| D/A Convertor: Short for digital-to-analog converter. This is a device that changes a digitally coded word into its equivalent quantized analog voltage or current. Just like the A/D device, there are very high-speed D/A?s available, capable of converting at data rates up to 1 GHz.
|
| D:S ratio: Optical resolution expressed as a ratio of the distance to the resolution spot divided by the diameter of the spot.
|
| Daltons Law: States that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the constituent gases. The partial pressure is the pressure each gas would exert if it alone occupied the volume of the mixture. |
| Damping: The reduction of response at the resonant frequency through the use of a damping media such as oil. Usually specified as the ratio of critical damping.
|
| Darcys Law: an empirical relationship between hydraulic gradient and the viscous flow of water in the saturated zone of a porous medium under conditions of laminar flow. The flux of vapors through the voids of the vadose zone can be related to a pressure gradient through the air permeability by Darcys Law.
|
| Dark Fiber: Unused fiber optic cable, sometimes referred to as "unlit glass." |
| Dark Matter: Matter that is in space but is not visible to us because it emits no radiation by which to observe it. The motion of stars around the centers of their galaxies implies that about 90% of the matter in a typical galaxy is dark. Physicists speculate that there is also dark matter between the galaxies but this is harder to verify. |
| DARPA: Defense Advanced Research Projects Agency. A US Dept of Defense agency that funds high-risk research projects and that funded the development of UNIX 4.2, and the TCP/IP communications protocol. One of the founders of the Internet.
|
| Data Base: A large amount of data stored in a well-organized manner. A data base management system (DBMS) is a program that allows access to the information.
|
| Data Compression: A method of reducing the number of bits that are needed to represent information. Data compression allows gigher communications speeds and allows more information to be stored on a disk.
|
| Dateometer: (day-TOM-uh-ter). A small calendar disc attached to motors and equipment to indicate the year in which the last maintenance service was performed. |
| dB (Decibel): 20 times the log to the base 10 of the ratio of two voltages. Every 20 dBs correspond to a voltage ratio of 10, every 10 dBs to a voltage ratio of 3.162. For instance, a CMR of 120 dB provides voltage noise rejection of 1,000,000/1. An NMR of 70 dB provides voltage noise rejection of 3,162/1.
|
| DC: Direct current; an electric current flowing in one direction only and substantially constant in value.
|
| Dead Band: 1. For chart records: the minimum change of input signal required to cause a deflection in the pen position. 2. For temperature controllers: the temperature band where heat is turned off upon rising temperature and turned on upon falling temperature expressed in degrees. The area where no heating (or cooling) takes place. |
| Dead Volume: The volume inside the pressure port of a transducer at room temperature and barometric pressure.
|
| Dead-Reckoning: A technique that calculates the current location of a vehicle by measuring the distance and direction that the vehicle has traveled since leaving a known starting point.
|
| Debug: The process of removing from a newly designed or manufactured system the components or design issues that have caused the system to not perform as desired. (Removing mistakes from the software or hardware of a computer system.)
|
| Dechlorination: The deliberate removal of chlorine from water. The partial or complete reduction of residual chlorine by any chemical or physical process. |
| Decibel: A unit (dB) for measuring the relative strength of signal power. The number of decibels equals ten times the logarithm (base 10) of the ratio of the measured signal power to a reference power. One tenth of a bell.
|
| Decimal: Refers to a base ten number system using the characters 0 through 9 to represent values.
|
| Decoupling-Network An electrical circuit which is used to insure that signals applied to one unit being tested, do not affect other units, instruments or systems not being tested.
|
| Default: The value(s) or option(s) that are assumed during operation when not specified.
|
| Deflection: The change in length along the primary axis or distance a diaphragm moves at the center between no-load and rated load conditions.
|
| Defluoridation: The removal of excess fluoride in drinking water to prevent the mottling (brown stains) of teeth. |
| Degasification: A water treatment process which removes dissolved gases from the water. The gases may be removed by either mechanical or chemical treatment methods or a combination of both. |
| Degradation: 1. The deterioration in quality, level, or standard of performance of a functional unit. 2. In communications, a condition in which one or more of the required performance parameters fall outside predetermined limits, resulting in a lower quality of service. |
| Degree R?aumur (?R?): An absolute temperature scale. ((?F - 32) x 4/9). (040)
|
| Degree: An incremental value in the temperature scale, i.e., there are 100? between the ice point and the boiling point of water in the Celsius scale and 180?F between the same two points in the Fahrenheit scale.
|
| Deliquescent: |
| Demineralization: A treatment process which removes dissolved minerals (salts) from water. |
| Density: Mass per unit of volume of a substance. I.E. grams/cu.cm. or pounds/cu.ft.
|
| Depleted Uranium: A by-product of uranium enrichment, the most common chemical form of which is depleted uranium hexafluoride (DUF6). Natural uranium is composed of three isotopes: uranium-238 (99.284 percent); uranium-235 (0.711 percent); and uranium-234 (0.005 percent), all of which are radioactive. The purpose of uranium enrichment is to concentrate uranium-235, the fissile isotope, in one stream. The other stream which is low in uranium-235, is called "depleted uranium," which contains about 0.2 to 0.3 percent uranium-235.
|
| Derivative: The derivative function senses the rate of rise or fall of the system temperature and automatically adjusts the cycle time of the controller to minimize overshoot or undershoot.
|
| Dermal Exposure: Contact between a chemical and the skin |
| Desalinization: The removal of dissolved salts (such as sodium chloride, NACI) from water by natural means (leaching) or by specific water treatment processes. |
| Desiccant: Any substance which exerts a drying action by chemically absorbing water vapor .
|
| Desiccation: A process used to thoroughly dry air; to remove virtually all moisture from air. |
| Desiccator: A closed container into which heated weighing or drying dishes are placed to coot in a dry environment. The dishes may be empty or they may contain a sample. Desiccators contain a substance, such as anhydrous calcium chloride, which absorbs moisture and keeps the relative humidity near zero so that the dish or sample will not gain weight from absorbed moisture. |
| Desorption: Release of adsorbed or absorbed material .
|
| Destratification: The development of vertical mixing within a lake or reservoir to eliminate (either totally or partially) separate layers of temperature, plant, or animal life. This vertical mixing can be caused by mechanical means (pumps) or through the use of forced air diffusers which release air into the lower layers of the reservoir. |
| Detention Lag: The time period between the moment a change is made and the moment when such a change is finally sensed by the associated measuring instrument. |
| Detention Time: 1) The theoretical (calculated) time required for a small amount of water to pass through a tank at a given rate of flow. 2) The actual time in hours, minutes or seconds that a small amount of water is in a settling basin, flocculating basin or rapid-mix chamber. In storage reservoirs, detention time is the length of time entering water will be held before being drafted for use (several weeks to years, several months being typical). Detention Time (hr) = Basin Volume (gal.)(24 hr/day)t Flow (gal/day) |
| Deviation: The difference between the value of the controlled variable and the value at which it is being controlled.
|
| Dew Point The temperature at which liquid first condenses when a vapor is cooled . |
| DFT: Discrete Fourier Transform.
|
| Diaphragm: The sensing membrane which is deformed when pressure is applied.
|
| diatomaceous earth filtration (DE filtra Filtration method resulting in substantial particulate removal, that uses a process in which: 1) a "precoat" cake of diatomaceous earth filter media is deposited on a support membrane (septum), and 2) while the water is filtered by passing through the cake on the septum, additional filter media, known as "body feed," is continuously added to the feed water to maintain the permeability of the filter cake. |
| Diatomaceous Earth: A fine, siliceous (made of silica) "earth" composed mainly of the skeletal remains of dia- toms, a type of free-floating, microscopic plant found in the ocean |
| Dielectric Constant: Related to the force of attraction between two opposite charges separated by a distance in a uniform medium.
|
| Differential Correction: A technique for overcoming GPS position determination errors; GPS receivers are placed at precisely identified control locations to measure the difference between indicated GPS positions versus actual positions.
|
| Differential Input: A signal-input circuit where SIG LO and SIG HI are electrically floating with respect to ANALOG GND (METER GND, which is normally tied to DIG GND). This allows the measurement of the voltage difference between two signals tied to the same ground and provides superior common-mode noise rejection.
|
| Differential Pressure: The difference in static pressure between two identical pressure taps at the same elevation located in two different locations in a primary device.
|
| Differential: For an on/off controller, it refers to the temperature difference between the temperature at which the controller turns heat off and the temperature at which the heat is turned back on. It is expressed in degrees. |
| Diffraction Grating: Material containing many parallel lines very closely spaced that produces a light spectrum by interference.
|
| Diffraction: The bending of a wave around objects placed in its path.
|
| Diffusion: The process by which molecules in a single phase equilibrate to a zero concentration gradient by random molecular motion Brownian motion. The flux of molecules is from regions of high concentration to low concentration and is governed by Ficks Second Law.
|
| Digit: A measure of the display span of a panel meter. By convention, a full digit can assume any value from 0 through 9, a 1/2-digit will display a 1 and overload at 2, a 3/4-digit will display digits up to 3 and overload at 4, etc. For example, a meter with a display span of ?3999 counts is said to be a 3-3/4 digit meter.
|
| Digital Filtering: The process of smoothing, or removing noise from a signal via mathematical functions that are performed on the digital data stream.
|
| Digital Light Processing (DLP): An all digital display technology that turns image data into light. Enabled by a DMD device, DLP is capable of projecting sharp, clear images of almost any size without losing any of the original image resolution.
|
| Digital Output: An output signal which represents the size of an input in the form of a series of discrete quantities.
|
| Digital Readout: Use of numbers to indicate the value or measurement of a variable. The readout of an instrument by a direct, numerical reading of the measured value. |
| Digital Signal Processor (DSP): This technology, when used in conjunction with mixed-signal devices and embedded software, is referred to as a DSP Solution, and it collects, processes, compresses, transmits and displays analog and digital data.
|
| Digital-to-Analog Converter (D/A or DAC) A device or circuit to convert a digital value to an analog signal level. |
| Dilute Solution: A solution that has been made weaker, usually by the addition of water |
| DIN 43760: The standard that defines the characteristics of a 100 ohm platinum RTD having a resistance vs. temperature curve specified by a = 0.00385 ohms per degree.
|
| DIN: A set of German standards recognized throughout the world. The 1/8 DIN standard for panel meters specifies an outer bezel dimension of 96 x 48 mm and a panel cutout of 92 x 45 mm.
|
| Discharge Time Constant: The time required for the output-voltage from a sensor or system to discharge 37% of its original value in response to a zero rise time step function input. This parameter determines a low frequency response.
|
| Disinfectant: Any oxidant, including but not limited to chlorine, chlorine dioxide, chloramines, and ozone, that is added to water in any part of the treatment or distribution process and is intended to kill or inactivate pathogenic microorganisms. |
| Disinfection: The process designed to kill most microorganisms in water, including essentially all pathogenic (disease- causing) bacteria. There are several ways to disinfect, with chlorine being most frequently used in water treatment. |
| Displacement: The measured distance traveled by a point from its position at rest. Peak to peak displacement is the total measured movement of a vibrating point between its positive and negative extremes. Measurement units expressed as inches or millinches.
|
| Display: A device that indicates in human readable form the result of a measurement of some variable. |
| Dissipation Constant: The ratio for a thermistor which relates a change in internal power dissipation to a resultant change of body temperature.
|
| Dissociation Constant (K): A value which quantitatively expresses the extent to which a substance dissociates in solution. The smaller the value of K, the less dissociation of the species in solution. This value varies with temperature, ionic strength, and the nature of the solvent.
|
| Dissonance: Two or more sounds that, when heard together, sound unpleasant.
|
| Distance Piece Haskel Pumps: A section inserted between the air drive and the hydraulic body to seperate them a distance greater then the travel(stroke) of the plunger/piston. The distance piece is vented, so that any leakage from the fluid end will not be able to contaminate the air drive, and visa versa. Many times, the fluid pumped is not compatible with the air drive "O" rings, and could cause swelling which would result in excessive friction and stoppage of the air drive. When critical fluids are used , it also protects the hydraulic section from air drive contaminants such as oil or moisture. The distance piece is also used when the fluids pumped are at temperature that could adversly affect the air drive seals. It provides a distance for heat transfer to minimize ther temperature differential . |
| Distillate: In the distillation of a sample, a portion is evaporated; the part that is condensed afterwards is the distillate. |
| Dithering: The technique of adding controlled amounts of noise to a signal to improve overall system loop control, or to smear quantizing error in an A/D convertor application.
|
| DLL: Dynamic Linked Library |
| DMA: Acronym direct memory access. A high speed data storage mode of the IBM PC.
|
| DNS: Domain Name System. A mechanism used in the Internet for translating names of host computers into addresses. The DNS also allows host computers not directly on the Internet to have registered names in the same style. |
| Domain Name: The unique name that identifies an Internet site. Domain Names always have 2 or more parts, separated by dots. The part on the left is the most specific, and the part on the right is the most general. A given machine may have more than one Domain Name but a given Domain Name points to only one machine. For example, the domain names: matisse.netmail.matisse.networkshop.matisse.netcan all refer to the same machine, but each domain name can refer to no more than one machine. Usually, all of the machines on a given Network will have the same thing as the right-hand portion of their Domain Names (matisse.net in the examples above). It is also possible for a Domain Name to exist but not be connected to an actual machine. This is often done so that a group or business can have an Internet e-mail address without having to establish a real Internet site. In these cases, some real Internet machine must handle the mail on behalf of the listed Domain Name. |
| Doping: The intentional alloying of semiconducting materials with controlled concentrations of donor or acceptor impurities.
|
| Doppler Shift: Change in wavelength due to relative motion source and detector. The change in the wavelength of sound emitted by a moving source. (Ex. Moving Fire Truck Siren, Moving Car Horn, Moving Train.)
|
| Dose-Response Curve: A graphical presentation of the relationship between degree of exposure to a chemical (dose) and observed biological effect or response |
| Dose-Response evaluation: A component of risk assessment that describes the quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease |
| Double Acting Gas Booster, Haskel: A booster designed to discharge gas on both strokes of the cycle. Depending on the check arrangement, the input "suction" of gas can be on both strokes |
| Double Ended Gas Booster, Haskel: A booster having gas sections on both ends of the air drive.It may be "single Stage" (as in the AGD-15) or (two Stage" (as in the AGt-15/30). |
| Double Ended Pump, Haskel: A pump having pumping sections on both ends of the air drive. It is normally "double acting"( as in the GWD -12 series pumps) |
| Double Precision: The degree of accuracy that requires two computer words to represent a number. Numbers are stored with 17 digits of accuracy and printed with up to 16 digits.
|
| Double-Acting Pump, Haskel: A pump designed to discharge fluid on both strokes of the cycle. Depending on the check valve arrangement, the input (suction) of the pumped fluid can be both strokes or only one. |
| Double-Pole, Double-Throw (DPDT): A term used to describe a switch or relay output contact form (form C). Two separate switches that operate simultaneously, each with a normally open and normally closed contact and a common connection. |
| Down Quark (d): The second flavour of quark (in order of increasing mass), with electric charge -1/3. |
| DPD: (pronounce as separate letters). A method of measuring the chlorine residual in water. The residual may be determined by either titrating or comparing a developed color with color standards. DPD stands for N,N-diethyl-p- phenylene-diamine. |
| DRAM: Dynamic Random Access Memory.
|
| Drift: A change of a reading or a set point value over long periods due to several factors including change in ambient temperature, time, and line voltage.
|
| Dripleg: Is a pipe extending downward from the bottom of the airline to collect any condensation flow in the pipe. |
| Droop: A common occurrence in time-proportional controllers. It refers to the difference in temperature between the set point and where the system temperature actually stabilizes due to the time-proportioning action of the controller. |
| Drop: A connection between a terminal and a subscriber. |
| Dry Bulb Temperature: Measured air temperature, usually paired with a "wet-bulb" temperature to derive a value of relative humidity .
|
| DSL - Digital Subscriber Loop: It shares the same phone line as the telephone service, but it uses a different part of the phone line bandwidth. It does not interfere with normal phone service because there is a significant amount of unused capacity in current phone wires. This will enable a person to hook up DSL modems that communicate with a local Internet Service Provider (ISP), but they will still be able to talk on the phone - both the modem and the voice telephone can use a single phone line simultaneously. |
| DSP: Digital signal processing or digital signal processor.
|
| Dual Element Sensor: A sensor assembly with two independent sensing elements.
|
| Dual-Slope A/D Converter: An analog-to-digital converter which integrates the signal for a specific time, then counts time intervals for a reference voltage to bring the integrated signal back to zero. Such converters provide high resolution at low cost, excellent normal-mode noise rejection, and minimal dependence on circuit elements. |
| Ductility: A measure of a materials ability to undergo appreciable plastic deformation before fracture; it may be expressed as percent elongation or percent area reduction from a tensile test.
|
| Duplex Wire: A pair of wires insulated from each other and with an outer jacket of insulation around the inner insulated pair.
|
| Duplex: Pertaining to simultaneous two-way independent data communication transmission in both direction. Same as "full duplex".
|
| Duty Cycle: The total time to one on/off cycle. Usually refers to the on/off cycle time of a temperature controller.
|
| Dynamic Calibration: Calibration in which the input varies over a specific length of time and the output is recorded vs. time |
| Dynamic Pressure: The difference in pressure levels from static pressure to stagnation pressure caused by an increase in velocity. Dynamic pressure increases by the square of the velocity.
|
| Dynamic Range: The range of input or output that a device can process without overflow or distortion |
Additions/Suggestions/Assistance
