chip capacitance, and excellent wideband performance.
vocabulary A list of operating codes or instructions available for writing the program for a given problem and for a specific computer.
vocoder Abbreviation for voice-operated coder. A device used to compress the frequency bandwidth requirement of voice communications. It consists of an electronic speech analyzer, which converts the speech waveform to several simultaneous analog signals, and an electronic speech synthesizer, which produces artificial sounds in accordance with analog control voltages.
vodas Abbreviation for voice-operated device, antising. A system for preventing the overall voice-frequency singing of a two-way telephone circuit by disabling one direction of transmission at all times.
voder Abbreviation for voice-operation demonstrator. An electronic device capable of artificially producing voice sounds. It uses active devices in connection with electrical filters controlled through a keyboard.
vogad Abbreviation for voice-operated gain-adjusting device. A voice-operated device used to give a substantially constant volume output for a wide range of inputs.
voice activated (sound activated) Refers to a bug that radiates radio frequencies or a recorder that is activated only when sound is present in target area.
voice analyzer An electronic instrument for printing out waveforms corresponding to vocal characteristics; an aid in identifying speech problems as well as speakers.
voice channel A transmission path suitable for carrying analog voice signals (covering a frequency band of 250 to 3400 Hz) between two points.
voice coder A device that converts a speech signal into digital form prior to encipherment for secure transmission, and converts the digital signals back into speech at the receiving point.
voice coil Also called a speaker voice coil. 1. A coil attached to the diaphragm of a dynamic speaker and moved through the air gap between the pole pieces. 2. The moving coil in a dynamic speaker. It is suspended in the field of a permanent magnet and is fixed to the speaker diaphragm.
voice/data system An integrated communications system for transmission of both voice and digital data signals.
voice filter A parallel-resonant circuit connected in series with a line feeding several speakers. Its purpose is to remove the tubbiness of the male voice. The frequency of resonance is adjusted somewhere between 125 and 300 Hz.
voice frequency Also called speech frequency. 1. Any of the frequencies within the band of 32 to 16,000 Hz that are audible to the human ear. 2. Any of the frequencies within the band of 300 to 3500 Hz that are normally used for telephone communication.
voice-frequency carrier telegraphy Carrier telegraphy in which the carrier currents have frequencies such that the modulated currents may be transmitted over a voice-frequency telephone channel.
voice-frequency dialing A method of dialing by which the direct-current pulses from the dial are transformed into voice-frequency alternating-current pulses.
voice-frequency telegraph system A telegraph system by which many channels can be carried on a single circuit. A different audio frequency is used for each channel and is keyed in the conventional manner. Each frequency is generated by an oscillator. At the receiving end, the various audio frequencies are separated by filter circuits and are fed to their respective receiving circuits.
voice-frequency telephony Telephony in which the frequencies of the components of the transmitted electric waves are substantially the same as the frequencies of corresponding components of the actuating acoustical waves.
voice grade A telephone circuit suitable for transmitting a bandpass from 300 to approximately 2700 Hz, or greater, with certain standards of noise and interference such that intelligible speech can be transmitted.
voice-grade channel 1. A channel suitable for the transmission of speech, digital or analog data, or facsimile, generally with a frequency range of about 300 to 3000 hertz. 2. A telephone circuit normally used for speech communication, accommodating frequencies from 300 to 3000 Hz.
voice-grade circuit A switched (dial-up) or leased (dedicated) telephone circuit suitable for the transmission of speech, digital or analog data, or facsimile, generally with a frequency range of about 300 to 3000 hertz.
voice-grade line A local telephone loop, or trunk, having a bandpass of approximately 300 to 3000 Hz.
voice mail Sophisticated telephone voice messages that are recorded and translated into digital bits for storage and manipulation. Voice mail systems use specialized hardware and software and can be incorporated into a PBX or used as stand-alone systems.
voice-operated coder See vocoder.
voice-operated device A device that permits the presence of voice or sound signals to affect a desired control.
voice-operated device, antising A system for preventing the overall voice-frequency singing of a two-way telephone circuit by disabling one direction of transmission at all times. Acronym: vodas.
voice-operated gain-adjusting device A voice-operated device used to give a substantially constant-volume output for a wide range of inputs.
voice-operated loss control and suppressor A voice-operated device that switches the loss out of the transmitting branch and inserts the loss into the receiving branch under control of the subscriber’s speech.
voiceprint A speech spectrograph sufficiently sensitive and detailed to identify individual human voices.
voice recognition The conversion of spoken words into computer text. Speech is first digitized and then matched against a dictionary of coded waveforms. The matches are then converted into text as if the words were typed on the keyboard.
voice-recognition equipment vocabulary size The number of utterances (words or short phrases) that can be distinctly recognized and digitally encoded. The larger the vocabulary, the more complex the source data that can be handled without special software.
voice spectrum The total fundamental frequency range of the human voice.
voice synthesis Technology that produces sound or voices by processing compressed digital signals and storing them in a memory in the same manner a human voice generates sound processed by the vocal tract and other organs.
void The absence of substance in a localized area.
volatila 1. A computer storage medium in which information cannot be retained without continuous power dissipation. 2. Capable of evaporating.
volatile memory 1. In computers, any memory that can return information only as long as energizing power is applied. The opposite of nonvolatile memory. 2. A read/write memory whose content is irretrievably lost when operating power is removed. Virtually all types of read/write semiconductor memories are volatile. See also nonvolatile memory.
volatile storage 1. A computer storage device in which the stored information is lost when the power is removed. 2. A storage medium in which data cannot be retained without continuous power dissipation (e.g., acoustic delay tines, electrostatics, capacitors).
volatile store A storage device in which stored data is lost when the applied power is removed (e.g., an acoustic delay line).
volatility With respect to memory, an inability to retain stored data in the absence of external power.
Voldicon The trade name of Adage, Inc., for a family of high-speed, all-semiconductor, current-balancing devices that use digital logic and readout far high-speed precision measurement of analog signals.
volt Letter symbol: V, 1. The unit of measurement of electromotive force. It is the difference of potential required to make a current of 1 ampere flow through a resistance of 1 ohm. 2. The difference of electric potential between two points of a conductor carrying a constant current of 1 ampere when the power dissipated between these points is equal to 1 watt.
Volta effect See contact potential.
voltage 1. Electrical pressure; i.e., the force that causes current through an electrical conductor. 2. Symbolized by E. The greatest effective difference of potential between any two conductors of a circuit 3. The term most often used in place of electromotive force, potential, potential difference, or voltage drop, to designate electric pressure that exists between two points and is capable of producing a flow of current when a closed circuit is connected between the two points. 4. Standard unit of magnitude of an electrical signal, named after Count A. Volta, inventor of the battery about 1800.
voltage amplification Also called voltage gain. 1. Ratio of the voltage across a specified load impedance connected to a transducer to the voltage across the input of the transducer. 2. The ratio of the voltage at the input of a device to the voltage at the output from the device, expressed in decibels.
voltage amplifier An amplifier used specifically to increase a voltage. It is usually capable of delivering only a small current.
voltage-amplifier tube A tube that is designed primarily as a voltage amplifier. It has high gain, but delivers very little output power.
voltage and power directional relay A device that permits or causes the connection of two circuits when the voltage difference between them exceeds a given value in a predetermined direction, and causes these two circuits to be disconnected from each other when the power flowing between them exceeds a given value in the opposite direction.
voltage attenuation Ratio of the voltage across the input of a transducer to the voltage delivered to a specified load impedance connected to the transducer.
voltage balance relay A device that operates on a given difference in voltage between two circuits.
voltage breakdown 1. The voltage necessary to cause insulation failure. 2. A rapid increase of current flow, from a relatively low value to a relatively high value, upon the application of a voltage to a pn junction or dielectric.
voltage-breakdown test A test whereby a specified voltage is applied between given points in a device to ascertain that no breakdown will occur at that specified voltage.
voltage calibrator Test equipment that supplies accurate ac voltages for comparison on a scope screen with other waveforms to determine their voltage level.
voltage coefficient of capacitance Also called voltage sensitivity. The quotient of the derivative with respect to voltage of a capacitance characteristic at a point divided by the capacitance at that point.
voltage coefficient of resistivity The maximum change in nominal resistance value due to the application of a voltage across a resistor, after correcting for self-heating effects; usually expressed in percent or per-unit (ppm) change in nominal resistance per volt applied.
voltage comparator 1. An amplifying device with a differential input that will provide an output polarity reversal when one input signal exceeds the other. When operating with open loop and without phase compensation, operational amplifiers make fast and accurate voltage comparators. 2. A circuit that compares two analog voltages and develops a logic output when the voltages being compared are equal or one is greater or less than the reference level.
voltage control A method of varying the magnitude of voltage in a circuit by means of amplitude control, phase contral, or both.
voltage-controlled capacitor See varactor.
voltage-controlled crystal oscillator A crystal oscillator whose operating frequency can be changed by applying a controlling voltage to introduce a phase shift in the oscillator circuit.
voltage-controlled oscillator Abbreviated VCO. 1. Any oscillator for which a change in tuning voltage results in a predetermined change in output frequency. Frequency tuning is accomplished by either changing the bias voltage on a varactor diode in the frequency-determining resonant network or the bias voltage to the active device. The former approach, although more complex than the latter method of tuning, is capable of multioctave bandwidth. 2. A circuit that creates an ac output signal whose frequency is a function of the dc input voltage. 3. An oscillator whose frequency can be changed by means of an external control voltage. It is commonly found in synthesizers.
voltage-controlled resistor Abbreviated VCR. A three-terminal variable resistor in which the resistance value between two of the terminals is controlled by a voltage potential applied to the third.
voltage corrector An active source of regulated power placed in series with the output of an unregulated supply. The voltage corrector senses changes in the output voltage (or current) and corrects for these changes automatically by varying its own output in the opposite direction so as to maintain the total output voltage constant.
voltage/current crossover The characteristic of a power supply that automatically converts the mode of operation of a power supply from voltage regulation to current regulation (or vice versa) as required by preset limits. The constant-current and constant-voltage settings are independently adjustable over specified limits. The region near the intersection of the constant-voltage and constant-current curves is designated by the term “crossover characteristics.”
voltage-dependent resistor Abbreviated VDR. Also called varistor or metal oxide varistor (MOV). A special type of resistor whose resistance changes appreciably, nonlinearly, and consistently in response to voltage across its terminals.
voltage-directional relay 1. A relay that functions in conformance with the direction of an applied voltage. 2. A device that operates when the voltage across an open circuit breaker or contactor exceeds a given value in a given direction.
voltage divider Also called a potential divider. 1. A resistor or reactor connected across a voltage and tapped to make a fixed or variable fraction of the applied voltage available. See also potentiometer, 1; rheostat. 2. High-voltage resistance string, tapped resistor, potentiometer, adjustable resistors, or a series arrangement of two or more fixed resistors connected across a voltage source. Of the total voltage, a desired fraction is obtained from the intermediate tap, movable contact, or resistor junction.
voltage doubler A voltage multiplier that rectifies each half cycle of the applied alternating voltage separately, and then adds the two rectified voltages to produce a direct voltage having approximately twice the peak amplitude of the applied alternating voltage.
voltage drop — 1. The difference in voltage between two points due to the loss of electrical pressure as a current flows through an impedance. 2. The voltage developed across the component or conductor by current through the resistance or impedance of that component or conductor. 3. The voltage developed between the terminals of a circuit component by current through the resistance or impedance of that part. See IR drop. 4. The decrease in voltage as a current traverses a resistance. 5. The voltage measured across a resistance through which a current is flowing. 6. The voltage existing across each element of a series circuit. (Also true of a contact in series with its load where a voltage drop also exists.) The voltage present across the load will be the line voltage less the voltage drops across each element in series with the load.
voltage endurance See corona resistance.
voltage feed Excitation of a transmitting antenna by applying voltage at a point of maximum potential (at a voltage loop or antinode).
voltage feedback A form of amplifier feedback in which the voltage drop across part of the load impedance is put in series with the input-signal voltage.
voltage frequency converter A circuit that produces an output frequency that varies with the voltage applied to its input.
voltage gain See voltage amplification.
voltage generator A two-terminal circuit element with a terminal voltage independent of the current through the element.
voltage gradient The voltage per unit length along a resistor or other conductive path.
voltage inverter A circuit having a response (output) proportional to a constant (the gain) times the input signal, but opposite in sign to it. In a unity-gain inverter, the output is — 1 times the input.
voltage jump An abrupt change or discontinuity in the tube voltage drop during operation of glow-discharge tubes.
voltage level Ratio of the voltage at any point in a transmission system to an arbitrary value of voltage used as a reference. In television and other systems where waveshapes are not sinusoidal or symmetrical about a zero axis and where the sum of the maximum positive and negative excursions of the wave is important in system performance, the two voltages are given as peak-to-peak values. This ratio is usually expressed in dBV, signifying decibels referred to 1 volt peak-to-peak.
voltage limit A control function that maintains a voltage between predetermined values.
voltage loop A point of maximum voltage in a stationary-wave system. A voltage loop exists at the ends of a half-wave antenna.
voltage loss The voltage between the terminals of a current-measuring instrument when the applied current has a magnitude corresponding to nominal end-scale deflection. In other instruments, the voltage loss is the voltage between the terminals at rated current.
voltage-measuring equipment Equipment for measuring the magnitude of an alternating or direct voltage.
voltage multiplier 1. A rectifying circuit that produces a direct voltage: approximately equal to an integral multiple of the peak amplitude of the applied alternating voltage. 2. A series arrangement of capacitors charged by rapidly rotating brushes in sequence, giving a high direct voltage equal to the source voltage multiplied by the number of capacitors in series. 3. A precision resistor used in series with a voltmeter to extend its measuring range.
voltage node 1. A point having zero voltage in a stationary-wave system (e.g., at the center of a half-wave antenna). 2. In a transmission system having standing waves, a point at which the voltage is a minimum.
voltage offset The amount of dc voltage present at an (instrumentation) amplifier’s output with a 0-volt input. Initial offset may be adjusted to zero; however, offset-voltage shifts during operation can cause errors. Systems containing microcomputers can often correct offset with an auto-zero cycle, or the offset can be removed by a control adjustment.
voltage plane A conductor or portion of a conductor layer on or in a printed board that is maintained at other than ground potential. It can also be used as a common voltage source for heat sinking or for shielding.
voltage quadrupler A rectifier circuit in which four diodes are employed to produce a dc voltage of four times the peak value of the ac input voltage.
voltage-range multiplier Also called an instrument multiplier. 1. A series resistor installed external to the measurement device to extend its voltage range. 2. A precision resistor placed in series with a voltmeter to enable measurement of a high voltage with a voltmeter having a lower voltage range.
voltage rating Also called the working voltage. 1. The maximum voltage that an electrical device or component can sustain without breaking down. 2. The maximum sustained voltage that can be safely applied to a capacitor up to a specified temperature without risking capacitor failure. 3. The maximum voltage at which a given device may be safely maintained during continuous use in a normal manner.
voltage ratio (of a transformer) Ratio of the rms primary terminal voltage to the rms secondary terminal voltage under specified load conditions.
voltage-ratio box See measurement voltage divider.
voltage reference A highly regulated voltage source used as a standard to which the output voltage of a power supply is continuously compared for purposes of regulation.
voltage-reference diode A diode that develops across its terminals a reference voltage of specified accuracy when biased to operate within a specified current range.
voltage-reference tube A gas tube in which the voltage drop is essentially constant over the operating range of current and is relatively stable at fixed values of current and temperature.
voltage reflection coefficient The ratio of the complex electric field strength or voltage of a reflected wave to that of the incident wave.
voltage-regulating transformer A saturated-core type of transformer that holds the output voltage to within a few percent, with input variations up to ±20 percent. Considerable harmonic distortion results unless extensive filters are employed.
voltage regulation A measure of the degree to which a power source maintains its output voltage stability under varying load conditions.
voltage regulator 1. A circuit that holds an output voltage at a predetermined value or causes it to vary according to a predetermined plan, regardless of normal input-voltage change or changes in the load impedance. 2. A gas-filled electronic tube that has the property of maintaining a nearly constant voltage across its terminals over a considerable range of current through the tube. It is used in an electronic voltage regulator. 3. An electronic circuit used for controlling and maintaining a voltage at a constant level.
voltage-regulator diode 1. A diode that develops across its terminals an essentially constant voltage throughout a specified current range. 2. A diode that is normally biased to operate in the breakdown region of its voltage-current characteristic and that develops across its terminals an essentially constant voltage throughout a specified current range.
voltage-regulator tube Also called a VR tube. A glow-discharge cold-cathode tube in which the voltage drop is essentially constant over the operating range of current, and which is designed to provide a regulated direct-voltage output.
voltage relay A relay that functions at a predetermined value of voltage.
voltage saturation See plate saturation.
voltage-sensitive resistor A resistor (e.g., a varistor) whose resistance varies with the applied voltage.
voltage sensitivity 1. The voltage that produces standard deflection of a galvanometer when impressed on a circuit made up of the galvanometer coil and the external critical-damping resistance. The voltage sensitivity is equal to the product of the current sensitivity and the total circuit resistance. 2. See voltage coefficient of capacitance.
voltage spectrum A function that is the square root of the spectral intensity; it is expressed in terms of voltage in a unit frequency band.
voltage-stabilizing tube A gas-filled glow-discharge tube normally working in that part of its characteristic where the voltage is practically independent of current drop within a given range.
voltage standard An accurately known voltage source (e.g., a standard cell) used for comparison with or calibration of other voltages.
voltage standing-wave ratio Abbreviated VSWR. In a stationary-wave system (such as in a waveguide or coaxial cable), the ratio of the amplitude of the electric field or voltage at a voltage maximum to that at an adjacent voltage minimum.
voltage stress That stress found within a material when subjected to an electrical charge.
voltage-to-frequency converter Abbreviated v/f converter. An electronic circuit that converts an input voltage into a train of digital output pulses at a rate that is directly proportional to the input.
voltage to ground The voltage between any live conductor of a circuit and earth (or common reference plane).
voltage transformer See potential transformer.
voltage transients Unpredictable and usually unavoidable spikes and surges of electrical power.
voltage tripler A rectifier circuit in which three diodes are employed to produce dc voltage equal to approximately three times the peak ac input voltage.
voltage-tunable magnetron A high-frequency continuous-wave oscillator operating in the microwave region. Power outputs begin in the milliwatts range and extend through hundreds of watts.
voltage-tunable tube An oscillator tube whose operating frequency can be changed by varying one or more of its electrode voltages (e.g., a backward-wave magnetron).
voltage-tuned cavity oscillator Primarily a cavity oscillator with the addition of a varactor diode to slightly modify the cavity’s resonant frequency. These oscillators are capable of FM and/or phase-locking.
voltage-tuned crystal oscillator A crystal-controlled oscillator with a varactor diode in the frequency-determining network that is used to slightly vary the crystal frequency.
voltage-type telemeter A telemeter in which the translating means is the magnitude of a single voltage.
voltage-variable capacitance diode Another name for varactor diode.
voltage-variable capacitor See varactor.
voltage velocity limit See slew rate, 2.
voltaic cell An electric cell having two electrodes of unlike metals immersed in a solution that chemically affects one or both of them, thus producing an electromotive force. The name is derived from Volta, a physicist who discovered this effect.
voltaic couple Two dissimilar metals in contact, resulting in a contact potential difference.
voltaic pile A voltage source consisting of alternate pairs of dissimilar metal discs separated by moistened pads, forming a number of elementary primary cells in series.
volt-ammeter An instrument calibrated to read both voltage and current.
voltampere Letter symbol: VA. A unit of apparent power in an ac circuit containing reactance. It is equal to the potential in volts multiplied by the current in amperes, without taking phase into consideration.
voltamperehour meter An electricity meter that measures the integral, usually in kilovoltamperehours, of the apparent power in the circuit where the meter is connected.
voltampere loss See apparent power loss.
voltampere meter An instrument for measuring the apparent power in an alternating-current circuit. Its scale is graduated in voltamperes or kilovoltamperes.
voltampere reactive Also called wattless power. Component of the apparent power in an alternating-current circuit that is delivered to the circuit during part of a cycle, but is returned to the source during another part of the cycle. The practical unit of reactive power is the var, equal to 1 reactive voltampere.
Volta’s law When two dissimilar conductors are placed in contact, the same contact potential is developed between them, whether the contact is direct or through one or more intermediate conductors.
volt box See measurement voltage divider.
volt-electron An obsolete expression for electron-volt.
voltmeter 1. An instrument for measuring potential difference between two points. Its scale is usually graduated in volts. If graduated in millivolts or kilovolts, the instrument is usually designated as a millivoltmeter or a kilovoltmeter. 2. An instrument used for the measurement of electric voltage. The instrument may be of the electrostatic or tube type, but usually consists of a moving-coil ammeter connected in series with a high resistance. The resistance of the meter being fixed, the current passing through it will be directly proportional to the voltage at the points where it is connected; thus, the instrument can be calibrated in volts.
voltmeter-ammeter A voltmeter and an ammeter combined into a single case, but with separate circuits.
voltmeter sensitivity The ratio, expressed in ohms per volt, of the total resistance of a voltmeter to its full-scale reading.
volt-ohm-milliammeter A test instrument with several ranges, for measuring voltage, current, and resistance.
volume Also called power level. I. The magnitude (measured on a standard volume indicator) of a complex audio-frequency wave, expressed in volume units. In addition, the term volume is used loosely to signify either the intensity of a sound or the magnitude of an audio-frequency wave. 2. The amount or a measure of energy in an electrical or acoustical train of waves. 3. A physical unit of storage media; for example, a reel of magnetic tape. A volume may contain part of a file, a complete file, or more than one file. Sections of one or more files may be contained in a volume, but not multiple sections of the same file. 4. The level of an audio signal or the intensity of a sound. 5. A unit of secondary storage media, such as a magnetic tape, disk pack, or flexible diskette.
volume bar When activated, a TV feature that displays a volume setting bar on-screen, showing the adjustment being made whenever volume levels are adjusted.
volume compression Also called automatic volume compression. The limiting of the volume range to about 30 to 40 decibels at the transmitter to permit a higher average percentage modulation without overmodulation. Also used in recording to raise the signal-to-noise ratio.
volume compressor Audio-frequency control circuit that limits the volume range of a (radio) program at the transmitter to permit using a higher average percent modulation without risk of overmodulation.
volume conductivity See conductivity, 1.
volume control A variable resistor for adjusting the loudness of a radio receiver or amplifying device.
volume equivalent A measure of the loudness of speech reproduced over a complete telephone connection. It is expressed numerically in terms of the trunk loss of a working reference system that has been adjusted to give equal loudness.
volume expander A circuit that provides volume expansion.
volume expansion See automatic volume expansion.
volume indicator An instrument for indicating the volume of a complex electric wave such as that corresponding to speech.
volume lifetime The average time interval between the generation and recombination of minority carriers in a homogeneous semiconductor.
volume limiter An amplifier whose gain is automatically reduced when the average input volume to the amplifier exceeds a predetermined value, so that the output volume is maintained substantially constant. The normal gain is restored whenever the input volume drops below the predetermined limit.
volume-limiting amplifier An amplifier that reduces the gain whenever the input volume exceeds a predetermined value, so that the output volume is maintained substantially constant. The normal gain is restored whenever the input volume drops below the predetermined limit.
volume magnetostriction The relative volume change of a body of ferromagnetic material when the magnetization of the body is increased from zero to a specified value (usually saturation) under specified conditions.
volume range 1. Of a transmission system, the difference, expressed in dB, between the maximum and minimum volumes that the system can satisfactorily handle. 2. Of a complex audio-frequency signal, the difference, expressed in dB, between the maximum and minimum volumes occurring over a specified period.
volume recombination rate The rate at which free electrons and holes recombine within the volume of a semiconductor.
volume resistance Ratio of the dc voltage applied to two electrodes in contact with or embedded in a specimen to the portion of the current between them distributed through the specimen.
volume resistivity 1. Ratio of the potential gradient parallel to the current in a material to the current density. See also resistivity, 1. 2. Also called specific insulation resistance. The electrical resistance between opposite faces of a 1-cm cube of insulating material, commonly expressed in ohm-centimeters. 3. The resistance of a material to dc current as a measure of volume. Expressed in ohm-centimeters.
volumetric displacement The change in volume required to displace the diaphragm of a pressure transducer from its rest position io a position corresponding to the application of a stimulus equal to the rated range of the transducer.
volumetric efficiency Also called packing factor. The ratio of parts volume to total equipment volume, expressed in percent, in modules, it is usually taken as the volume of component bodies only (not including leads, other interconnecting media, insulators, heat sinks, and so on) and based on nominal sizes of components and nominal outside module dimensions.
volumetric radar A radar capable of producing three-dimensional position data on several targets.
volumetric sensor A sensor with a detection zone that extends over a volume such as an entire room, part of a room or a passageway. Ultrasonic motion detectors and sonic motion detectors are examples of volumetric sensors.
volume unit Abbreviated vu. 1. The unit of transmission measurement for measuring the level of non-steady-state currents. Zero level is the steady-state reference power of 1 milliwatt in a circuit of 600 ohms characteristic impedance. 2. A measure of the power level of the voice wave. Zero volume unit is equivalent to +4 dBm for simple electrical waves (single frequencies). 3. An arbitrary sound-level standard related to the decibel and used for calibrating recording levels.
volume-unit indicator Also called a vu indicator or volume-unit meter. An instrument calibrated to read audio-frequency power levels directly in volume units.
volume-unit meter See vu meter.
volume velocity The rate at which a medium flows through a specified area due to a sound wave.
Von Hippel breakdown theory Also called low-energy criterion. Breakdown occurs at fields for which the rate of recombination of electrons and positive holes is less than the rate of collisional ionization. Assumes no distribution in electron energies.
VOR Abbreviation for VHF omnirange.
vortex amplifier 1. A fluidic device in which the angular rate of a vortex is controlled to alter the output. 2. A fluidic amplifier using momentum interaction to produce stream rotation and consequent output modification.
vowel articulation The percent of articulation obtained when the speech units considered are vowels, usually combined with consonants into meaningless syllables.
V-ring In commutator construction, a specially shaped insulating structure having one or more V-shaped sections.
VRR Abbreviation for visual radio range.
VR tube Abbreviation for voltage-regulator tube.
VSWR Abbreviation for voltage standing-wave ratio.
VTF Abbreviation for vertical tracking force.
VTL Abbreviation for variable threshold logic.
VTM See voltage-tunable magnetron.
VTR Abbreviation for videotape recording or videotape recorder.
VTVM Abbreviation for vacuum-tube voltmeter.
vu Abbreviation for volume unit.
vu indicator Abbreviation for volume-unit indicator.
vulcanized fiber A dense, homogeneous, cellulosic material that has been partially gelantinized by swelling with a zinc chloride solution. It may be made in the form of sheets, rods, coils, or tubes, and it may be used for electrical insulation as well as in mechanical applications.
vu meter Abbreviation for volume-unit meter. 1. A volume indicator with a decibel scale and specified dynamic and other characteristics. It is used to obtain correlated readings of speech power necessitated by the rapid fluctuations in a level of voice currents. 2. Strictly, a recording-level meter whose indicator needle’s motion is damped according to a specified standard to allow it to respond at a certain speed to sudden impulses without overshooting the mark by more than a certain amount. The term vu meter is loosely applied to practically any recording-level indicator that uses an indicator needle, 3. A type of recording-level indicator that shows average signal levels in decibels relative to a fixed 0-dB reference level or in percent of maximum recommended modulation. The term is frequently used for any level meter using this scale, but it applies mostly to meters having a specified, standard degree of damping.
