Absolute Pressure Transducer: A transducer which measures pressure in relation to zero pressure
(a vacuum on one side of the diaphragm).
Absolute
Pressure: Gage pressure plus atmospheric pressure.
Absolute
Zero: Temperature at which thermal energy is at a minimum. Defined as 0
Kelvin, calculated to be -273.15°C or -459.67°F.
ac:
Alternating current; an electric current that reverses its direction at
regularly recurring intervals.
Acceleration: A
change in the velocity of a body or particle with respect to time. The
parameter that an accelerometer measures (dv/dt). Units expressed in
"g".
Accelerometer: A
device which converts the effects of mechanical motion into an electrical
signal that is proportional to the acceleration value of the motion. A sensor.
A transducer.
Accuracy: The
closeness of an indication or reading of a measurement device to the actual
value of the quantity being measured. Usually expressed as ± percent of full
scale output or reading.
Acoustics: The
degree of sound. The nature, cause, and phenomena of the vibrations of elastic
bodies; which vibrations create compressional waves or wave fronts which are
transmitted through various media, such as air, water, wood, steel, etc.
Activity
(ai): A thermodynamic term for the apparent or active concentration of
a free ion in solution. It is related to concentration by the activity
coefficient.
Activity
Coefficient (fi): A ratio of the activity of species i(ai) to its molality (C). It
is a correction factor which makes the thermodynamic calculations correct. This
factor is dependent on ionic strength, temperature, and other parameters.
Individual
ionic activity coefficients, f+ for cation and f- for an anion, cannot be
derived thermodynamically. They can be calculated only by using the
Debye-Huckel law for low concentration solutions in which the interionic forces
depend primarily on charge, radius, and distribution of the ions and on the
dielectric constant of the medium rather than on the chemical properties of the
ions.
Mean
ionic activity coefficient (f±) or the activity of a salt, on the other hand,
can be measured by a variety of techniques such as freezing point depression
and vapor pressure as well as paired sensing electrodes. It is the geometric
mean of the individual ionic activity coefficients: f± = (f+n+f-n-)1/n
Adapter: A
mechanism or device for attaching non-mating parts.
ADC:
Analog-to-Digital Converter: an electronic device which converts analog signals
to an equivalent digital form, in either a binary code or a
binary-coded-decimal code. When used for dynamic waveforms, the sampling rate
must be high to prevent aliasing errors from occurring.
Address: The
label or number identifying the memory location where a unit of information is
stored.
Aliasing: If the sample
rate of a function (fs) is less than two times the highest frequency value of
the function, the frequency is ambiguously presented. The frequencies above
(fs/2) will be folded back into the lower frequencies producing erroneous data.
Alloy
11: A compensating alloy used in conjunction with pure copper as the
negative leg to form extension wire for platinum-platinum rhodium thermocouples
Types R and S.
Alloy
200/226: The combination of compensating alloys used with tungsten vs.
tungsten 26% rhenium thermocouples as extension cable for applications under
200°C.
Alloy
203/225: The combination of compensating alloys used with tungsten 3%
rhenium vs. tungsten 150 rhenium thermocouples as extension cable for
applications under 200°C.
Alloy
405/426: The combination of compensating alloys used with tungsten 5%
rhenium vs. tungsten 26% rhenium thermocouples as extension cable for
applications under 870°C.
ALOMEGA® An
aluminum nickel alloy used in the negative leg of a type K thermocouple
(registered trademarks of OMEGA ENGINEERING, INC.).
Alphanumeric: A
character set that contains both letters and digits.
ALU:
Arithmetic Logic Unit. The part of a CPU where binary data is acted upon with
mathematical operations.
Alumel: An
aluminum nickel alloy used in the negative leg of a Type K thermocouple (Trade
name of Hoskins Manufacturing Company).
Ambient
Compensation: The design of an instrument such that changes in ambient
temperature do not affect the readings of the instrument.
Ambient
Conditions: The conditions around the transducer (pressure, temperature,
etc.).
Ambient
Pressure: Pressure of the air surrounding a transducer.
Ambient
Temperature: The average or mean temperature of the surrounding air which
comes in contact with the equipment and instruments under test.
Ammeter: An
instrument used to measure current.
Ampere
(amp): A unit used to define the rate of flow of electricity (current)
in a circuit; units are one coulomb (6.28 x 1018 electronics) per
second.
Amplifier: A
device which draws power from a source other than the input signal and which
produces as an output an enlarged reproduction of the essential features of its
input.
Amplitude
Span: The Y-axis range of a graphic display of data in either the time
or frequency domain. Usually a log display (dB) but can also be linear.
Amplitude: A
measurement of the distance from the highest to the lowest excursion of motion,
as in the case of mechanical body in oscillation or the peak-to-peak swing of
an electrical waveform.
Analog
Output: A voltage or current signal that is a continuous function of the
measured parameter.
Analog-to-Digital
Converter (A/D or ADC): A device or circuit that outputs a binary
number corresponding to an analog signal level at the input.
Anemometer: An
instrument for measuring and/or indicating the velocity of air flow.
Angstrom: Ten to
the minus tenth meters (10-10) or one millimicron, a unit used to define the
wave length of light. Designated by the symbol ‰.
Angular
Frequency: The motion of a body or a point moving circularly, referred to as
the circular frequency O which is the frequency in cycles per second (cps)
multiplied by the term (2) and expressed in radians per second (2pf).
Anion: A
negatively charged ion (Cl-, NO3-, S2- etc.)
ANSI:
American National Standards Institute.
Anti-reset
Windup: This is a feature in a three-mode PID controller which prevents
the integral (auto reset) circuit from functioning when the temperature is
outside the proportional band.
Application
Program: A computer program that accomplishes specific tasks, such as word
processing.
ASCII:
American Standard Code for Information Interchange. A seven or eight bit code
used to represent alphanumeric characters. It is the standard code used for
communications between data processing systems and associated equipment.
ASME:
American Society of Mechanical Engineers.
Assembler: A
program that translates assembly language instructions into machine language
instructions.
Assembly
Language: A machine oriented language in which mnemonics are used to
represent each machine language instruction. Each CPU has its own specific
assembly language.
ASTM:
American Society for Testing and Materials.
Asymmetry
Potential: The potential developed across the glass membrane with identical
solutions on both sides. Also a term used when comparing glass electrode
potential in pH 7 buffer.
Asynchronous: A
communication method where data is sent when it is ready without being
referenced to a timing clock, rather than waiting until the receiver signals
that it is ready to receive.
ATC:
Automatic temperature compensation.
Auto-Zero: An
automatic internal correction for offsets and/or drift at zero voltage input.
Automatic
Reset: 1. A feature on a limit controller that automatically resets the
controller when the controlled temperature returns to within the limit
bandwidth set. 2. The integral function on a PID controller which adjusts the
proportional bandwidth with respect to the set point to compensate for droop in
the circuit, i.e., adjusts the controlled temperature to a set point after the
system stabilizes.
AWG:
American Wire Gage.
Axis of
Rotation (Spin Axis): The axis of rotation (spin axis) is that straight line about
which a body rotates.
Background
Noise: The total noise floor from all sources of interference in a
measurement system, independent of the presence of a data signal.
Backup: A
system, device, file or facility that can be used as an alternative in case of
a malfunction or loss of data.
Bandwidth: A
symmetrical region around the set point in which proportional control occurs.
Basic
Transportation Reference: The basic transportation section of the
U.S. Government Test Specification MIL-STD-810D, Method 514.3, Paragraph
I-3.2.1, Page 514.3-5. Basic transportation defines the test profiles that have
been defined for equipment that is shipped as secured cargo; by land, by sea or
by air. The test levels are based upon land transport stress levels because
these are higher than stresses imposed by air or sea transportation
environments.
Basic: A
high-level programming language designed at Dartmouth College
Baud: A unit
of data transmission speed equal to the number of bits (or signal events) per
second; 300 baud = 300 bits per second.
BCD,
Buffered: Binary-coded decimal output with output drivers, to increase
line-drive capability.
BCD,
Parallel: A digital data output format where every decimal digit is
represented by binary signals on four lines and all digits are presented in
parallel. The total number of lines is 4 times the number of decimal digits.
BCD,
Serial: A digital data output format where every decimal digit is
represented by binary signals on four lines and up to five decimal digits are
presented sequentially. The total number of lines is four data lines plus one
strobe line per digit.
BCD,
Three-State: An implementation of parallel BCD, which has 0, 1 and
high-impedance output states. The high-impedance state is used when the BCD
output is not addressed in parallel connect applications.
Bearing: A part
which supports a journal and in which a journal revolves.
Beat
Frequency: Beat frequencies are periodic vibrations that result from the
addition and subtraction of two or more sinusoids. For example, in the case of
two turbine aircraft engines that are rotating at nearly the same frequency but
not precisely at the same frequency; Four frequencies are generated:(f1) the
rotational frequency of turbine one, (f2) the rotational frequency of turbine
two, (f1 + f2) the sum of turbine rotational frequencies one and two, and (f1 -
f2) which is the difference or "beat" frequency of turbines one and
two. The difference of the two frequencies is the lower frequency and is the
one that is "felt" as a beat or "wow" in this case.
Beryllia: BeO
(Beryllium Oxide) A high-temperature mineral insulation material; toxic when in
powder form.
Best Fit
Straight Line (BFSL): A line midway between two parallel straight lines enclosing all
output vs. pressure values.
Beta Ratio: The
ratio of the diameter of a pipeline constriction to the unconstricted pipe
diameter.
BIAS
Current: A very low-level DC current generated by the panel meter and
superimposed on the signal. This current may introduce a measurable offset
across a very high source impedance.
Binary
Coded Decimal (BCD): The representation of a decimal number (base 10, 0 through 9) by
means of a 4 bit binary nibble.
Binary: Refers
to base 2 numbering system, in which the only allowable digits are 0 and 1.
Pertaining to a condition that has only two possible values or states.
BIOS: Acronym
for basic input/output system. The commands used to tell a CPU how it will
communicate with the rest of the computer.
Bipolar: The
ability of a panel meter to display both positive and negative readings.
Bit: Acronym
for binary digit. The smallest unit of computer information, it is either a
binary 0 or 1.
Blackbody: A
theoretical object that radiates the maximum amount of energy at a given
temperature, and absorbs all the energy incident upon it. A blackbody is not
necessarily black. (The name blackbody was chosen because the color black is
defined as the total absorption of light energy.)
BNC: A quick
disconnect electrical connector used to inter-connect and/or terminate coaxial
cables.
Boiling
Point: The temperature at which a substance in the liquid phase
transforms to the gaseous phase; commonly refers to the boiling point of water
which is 100°C (212°F) at sea level.
BPS: Bits
per second.
Breakdown
Voltage Rating: The dc or ac voltage which can be applied across insulation
portions of a transducer without arcing or conduction above a specific current
value.
Bridge
Resistance: See Input impedance and Output impedance.
BTU: British
thermal units. The quantity of thermal energy required to raise one pound of
water at its maximum density, 1 degree F. One BTU is equivalent to .293 watt
hours, or 252 calories. One kilowatt hour is equivalent to 3412 BTU.
Buffer
Capacity (B): A measure of the ability of the solution to resist pH change when
a strong acid or base is added.
Buffer: 1. A
storage area for data that is used to compensate for a speed difference, when
transferring data from one device to another. Usually refers to an area
reserved for I/O operations, into which data is read, or from which data is
written.2. Any substance or combination of substances which, when dissolved in
water, produces a solution which resists a change in its hydrogen ion
concentration on the addition of an acid or alkali.
Bulb
(Liquid-in-Glass Thermometer): The area at the tip of a
liquid-in-glass thermometer containing the liquid reservoir.
Burn-In: A long
term screening test (either vibration, temperature or combined test) that is
effective in weeding out infant mortalities because it simulates actual or
worst case operation of the device, accelerated through a time, power, and
temperature relationship.
Burst
Pressure: The maximum pressure applied to a transducer sensing element or
case without causing leakage.
Burst
Proportioning: A fast-cycling output form on a time proportioning controller
(typically adjustable from 2 to 4 seconds) used in conjunction with a solid
state relay to prolong the life of heaters by minimizing thermal stress.
Bus:
Parallel lines used to transfer signals between devices or components.
Computers are often described by their bus structure (i.e., S-100, IBM PC).
Calender-van
Dusen Equation: An equation that defines the resistance-temperature value of any
pure metal that takes the form of RT = RO(1 + AT + BT2) for values between the
ice point (0°C) and the freezing point of antimony (630.7°C) and the form RT =
RO[1 + AT + BT2 + C(T-100)T2] between the oxygen point (-183.0°C) and the ice
point (0°C).
Calibration: The
process of adjusting an instrument or compiling a deviation chart so that its
reading can be correlated to the actual value being measured.
Calorie: The
quantity of thermal energy required to raise one gram of water 1°C at 15°C.
Cation: A
positively charged ion (Na+, H+).
Cavitation: The
boiling of a liquid caused by a decrease in pressure rather than an increase in
temperature.
Celsius
(centrigrade): A temperature scale defined by 0°C at the ice point and 100°C at
boiling point of water at sea level.
Center
of Gravity (Mass Center
Centripetal
Force: A force exerted on an object moving in a circular path which is
exerted inward toward the center of rotation.
Ceramic
Insulation: High-temperature compositions of metal oxides used to insulate a
pair of thermocouple wires The most common are Alumina (Al2O3), Beryllia (BeO),
and Magnesia (MgO). Their application depends upon temperature and type of
thermocouple. High-purity alumina is required for platinum alloy thermocouples.
Ceramic insulators are available as single and multihole tubes or as beads.
Ceramic:
Polycrystalline ferroelectric materials which are used as the sensing units in
piezoelectric accelerometers. There are many different grades, all of which can
be made in various configurations to satisfy different design requirements.
CFM: The
volumetric flow rate of a liquid or gas in cubic feet per minute.
Character: A
letter, digit or other symbol that is used as the representation of data. A
connected sequence of characters is called a character string.
Charge
Sensitivity: For accelerometers that are rated in terms of charge sensitivity,
the output voltage (V)is proportional to the charge (Q) divided by the shunt
capacitance (C). This type of accelerometer is characterized by a high output
impedance. The sensitivity is given in terms of charge; picocoulombs per unit
of acceleration (g).
Chatter: The
rapid cycling on and off of a relay in a control process due to insufficient
bandwidth in the controller.
CHROMEGA®: A
chromium-nickel alloy which makes up the positive leg of type K and type E
thermocouples (registered trademarks of OMEGA ENGINEERING, INC.).
Clear: To
restore a device to a prescribed initial state, usually the zero state.
Clipping: The
term applied to the phenomenon which occurs when an output signal is limited in
some way by the full range of an amplifier, ADC or other device. When this
occurs, the signal is flattened at the peak values, the signal approaches the
shape of a square wave, and high frequency components are introduced. Clipping
may be hard, as is the case when the signal is strictly limited at some level;
or it may be soft, in which case the clipping signal continues to follow the
input at some reduced gain.
Clock: The
device that generates periodic signals for synchronization.
Closeness
of Control: Total temperature variation from a desired set point of system.
Expressed as "closeness of control" is ±2°C or a system bandwidth
with 4°C, also referred to as amplitude of deviation.
CMR
(Common-Mode Rejection): The ability of a panel meter to eliminate
the effect of AC or DC noise between signal and ground. Normally expressed in
dB at dc to 60 Hz. One type of CMR is specified between SIG LO and PWR GND. In
differential meters, a second type of CMR is specified between SIG LO and ANA
GND (METER GND).
CMV (Common-Mode
Voltage): The AC or DC voltage which is tolerable between signal and
ground. One type of CMV is specified between SIG LO and PWR GND. In
differential meters, a second type of CMV is specified between SIG HI or LO and
ANA GND (METER GND).
Coherence
Function.: A frequency domain function computed to show the degree of a
linear, noise-free relationship between a system's input and output. The value
of the coherence function ranges between zero and one, where a value of zero
indicates there is no causal relationship between the input and the output. A
value of one indicates the existence of linear noise-free frequency response
between the input and the output.
Color
Code: The ANSI established color code for thermocouple wires in the
negative lead is always red. Color Code for base metal thermocouples is yellow
for Type K, black for Type J, purple for Type E and blue for Type T.
Common
Mode Rejection Ratio: The ability of an instrument to reject interference from a common
voltage at its input terminals with relation to ground. Usually expressed in db
(decibels).
Common
Mode: The output form or type of control action used by a temperature
controller to control temperature, i.e. on/off, time proportioning, PID.
Communication:
Transmission and reception of data among data processing equipment and related
peripherals.
Compensated
Connector: A connector made of thermocouple alloys used to connect
thermocouple probes and wires.
Compensating
Alloys: Alloys used to connect thermocouples to instrumentation. These
alloys are selected to have similar thermal electric properties as the
thermocouple alloys (however, only over a very limited temperature range).
Compensating
Loop : Lead wire resistance
compensation for RTD elements where an extra length of wire is run from the
instrument to the RTD and back to the instrument, with no connection to the
RTD.
Compensation: An
addition of specific materials or devices to counteract a known error.
Compiler: A
program that translates a high-level language, such as Basic, into machine
language.
Complex
Function: Any mathematically defined relationship given by the following
expression:
y(x) = a(x) + ib(x)
Where:
x = the real variable
a(x) = the
real part of y(x)
b(x) = the
imaginary part of y(x)
Complex functions are usually expressed in terms of both their
amplitude and phase.
Complex
Wave: The resultant form of a number of sinusoidal waves that are
summed together forming a periodic wave. Such waves may be analyzed in the
frequency domain to readily determine their component parts.
Conductance: The
measure of the ability of a solution to carry an electrical current. (See
Equivalent Conductance)
Conduction: The
conveying of electrical energy or heat through or by means of a conductor.
Confidence
Level: The range (with a specified value of uncertainty, usually
expressed in percent) within which the true value of a measured quantity
exists.
Conformity
Error: For thermocouples and RTDs, the difference between the actual
reading and the temperature shown in published tables for a specific voltage
input.
Connection
Head: An enclosure attached to the end of a thermocouple which can be
cast iron, aluminum or plastic within which the electrical connections are
made.
Constantan: A
copper-nickel alloy used as the negative lead in Type E, Type J, and Type T
thermocouples.
Continuous
Spectrum: A frequency spectrum that is characterized by non-periodic data
The spectrum is continuous in the frequency domain and is characterized by an
infinite number of frequency components.
Control
Character: A character whose occurrence in a particular context starts,
modifies or stops an operation that effects the recording, processing,
transmission or interpretation of data.
Control
Mode: The output form or type of control action used by a temperature
controller to control temperature, i.e., on/off, time proportioning, PID.
Control
Point: The temperature at which a system is to be maintained.
Convection: 1. The
circulatory motion that occurs in a fluid at a non-uniform temperature owing to
the variation of its density and the action of gravity. 2. The transfer of heat
by this automatic circulation of fluid.
Coriolis
Force: A result of centripetal force on a mass moving with a velocity
radially outward in a rotating plane.
Correction
(Balancing) Plane: A plane perpendicular to the shaft axis of a rotor in which
correction for unbalance is made.
Coulomb
Sensitivity: Charge/unit acceleration, expressed in Pc/g (charge sensitivity).
Coulomb: A
measurement of the quantity of electrical charge, usually expressed as pico
coulomb (10-12 coulombs).
Counter
Weight: A weight added to a body so as to reduce a calculated unbalance
at a desired place.
Counts: The
number of time intervals counted by the dual-slope A/D converter and displayed
as the reading of the panel meter, before addition of the decimal point.
CPS: Cycles
per second; the rate or number of periodic events in one second, expressed in
Hertz (Hz).
CPU: Central
processing unit. The part of the computer that contains the circuits that
control and perform the execution of computer instructions.
Critical
Damping: Critical damping is the smallest amount of damping at which a
given system is able to respond to a step function without overshoot.
Critical
Speed: The rotational speed of the rotor or rotating element at which
resonance occurs in the system. The shaft speed at which at least one of the
"critical" or natural frequencies of a shaft is excited.
Cryogenics:
Measurement of temperature at extremely low values, i.e., below -200°C.
CSA:
Canadian Standards Administration.
Cure
Point: The temperature at which a normally magnetic material goes
through a magnetic transformation and becomes non-magnetic.
Current
Proportioning: An output form of a temperature controller which provides a
current proportional to the amount of control required. Normally is a 4 to 20
milliamp current proportioning band.
Current: The
rate of flow of electricity. The unit of the ampere (A) defined as 1 ampere = 1
coulomb per second.
Curve
Fitting: Curve fitting is the process of computing the coefficients of a
function to approximate the values of a given data set within that function.
The approximation is called a "fit". A mathematical function, such as
a least squares regression, is used to judge the accuracy of the fit.
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
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.
g: The
force of acceleration due to gravity equal to 32.1739 ft/sec2 or 386 in./sec2.
Gage
Factor: A measure of the ratio of the relative change of resistance to
the relative change in length of a piezoresistive strain gage.
Gage
Length: The distance between two points where the measurement of strain
occurs.
Gage
Pressure Transducer: A transducer which measures pressure in relation to the ambient
pressure.
Gage
pressure: Absolute pressure minus local atmospheric pressure.
Gain: The
amount of amplification used in an electrical circuit.
Galvanometer: An
instrument that measures small electrical currents by means of deflecting
magnetic coils.
GPH:
Volumetric flow rate in gallons per hour.
GPM:
Volumetric flow rate in gallons per minute.
Ground: 1. The
electrical neutral line having the same potential as the surrounding earth. 2.
The negative side of DC power supply. 3. Reference point for an electrical
system.
Grounded
Junction: A form of construction of a thermocouple probe where the hot or
measuring junction is in electrical contact with the sheath material so that
the sheath and thermocouple will have the same electrical potential.
Half
Bridge: Two active elements or strain gages.
Half-Duplex: One way
at a time data communication; both devices can transmit and receive data, but
only one at a time.
Handshake: An
interface procedure that is based on status/data signals that assure orderly
data transfer as opposed to asynchronous exchange.
Hardcopy: Output
in a permanent form (usually a printout) rather than in temporary form, as on
disk or display terminal.
Hardware: The
electrical, mechanical and electromechanical equipment and parts associated
with a computing system, as opposed to its firmware or software.
Head
Loss: The loss of pressure in a flow system measured using a length
parameter (i.e., inches of water, inches of mercury).
Head
Pressure: Pressure in terms of the height of fluid, P = yrg, where r =
fluid density and y = the fluid column heights. Expression of a pressure in
terms of the height of fluid, r = yrg, where r is fluid density and y = the
fluid column height. g = the acceleration of gravity.
Heat
Sink: 1. Thermodynamic. A body which can absorb thermal energy. 2.
Practical. A finned piece of metal used to dissipate the heat of solid state
components mounted on it.
Heat
Transfer: The process of thermal energy flowing from a body of high energy
to a body of low energy. Means of transfer are: conduction; the two bodies
contact. Convection; a form of conduction where the two bodies in contact are
of different phases, i.e. solid and gas. Radiation: all bodies emit infrared
radiation.
Heat
Treating: A process for treating metals where heating to a specific
temperature and cooling at a specific rate changes the properties of the metal.
Heat: Thermal
energy. Heat is expressed in units of calories or BTU's.
Hertz
(Hz): Units in which frequency is expressed. Synonymous with cycles per
second.
Hexadecimal: Refers
to a base sixteen number system using the characters 0 through 9 and A through
F to represent the values. Machine language programs are often written in
hexadecimal notation.
Hold: Meter
HOLD is an external input which is used to stop the A/D process and freeze the
display. BCD HOLD is an external input used to freeze the BCD output while
allowing the A/D process to continue operation.
Hooke's
Law: Defines the basis for the measurement of mechanical stresses via
the strain measurement. The gradient of Hooke's line is defined by the ratio of
which is equivalent to the Modulus of Elasticity E (Young's Modulus).
Host: The
primary or controlling computer in a multiple part system.
Hydrogen
Ion Activity (aH+): Activity of the hydrogen ion in solution. Related to hydrogen ion
concentration (CH+) by the activity coefficient for hydrogen (f H+).
Hysteresis
(Electrode Memory): When an electrode system is returned to a solution, equilibrium
is usually not immediate. This phenomenon is often observed in electrodes that
have been exposed to the other influences such as temperature, light, or
polarization.
Hysteresis: The
difference in output when the measurand value is first approached with
increasing and then with decreasing values. Expressed in percent of full scale
during any one calibration cycle. See also Deadband.
Icon: A
graphic functional symbol display. A graphic representation of a function or
functions to be performed by the computer.
ICP:
Integrated Circuit Piezoelectric; term sometimes used to describe an
accelerometer with built-in electronics.
Impedance: The
total opposition to electrical flow (resistive plus reactive).
Infrared: An area
in the electromagnetic spectrum extending beyond red light from 760 nanometers
to 1000 microns (106 nm). It is the form of radiation used for making
non-contact temperature measurements.
Initial
Unbalance: Initial unbalance is that unbalance of any kind that exists in
the rotor before balancing.
Input
Impedance: The resistance measured across the excitation terminals of a
transducer.
Input
Impedance: The resistance of a panel meter as seen from the source. In the
case of a voltmeter, this resistance has to be taken into account when the
source impedance is high; in the case of an ammeter, when the source impedance
is low.
Input
Resistance (Impedance): The input resistance of a pH meter is the
resistance between the glass electrode terminal and the reference electrode
terminal. The potential of a pH-measuring electrode chain is always subject to
a voltage division between the total electrode resistance and the input
resistance.
Insulated
Junction: See Ungrounded Junction
Insulation
Resistance: The resistance measured between two insulated points on a
transducer when a specific dc voltage is applied at room temperature.
Integral: A form
of temperature control. See Automatic Reset, #2
Interchangeability
Error: A measurement error that can occur if two or more probes are used
to make the same measurement. It is caused by a slight variation in
characteristics of different probes.
Interface: The
means by which two systems or devices are connected and interact with each
other.
Internal
Reference electrode (Element): The reference electrode placed
internally in a glass electrode.
Interpreter: A
system program that converts and executes each instruction of a high-level
language program into machine code as it runs, before going onto the next
instruction.
Interrupt: To stop
a process in such a way that it can be resumed.
Intrinsically
Safe: An instrument which will not produce any spark or thermal effects
under normal or abnormal conditions that will ignite a specified gas mixture.
Ionic
Mobility: Defined similarly to the mobility of nonelectrolytic particles,
viz., as the speed that the ion obtains in a given solvent when influenced by
unit power.
Ionic
Strength: The weight concentration of ions in solution, computed by
multiplying the concentration of each ion in solution (C) by the corresponding
square of the charge on the ion (Z) summing this product for all ions in
solution and dividing by 2:ionic strength - 1/2 _ Z2 C.
IPTS-48:
International Practical Temperature Scale of 1948. Fixed points in thermometry
as specified by the Ninth General Conference of Weights and Measures which was
held in 1948.
IPTS-68:
International Practical Temperature Scale of 1968. Fixed points in thermometry
set by the 1968 General Conference of Weights and Measures.
ISA:
Instrument Society of America
Isolation: The
reduction of the capacity of a system to respond to an external force by use of
resilient isolating materials.
Isopotential
Point: A potential which is not affected by temperature changes. It is
the pH value at which dE/dt for a given electrode pair is zero. Normally, for a
glass electrode and SCE reference, this potential is obtained approximately
when immersed in pH 7 buffer.
Joule: The
basic unit of thermal energy.
Journal: A
journal is that part of a rotor that is in contact with or supported by a
bearing in which it revolves.
K: When
referring to memory capacity, two to the tenth power (1024 in decimal
notation).
Kelvin: Symbol
K. The unit of absolute or thermodynamic temperature scale based upon the
Celsius scale with 100 units between the ice point and boiling point of water.
0°C = 273.15K (there is no degree (°) symbol used with the Kelvin scale).
Kilowatt
(kw): Equivalent to 1000 watts.
Kilowatt
Hour (kwh): 1000 watthours. Kilovolt amperes (kva): 1000 volt amps.
Kinetic
Energy: Energy associated with mass in motion, i.e., 1/2 rV2 where r is
the density of the moving mass and V is its velocity.
Lag: 1. A
time delay between the output of a signal and the response of the instrument to
which the signal is sent. 2. A time relationship between two waveforms where a
fixed reference point on one wave occurs after the same point of the reference
wave.
Laminar
Flow: Streamlined flow of a fluid where viscous forces are more
significant than inertial forces, generally below a Reynolds number of 2000.
Large
Scale Integration (LSI): The combining of about 1,000 to 10,000
circuits on a single chip. Typical examples of LSI circuits are memory chips
and microprocessor.
Latent
Heat: Expressed in BTU per pound. The amount of heat needed (absorbed)
to convert a pound of boiling water to a pound of steam.
Leakage
Rate: The maximum rate at which a fluid is permitted or determined to
leak through a seal. The type of fluid, the differential Limits of Error: A
tolerance band for the thermal electric response of thermocouple wire expressed
in degrees or percentage defined by ANSI specification MC-96.1 (1975).
Least-squares
Line: The straight line for which the sum of the squares of the
residuals (deviations) is minimized.
Life
Cycle: The minimum number of pressure cycles the transducer can endure
and still remain within a specified tolerance.
Limits
of Error: A tolerance band for the thermal electric response of
thermocouple wire expressed in degrees or percentage defined by ANSI
specification MC-96.1 (1975).
Linearity: The
closeness of a calibration curve to a specified straight line. Linearity is
expressed as the maximum deviation of any calibration point on a specified
straight line during any one calibration cycle.
Liquid
Junction Potential: The potential difference existing between a liquid-liquid
boundary. The sign and size of this potential depends on the composition of the
liquids and the type of junction used.
Load
Impedance: The impedance presented to the output terminals of a transducer
by the associated external circuitry.
Load: The
electrical demand of a process expressed as power (watts), current (amps) or
resistance (ohms).
Logarithmic
Scale: A method of displaying data (in powers of ten) to yield maximum
range while keeping resolution at the low end of the scale.
Loop
Resistance: The total resistance of a thermocouple circuit caused by the
resistance of the thermocouple wire. Usually used in reference to analog
pyrometers which have typical loop resistance requirements of 10 ohms.
LS-TTL
Compatible: For digital input circuits, a logic 1 is obtained for inputs of
2.0 to 5.5 V which can source 20 µA, and a logic 0 is obtained for inputs of 0
to 0.8 V which can sink 400 µA. For digital output signals, a logic 1 is
represented by 2.4 to 5.5 V with a current source capability of at least 400
µA; and a logic 0 is represented by 0 to 0.6 V with a current sink capability
of at least 16 MA. "LS" stands for low-power Schottky.
LS-TTL
Unit Load: A load with LS-TTL voltage levels, which will draw 20 µA for a
logic 1 and -400 µA for a logic 0.
M: Mega;
one million. When referring to memory capacity, two to the twentieth power
(1,048,576 in decimal notation).
Machine
Language: Instructions that are written in binary form that a computer can
execute directly. Also called object code and object language.
Mandrel
(Balancing Arbor): An accurately machined shaft on which work is mounted for
balancing.
Manual
Reset (Adjustment): The adjustment on a proportioning controller which shifts the
proportioning band in relationship to the set point to eliminate droop or
offset errors.
Manual
Reset (Switch): The switch in a limit controller that manually resets the
controller after the limit has been exceeded.
Mass
Flow Rate: Volumetric flowrate times density, i.e. pounds per hour or
kilograms per minute.
Mass
Storage: A device like a disk or magtape that can store large amounts of
data readily accessible to the central processing unit.
Maximum
Elongation: The strain value where a deviation of more than ±5% occurs with
respect to the mean characteristic (diagram of resistance change vs strain).
Maximum
Excitation: The maximum value of excitation voltage or current that can be
applied to the transducer at room conditions without causing damage or
performance degradation beyond specified tolerances.
Maximum
Operating Temperature: The maximum temperature at which an instrument or sensor can be
safely operated.
Maximum
Power Rating: The maximum power in watts that a device can safely handle.
Mean
Ionic Activity Coefficient: See Activity coefficient.
Mean
Temperature: The average of the maximum and minimum temperature of a
processequilibrium.
Measurand: A
physical quantity, property, or condition which is measured.
Measuring
Junction: The thermocouple junction referred to as the hot junction that is
used to measure an unknown temperature.
Mechanical
Hysteresis: The difference of the indication with increasing and decreasing
strain loading, at identical strain values of the specimen.
Medium
Effect (f m): For solvents other than water the medium effect is the activity
coefficient related to the standard state in water at zero concentration. It
reflects differences in the electrostatic and chemical interactions of the ions
with the molecules of various solvents. Solvation is the most significant
interaction.
Melting
Point: The temperature at which a substance transforms from a solid
phase to a liquid phase.
Membrane: The
pH-sensitive glass bulb is the membrane across which the potential difference
due to the formation of double layers with ion-exchange properties on the two
swollen glass surfaces is developed. The membrane makes contact with and
separates the internal element and filling solution from the sample solution.
Method
of Correction: A procedure whereby the mass distribution of a rotor is adjusted
to reduce unbalance, or vibration due to unbalance, to an acceptable value.
Corrections are usually made by adding material to, or removing it from, the
rotor.
Mica: A
transparent mineral used as window material in high-temperature ovens.
Microamp: One
millionth of an ampere, 10-6 amps, µA.
Microcomputer: A
computer which is physically small. It can fit on top of or under a desk; based
on LSI circuitry, computers of this type are now available with much of the
power currently associated with minicomputer systems.
Micron: One
millionth of a meter, 10-6 meters.
Microvolt: One
millionth of a volt, 10-6 volts.
Mil: One
thousandth of an inch (.001").
Milliamp: One
thousandth of an amp, 10-3 amps, symbol mA.
Millimeter: One
thousandth of a meter, symbol mm.
Millivolt: Unit of
electromotive force. It is the difference in potential required to make a
current of 1 millampere flow through a resistance of 1 ohm; one thousandth of a
volt, symbol mV.
Mineral-insulated
Thermocouple: A type of thermocouple cable which has an outer metal sheath and
mineral (magnesium oxide) insulation inside separating a pair of thermocouple
wires from themselves and from the outer sheath. This cable is usually drawn
down to compact the mineral insulation and is available in diameters from .375
to .010 inches. It is ideally suited for high-temperature and severe-duty
applications.
Minor
Scale Division: On an analog scale, the smallest indicated division of units on
the scale.
Modem:
Modulator/Demodulator. A device that transforms digital signals into audio
tones for transmission over telephone lines, and does the reverse for
reception.
Molality: A
measure of concentration expressed in mols per kilogram of solvent.
Monovalent
Ion: An ion with a single positive or negative charge (H+, C1-).
Motherboard: The pc
board of a computer that contains the bus lines and edge connectors to
accommodate other boards in the system. In a microcomputer, the motherboard
contains the microprocessor and connectors for expansion boards.
Mounting
Error: The error resultant from installing the transducer, both
electrical and mechanical.
MSD
(Most-Significant Digit): The leftmost digit of the display.
Multiplex: A
technique which allows different input (or output) signals to use the same
lines at different times, controlled by an external signal. Multiplexing is
used to save on wiring and I/O ports.
N/C (No
Connection): A connector point for which there is no internal connection.
NBS:
National Bureau of Standards.
NEC:
National Electric Codes.
Negative
Temperature Coefficient: A decrease in resistance with an increase
in temperature.
NEMA-4: A
standard from the National Electrical Manufacturers Association, which defines
enclosures intended for indoor or outdoor use primarily to provide a degree of
protection against windblown dust and rain, splashing water, and hose-directed
water.
NEMA-7: A
standard from the National Electrical Manufacturers Association, which defines
explosion-proof enclosures for use in locations classified as Class I, Groups
A, B, C or D, as specified in the National Electrical Code.
NEMA-12: A
standard from the National Electrical Manufacturers Association, which defines
enclosures with protection against dirt, dust, splashes by non-corrosive
liquids, and salt spray.
NEMA-Size
Case: An older US
Nernst
Equation: A mathematical description of electrode behavior: E is the total
potential, in millivolts, developed between the sensing and reference
electrodes; Ex varies with the choice of electrodes, temperature, and pressure:
2.3RT/nF is the Nernst factor (R and F are constants, n is the charge on the
ion, including sign, T is the temperature in degrees Kelvin), and ai is the
activity of the ion to which the electrode is responding.
Nernst
Factor (S, Slope); The term 2.3RT/nF is the Nernst equation, which is equal (at T =
25°C) to 59.16 mV when n = 1 and 29.58 mV when n - 2, and which includes the
sign of the charge on the ion in the term n. The Nerst factor varies with
temperature.
Network: A group
of computers that are connected to each other by communications lines to share
information and resources.
Nibble: One
half of a byte.
Nicrosil/Nisil: A
nickel chrome/nickel silicone thermal alloy used to measure high temperatures.
Inconsistencies in thermoelectric voltages exist in these alloys with respect
to the wire gage.
NMR
(Normal-Mode Rejection): The ability of a panel meter to filter out
noise superimposed on the signal and applied across the SIG HI to SIG LO input
terminals. Normally expressed in dB at 50/60 Hz.
Noise: An
unwanted electrical interference on the signal wires.
Normal
(axial) Stress: The force per unit area on a given plane within a body a = F/A
Normal
Hydrogen Electrode: A reversible hydrogen electrode (Pt) in contact with hydrogen gas
at 1 atmosphere partial pressure and immersed in a solution containing hydrogen
ions at unit activity.
Normal-mode
Rejection Ratio: The ability of an instrument to reject interference usually of
line frequency (50-60 Hz) across its input terminals.
NPT:
National Pipe Thread.
O.D.: Outside
diameter.
Octal:
Pertaining to a base 8 number system.
Offset: The
difference in temperature between the set point and the actual process
temperature. Also, referred to as droop.
ofhc:
Oxygen-free high-conductivity copper. The industrial designation of the pure
copper used in a Type T thermocouple.
Ohmeter: An
instrument used to measure electrical resistance.
On/off
Controller: A controller whose action is fully on or fully off.
Open
Circuit: The lack of electrical contact in any part of the measuring
circuit. An open circuit is usually characterized by rapid large jumps in
displayed potential, followed by an off-scale reading.
Operating
System: A collection of programs that controls the overall operation of a
computer and performs such tasks as assigning places in memory to programs and
data, processing interrupts, scheduling jobs and controlling the overall
input/output of the system.
Operational
pH: The determination of sample pH by relating to pH measurements in
a primary standard solution. This relationship assumes that electrode errors
such as sensitivity and changes in asymmetry potential can be disregarded or
compensated for, provided the liquid junction potential remains constant between
standard and sample.
Optical
Isolation: Two networks which are connected only through an LED transmitter
and photoelectric receiver with no electrical continuity between the two
networks.
Outboard
Rotor: A two-journal rotor which has its center of gravity between the
journals.
Output
Impedance: The resistance as measured on the output terminals of a pressure
transducer.
Output
Noise: The RMS, peak-to-peak (as specified) ac component of a
transducer's dc output in the absence of a measurand variation.
Output: The
electrical signal which is produced by an applied input to the transducer.
Overshoot: The
number of degrees that a process exceeds the set point temperature when coming
up to the set point temperature.
Parallax: An
optical illusion which occurs in analog meters and causes reading errors. It
occurs when the viewing eye is not in the same plane, perpendicular to the
meter face, as the indicating needle.
Parallel
Transmission: Sending all data bits simultaneously. Commonly used for
communications between computers and printer devices.
Parity: A
technique for testing transmitting data. Typically, a binary digit is added to
the data to make the sum of all the digits of the binary data either always
even (even parity) or always odd (odd parity).
Peltier
Effect: When a current flows through a thermocouple junction, heat will
either be absorbed or evolved depending on the direction of current flow. This
effect is independent of joule I2 R heating.
Perfectly
Balanced Rotor: A rotor is perfectly balanced when its mass distribution is such
that it transmits no vibratory force or motion to its bearings as a result of
centrifugal forces.
Peripheral: A
device that is external to the CPU and main memory, i.e., printer, modem or
terminal, but is connected by the appropriate electrical connections.
pH
Junctions: The Junction of a reference electrode or combination electrode is
a permeable membrane through which the fill solution escapes (called the liquid
junction).
pH(S)
(Standard pH Scale): The conventional standard pH scale established on the basis that
an individual ionic activity coefficient can be calculated from the
Debye-H¸ckel law for primary buffers.
Phase
Difference: The time expressed in degrees between the same reference point on
two periodic waveforms.
Phase
Proportioning: A form of temperature control where the power supplied to the
process is controlled by limiting the phase angle of the line voltage.
Phase: A time
based relationship between a periodic function and a reference. In electricity,
it is expressed in angular degrees to describe the voltage or current
relationship of two alternating waveforms.
PID:
Proportional, integral, derivative. A three mode control action where the
controller has time proportioning, integral (auto reset) and derivative rate
action.
Piezoelectric
Accelerometer: A transducer that produces an electrical charge in direct
proportion to the vibratory acceleration.
Piezoresistance:
Resistance that changes with stress.
Pixel: Picture
element. Definable locations on a display screen that are used to form images
on the screen. For graphic displays, screens with more pixels provide higher
resolution.
Plane
Separation: Of a balancing machine, is the operation of reducing the
correction plane interference ratio for a particular rotor.
Platinel: A
non-standard, high temperature platinum thermocouple alloy whose thermoelectric
voltage nearly matches a Type K thermocouple (Trademark of Englehard
Industries).
Platinum
6% Rhodium: The platinum-rhodium alloy used as the negative wire in
conjunction with platinum-30% rhodium to form a Type B thermocouple.
Platinum
10% Rhodium: The platinum-rhodium alloy used as the positive wire in
conjunction with pure platinum to form a Type S thermocouple.
Platinum
13% Rhodium: The platinum-rhodium alloy used as the positive wire in
conjunction with pure platinum to form a Type R thermocouple.
Platinum
30% Rhodium: The platinum-rhodium alloy used as the positive wire in
conjunction with platinum 6% rhodium to form a Type B thermocouple.
Platinum
67: To develop thermal emf tables for thermocouples, the National
Bureau of Standards paired each thermocouple alloy against a pure platinum wire
(designated Platinum 2 prior to 1973, and currently Platinum 67). The thermal
emf's of any alloy combination can be determined by summing the "vs.
Pt-67" emf's of the alloys, i.e., the emf table for a Type K thermocouple
is derived from the Chromel vs. Pt-67 and the Alumel vs. Pt-67 values.
Platinum: A noble
metal which in its pure form is the negative wire of Type R and Type S
thermocouples.
Poisson
Ratio: The ratio between the strain of expansion in the direction of
force and the strain of contraction perpendicular to that force v = -Et/E1.
Polarity: In
electricity, the quality of having two oppositely charged poles, one positive
one negative.
Polarization: The
inability of an electrode to reproduce a reading after a small electrical
current has been passed through the membrane. Glass pH electrodes are
especially prone to polarization errors caused by small currents flowing from
the pH meter input circuit and from static electrical charges built up as the
electrodes are removed from the sample solution, or when the electrodes are
wiped.
Port: A
signal input (access) or output point on a computer.
Positive
Temperature Coefficient: An increase in resistance due to an
increase in temperature.
Potential
Energy: Energy related to the position or height above a place to which
fluid could possibly flow.
Potentiometer: 1. A
variable resistor often used to control a circuit. 2. A balancing bridge used
to measure voltage.
Power
Supply: A separate unit or part of a circuit that supplies power to the
rest of the circuit or to a system.
PPM:
Abbreviation for "parts per million," sometimes used to express temperature
coefficients. For instance, 100 ppm is identical to 0.01%.
Primary
Device: Part of a flowmeter which is mounted internally or externally to
the fluid conduit and produces a signal corresponding to the flowrate and from
which the flow may be determined.
Primary
Standard (NBS): The standard reference units and physical constants maintained by
the National Bureau of Standards upon which all measurement units in the United States
Primary
Standards: Aqueous pH buffer solutions established by the National Bureau of
Standards within the 2.5 to 11.5 pH range of ionic strength less than 0.1 and
which provide stable liquid junction potential and uniformity of electrode
sensitivity.
Principal
Axes: The axes of maximum and minimum normal stress.
Probe: A
generic term that is used to describe many types of temperature sensors.
Process
Meter: A panel meter with sizeable zero and span adjustment
capabilities, which can be scaled for readout in engineering units for signals
such as 4-20 mA, 10-50 mA and 1-5 V.
Program: A list
of instructions that a computer follows to perform a task.
Prom:
Programmable read-only memory. A semiconductor memory whose contents cannot be
changed by the computer after it has been programmed.
Proof
Pressure: The specified pressure which may be applied to the sensing
element of a transducer without causing a permanent change in the output
characteristics.
Proportioning
Band: A temperature band expressed in degrees within which a
temperature controller's time proportioning function is active.
Proportioning
Control Mode: A time proportioning controller where the amount of time that the
relay is energized is dependent upon the system's temperature.
Proportioning
Control plus Derivative Function: A time proportioning controller
with derivative function. The derivative function senses the rate at which a
system's temperature is either increasing or decreasing and adjusts the cycle
time of the controller to minimize overshoot or undershoot.
Proportioning
Control plus Integral: A two-mode controller with time proportioning and integral (auto
reset) action. The integral function automatically adjusts the temperature at
which a system has stabilized back to the setpoint temperature, thereby
eliminating droop in the system.
Proportioning
Control with Integral and Derivative Functions: Three
mode PID controller. A time proportioning 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. 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.
Protection
Head: An enclosure usually made out of metal at the end of a heater or
probe where connections are made.
Protection
Tube: A metal or ceramic tube, closed at one end into which a
temperature sensor is inserted. The tube protects the sensor from the medium
into which it is inserted.
Protocol: A
formal definition that describes how data is to be exchanged.
PSIA: Pounds
per square inch absolute. Pressure referenced to a vacuum.
PSID: Pounds
per square inch differential. Pressure difference between two points.
PSIG: Pound
per square inch gage. Pressure referenced to ambient air pressure.
PSIS: Pounds
per square inch standard. Pressure referenced to a standard atmosphere.
Pulse
Width Modulation: An output in the form of duty cycle which varies as a function of
the applied measurand.
Radiation: See
Infrared
Random
Access Memory (RAM): Memory that can be both read and changed during computer
operation. Unlike other semi-conductor memories, RAM is volatile-if power to
the RAM is disrupted or lost, all the data stored is lost.
Range: Those
values over which a transducer is intended to measure, specified by its upper
and lower limits.
Rangeability: The
ratio of the maximum flowrate to the minimum flowrate of a meter.
Rankine
(°R): An absolute temperature scale based upon the Fahrenheit scale
with 180° between the ice point and boiling point of water. 459.67°R = 0°F.
Rate
Action: The derivative function of a temperature controller.
Rate
time: the time interval over which the system temperature is sampled
for the derivative function.
Ratiometric
Measurement: A measurement technique where an external signal is used to
provide the voltage reference for the dual-slope A/D converter. The external
signal can be derived from the voltage excitation applied to a bridge circuit or
pick-off supply, thereby eliminating errors due to power supply fluctuations.
Read
Only Memory (ROM): Memory that contains fixed data. The computer can read the data,
but cannot change it in any way.
Real
Time: The time interval over which the system temperature is sampled
for the derivative function.
Record: A
collection of unrelated information that is treated as a single unit.
Recovery
Time: The length of time which it takes a transducer to return to
normal after applying a proof pressure.
Redox Potential: The
potential developed by a metallic electrode when placed in a solution
containing a species in two different oxidation states.
Reference
Junction: The cold junction in a thermocouple circuit which is held at a
stable known temperature. The standard reference temperature is 0°C (32°F).
However, other temperatures can be used.
Reference
Mark: Any diagnostic point or mark which can be used to relate a
position during rotation of a part to its location when stopped.
Reference
Plane: Any plane perpendicular to the shaft axis to which an amount of
unbalance is referred.
Refractory
Metal Thermocouple: A class of thermocouples with melting points above 3600°F. The
most common are made from tungsten and tungsten/rhenium alloys Types G and C.
They can be used for measuring high temperatures up to 4000°F (2200°C) in
non-oxidizing, inert, or vacuum environments.
Register: A
storage device with a specific capacity, such as a bit, byte or word.
Relay
(Mechanical): An electromechanical device that completes or interrupts a
circuit by physically moving electrical contacts into contact with each other.
Relay (Solid State
Remote: Not
hard-wired; communicating via switched lines, such as telephone lines. Usually
refers to peripheral devices that are located a site away from the CPU.
Repeatability: The
ability of a transducer to reproduce output readings when the same measurand
value is applied to it consecutively, under the same conditions, and in the
same direction. Repeatability is expressed as the maximum difference between
output readings.
Reserved
Word: A word that has a defined function in the language, and cannot be
used as a variable name.
Residual
(Final) Unbalance: Residual unbalance is that unbalance of any kind that remains
after balancing.
Resistance
Ratio Characteristic: For thermistors, the ratio of the resistance of the thermistor at
25°C to the resistance at 125°C.
Resistance
Temperature Characteristic: A relationship between a thermistor's
resistance and the temperature.
Resistance: The
resistance to the flow of electric current measured in ohms (1/2) for a
conductor. Resistance is function of diameter, resistivity (an intrinsic property
of the material) and length.
Resolution: The
smallest detectable increment of measurement. Resolution is usually limited by
the number of bits used to quantize the input signal. For example, a 12-bit A/D
can resolve to one part in 4096 (2 to the 12 power equals 4096).
Resonant
Frequency: The measurand frequency at which a transducer responds with
maximum amplitude.
Response
Time (time constant): The time required by a sensor to reach 63.2% of a step change in
temperature under a specified set of conditions. Five time constants are
required for the sensor to stabilize at 600 of the step change value.
Response
Time: The length of time required for the output of a transducer to
rise to a specified percentage of its final value as a result of a step change
of input.
Reynolds
Number: The ratio of inertial and viscous forces in a fluid defined by
the formula Re = rVD/µ, where: r = Density of fluid, µ = Viscosity in
centipoise (CP), V = Velocity, and D = Inside diameter of pipe.
RFI: Radio
frequency interference.
Rheostat: A
variable resistor.
Rigid
Rotor: A rotor is considered rigid when it can be corrected in any two
(arbitrarily selected) planes [see "Correction (Balancing)Plane"] and
after that correction, its unbalance does not significantly exceed the
balancing tolerances (relative to the shaft axis) at any speed up to maximum
operating speed and when running under conditions which approximate closely to
those of the final supporting system.
Rise
Time: The time required for a sensor or system to respond to an
instantaneous step function, measured from the 10% to 90% points on the
response waveforms.
Room
Conditions: Ambient environmental conditions under which transducers must
commonly operate.
Root
Mean Square (RMS): Square root of the mean of the square of the signal taken during
one full cycle.
Rotor: A rotor
is a rotating body whose journals are supported by bearings.
Salt
Effect (fx): The effect on the activity coefficient due to salts in the
solution.
SAMA:
Scientific Apparatus Makers Association. An association that has issued
standards covering platinum, nickel, and copper resistance elements (RTDs).
SCE:
Saturated calomel electrode.
SCR:
Ssilicone controlled rectifier.
Scroll: To move
all or part of the screen material up to down, left or right, to allow new
information to appear.
Secondary
Device: A part of the flowmeter which receives a signal proportional to
the flowrate, from the primary device, and displays, records and/or transmits
the signal.
Secondary
Standard: pH buffer solutions which do not meet the requirements of primary
standard solutions but provide coverage of the pH range not covered by primary
standards. Used when the pH value of the primary standard is not close to the
sample pH value.
Seebeck
Coefficient: The derivative (rate of change) of thermal EMF with respect to
temperature normally expressed as millivolts per degree.
Seebeck
Effect: When a circuit is formed by a junction of two dissimilar metals
and the junctions are held at different temperatures, a current will flow in
the circuit caused by the difference in temperature between the two junctions.
Seebeck
EMF: The open circuit voltage caused by the difference in temperature
between the hot and cold junctions of a circuit made from two dissimilar
metals.
Self
Heating: Internal heating of a transducer as a result of power
dissipation.
Sensing
Element: That part of the transducer which reacts directly in response to
the input.
Sensitivity
Shift: A change in slope of the calibration curve due to a change in
sensitivity.
Sensitivity: The
minimum change in input signal to which an instrument can respond.
Sequential
Access: An access mode in which records are retrieved in the same order
in which they were written. Each successive access to the file refers to the
next record in the file.
Serial
transmission: Sending one bit at a time on a single transmission line. Compare
with parallel transmission.
Set
Point: The temperature at which a controller is set to control a system.
Settling
Time: The time taken for the display to settle within one digit final
value when a step is applied to the meter input.
Shear
Modulus: The ratio of the shear stress and the angular shear distortion.
Shear
Stress: Where normal stress is perpendicular to the designated plane,
shear stress is parallel to the plane.
Shearing
Strain: A measure of angular distortion also directly measurable, but not
as easily as axial strain.
Sheath
Thermocouple: A thermocouple made out of mineral-insulated thermocouple cable
which has an outer metal sheath.
SI: System
Internationale. The name given to the standard metric system of units.
Signal
Conditioner: A circuit module which offsets, attenuates, amplifies, linearizes
and/or filters the signal for input to the A/D converter. The typical output
signal conditioner is +2 V dc.
Signal
Conditioning: To process the form or mode of a signal so as to make it
intelligible to, or compatible with, a given device, including such
manipulation as pulse shaping, pulse clipping, compensating, digitizing, and
linearizing.
Signal: An
electrical transmittance (either input or output) that conveys information.
Single
Precision: The degree of numeric accuracy that requires the use of one
computer word. In single precision, seven digits are stored, and up to seven
digits are printed. Contrast with double precision.
Single-ended
Input: A signal-input circuit where SIG LO (or sometimes SIG HI) is tied
to METER GND. Ground loops are normally not a problem in AC-powered meters,
since METER GND is transformer-isolated from AC GND.
Single-Plane
(Static) Balancing Machine: A single plane balancing machine is a
gravitational or centrifugal balancing machine that provides information for
accomplishing single plane balancing.
Slope
(Electrode Sensitivity, Span): See Nernst factor.
Smallest
Bending Radius: The smallest radius that a strain gage can withstand in one
direction, without special treatment, without suffering visible damage.
Software:
Generally, programs loaded into a computer from external mass storage but also
extended to include operating systems and documentation.
Solvation: Ions in
solution are normally combined with at least one molecule of solvent. This
phenomenon is termed solvation.
Source
Code: A non-executable program written in a high-level language. A
compiler or assembler must translate the source code into object code (machine
language) that the computer can understand and process.
Span
Adjustment: The ability to adjust the gain of a process or strain meter so
that a specified display span in engineering units corresponds to a specified
signal span. For instance, a display span of 200°F may correspond to the 16 mA
span of a 4-20 mA transmitter signal.
Span: The
difference between the upper and lower limits of a range expressed in the same
units as the range.
Spare: A
connector point reserved for options, specials, or other configurations. The
point is identified by an (E#) for location on the electrical schematic.
Specific
Gravity: The ratio of mass of any material to the mass of the same volume
of pure water at 4°C.
Specific
Heat: The ratio of thermal energy required to raise the temperature of
a body 1° to the thermal energy required to raise an equal mass of water 1°.
Spectral
Filter: A filter which allows only a specific band width of the
electromagnetic spectrum to pass, i.e., 4 to 8 micron infrared radiation.
Spectrum
Analysis: Utilizing frequency components of a vibration signal to determine
the source and cause of vibration.
Spectrum: The
resolving of overall vibration into amplitude components as a function of
frequency.
Spot
Size: The diameter of the circle formed by the cross section of the
field of view of an optical instrument at a given distance.
Spurious
Error: Random or erratic malfunction.
SSR: Solid
state relay (see relay, solid state).
Stability: The
quality of an instrument or sensor to maintain a consistent output when a
constant input is applied.
Stagnation
Pressure: The sum of the static and dynamic pressure.
Standard
Electrode Potential (E0): The standard potential E0 of an electrode
is the reversible emf between the normal hydrogen electrode and the electrode
with all components at unit activity.
Standardization: a
process of equalizing electrode potentials in one standardizing solution
(buffer) so that potentials developed in unknown solutions can be converted to
pH values.
Static
Calibration: A calibration recording pressure versus output at fixed points at
room temperature.
Static
Error Band: The error band applicable at room temperature.
Static
Pressure: Pressure of a fluid whether in motion or at rest. It can be sensed
in a small hole drilled perpendicular to and flush with the flow boundaries so
as not to disturb the fluid in any way.
Static
Unbalance: Static unbalance is that condition of unbalance for which the
central principal axis is displayed only parallel to the shaft axis
Steady
Flow: A flow rate in the measuring section of a flow line that does not
vary significantly with time.
Steady
State Vibration: That condition of vibration induced by an unchanging continuing
periodic force.
Stiffness: The
ratio of the force required to create a certain deflection or movement of a
part expressed as (Force/deflection) lbs/in or grams/cm.
Stop
Bit: A signal following a character or block that prepares the
receiving device to receive the next character or block.
Strain
Gage: A measuring element for converting force, pressure, tension,
etc., into an electrical signal.
Strain: The
ratio of the change in length to the initial unstressed reference length.
String: A
sequence of characters.
Strouhal
Number: A nondimensional parameter important in vortex meter design
defined as: s = Fh/V where f = frequency, V = velocity, and h = a reference
length
Super
Cooling: The cooling of a liquid below its freezing temperature without
the formation of the solid phase.
Super
Heating: 1. The heating of a liquid above its boiling temperature without
the formation of the gaseous phase. 2. The heating of the gaseous phase
considerably above the boiling-point temperature to improve the thermodynamic
efficiency of a system.
Surge
Current: A current of short duration that occurs when power is first
applied to capacitive loads or temperature dependent resistive loads such as
tungsten or molybdenum heaters-usually lasting no more than several cycles.
Suspension
Effect: The source of error due to varied reference liquid junction
potential depending upon whether the electrodes are immersed in the supernatant
fluid or deeper in the sediment. Normally encountered with solutions containing
resins or charged colloids.
Tape: A
recording media for data or computer programs. Tape can be in permanent form,
such as perforated paper tape, or erasable, such as magnetic tape. Generally,
tape is used as a mass storage medium, in magnetic form, and has a much higher
storage capacity than disk storage, but it takes much longer to write or
recover data from tape than from a disk.
PFA: A
fluorocarbon polymer used for insulation of electrical wires .
Telecommunication: Synonym
for data communication. The transmission of information from one point to
another.
TEMPCO:
Abbreviation for "temperature coefficient": the error introduced by a
change in temperature. Normally expressed in %/°C or ppm/°C.
Temperature
Error: The maximum change in output, at any measurand value within the
specified range, when the transducer temperature is changed from room
temperature to specified temperature extremes.
Terminal: An
input/output device used to enter data into a computer and record the output.
Thermal
Coefficient of Resistance: The change in resistance of a
semiconductor per unit change in temperature over a specific range of
temperature.
Thermal
Conductivity: The property of a material to conduct heat in the form of thermal
energy.
Thermal
emf: See Seebeck emf
Thermal
Expansion: An increase in size due to an increase in temperature expressed
in units of an increase in length or increase in size per degree, i.e.
inches/inch/degree C.
Thermal
Gradient: The distribution of a differential temperature through a body or
across a surface.
Thermal
Sensitivity Shift: The sensitivity shift due to changes of the ambient temperature
from room temperature to the specified limits of the compensated temperature
range.
Thermal
Zero Shift: An error due to changes in ambient temperature in which the zero
pressure output shifts. Thus, the entire calibration curve moves in a parallel
displacement.
Thermistor: A
temperature-sensing element composed of sintered semiconductor material which
exhibits a large change in resistance proportional to a small change in
temperature. Thermistors usually have negative temperature coefficients.
Thermocouple
Type Material
(ANSI Symbol)
J Iron/Constantan
K CHROMEGA®/ALOMEGA®
T Copper/Constantan
E CHROMEGA®/Constantan
R Platinum/Platinum 13% Rhodium
S Platinum/Platinum 10% Rhodium
B Platinum 6% Rhodium/Platinum30% Rhodium
G* Tungsten/Tungsten 26% Rhenium
C* Tungsten 5% Rhenium/Tungsten 26% Rhenium
D* Tungsten 3% Rhenium/Tungsten 150 Rhenium
*Not ANSI symbols.
(ANSI Symbol)
J Iron/Constantan
K CHROMEGA®/ALOMEGA®
T Copper/Constantan
E CHROMEGA®/Constantan
R Platinum/Platinum 13% Rhodium
S Platinum/Platinum 10% Rhodium
B Platinum 6% Rhodium/Platinum30% Rhodium
G* Tungsten/Tungsten 26% Rhenium
C* Tungsten 5% Rhenium/Tungsten 26% Rhenium
D* Tungsten 3% Rhenium/Tungsten 150 Rhenium
*Not ANSI symbols.
Thermocouple: The
junction of two dissimilar metals which has a voltage output proportional to
the difference in temperature between the hot junction and the lead wires (cold
junction) (refer to Seebeck emf).
Thermopile: An
arrangement of thermocouples in series such that alternate junctions are at the
measuring temperature and the reference temperature. This arrangement amplifies
the thermoelectric voltage. Thermopiles are usually used as infrared detectors
in radiation pyrometry.
Thermowell: A
closed-end tube designed to protect temperature sensors from harsh
environments, high pressure, and flows. They can be installed into a system by
pipe thread or welded flange and are usually made of corrosion-resistant metal
or ceramic material depending upon the application.
Thomson
Effect: When current flows through a conductor within a thermal gradient,
a reversible absorption or evolution of heat will occur in the conductor at the
gradient boundaries.
Transducer
Vibration: Generally, any device which converts movement, either shock or
steady state vibration, into an electrical signal proportional to the movement;
a sensor.
Transducer: A
device (or medium) that converts energy from one form to another. The term is
generally applied to devices that take physical phenomenon (pressure,
temperature, humidity, flow, etc.) and convert it to an electrical signal.
Transient
Vibration: A temporary vibration or movement of a mechanical system.
Transitional
Flow: Flow between laminar and turbulent flow, usually between a pipe
Reynolds number of 2000 and 4000.
Transmitter
(Two-Wire): 1. A device which is used to transmit data from a sensor via a
two-wire current loop. The loop has an external power supply and the
transmitter acts as a variable resistor with respect to its input signal. 2. A
device which translates the low level output of a sensor or transducer to a
higher level signal suitable for transmission to a site where it can be further
processed.
Triac: A solid
state switching device used to switch alternating current wave forms.
Triboelectric
Noise: The generation of electrical charges caused by layers of cable
insulation. This is especially troublesome in high impedance accelerometers.
Triple
Point (Water): The thermodynamic state where all three phases, solid, liquid,
and gas may all be present in equilibrium. The triple point of water is .01°C.
Triple
Point: The temperature and pressure at which solid, liquid, and gas phases
of a given substance are all present simultaneously in varying amounts.
True
RMS: The true root-mean-square value of an AC or AC-plus-DC signal,
often used to determine power of a signal. For a perfect sine wave, the RMS
value is 1.11072 times the rectified average value, which is utilized for
low-cost metering. For significantly non-sinusoidal signals, a true RMS
converter is required.
TTL Unit
Load: A load with TTL voltage levels, which will draw 40 µA for a logic
1 and -1.6 mA for a logic 0.
TTL-Compatible: For
digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5 V which
can source 40 µA, and a logic 0 is obtained for inputs of 0 to 0.8 V which can
sink 1.6 mA. For digital output signals, a logic 1 is represented by 2.4 to 5.5
V with a current source capability of at least 400 µA; and a logic 0 is
represented by 0 to 0.6 V with a current sink capability of at least 16 mA.
TTL:
Transistor-to-transistor logic. A form of solid state logic which uses only
transistors to form the logic gates.
Turbulent
Flow: When forces due to inertia are more significant than forces due
to viscosity. This typically occurs with a Reynolds number in excess of 4000.
Typical: Error
is within plus or minus one standard deviation (±1%) of the nominal specified
value, as computed from the total population.
UL:
Underwriters Laboratories, Inc. An independent laboratory that establishes
standards for commercial and industrial products.
Ultraviolet: That
portion of the electromagnetic spectrum below blue light (380 nanometers).
Unbalance: That
condition which exists in a rotor when vibratory force or motion is imparted to
its bearings as a result of centrifugal forces.
Unbalance
Tolerance: The unbalance tolerance with respect to a radial plane (measuring
plane or correction plane) is that amount of unbalance which is specified as
the maximum below which the state of unbalance is considered acceptable.
Undershoot: The
difference in temperature between the temperature a process goes to, below the
set point, after the cooling cycle is turned off and the set point temperature.
Ungrounded
Junction: A form of construction of a thermocouple probe where the hot or
measuring junction is fully enclosed by and insulated from the sheath material.
Vacuum: Any
pressure less than atmospheric pressure.
Velocity: The
time rate of change of displacement; dx/dt.
Vibration
Error Band: The error recorded in output of a transducer when subjected to a
given set of amplitudes and frequencies.
Vibration
Error: The maximum change in output of a transducer when a specific
amplitude and range of frequencies are applied to a specific axis at room
temperature.
Viscosity: The
inherent resistance of a substance to flow.
Volt: The
(electrical) potential difference between two points in a circuit. The
fundamental unit is derived as work per unit charge-(V = W/Q). One volt is the
potential difference required to move one coulomb of charge between two points
in a circuit while using one joule of energy.
Voltage: An
electrical potential which can be measured in volts.
Voltmeter: An
instrument used to measure voltage.
Volume
Flow Rate: Calculated using the area of the full closed conduit and the average
fluid velocity in the form, Q = V x A, to arrive at the total volume quantity
of flow. Q = volumetric flowrate, V = average fluid velocity, and A = cross
sectional area of the pipe.
Watt
Density: The watts emanating from each square inch of heated surface area
of a heater. Expressed in units of watts per square inch.
Wheatstone
Bridge: A network of four resistances, an emf source, and a galvanometer
connected such that when the four resistances are matched, the galvanometer
will show a zero deflection or "null" reading.
Window: In
computer graphics, a defined area in a system not bounded by any limits;
unlimited "space" in graphics.
Word: Number
of bits treated as a single unit by the CPU. In an 8-bit machine, the word
length is 8 bits; in a sixteen bit machine, it is 16 bits.
Working
Standard: A standard of unit measurement calibrated from either a primary
or secondary standard which is used to calibrate other devices or make
comparison measurements.
Young's
Modulus: Young's Modulus (the Modulus of Elasticity) is equivalent to the
ratio of normal stress to strain.
Zero
Adjustment: The ability to adjust the display of a process or strain meter so
that zero on the display corresponds to a non-zero signal, such as 4 mA, 10 mA,
or 1 V dc. The adjustment range is normally expressed in counts.
Zero
Offset: 1. The difference expressed in degrees between true zero and an
indication given by a measuring instrument. 2. See Zero Suppression
Zero
Point: The electrical zero point where zero millivolts would be
displayed. Used in conjunction with the slope control to provide a narrower
range calibration.
Zero
Power Resistance: The resistance of a thermistor or RTD element with no power being
dissipated.
Zero
Suppression: The span of an indicator or chart recorder may be offset from
zero (zero suppressed) such that neither limit of the span will be zero. For
example, a temperature recorder which records a 100° span from 400° to 500° is
said to have 400° zero suppression.
Zero
Voltage Switching: The making or breaking of circuit timed such that the transition
occurs when the voltage wave form crosses zero voltage; typically only found in
solid state switching devices.
Zooming: In computer graphics, causing an object to appear smaller or
larger by moving the window and specifying various window sizes.
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