Power Utilities/Power Utilities.iso/utility/pro139/glossary.asc

Text File | 1992-03-14 | 36.6 KB | 1,397 lines

 Permission to upload this ASCII 37K communications glossary has
 been obtained (3/12/92) from QUATECH of Akron, Ohio. A hi-end
 manufacturer of communication, data acquisition and control
 products for the IBM PC/XT, PC/AT, PS/2 Micro Channel and
 compatible systems. They may be contacted at:

        QUATECH
        662 Wolf Ledges Pkwy.
        Akron, Ohio 44311
        Order phone: [phone]   Fax [phone]

 Above note and upload by Dick Sadler of the Golden Gate Computer
 Society, Marin County, California.  BBS no. [phone] 8,N,1



active filter- An electronic filter that combines active circuit
devices, usually amplifiers, with passive circuit elements, such
as resistors and capacitors.  Active filters typically have
characteristics that more closely match ideal filters than do
strictly passive filters.



address- A unique designation for location of data or the
identity of a peripheral device; allows each device on a single
communications line to respond to its own message.



algorithm- A set of rules or detailed plan, with a finite
number of  steps, for solving a problem. An algorithm can be
used  as  a model for a computer program.



alias  frequency- A false lower frequency component that
appears in  analog data reconstructed from original  data
acquired at  an insufficient sampling rate.



analog- Continuous real time phenomena.



analog-to-digital (A/D) conversion-  The process of  changing
an analog signal into a digital value that represents the
magnitude of the signal at the moment of conversion.



analog-to-digital  converter(ADC)- An  electronic  device, often
 an  integrated  circuit, that produces  a  digital  output
directly proportional to an analog signal input.



ANSI- American National Standards Institute.



array- Data  arranged  in  single  or  multidimensional  rows
and columns.



ASCII- American Standard Code for Information Interchange. A
very popular standard method of encoding alphanumeric characters
 into 7 or 8 binary bits.



assembler-   A   program  that  converts  a  list   of
computer instructions written in a specific assembly-language
format  into binary instructions that can be executed by a
specific processor.



assembly-language  program-  A  program  written  directly
with processor commands using mnemonic reprentations of the
commands. The  program  is  then  processed  by  an  assembler
to  produce executable machine code.



asynchronous- A communications protocol where information can
be transmitted  at  an  arbitrary,  unsynchronized  point  in
time, without synchronization to a reference timer or "clock."



attenuation- The decrease in magnitude of a signal.



bandpass  filter- A type of filter that allows a band  of
signal frequencies between two set frequencies to pass while
attenuating all signal frequencies outside the bandpass range.



bandwidth- The range of frequencies available for signaling; the
difference between the highest and lowest frequencies of a band
expressed in Hertz.



base  address-  A  memory  address that  serves  as  a  point
of reference. All other points are located by offsetting (adding
 to or subtracting from) in relation to the base address.



BASIC-   The   most  common  computer  language,  BASIC   is
an abbreviation for Beginners All-purpose Symbolic Instruction
Code. Relies  on  English-like  instructions  which  accounts
for  its popularity and ease of learning.



baud- Unit of signaling speed. The speed in baud is the number
of discrete conditions or events per second. If each event
represents  only one bit condition, baud rate equals bps. When
each event represents more than one bit (e.g., dibit), baud rate
does not equal bps.



baud  rate-  Serial communications data  transmission  rate;
normally the number of bits-per-second.



binary-coded decimal(BCD)- A code for representing decimal
digits in a binary format.



bipolar- A signal range that includes both positive and
negative values.



Bisynchronous Transmission (BSC or BISYNC)- A byte- or
character-oriented communications protocol that has become the
industry standard. It uses a defined set of control characters
for synchronized transmission of binary-coded data between
stations in a data-communications system.



bit (Binary Digit)- Contraction of "binary digit," the smallest
unit of information in a binary system; a true or false
condition.



BIOS (Basic Input/Output System)-A program, usually stored in
ROM, which provides the fundamental services required for the
operation of the computer. These services range from peripheral
control to updating the time of day.



BPS (bits per Second)- Unit of data-transmission rate.



buffer- 1) A temporary-storage device used to compensate for a
difference in data rate and data flow between two devices
(typically a computer and a printer); also called a spooler. 2)
An amplifier to increase the drive capability, current or
distance, of an analog or digital signal.



bus-  A data path shared by many devices (e.g., multipoint line)
with one or more conductors for transmitting signals, data, or
power. In LAN technology, a bus is a type of linear network
topology.



byte-  A  term referring to eight related  bits  of
information. Eight bits equals one byte.



C-  A  programming  language, developed  around  the  concept
of structured  programming,  that  bears  a  strong  resemblance
 to PASCAL.



cache  memory- Fast memory used to improve the performance  of
a CPU. Instructions that will soon be executed are placed in
cache memory shortly before they are needed. This process speeds
up the operation of the CPU.



CAE-  Computer-aided engineering. A computer system designed  to
aid engineering development.



CAM-  Computer-aided  manufacturing. A computer system  used
for automating manufacturing operations.



call- A software instruction used to pass control to a
subroutine of  a program. At the completion of this subroutine,
control  is returned  to  the  original program at the point  of
 the  "call" statement.  Often used for specialized routines
such  as  "analog read" from a data acquisition system or
communication transmission/reception.



CCITT (International Consultative Committee for Telephone and
Telegraph)- An international association that sets worldwide
communications standards (e.g., V.21, V.22, V.22 bis).



central  processing  unit(CPU)- The central part  of  a
computer system  that performs operations on data. In a personal
 computer the CPU is typically a single microprocessor
integrated circuit.



Character- Letter, numeral, punctuation, control figure, or any
other symbol contained in a message.



clock- The source(s) of  timing signals for sequencing
electronic events. (e.g. synchronous data transfer)



code-  As a noun, the text of a computer program. As a  verb,
to "code" means to write a program.



cold-junction  compensation- A method of providing an
artificial reference   level  and  compensation  for   ambient
temperature veriations in thermocouple circuits.



common-mode rejection ratio (CMRR)- A measure of an
instrument's ability to ignore or reject interference from a
voltage common to its input terminals relative to ground. CMRR
is usually expressed in decibels (DB).



communication protocol- The rules governing the exchange of
information between devices on a data link.



comparator- An electronic circuit used to compare two values
and set an indicator that identifies which value is greater.



compiler- A computer program used to translate or interpret a
higher order language into its relocatable or absolute machine
code equilavent.



concurrent-  Software  that  can  perform  more  than  one
task simultaneously.



contact closure- The closing of a switch, often controlled by
an electromagnetic relay.



conversion time- The time required, in an analog input or
output system, from the moment a channel is interrogated (such
as with  a read instruction) to the moment that accurate data is
 available. This  could include: switching time, settling  time,
 acquisition time, A/D conversion time, etc.



coprocessor-  Another  computer processor unit that  operates
in conjunction  with  the  standard  CPU. Can  be  used  to
enhance execution speed. For example, the 8087 is designed to
perform floating point arithmetic.



counter- In software, a memory location used by a program for
the purpose  of counting certain occurrences. In hardware, a
circuit that can count events.



CPU- (See Central Processing Unit)



cross  assembler-  A  computer program  that  translates
machine language code so that it can be read by a different type
of CPU.



crossover- In communications, a conductor which runs through the
cable and connects to a different pin number at each end.



crosstalk-  In communications, a phenomenon in which a signal
in one  or  more  channels interferes with a signal  or  signals
 in other channels. In an analog multiplexer, the ratio of the
output voltage  to  the  input voltage with all  channels
connected  in parallel and turned off.



current  loop-  Communications  method that  allows  data  to
be transmitted over relatively long distances and through
relatively high noise environments. Levels of current, rather
than voltage are detected and translated into binary data.



data  acquisition-  Gathering information from  sources  such
as sensors  and  transducers in an accurate,  timely  and
organized manner.  Modern systems convert this information to
digital  data which can be stored and processed by a computer.



data  reduction- The process of analyzing a large volume of
data to  extract and refine a subset of the data for  some
particular purpose, as in the statistical summarization of data.



DCE (Data Communications Equipment)- Devices that provide the
functions required to establish, maintain, and terminate a
data-transmission connection; e.g., a modem.



debouncing-  Either  a  hardware circuit or a  delay in software
 to prevent false inputs from a bouncing key  or  switch contact.



decibel- A logarithmic measure of the ratio of two signal
levels: dB=20Log10 (V1/V2)=10Log10 (P1/P2).



default- A value assigned or an action taken automatically
unless another is specified.



digital-  A signal which has distinct states.  Digital
computers process data as binary information having either true
or false states.



digital data- Information transmitted in a coded form (from a
computer), represented by discrete signal elements.



digital-to-analog (D/A) conversion- The process of translating
discrete data  into  a  continuously varying signal. Common
uses  are  to present the output of a digital computer as a
graphic display  or as a test stimulus.



digital-to-analog converter(DAC)- A device that converts
digital information into a corresponding analog voltage or
current.



DIP- Acronym for "dual in-line package." A physical form factor
for integrated circuits and switches.



DIP switches- A bank of switches typically used in setting the
hardware configuration and base address of an option card.



direct  memory access(DMA)- A method by which information can
be transferred from the computer memory to a device on the bus
without using the processor.



DOS- Disk operating system.



down-load-  The  copying  of information  from  one  computer
to another.



driver-(hardware) An electronic circuit that provides input to
another electronic circuit.



driver-(software) A program that exercises a system or system
component by simulating the activity of a higher level component.



DSR (Data Set Ready)- A modem interface control signal which
indicates that the terminal is ready for transmission.



DTE (Data Terminal Equipment)- Devices acting as data source,
data sink, or both.



duplex-  The ability to both send and receive data
simultaneously over the same communications line.



dynamic range- The ratio of the full scale range (FSR) of a
data converter  to  the smallest difference it  can  resolve.
Dynamic Range  (DR)=2n. Generally expressed in dB, DR=20log2n.
"n" is  the resolution in bits.



EBCDIC (Extended Binary Coded Decimal Interchange Code)- An
eight-bit character code used primarily in IBM equipment. The
code allows for 256 different bit patterns.



EIA (Electronic Industries Association)- A standards
organization in the U.S.A. specializing in the electrical  and
functional characteristics of interface equipment.

EMI/RFI (Electromagnetic Interference/Radio Frequency
Interference) "Background noise" that could alter or destroy
data transmission.



Emulation- The imitation of a computer system, performed by a
combination of hardware and software, that allows programs to
run between incompatible systems.



even parity- A  data-verification method in which each character
must have an even number of "true" bits.



event counter- A circuit used to count pulses that are related
to the  occurrences of a certain condition. An event counter can
 typically be preset, reset and can totalize.



expansion  board- A plug-in circuit board that adds  features
or capabilities  beyond  those basic to a computer, such as  a
data acquisition system expansion board.



expansion chassis- An enclosure used to increase the
capabilities of a computer system by providing space for
additional  expansion boards.



expansion slots- The spaces provided in a computer for
expansion boards that enhance the basic operation of the
computer.



FCC- Federal Communications Commission.



firmware-  A computer program or software stored permanently in
PROM or ROM or semipermanently in EPROM.



floating-point numbers- Numbers that contain decimal parts or
are represented in scientific notation. Also known as "real"
numbers.



flow control- The procedure for regulating the flow of data
between two devices; prevents the loss of data once a device's
buffer has reached its capacity.

foreground-  In  a  PC system, the  activity  subject  to
direct operator intervention. Other (background) activities
continue  as previously defined.



FORTRAN- FORmula TRANslation. A high level programming typically
used for mathematically intense applications.



front  end- The preprocessing of data before a program  uses
it. Could refer to signal conditioning in a data acquisition
system.



Full Duplex (FDX)- Simultaneous, two-way, independent
transmission in both directions.



gain amplifier- An electronic circuit that allows the input of
low level signals (e.g. thermocouple microphone)



GPIB-  General  Purpose Interface Bus. A standard  bus  used
for controlling   electronic  instruments  with  a   computer.
Also designated IEEE-488.



ground- An electrically neutral circuit having the same
potential as the  surrounding earth. Normally, a non-current
carrying  circuit intended  for  the  safety purposes. A
reference  point  for  an electrical system.



Half Duplex (HDX)- Transmission in either direction, but not
simultaneous.



handshaking- Exchange of predetermined signals between two
devices establishing a connection. Usually part of a
communications protocol.



hardware-  The  visible parts of a computer system, such  as
the circuit boards, chassis, enclosures, peripherals, cables,
etc. It does not include data or computer programs.



HDLC (High-Level Data Link Control)- The international standard
communication protocol defined by ISO.



hertz(Hz)- Cycles per second. A measure of frequency or
bandwidth.



hexadecimal- A numbering system to the base 16.



hierarchical-  A  method  of organizing data  with  a  series
of levels,  each with further subdivisions, as in a pyramid or
tree structure.



high-level  language- A program used to simplify the creation
of computer  code.  Allows the specification of  a  computer
action using fewer steps than assembly language.



IEEE- (Institute of Electrical and Electronic  Engineers)- An
international professional society that issues its own standards
and is a member of ANSI and ISO.



input/output(I/O)- The process of transferring data from or to
a computer  system  including  communication channels, operator
interface devices, or data acquisition and control channels.



instrumentation  amplifier(IA)-  A precision amplifier circuit
with  both high-impedance   differential   inputs   and   high
common-mode rejection.



integer-  A  whole number, not requiring a  fraction,  a
decimal point or scientific notation for representation.



integrating  A/D converter- An A/D conversion technique in
which the  analog  input is integrated over time.  Different
types  of integrating A/D converters include dual slope, triple
slope,  and charge balancing types.



interface- A shared boundary defined by common physical
interconnection characteristics, signal characteristics, and
meanings of interchanged signals.



interpreter-   A  high-level  language  in  which   the
command statements are converted, one at a time and in the order
they are used, into code that can be executed by the processor.



interrupt-  An external event indicating that  the  CPU  should
suspend its current task to service a designated activity.



interrupt  handler-  The section of a program that  performs
the necessary operations to service an interrupt when it occurs.



interrupt service routine- See interrupt handler.



I/O- Input/output, see above.



I/O address- A method that allows the CPU to distinguish
between the different boards in a system. All boards must have
different addresses.



I/O  mapping- Method of connecting I/O devices to the CPU  in
an addressable  fashion  without using memory  space.  Disk
drives, printers and monitors are usually I/O mapped.



ISO- International Standards Organization.



isolation  amplifier-  An  amplifier  with  electrically
isolated inputs  and  outputs  which allow it to  amplify  a
differential signal superimposed on a high common-mode voltage.



isolation  voltage-  The voltage which an  isolated  circuit
can normally  withstand. Isolation voltage is usually specified
from input to input and/or from any input to the amplifier
output,  or to the computer bus.



isothermal-  A process or area that is maintained at  a
constant temperature.



jumper- A wire which connects a number of pins on one end of a
cable only, such as looping back Request to Send from Clear to
Send.



K- Kilo. In referring to computers, a "kilo" is 1024 or 2 to
the 10th power. (Note that it is actually slightly more than an
even 1000.)



latch- A term used to indicate that the state of a digital
signal will remain stored until changed by the CPU or specified
external command signal.



LDM (Limited Distance Modem)- A signal converter which
conditions and boosts a digital signal so that it may be
transmitted further than a standard RS-232 signal.



linearity-  The  adherence of a device's response to  a
straight line relationship. Output is directly proportional to
input.



line driver- A signal converter that conditions a signal to
ensure reliable transmission over an extended distance.



linker- A program which combines different sections of a
compiled program.



listener- A device on the GPIB bus that receives information
from the bus.



Local Area Network (LAN)- A data-communications system confined
to a limited geographic area (typically up to 6 miles or about
10 kilometers) with moderate to high data rates (100 Kbps to 50
Mbps). The area served may consist of a single building, a
cluster of buildings, or a campus-type arrangement. The network
uses some type of switching technology, and does not use common
carrier circuits (i.e. telephone lines) although it may provide
access to other public or private networks.



loopback- Type of diagnostic test in which the transmitted
signal is returned to the sending device after passing through
all, or a portion of, a data-communications link or network. A
loopback test permits the comparison of a returned signal with
the transmitted signal.



machine  language-  Binary code that is executed  directly  by
a computer  CPU  and translated into  electronic  actions.
Machine language is different for each CPU type.



macro- A small set of program steps combined to act as a
single, more powerful, program step.



mainframe- A large-scale computer system that can house
comprehensive software and several peripherals.



Mean Time Between Failures(MTBF)- The average length of time
that a system or component works without failure.



Mean Time to Repair(MTTR)- The average time it takes between
system failure and repair.



memory-  Electronic devices that enable a computer to  store
and recall  information. In its broadest sense, memory refers to
 any hardware  capable  of serving that end, e.g.,  disk,  tape,
 or semiconductor storage.



menu- The list of available functions for selection by the
operator, usually displayed on the computer screen once a
program has been entered.



mnemonics- A method of helping a software programmer remember
the various  commands  of a specific computer  system.  A
relatively easy-to-remember alphabetic code is assigned to each
machine language command  and usually  consists of letters
extracted from, and thus  suggestive of, the command it
symbolizes.



modem(Modulator-Demodulator)- A device used to convert serial
digital data from a transmitting terminal to a signal suitable
for transmission over a common carrier, or to reconvert the
transmitted signal to digital data for acceptance by a receiving
terminal.



modem eliminator- A device used to connect a local terminal and
a computer port in lieu of the pair of modems to which they
would ordinarily connect, allows DTE-to-DTE data and control
signal connections otherwise not easily achieved by standard
cables or connectors.



modular-(hardware) The use of smaller, application specific
components to derrive a customized complete system.



modular-(software) The practice of writing routines to
accomplish a specific task and collecting these routines into a
larger program.



monotonicity- The desirable characteristic of a
digital-to-analog converter to produce a continuously increasing
analog output  for a correspondingly increased digital input
code.



multidrop-  A single communication line or bus used to connect
three  or more points.



multiplexer(mux)- An array of semiconductor or
electromechanical switches with a common output used for
selecting one of a  number of input signals.



multipoint line- See multidrop.



multitasking-  The  characteristic of an  operating  system
and/or CPU that allows a processor to perform several operations
at once.



noise- Unwanted disturbances superimposed upon a useful signal
that tend to obscure its information content.



nonvolatile-  A  memory or data storage device that  retains
its information  content when electrical power is  removed.
Ordinary RAM  is  volatile whereas ROM, bubble  memory,
battery-backed-up CMOS RAM, floppy, and hard disks are
nonvolatile.



null modem- A device that connects two DTE devices directly by
emulating the physical connections of a DTE device. See modem
eliminator.



Nyquist  Sampling  Theorem-  If a  continuous  bandwidth
limited signal  contains no frequency components higher than a
specified frequency  then  the  original signal can  be
recovered  without distortion  if  it  is sampled at a rate of
at  least  twice  the specified frequency.



operating  system(O/S)-  The master control program that
governs  the operation of a computer system. Software of
firmware that manages the  internal  memory allocation and the
control  of  peripheral devices for applications programs.



optical  isolation-  Two  networks  connected  only  through
an optoelectric   transmitter  and  receiver  with   no
electrical continuity between the two networks.



overhead-  The amount of computer processing resources,  such
as time or memory, required to accomplish some task.



parity bit- A bit that is set at "0" or "1" in a character to
ensure that the total number of 1 bits in the data field is even
or odd.



parity check- the addition of noninformation bits that make up a
transmission block to ensure that the total number of 1s is
always either even (even parity) or odd (odd parity); used to
detect transmission errors.



passive   filter-   A  filter  circuit  using   only
resistors, capacitors, and inductors. (No active devices such as
integrated-circuit amplifiers).



Pascal- A high-level programming language originally developed
as a  tool for teaching the concepts of structured  programming.
 It has evolved into a powerful general-purpose language popular
 for writing scientific and business programs.



peripheral- The input/output and data storage devices attached
to a  computer such as disk drives, printers,  keyboards,
displays, data acquisition systems, etc.



PID-  Proportional,  integral, derivative. A  three-mode
control algorithm.



point-to-point(link)- A connection between two, and only two,
pieces of equipment.



polling-  A means of controlling devices on a multipoint line. A
controller will query devices for a response.



port- A place of access to a device or network, used for
input/output of digital and analog signals.



protocol- A formal set of conventions governing the formatting
and relative timing of message exchange between two
communicating systems.



quantizing  error-  The  inherent uncertainty  in  digitizing
an analog  value  due  to the finite resolution  of  the
conversion process.  This  error  can  be reduced  only  by
increasing  the resolution of the converter.



queue- A temporary storage location or list of things to be
done such as messages that are awaiting transmission, or
instruction for the CPU.



RAM (Random Access Memory)- Semiconductor read/write volatile
memory. Data stored is lost if power is removed.



range-  Refers to the maximum allowable full-scale signal
(input or output) that yields a specified performance level.



rate  generator- A device that provides an output pulse at a
software-programmable frequency.



read-only  memory(ROM)-  Computer  memory in which  data  can
be routinely read but written to only once using special means
when  the ROM is manufactured. ROM is used for storing data or
programs (e.g. operating systems) on a permanent basis.



real  numbers- Numbers that can express a fractional value.
Also called floating-point numbers.



real   time-  Data  acted  upon  immediately  instead  of
being accumulated and processed at a later time.



real-world-  Referring  to events, signals  and  conditions
that occur naturally or in everyday life.



repeatability-  The  ability of an instrument to  give  the
same result under repeated identical conditions.



resolution-   The   smallest  significant  number  to   which
a measurement can be determined. For example, a converter with
12-bit resolution can resolve 1 part in 4096.



response time- The elapsed time between the generation of the
last character of a message at a terminal and the receipt of the
first character of the reply. It includes terminal delay and
network delay.



ribbon  cable- A flat cable in which the conductors are  side
by side rather than in a bundle.



ROM- (See read- only memory)



routine-  A  self-contained  program  designed  to  accomplish
a specific task.



RS- Recommended standard. Standards defined for serial data
interchange (e.g. RS-232C) newer designations use "EIA" instead
of "RS" (e.g. EIA-232C).



RS-232C-  A serial asynchronous communications standard  used
to connect  modems, terminals and printers with  serial
interfaces. RS-232C has a specified distance limitation of 50
feet at a maximum data rate of 19,200 baud.



RS-422- Electrical characteristics of balanced-voltage digital
interface circuits. Maximum connection distance of 4000 feet.



RS-423- Electrical characteristics of unbalanced-voltage digital
interface circuits.



RS-449- General purpose 37-pin and 9-pin interface for data
terminal equipment and data circuit-termining equipment,
employing serial binary data interchange.



RS-485- The recommended standard of the Electronic Industry
Association that specifies the electrical characteristics of
drivers and recievers for use in balanced digital multipoint
systems.



RTD-  Resistance  temperature  detector.  An  electrical
circuit element characterized by a positive coefficient of
resistivity.



R/W- Read/write.



sample and hold- A circuit which acquires and stores  an  analog
voltage  for a short period of time. Typically used to stablize
the input of an analog to digital converter during conversion.



sampling theorem- See Nyquist Sampling Theorem.



SDLC (Synchronous Data Link Control)- IBM standard bit oriented
protocol, superseding BSE.



Seebeck effect- The basic principal behind thermocouples. When
a circuit is created by the junctions of two dissimilar metals
and the  junctions  are  held at different  temperatures,  a
current caused by the difference in temperature between the two
junctions will flow in the circuit.



sensitivity-  A measure of the minimum change in an input signal
that an instrument can detect.



sensor-  A  device that responds to a  physical  stimuli (heat,
light, sound, pressure, motion, etc) and produces a
corresponding electrical output.



serial I/O- A common form of data transmission, in which the
bits of each character are sent one at a time over the line.



serial  port- A communications interface that uses one data
line to transfer data bits sequentially. On the IBM PC the
serial port refers to a standard asynchronous serial interface
which uses the 8250/16450 family of UART's.



set point- A "level" or control point in a feedback system.



settling  time-  The time required, after application of  a
step input signal, for the output voltage to settle and remain
within a specified error band around the final value. The
settling  time of a system includes that of all of the
components of the system.



shielding- Protective covering that eliminates electromagnetic
and radio frequency interference.



shielded cable- A cable with foil or other sheathing around it
to stop  radio  frequency  interference  and  magnetic  fields
from generating extraneous signals on the cable conductors.



signal-to-noise  ratio- The  ratio  of signal strength to the
level of noise.



simplex transmission- Data transmission in one direction only.



Simultaneous Sample and Hold (SSH)- A data acquisition system in
 which several  sample and hold circuits are used to sample a
number  of analog  channels  at the same instant. One sample
and  hold  per analog channel is required.



software-  The  non-physical  parts of  a  computer  system
that includes  computer programs such as the operating  system,
high-level languages, applications programs, etc.



span-  The  difference between the lower and upper  limits  of
a range. Span is expressed in the same units as the range.



spike- A transient disturbance of an electrical circuit. (e.g.
lightning or other electrostatic sources.)



spike protector- A device placed in an electrical circuit to
prevent spikes and some surges that might otherwise damage
electronic equipment connected to that circuit.



stability-  The ability of an instrument or sensor to maintain
a consistent output when a constant input is applied.



straight-through pinning- RS-232 and RS-422 configuration that
matches DTE to DCE, pin for pin (pin 1 with pin 1, pin 2 with
pin 2, and so on).



strain relief- A bracket or clamp used to secure a cable so
that it  does not become disconnected accidentally or apply
stress  at the point of connection to the system.



subroutine-  A sequence of computer instructions that  perform
a specific task and can be called repeatedly in a program
whenever that specific task is required.



successive-approximation  A/D  converter-  An
analog-to-digital conversion method that sequentially compares a
series of  binary-weighted values with an analog input to
produce an output digital word  in  "n" steps, where "n" is the
bit resolution of  the  A/D converter.  This  process  is
analogous to  weighing  an  unknown quantity  on  a  balance
scale using a  set  of  binary  standard weights.



surge- A sudden change (usually an increase) in the voltage on
a power line. A surge is similar to a spike, but  is of longer
duration.



synchronization-  The coordination of the activities  of
several circuit elements.



synchronous transmission- Transmission in which data bits are
sent at a fixed rate, with the transmitter and reciever
synchronized. Synchronized transmission eliminates the need for
start and stop bits with every character.



syntax- Comparable to the grammar of a human language, syntax
is the  set  of rules used for forming statements  in  a
particular programming language.



talker- A device on the GPIB bus that simply sends information
on to the bus without actually controlling the bus.



termination- Placement of a connector on a cable.



termination  panel- A circuit board with screw  terminals  or
other  connector  system that allows convenient  connection  of
field signals to a data acquisition or communication system.



throughput  rate-  The maximum repetitive rate at  which  a
data conversion  system can operate with a specified accuracy.
It  is determined by summing the various times required for each
part of the system and then by taking the inverse of this time.



time stamp- Information added to a message, record, or other
unit of  data  indicating the time at which it was  processed
by  the system.



transducer- A device that converts length, position,
temperature, pressure,  level, etc., to a different energy form
(i.e.,  voltage or current).

transient- An abrupt change in voltage, of short duration (e.g.,
a brief pulse caused by the operation of a switch).



triac- A solid-state switching device used to switch
alternating current waveforms.



turnkey-  A  system that combines all the hardware  and
software required for a specific application.



UART- Universal Asynchronous Receiver-Transmitter, see below.



universal asynchronous receiver-transmitter(UART)- An
electronic circuit that translates  the data  format  between a
parallel  representation within the computer and the  serial
method   of transmitting data over a communications line.



uninterruptible  power  supply(UPS)- A  power  conditioning
unit placed  between  the commercial  power service and  the
protected device. The UPS uses line power to charge batteries,
which, in the case of a power failure, can drive electronic
circuitry to produce the appropriate AC requirements for some
time period.



UPS- Uninterruptible power supply, see above.



virtual  memory- A method of making disk storage appear like
RAM memory  to the CPU, thus allowing programs  that need  more
RAM  memory  than is installed to run in the system. This
technique  is slow compared to "real" memory.



volatile  memory- A storage medium that loses all data when
power is removed.



voltage-to-frequency  converter(VFC)- A device which converts
an analog  input  voltage  into a sequence of  digital  pulses
with frequency proportional to the input voltage.



word-  The  standard number of bits that a  processor  or
memory manipulates  at one time. Microprocessors typically use 8
or  16-bit words.



X.21- dYCCITT standard governing interface between data terminal
equipment (DTE) and data circuit terminating equipment (DCE) for
synchronous operation on public data networks.



X.25- CCITT standard governing interface between data terminal
equipment (DTE) and data circuit terminating equipment (DCE) for
terminals operating in the packet mode on public data networks.



X.25 Pad- A device that permits communication between non-X.25
devices and the devices in an X.25 network.



X-ON/X-OFF (Transmitter On/Transmitter Off)- Control characters
used for flow control, instructing a terminal to start
transmission(X-ON) and end transmission(X-OFF).