GLOSSARY
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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Damping: The reduction of vibratory movement through dissipation of energy.
Types include viscous, coulomb, and solid.
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; 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 of the pressure port of a transducer at room temperature and
ambient barometric pressure.
Debug: To find and correct mistakes in a program.
Debye-H¸ckel Equation: Used in relating the activity coefficient (fi) to ion strength (see
Activity coefficient):where I is the ionic strength, A and B the temperature-dependent constants
(see Table A.5), Zi the valence of the ion (i), and  the ion-size parameter in angstroms.
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.
Diaphragm: The sensing element consisting of a membrane which is deformed by the pressure
differential applied across it.
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.
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.
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 Output: An output signal which represents the size of an input in the form of a
series of discrete quantities.
Digital-to-Analog Converter (D/A or DAC): A device or circuit to convert a digital value to
an analog signal level.
DIN (Deutsche Industrial Norm): 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.
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.
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.
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.
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.
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.
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. Usually refers to the on/off cycle time of
a temperature controller.
Dynamic (Two-Plane) Balancing Machine: A dynamic balancing machine is a centrifugal
balancing machine that furnishes information for performing two-plane balancing.
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 Unbalance: Dynamic unbalance is that condition in which the central principal axis
is not coincident with the shaft axis.
Echo: To reflect received data to the sender. For example, keys depressed
on a keyboard are usually echoed as characters displayed on the screen.
Electrical Interference: Electrical noise induced upon the signal wires that obscures the
wanted information signal.
Electrode Potential (E): The difference in potential established between an electrode and a
solution when the electrode is immersed in the solution.
Electrode: See Isopotential point.
Electrolyte: Any substance which, when in solution will conduct an electric current. Acids,
bases, and salts are common electrolytes.
Electromotive Force (emf): The potential difference between the two electrodes in a cell.
The cell emf is the cell voltage measured when no current is flowing through the cell. It can be
measured by means of a pH meter with high input impedance.
Electronic Industries Association (EIA): A standards organization specializing in the
electrical and functional characteristics of interface equipment.
EMF: Electromotive force. A rise in (electrical) potential energy. The principal unit is
the volt.
EMI: Electromagnetic interference.
Emissivity: The ratio of energy emitted by an object to the energy emitted by a blackbody
at the same temperature. The emissivity of an object depends upon its material and surface texture; a
polished metal surface can have an emissivity around 0.2 and a piece of wood can have an emissivity
around 0.95.
End Point (Potentiometric): The apparent equivalence point of a titration at which a
relatively large potential change is observed.
End Points: The end points of a full scale calibration curve.
Endothermic: Absorbs heat. A process is said to be endothermic when it absorbs heat.
Enthalpy: The sum of the internal energy of a body and the product of its volume multiplied
by the pressure.
Environmental Conditions: All conditions in which a transducer may be exposed during
shipping, storage, handling, and operation.
Eprom: Erasable Programmable Read-Only Memory. The PROM can be erased by ultraviolet light
or electricity.
Equilibrium Constant: The product of the concentrations (or activities) of the substances
produced at equilibrium in a chemical reaction divided by the product of concentrations of the
reacting substances, each concentration raised to that power which is the coefficient of the
substance in the chemical equation.
Equitransference: Equal diffusion rates of the positively and negatively charged ions of an
electrolyte across a liquid junction without charge separation.
Equivalent Conductance (l): Equivalent conductance of an electrolyte is defined as the
conductance of a volume of solution containing one equivalent weight of dissolved substances when
placed between two parallel electrodes 1 cm apart, and large enough to contain between them all of
the solution. l is never determined directly, but is calculated from the specific conductance (Ls).
If C is the concentration of a solution in gram equivalents per liter, then the concentration of a
solution in gram equivalents per liter, then the concentration per cubic centimeter is C/1000, and
the volume containing one equivalent of the solute, is, therefore, 1000/C.
Error Band: The allowable deviations to output from a specific reference norm. Usually
expressed as a percentage of full scale.
Error: The difference between the value indicated by the transducer and the true value of
the measurand being sensed. Usually expressed in percent of full scale output.
Eutectic Temperature: The lowest possible melting point of a mixture of alloys.
Excitation: The external application of electrical voltage current applied to a transducer
for normal operation.
Exothermic: Gives off heat. A process is said to be exothermic when it releases heat.
Expansion Factor: Correction factor for the change in density between two pressure
measurement areas in a constricted flow.
Explosion-proof Enclosure: An enclosure that can withstand an explosion of gases within it
and prevent the explosion of gases surrounding it due to sparks, flashes or the explosion of the
container itself, and maintain an external temperature which will not ignite the surrounding gases.
Exposed Junction: A form of construction of a thermocouple probe where the hot or measuring
junction protrudes beyond the sheath material so as to be fully exposed to the medium being measured.
This form of construction usually gives the fastest response time.
Fahrenheit: A temperature scale defined by 32° at the ice point and
212° at the boiling point of water at sea level.
Ferrule: A compressible tubular fitting that is compressed onto a probe inside a
compression fitting to form a gas-tight seal.
Field Balancing Equipment: An assembly of measuring instruments for performing balancing
operations on assembled machinery which is not mounted in a balancing machine.
Field of View: A volume in space defined by an angular cone extending from the focal plane
of an instrument.
File: A set of related records or data treated as a unit.
Filling Solution: A solution of defined composition to make contact between an internal
element and a membrane or sample. The solution sealed inside a pH glass bulb is called an internal
filling solution. This solution normally contains a buffered chloride solution to provide a stable
potential and a designated zero potential point. The solution which surrounds the reference electrode
internal and periodically requires replenishing is called the reference filling solution. It provides
contact between the reference electrode internal and sample through a junction.
Firmware: Programs stored in PROMs.
Flag: Any of various types of indicators used for identification of a condition or event;
for example, a character that signals the termination of a transmission.
Floppy Disk: A small, flexible disk carrying a magnetic medium in which digital data is
stored for later retrieval and use.
Flow Rate: Actual speed or velocity of fluid movement .
Flow: Travel of liquids or gases in response to a force (i.e. pressure or gravity).
Flowmeter: A device used for measuring the flow or quantity of a moving fluid.
FM Approved: An instrument that meets a specific set of specifications established by
Factory Mutual Research Corporation.
FM: Factory Mutual Research Corporation. An organization which sets industrial safety
standards.
Forced Vibration: Vibration of a system caused by an imposed force. Steady-state vibration
is an unchanging condition of periodic or random motion.
FORTRAN: Formula Translation language. A widely used high-level programming language well
suited to problems that can be expressed in terms of algebraic formulas. It is generally used in
scientific applications.
FPM: Flow velocity in feet per minute.
FPS: Flow velocity in feet per second.
Freezing Point: The temperature at which the substance goes from the liquid phase to the
solid phase.
Frequency Modulated Output: A transducer output which is obtained in the form of a
deviation from a center frequency, where the deviation is proportional to the applied stimulus.
Frequency of Vibration: The number of cycles occurring in a given unit of time. RPM -
revolutions per minute. CPM- cycles per minute.
Frequency Output: An output in the form of frequency which varies as a function of the
applied input.
Frequency, Natural: The frequency of free (not forced) oscillations of the sensing element
of a fully assembled transducer.
Frequency: The number of cycles over a specified time period over which an event occurs.
The reciprocal is called the period.
Full Bridge: A Wheatstone bridge configuration utilizing four active elements or strain
gages.
Full Scale Output: The algebraic difference between the minimum output and maximum output.
Functions: Three mode PID controller. A timeproportioning controller with integral and
derivative functions. The integral function automatically adjusts the system temperature to the set
point temperature to eliminate droop due to the time proportioning function.
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