ge, or the extent to which an image is brought into sharp relief. 2. The degree with which a communica tion system reproduces sound images or messages.
definition phase See requirements phase.
definitive method of measurement A method of measurement of a quantity in accordance with a defi nition of the unit of that quantity.
deflaking Separation of fibers in knots and bundles, small flakes of paper or pulp etc. which have resisted kneader pulping or slushing.
deflashing Removing fins or protrusions from the parting line of a die casting or molded plastics part.
deflecting force (direct-current recording in strument) At any part of the scale (particularly full scale), the force for that position, measured at the marking device, and produced by the electrical quantity to be measured, acting through the mecha nism.
deflecting torque, driving torque Pertaining to electrical measuring instruments a torque resulting from e.g. electrostatic effects on the moving element.
deflection technique A flow measuring technique which, in principle, utilizes some energy source which is introduced to the fluid in a pipe or duct. At zero flow, the energy source crosses the pipe or duct and the location of the received source on the other side of the pipe is noted. When flow is initiated, the flowing fluid deflects the energy source and the location of the deflected source is monitored on the opposite pipe wall. The distance between the zero flow location and the flowing location of the detected energy source is the indication of flow rate.
deflection voltage The voltage applied to the elec trostatic plates of a cathode-ray tube to control the movement of the electron beam.
DEF STAN Abbreviation for defence standard (Eng land).
degauss To neutralize the existing magnetic field.
degenerate modes A set of modes having the same resonance frequency (or propagation constant). The members of a set of degenerate modes are not unique.
degeneration 111 Delphi technique degeneration Se negative feedback.
degenerative feedback A technique which returns part of the output of a machine, system or process to input it in a way as to cause a larger quantity to be de ducted from the input with an increase of output re sults. See also under negative feedback.
degradation (electromagnetic interference) In susceptibility specification testing, degradation is an unwanted change in the operational performance of a specimen due to electromagnetic interference. This does not necessarily mean malfunction or catastrophic failure. The ESD test specification generally requires stating the criteria for degradation of performance.
degradation (of performance) An undesired de parture in the operational performance of any device, equipment or system from its intended performance.
degradation failure A failure which is both a gradu al failure and a partial failure.
degreasing Part of procedures for cleaning industri al-process measurement and control equipment to be used for oxygen service. The degreasing methods and procedures are outlined in IEC publication 877 (1986).
degree Celsius (°C) Unit for temperature according to the Celsius temperature scale based on the freezing point of water defined as 0°C and the boiling point as 100°C, both under conditions of normal atmospheric pressure (760 mm of mercury). Write degrees Celsius, not degrees centigrade. See also International System of Units and additional units.
dehumidification Reducing the moisture content of air, which increases its cooling power.
dehydrated air Air that has all traces of moisture re- moved; instrument air.
dehydration reaction The reverse of hydration; de- hydration is the transfer of H2O from a mineral into
the fluid phase or into free water. See hydration reac tion.
dehydrator A tank or tower through which gas is run to remove entrained water. A common method of gas dehydration is through the use of various glycols – diethylene, triethylene, and tetraethylene. Dehydra tion is accomplished by contact of the wet gas with a pure or lean glycol solution. Gas is fed into the bottom of a trayed or packed column in the presence of the glycol solution. As the gas percolates upward through the solution, the “lean” glycol absorbs the entrained water and dry gas is taken off at the top of the tower.
deicing Using heat, chemicals or mechanical rupture to remove ice deposits, especially those that form on motor vehicles and aircraft at low temperatures or high altitudes.
deinking The removal from waste paper of printing ink, dyestuffs, fillers and other additives.
deionization The process by which an ionized gas re- turns to its neutral state after all sources of ionization have been removed.
deionization (water quality) The substantial or complete removal of ionic species, particularly by the use of ion-exchange resins.
deionized water Water which has been treated to re- move ions.
delay The amount of time by which a signal is delay ed. It may be expressed in time (milliseconds, micro- seconds, etc.) or in number of characters (pulse times, word times, major cycles, minor cycles etc.).
delay coincidence circuit A coincidence circuit ac tuated by two pulses, one of which is delayed a speci fic amount with respect to the other.
delay counter In a computer, a device that can tem porarily delay a program a sufficient length of time for the completion of an operation.
delay dispersion The change in phase delay over a specified operating frequency range.
delay distorsion A form of distorsion in a transmit ted radio wave that occurs when the rate of change of phase shift with frequency is not constant over the transmission-frequency range.
delayed combustion A continuation of combustion beyond the furnace. See also secondary combustion.
delay element A device that yields, after a given time interval, an output signal essentially similar to a previously introduced input signal.
delay (D) flip-flop A flip-flop whose output is a func tion of the input which appeared one pulse earlier: For example, if a 1 appeared at the input, the output after the next clock pulse will be a 1.
delay-interval timer A timing device which is elec trically reset to delay energization or deenergization of a circuit for an interval of time up to 10 min follo wing a specific event such as restoration of power af ter a power failure or turning a manual switch off.
delay line A line or network designed to introduce a desired delay in the transmission of a signal.
(delay-line memory), delay-line storage A me mory or storage device consisting of a delay line and means for regenerating and reinserting information into the delay line.
delay modulation A method of data encording for serial data transmission and recording.
delay-on-make timer A timing device that holds its main contacts open for a preset period of time after it receives in initiating signal, then closes the contacts and allows current to flow in the main circuit; when the timer receives a stopping signal, the contacts open and after a short interval the timer automatically resets so it can repeat the cycle.
delay on break A term used to describe a mode of operation relative to timing devices. The delay begins when the initiate switch is opened (delay on break of initiate switch).
delayed command Command which is issued after a specified delay time after the associated step has been activated, and which ends as soon as the associa ted step is deactivated. The command will not be is- sued if the associated step is activated and deactivated within the specified delay time. The delayed com mand is identified in IEC 848 by the conventional let ter ”D”.
delete character A distinct operational character de- signed to be used to obliterate erroneous or undesired characters.
deletion record In a computer, a new record to re- place or remove an existing record in a master file.
delignification Treatment intended to reduce the content of lignin in vegetable fiber raw materials.
delimiter One or more characters used to indicate the beginning or the end of a character string.
deliquescent type dryer Moisture is separated by using the absorptive properties of special hygroscopic compounds.
delivery (software) 1. The point in the software de
velopment cycle at which a product is released to its intended user for operational use. 2. The point in the software development cycle at which a product is ac cepted by its intended user.
Delphi technique A unique forecasting method for use when there is no directly relevant historical data available. It is an intuitive forecast mode after combi ning the views of many experts in the particular field.
delta 112 deoxygenation delta The Greek letter delta represents any quantity
which is much smaller than any other quantity of the same units appearing in the same problem.
delta circuit A three-phase circuit in which the win- dings of the system are connected in the form of a clo sed ring and the instantaneous voltage around the ring equal zero. There is no common or neutral wire, so the system is used only for three-wire systems or genera- tors.
delta connection In a three-phase system, the termi nal connections. So called because they are triangular like the Greek letter delta.
delta modulator A closed-loop sampled-data control system that transmits binary output pulses whose po larity depends on the difference between the input sig nal being sampled and a quantized approximation of the preceding input signal.
delta network A set of three branches connected in series to form a mesh.
delta P sizing Pertaining to specifications for control valves, pressure drop (inlet pressure minus outlet pressure with units; psi, inches w.c. etc.). For all flows for sizing of valve port(s).
demagnetization Partial or complete reduction of residual magnetism.
demagnetizing force A magnetizing force applied in such a direction as to reduce the remanent induc tion in a magnetized body.
demand An input/output coding technique in which a read or write order is initiated as the need to read a new block or write a new block of data occurs. Opera tions do not take place in parallel.
demand deviation (metering) The difference bet- ween the indicated or recorded demand and the true demand, expressed as a percentage of the full-scale value of the demand meter or register.
demand factor The ratio of the maximum demand of an electrical system, or part of a system, to the total connected load of a system or that part of a system un der consideration.
demand failure rate The probability (per demand) of failure that a component will fail to operate upon demand when required to start, change state, or func tion.
demand load The load that is drawn from the source of supply at the receiving terminals, averaged over a suitable and specified interval of time, expressed in kilowatts, amperes, etc.
demand meter (metering) A metering device that indicates or records the demand, maximum demand, or both. Note: Since demand involves both an electri cal factor and a time factor, mechanisms responsive to each of these factors are required, as well as an indica ting or recording mechanism.
demand paging The transfer of a page from auxilia ry storage to real storage at the moment of need.
demand register (metering) A mechanism, for use with an integrating electricity meter, that indicates maximum demand and also registers electric energy (or other integrated quantity).
DEM, DEMOD See demodulator.
demineralization The reduction of the content of dissolved salts or inorganic substances in water by a physical, chemical or biological process.
demineralized water Water which has been treated to remove the minerals that are normally present in hard water. Demineralized water is required in some electronic applications where extreme precautions must be taken to prevent contamination. See also deionized water.
DEMOD See demodulator.
demodulation The process of retrieving intelligence (data) from a modulated carrier wave. The reverse of modulation.
demodulator A functional unit that converts a modu lated signal into the original signal.
demodulator probe A probe designed for use with an oscilloscope, for displaying modulated high-fre quency signals.
demon, deamon A procedure that is invoked wit hout being called explicitly whenever an alteration, an addition, or a deletion occurs.
DeMorgan’s theorem An equivalence statement used in a logical truth table.
demultiplexer A device that recovers as output sig nals, each of the signals combined by a preceding multiplexer.
demultiplexing Dividing of information streams into a larger number of streams (contrasted with multip lexing).
denary, decimal 1. Characterized by a selection,
choice or condition that has ten possible different va lues or states. 2. Of a fixed radix numeration system, having a radix of ten.
dendrite A semiconductor crystal with a heavily branched, treelike structure which grows from the nu cleus as the metal becomes solidified.
denitrification (water quality) The reduction of ni trate or nitrite to liberate nitrogen or nitrous oxide, usually by the action of bacteria.
dense binary code A code in which all possible sta tes of the binary pattern are used.
densimeter An instrument for determining the densi ty of a substance in absolute units, or for determining its specific gravity – that is, its relative density with respect to that of pure water. Also known as densito meter; density gage; density indicator; gravitometer.
densitometer An instrument for measuring the opti cal density (photographic transmission, photographic reflection, visual transmission, and so forth) of a ma terial.