   Glossary D
Damping: The reduction of vibratory movement through dissipation of energy. Types include viscous, coulomb, and solid.

Darlington Pair: Two directly coupled transistors in which the emitter of the first drives the base of the second.

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.

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): A signal with a constant voltage and current.

Debug: To find and correct mistakes in a program.

Decimal: Refers to a base ten number system using the characters 0 through 9 to represent values.

Default: The value(s) or option(s) that are assumed during operation when not specified.

Degree: An incremental value in the temperature scale, i.e., there are 100 degrees 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.

Density: Mass per unit of volume of a substance. I.E.: grams/cu.cm. or pounds/cu.ft.

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.

Deviation: The difference between the value of the controlled variable and the value at which it is being controlled.

Dielectric Constant: Related to the force of attraction between two opposite charges separated by a distance in a uniform medium.

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.

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-to-Analog Converter (D/A or DAC): A device or circuit to convert a digital value to an analog signal level.

Digital Electronics: The branch of electronics dealing with information in binary form.

Digital Output: An output signal which represents the size of an input in the form of a series of discrete quantities.

Digital Phosphor Oscilloscope (DPO): A digitizing oscilloscope that closely models the display characteristics of an analog oscilloscope while providing traditional digitizing oscilloscope benefits (waveform storage, automated measurements, etc.) The DPO uses a parallel processing architecture to pass the signal to the raster-type display. This provides intensity graded viewing characteristics.

Diode: A semiconductor that allows current to flow in one direction only.

Diode drop: The forward voltage developed across a diode when it is operating.

Dipole: A balanced antenna, usually half a wavelength long and fed (or taken off) at its centre.

Direct Current (DC): A current that does not change in direction.

Direct coupled amplifier(dc amplifier): An amplifier in which the output of one stage is coupled to the input of the next without the use of a capacitor. This type of amplifier will amplify Direct Currents and low frequency waveforms.

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.

Discrete: A term used for circuit made up of individual components.

Distortion: The amount by which a circuit or component fails to reproduce accurately the characteristics of the input.

Disk Operating System (DOS): Program used to control the transfer of information to and from a disk, such as MS DOS.

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.

Division: 1) Measurement markings on a scale 2) Measurement markings on the CRT graticule of the oscilloscope.
DMA: Acronym direct memory access. A high speed data storage mode of the IBM PC.

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.

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.

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.

DSP: Digital Signal Processing

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.

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.

Dynamic Calibration: Calibration in which the input varies over a specific length of time and the output is recorded vs. time.