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Programmable logic controllers ( plc) combined glossary of terms.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
abort - the disruption of normal operation
absolute pressure - a pressure measured relative to zero pressure
absorption loss - when sound or vibration energy is lost in a transmitting or reflecting medium. This is the
result of generation of other forms of energy such as heat
absorptive law - a special case of Boolean algebra where A(A+B) becomes A
AC (Alternating Current) - most commonly an electrical current and voltage that changes in a sinusoidal
pattern as a function of time. It is also used for voltages and currents that are not steady (DC)
Electrical power is normally distributed at 60Hz or 50Hz
AC contactor - a contactor designed for AC power
acceptance test - a test for evaluating a newly purchased system’s performance, capabilities, and conformity
to specifications, before accepting, and paying the supplier
accumulator - a temporary data register in a computer CPU
accuracy - the difference between an ideal value and a physically realizable value. The companion to
accuracy is repeatability
acidity - a solution that has an excessive number of hydrogen atoms. Acids are normally corrosive
acoustic - another term for sound
acknowledgement (ACK) - a response that indicates that data has been transmitted correctly
actuator - a device that when activated will result in a mechanical motion. For example a motor, a solenoid
valve, etc
A/D - Analog to digital converter (see ADC)
ADC (Analog to Digital Converter) - a circuit that will convert an analog voltage to a digital value, also
referred to as A/D
ADCCP (Advanced Data Communications Procedure) - ANSI standard for synchronous communication
links with primary and secondary functions
address - a code (often a number) that specifies a location in a computers memory
address register - a pointer to memory locations
adsorption - the ability of a material or apparatus to adsorb energy
agitator - causes fluids or gases to mix
AI (Artificial Intelligence) - the use of computer software to mimic some of the cognitive human processes
algorithms - a software procedure to solve a particular problem
aliasing - in digital systems there are natural limits to resolution and time that can be exceeded, thus aliasing
the data. For example. an event may happen too fast to be noticed, or a point may be too small to
be displayed on a monitor
alkaline - a solution that has an excess of HO pairs will be a base. This is the compliment to an acid
alpha rays - ions that are emitted as the result of atomic fission or fusion
alphanumeric - a sequence of characters that contains both numbers and letters
ALU (Arithmetic Logic Unit) - a part of a computer that is dedicated to mathematical operations
AM (Amplitude Modulation) - a fixed frequency carrier signal that is changed in amplitude to encode a
change in a signal
ambient - normal or current environmental conditions
ambient noise - a sort of background noise that is difficult to isolate, and tends to be present throughout the
volume of interest
ambient temperature - the normal temperature of the design environment
analog signal - a signal that has continuous values, typically voltage
analysis - the process of review to measure some quality
and - a Boolean operation that requires all arguments to be true before the result is true
annealing - heating of metal to relieve internal stresses. In many cases this may soften the material
annotation - a special note added to a design for explanatory purposes
ANSI (American National Standards Institute) - a developer of standards, and a member of ISO
APF (All Plastic Fiber cable) - fiber optic cable that is made of plastic, instead of glass
API (Application Program Interface) - a set of functions, and procedures that describes how a program will
use another service/library/program/etc
APT (Automatically Programmed Tools) - a language used for directing computer controlled machine tools
application - the task which a tool is put to, This normally suggests some level of user or real world
interaction
application layer - the top layer in the OSI model that includes programs the user would run, such as a mail
reader
arc - when the electric field strength exceeds the dielectric breakdown voltage, electrons will flow
architecture - they general layout or design at a higher level
armature - the central rotating portion of a DC motor or generator, or a moving part of a relay
ARPA (Advanced Research Projects Agency) - now DARPA. Originally funded ARPANET
ARPANET - originally sponsored by ARPA. A packet switching network that was in service from the early
1970s, until 1990
ASCII (American Standard Code for Information Interchange) - a set of numerical codes that correspond to
numbers, letters, special characters, and control codes. The most popular standard
ASIC (Application Specific Integrated Circuit) - a specially designed and programmed logic circuit. Used
for medium to low level production of complex functions
aspirator - a device that moves materials with suction
assembler - converts assembly language into machine code
assembly language - a mnemonic set of commands that can be directly converted into commands for a CPU
associative dimensioning - a method for linking dimension elements to elements in a drawing
associative laws - Boolean algebra laws A+(B+C) = (A+B)+C or A(BC) = (AB)C
asynchronous - events that happen on an irregular basis, and are not predictable
asynchronous communications (serial) - strings of characters (often ASCII) are broken down into a series of
on/off bits. These are framed with start/stop bits, and parity checks for error detection, and then
send out one character at a time. The use of start bits allows the characters to be sent out at
irregular times
attenuation - to decrease the magnitude of a signal
attenuation - as the sound/vibration energy propagates, it will undergo losses. The losses are known as
attenuation, and are often measured in dB. For general specifications, the attenuation may be tied
to units of dB/ft
attribute - a nongraphical feature of a part, such as color
audible range - the range of frequencies that the human ear can normally detect from 16 to 20,000 Hz
automatic control - a feedback of a system state is compared to a desired value and the control value for the
system is adjusted by electronics, mechanics and/or computer to compensate for differences
automated - a process that operates without human intervention
auxiliary power - secondary power supplies for remote or isolated systems
AWG (American Wire Gauge) - specifies conductor size. As the number gets larger, the conductors get
smaller
B
B-spline - a fitted curve/surface that is commonly used in CAD and graphic systems
backbone - a central network line that ties together distributed networks
background - in multitasking systems, processes may be running in the background while the user is
working in the foreground, giving the user the impression that they are the only user of the
machine (except when the background job is computationally intensive)
background suppression - the ability of a sensing system to discriminate between the signal of interest, and
background noise or signals
backplane - a circuit board located at the back of a circuit board cabinet. The backplane has connectors that
boards are plugged into as they are added
backup - a redundant system to replace a system that has failed
backward chaining - an expert system looks at the results and looks at the rules to see logically how to get
there
band pressure Level - when measuring the spectrum of a sound, it is generally done by looking at
frequencies in a certain bandwidth. This bandwidth will have a certain pressure value that is an
aggregate for whatever frequencies are in the bandwidth
base - 1. a substance that will have an excess of HO ions in solution form. This will react with an acid. 2. the
base numbering system used. For example base 10 is decimal, base 2 is binary
baseband - a network strategy in which there is a single carrier frequency, that all connected machines must
watch continually, and participate in each transaction
BASIC (Beginner’s All-purpose Symbolic Instruction Code) - a computer language designed to allow easy
use of the computer
batch processing - an outdated method involving running only one program on a computer at once,
sequentially. The only practical use is for very intensive jobs on a supercomputer
battery backup - a battery based power supply that keeps a computer (or only memory) on when the master
power is off
BAUD - The maximum number of bits that may be transmitted through a serial line in one second. This also
includes some overhead bits
baudot code - an old code similar to ASCII for teleprinter machines
BCC (Block Check Character) - a character that can check the validity of the data in a block
BCD (Binary Coded Decimal) - numerical digits (0 to 9) are encoded using 4 bits. This allows two
numerical digits to each byte
beam - a wave of energy waves such as light or sound. A beam implies that it is not radiating in all
directions, and covers an arc or cone of a few degrees
bearing - a mechanical support between two moving surfaces. Common types are ball bearings (light
weight) and roller bearings (heavy weight), journal bearings (rotating shafts)
beats - if two different sound frequencies are mixed, they will generate other frequencies. if a 1000Hz and
1001Hz sound are heard, a 1Hz (=1000-1001) sound will be perceived
benchmark - a figure to compare with. If talking about computers, these are often some numbers that can be
use to do relative rankings of speeds, etc. If talking about design, we can benchmark our products
against our competitors to determine our weaknesses
Bernoulli’s principle - a higher fluid flow rate will result in a lower pressure
beta ratio - a ratio of pipe diameter to orifice diameter
beta rays - electrons are emitted from a fission or fusion reaction
beta site - a software tester who is actually using the software for practical applications, while looking for
bugs. After this stage, software will be released commercially
big-endian - a strategy for storing or transmitting the most significant byte first
BIOS (Basic Input Output System) - a set of basic system calls for accessing hardware, or software services
in a computer. This is typically a level lower than the operating system
binary - a base 2 numbering system with the digits 0 and 1
bit - a single binary digit. Typically the symbols 0 and 1 are used to represent the bit value
bit/nibble/byte/word - binary numbers use a 2 value number system (as opposed to the decimal 0-9, binary
uses 0-1). A bit refers to a single binary digit, and as we add digits we get larger numbers. A bit is
1 digit, a nibble is 4 digits, a byte is 8 digits, and a word is 16 digits
BITNET (Because It’s Time NET) - An academic network that has been merged with CSNET
blackboard - a computer architecture when different computers share a common memory area (each has its
own private area) for sharing/passing information
block - a group of bytes or words
block diagrams - a special diagram for illustrating a control system design
binary - specifies a number system that has 2 digits, or two states
binary number - a collection of binary values that allows numbers to be constructed. A binary number is
base 2, whereas normal numbering systems are base 10
blast furnace - a furnace that generates high temperatures by blowing air into the combustion
bleed nozzle - a valve or nozzle for releasing pressure from a system
block diagram - a symbolic diagram that illustrates a system layout and connection. This can be ued for
analysis, planning and/or programming
BOC (Bell Operating Company) - there are a total of 7 regional telephone companies in the U.S.A
boiler - a device that will boil water into steam by burning fuel
BOM (Bills Of Materials) - list of materials needed in the production of parts, assemblies, etc. These lists are
used to ensure all required materials are available before starting an operation
Boolean - a system of numbers based on logic, instead of real numbers. There are many similarities to
normal mathematics and algebra, but a separate set of operators, axioms, etc. are used
bottom-up design - the opposite of top-down design. In this methodology the most simple/basic functions
are designed first. These simple elements are then combined into more complex elements. This
continues until all of the hierarchical design elements are complete
bounce - switch contacts may not make absolute contact when switching. They make and break contact a
few times as they are coming into contact
Bourdon tube - a pressure tube that converts pressure to displacement
BPS (Bits Per Second) - the total number of bits that can be passed between a sender and listener in one
second. This is also known as the BAUD rate
branch - a command in a program that can cause it to start running elsewhere
bread board - a term used to describe a temporary electronic mounting board. This is used to prototype a
circuit before doing final construction. The main purpose is to verify the basic design
breadth first search - an AI search technique that examines all possible decisions before making the next
move
breakaway torque - the start-up torque. The value is typically high, and is a function of friction, inertia,
deflection, etc
breakdown torque - the maximum torque that an AC motor can produce at the rated voltage and frequency
bridge - 1. an arrangement of (typically 4) balanced resistors used for measurement. 2. A network device
that connects two different networks, and sorts out packets to pass across
broadband networks - multiple frequencies are used with multiplexing to increase the transmission rates in
networks
broad-band noise - the noise spectrum for a particular noise source is spread over a large range of
frequencies
broadcast - a network term that describes a general broadcast that should be delivered to all clients on a
network. For example this is how Ethernet sends all of its packets
brush - a sliding electrical conductor that conducts power to/from a rotor
BSC (Binary Synchronous Communication) - a byte oriented synchronous communication protocol
developed by IBM
BSD (Berkeley Software Distribution) - one of the major versions of UNIX
buffer - a temporary area in which data is stored on its way from one place to another. Used for
communication bottlenecks and asynchronous connections
bugs - hardware or software problems that prevent desired components operation
burn-in - a high temperature pre-operation to expose system problems
burner - a term often used for a device that programs EPROMs, PALs, etc. or a bad cook
bus - a computer has buses (collections of conductors) to move data, addresses, and control signals between
components. For example to get a memory value, the address value provided the binary memory
address, the control bus instructs all the devices to read/write, and to examine the address. If the
address is valid for one part of the computer, it will put a value on the data bus that the CPU can
then read
byte - an 8 bit binary number. The most common unit for modern computers.
C
C - A programming language that followed B (which followed A). It has been widely used in software development in the 80s and 90s. It has grown up to become C++ and Java
CAA (Computer Aided Analysis) - allows the user to input the definition of a part and calculate the
performance variables
cable - a communication wire with electrical and mechanical shielding for harsh environments
CAD (Computer Aided Design) - is the creation and optimization of the design itself using the computer as
a productivity tool. Components of CAD include computer graphics, a user interface, and
geometric modeling
CAD (Computer Aided Drafting) - is one component of CAD which allows the user to input engineering
drawings on the computer screen and print them out to a plotter or other device
CADD (Computer Aided Design Drafting) - the earliest forms of CAD systems were simple electronic
versions of manual drafting, and thus are called CADD
CAE (Computer Aided Engineering) - the use of computers to assist in engineering. One example is the use
of Finite Element Analysis (FEA) to verify the strength of a design
CAM (Computer Aided Manufacturing) - a family of methods that involves computer supported
manufacturing on the factory floor
capacitor - a device for storing energy or mass
capacitance - referring to the ability of a device to store energy. This is used for electrical capacitors, thermal
masses, gas cylinders, etc
capacity - the ability to absorb something else
carrier - a high/low frequency signal that is used to transmit another signal
carry flag - an indication when a mathematical operator has gone past the limitations of the hardware/
software
cascade - a method for connecting devices to increase their range, or connecting things so that they operate
in sequence. This is also called chaining
CASE (Computer Aided Software Engineering) - software tools are used by the developer/programmer to
generate code, track changes, perform testing, and a number of other possible functions
cassette - a holder for audio and data tapes
CCITT (Consultative Committee for International Telegraph and Telephone) - recommended X25. A
member of the ITU of the United Nations
CD-ROM (Compact Disc Read Only Memory) - originally developed for home entertainment, these have
turned out to be high density storage media available for all platforms at very low prices (< $100
at the bottom end). The storage of these drives is well over 500 MB
CE (Concurrent Engineering) - an engineering method that involves people from all stages of a product
design, from marketing to shipping
CE - a mark placed on products to indicate that they conform to the standards set by the European Common
Union
Celsius - a temperature scale the uses 0 as the freezing point of water and 100 as the boiling point
centrifugal force - the force on an orbiting object the would cause it to accelerate outwards
centripetal force - the force that must be applied to an orbiting object so that it will not fly outwards
channel - an independent signal pathway
character - a single byte, that when displayed is some recognizable form, such as a letter in the alphabet, or a
punctuation mark
checksum - when many bytes of data are transmitted, a checksum can be used to check the validity of the
data. It is commonly the numerical sum of all of the bytes transmitted
chip - a loose term for an integrated circuit
chromatography - gases or liquids can be analyzed by how far their constituent parts can migrate through a
porous material
CIM (Computer Integrated Manufacturing) - computers can be used at a higher level to track and guide
products as they move through the facility. CIM may or may not include CAD/CAM
CL (Cutter Location) - an APT program is converted into a set of x-y-z locations stored in a CL file. In turn
these are sent to the NC machine via tapes, etc
clear - a signal or operation to reset data and status values
client-server - a networking model that describes network services, and user programs
clipping - the automatic cutting of lines that project outside the viewing area on a computer screen
clock - a signal from a digital oscillator. This is used to make all of the devices in a digital system work
synchronously
clock speed - the rate at which a computers main time clock works at. The CPU instruction speed is usually
some multiple or fraction of this number, but true program execution speeds are loosely related at
best
closed loop - a system that measures system performance and trims the operation. This is also known as
feedback. If there is no feedback the system is called open loop
CMOS (Complimentary Metal Oxide Semi-conductor) - a low power microchip technology that has high
noise immunity
CNC (Computer Numerical Control) - machine tools are equipped with a control computer, and will perform
a task. The most popular is milling
coalescing - a process for filtering liquids suspended in air. The liquid condenses on glass fibers
coaxial cable - a central wire contains a signal conductor, and an outer shield provides noise immunity. This
configuration is limited by its coaxial geometry, but it provides very high noise immunity
coax - see coaxial cable
cogging - a machine steps through motions in a jerking manner. The result may be low frequency vibration
coil - wire wound into a coil (tightly packed helix) used to create electromagnetic attraction. Used in relays,
motors, solenoids, etc. These are also used alone as inductors
collisions - when more than one network client tries to send a packet at any one time, they will collide. Both
of the packets will be corrupted, and as a result special algorithms and hardware are used to abort
the write, wait for a random time, and retry the transmission. Collisions are a good measure of
network overuse
colorimetry - a method for identifying chemicals using their colors
combustion - a burning process generating heat and light when certain chemicals are added
command - a computer term for a function that has an immediate effect, such as listing the files in a
directory
communication - the transfer of data between computing systems
commutative laws - Booleans algebra laws A+B = B+A and AB=BA
compare - a computer program element that examines one or more variables, determines equality/inequality,
and then performs some action, sometimes a branch
compatibility - a measure of the similarity of a design to a standard. This is often expressed as a percentage
for software. Anything less than 100% is not desirable
compiler - a tool to change a high level language such as C into assembler
compliment - to take the logical negative. TRUE becomes false and vice versa
component - an interchangeable part of a larger system. Components can be used to cut down manufacturing
and maintenance difficulties
compressor - a device that will decrease the volume of a gas - and increase the pressure
computer - a device constructed about a central instruction processor. In general the computer can be
reconfigured (software/firmware/hardware) to perform alternate tasks
Computer Graphics - is the use of the computer to draw pictures using an input device to specify geometry
and other attributes and an output device to display a picture. It allows engineers to communicate
with the computer through geometry
concentric - a shared center between two or more objects
concurrent - two or more activities occur at the same time, but are not necessarily the same
concurrent engineering - all phases of the products life are considered during design, and not later during
design review stages
condenser - a system component that will convert steam to water. Typically used in power generators
conduction - the transfer of energy through some medium
configuration - a numbers of multifunction components can be connected in a variety of configurations
connection - a network term for communication that involves first establishing a connection, second data
transmission, and third closing the connection. Connectionless networking does not require
connection
constant - a number with a value that should not vary
constraints - are performance variables with limits. Constraints are used to specify when a design is feasible
If constraints are not met, the design is not feasible
contact - 1. metal pieces that when touched will allow current to pass, when separated will stop the flow of
current. 2. in PLCs contacts are two vertical lines that represent an input, or internal memory
location
contactor - a high current relay
continuous Noise - a noise that is ongoing, and present. This differentiates from instantaneous, or
intermittent noise sources
continuous Spectrum - a noise has a set of components that are evenly distributed on a spectral graph
control relay - a relay that does not control any external devices directly. It is used like a variable in a high
level programming language
control variable - a system parameter that we can set to change the system operation
controls - a system that is attached to a process. Its purpose is to direct the process to some set value
convection - the transfer of heat energy to liquid or gas that is moving past the surface of an object
cook’s constant - another name for the fudge factor
core memory - an outdated term describing memory made using small torii that could be polarized
magnetically to store data bits. The term lives on when describing some concepts, for example a
‘core dump’ in UNIX. Believe it or not this has not been used for decades but still appears in
many new textbooks
Coriolis force - a force that tends to cause spinning in moving frames of reference. Consider the direction of
the water swirl down a drain pipe, it changes from the north to the south of the earth
correction factor - a formal version of the ‘fudge factor’. Typically a value used to multiply or add another
value to account for hard to quantify values. This is the friend of the factor of safety
counter - a system to count events. This can be either software or hardware
cps (characters per second) - This can be a good measure of printing or data transmission speed, but it is not
commonly used, instead the more confusing ‘baud’ is preferred
CPU (Central Processing Unit) - the main computer element that examines machine code instructions and
executes results
CRC (Cyclic Redundancy Check) - used to check transmitted blocks of data for validity
criteria - are performance variables used to measure the quality of a design. Criteria are usually defined in
terms of degree - for example, lowest cost or smallest volume or lowest stress. Criteria are used to
optimize a design
crosstalk - signals in one conductor induce signals in other conductors, possibly creating false signals
CRT (Cathode Ray Tubes) - are the display device of choice today. A CRT consists of a phosphor-coated
screen and one or more electron guns to draw the screen image
crucible - 1. a vessel for holding high temperature materials 2
CSA (Canadian Standards Association) - an association that develops standards and does some product
testing
CSMA/CD (Carrier Sense Multiple Access with Collision Detection) - a protocol that causes computers to
use the same communication line by waiting for turns. This is used in networks such as Ethernet
CSNET (Computer+Science NETwork) - a large network that was merged with BITNET
CTS (Clear To Send) - used to prevent collisions in asynchronous serial communications
current loop - communications that use a full electronic loop to reduce the effects of induced noise. RS-422
uses this
current rating - this is typically the maximum current that a designer should expect from a system, or the
maximum current that an input will draw. Although some devices will continue to work outside
rated values, not all will, and thus this limit should be observed in a robust system. Note:
exceeding these limits is unsafe, and should be done only under proper engineering conditions
current sink - a device that allow current to flow through to ground when activated
current source - a device that provides current from another source when activated
cursors - are movable trackers on a computer screen which indicate the currently addressed screen position,
or the focus of user input. The cursor is usually represented by an arrow, a flashing character or
cross-hair
customer requirements - the qualitative and quantitative minimums and maximums specified by a customer
These drive the product design process
cycle - one period of a periodic function
cylinder - a piston will be driven in a cylinder for a variety of purposes. The cylinder guides the piston, and
provides a seal between the front and rear of the piston
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