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
G
galvonometer - a simple device used to measure currents. This device is similar to a simple DC motor
gamma rays - high energy electromagnetic waves resulting from atomic fission or fusion
gate - 1. a circuit that performs on of the Boolean algebra function (i.e., and, or, not, etc.) 2. a connection
between a runner and a part, this can be seen on most injection molded parts as a small bump
where the material entered the main mold cavity
gateway - translates and routes packets between dissimilar networks
Geiger-Mueller tube - a device that can detect ionizing particles (eg, atomic radiation) using a gas filled
tube
global optimum - the absolute best solution to a problem. When found mathematically, the maximum or
minimum cost/utility has been obtained
gpm (gallons per minute) - a flow rate
grafcet - a method for programming PLCs that is based on Petri nets. This is now known as SFCs and is part
of the IEC 1131-3 standard
gray code - a modified binary code used for noisy environments. It is devised to only have one bit change at
any time. Errors then become extremely obvious when counting up or down
ground - a buried conductor that acts to pull system neutral voltage values to a safe and common level. All
electrical equipment should be connected to ground for safety purposes
GUI (Graphical User Interface) - the user interacts with a program through a graphical display, often using a
mouse. This technology replaces the older systems that use menus to allow the user to select
actions.
H
half cell - a probe that will generate a voltage proportional to the hydrogen content in a solution
half duplex - see HDX
handshake - electrical lines used to establish and control communications
hard copy - a paper based printout
hardware - a mechanical or electrical system. The ‘functionality’ is ‘frozen’ in hardware, and often difficult
to change
HDLC (High-level Data Link Control) - an ISO standard for communications
HDX (Half Duplex) - a two way serial connection between two computer. Unlike FDX, characters that are
sent are not reflected back to the sender
head - pressure in a liquid that is the result of gravity
hermetic seal - an airtight seal
hertz - a measure of frequency in cycles per second. The unit is Hz
hex - see hexadecimal
hexadecimal - a base 16 number system where the digits are 0 to 9 then A to F, to give a total of 16 digits
This is commonly used when providing numbers to computers
high - another term used to describe a Boolean true, logical positive, or one
high level language - a language that uses very powerful commands to increase programming productivity
These days almost all applications use some form of high level language (i.e., basic, Fortran,
Pascal, C, C++, etc.)
horsepower - a unit for measuring power
host - a networked (fully functional) computer
hot backup - a system on-line that can quickly replace a failed system
hydraulic - 1. a study of water 2. systems that use fluids to transmit power
hydrocarbon - a class of molecules that contain carbon and hydrogen. Examples are propane, octane
hysteresis - a sticking or lagging phenomenon that occurs in many systems. For example, in magnetic
systems this is a small amount of magnetic repolarization in a reversing field, and in friction this
is an effect based on coulomb friction that reverses sticking force
Hz - see hertz
I
IAB (internet Activities Board) - the developer of internet standards
IC (Integrated Circuit) - a microscopic circuit placed on a thin wafer of semiconductor
IEC (International Electrical Commission) -
IEEE (Institute of Electrical and Electronics Engineers) -
IEEE802 - a set of standards for LANs and MANs
IGES (Initial Graphics Exchange Specification) - a standard for moving data between various CAD systems
In particular the format can handle basic geometric entities, such as NURBS, but it is expected to
be replaced by PDES/STEP in the near future
impact instrument - measurements are made based by striking an object. This generally creates an impulse
function
impedance - In electrical systems this is both reactive and real resistance combined. This also applies to
power transmission and flows in other types of systems
impulse Noise - a short duration, high intensity noise. This type of noise is often associated with explosions
increment - increase a numeric value
inductance - current flowing through a coil will store energy in a magnetic field
inductive heating - a metal part is placed inside a coil. A high frequency AC signal is passed through the coil
and the resulting magnetic field melts the metal
infrared - light that has a frequency below the visible spectrum
inertia - a property where stored energy will keep something in motion unless there is energy added or
released
inference - to make a decision using indirect logic. For example if you are wearing shoes, we can infer that
you had to put them on. Deduction is the complementary concept
inference engine - the part of an expert system that processes rules and facts using forward or backward
chaining
Insertion Loss - barriers, hoods, enclosures, etc. can be placed between a sound source, and listener, their
presence increases reverberant sound levels and decreases direct sound energy. The increase in
the reverberant sound is the insertion loss
instruction set - a list of all of the commands that available in a programmable system. This could be a list of
PLC programming mnemonics, or a list of all of the commands in BASIC
instrument - a device that will read values from external sensors or probes, and might make control decision
intake stroke - in a piston cylinder arrangement this is the cycle where gas or liquid is drawn into the
cylinder
integral control - a control method that looks at the system error over a long period of time. These controllers
are relatively immune to noise and reduce the steady state error, but the do not respond quickly
integrate - to combine two components with clearly separable functions to obtain a new single component
capable of more complex functions
intelligence - systems will often be able to do simple reasoning or adapt. This can mimic some aspects of
human intelligence. These techniques are known as artificial intelligence
intelligent device - a device that contains some ability to control itself. This reduces the number of tasks that
a main computer must perform. This is a form of distributed system
interface - a connection between a computer and another electrical device, or the real world
interlock - a device that will inhibit system operation until certain conditions are met. These are often required
for safety on industrial equipment to protect workers
intermittent noise - when sounds change level fluctuate significantly over a measurement time period
internet - an ad-hoc collection of networks that has evolved over a number of years to now include millions
of computers in every continent, and by now every country. This network will continue to be the
defacto standard for personal users. (commentary: The information revolution has begun already,
and the internet has played a role previously unheard of by overcoming censorship and
misinformation, such as that of Intel about the Pentium bug, a military coup in Russia failed
because they were not able to cut off the flow of information via the internet, the Tiananmen
square massacre and related events were widely reported via internet, etc. The last stage to a
popular acceptance of the internet will be the World Wide Web accessed via Mosaic/Netscape.)
internet address - the unique identifier assigned to each machine on the internet. The address is a 32 bit
binary identifier commonly described with the dotted decimal notation
interlacing - is a technique for saving memory and time in displaying a raster image. Each pass alternately
displays the odd and then the even raster lines. In order to save memory, the odd and even lines
may also contain the same information
interlock - a flag that ensures that concurrent streams of execution do not conflict, or that they cooperate
interpreter - programs that are not converted to machine language, but slowly examined one instruction at a
time as they are executed
interrupt - a computer mechanism for temporarily stopping a program, and running another
inverter - a logic gate that will reverse logic levels from TRUE to/from FALSE
I/O (Input/Output) - a term describing anything that goes into or out of a computer
IOR (Inclusive OR) - a normal OR that will be true when any of the inputs are true in any combinations. also
see Exclusive OR (EOR)
ion - an atom, molecule or subatomic particle that has a positive or negative charge
IP (internet Protocol) - the network layer (OSI model) definitions that allow internet use
IP datagram - a standard unit of information on the internet
ISDN (Integrated Services Digital Network) - a combined protocol to carry voice, data and video over 56KB
lines
ISO (International Standards Organization) - a group that develops international standards in a wide variety
of areas
isolation - electrically isolated systems have no direct connection between two halves of the isolating device
Sound isolation uses barriers to physically separate rooms
isolation transformer - a transformer for isolating AC systems to reduce electrical noise.
J
JEC (Japanese Electrotechnical Committee) - A regional standards group
JIC (Joint International Congress) - an international standards group that focuses on electrical standards
They drafted the relay logic standards
JIT (Just in Time) - a philosophy when setting up and operating a manufacturing system such that materials
required arrive at the worksite just in time to be used. This cuts work in process, storage space,
and a number of other logistical problems, but requires very dependable supplies and methods
jog - a mode where a motor will be advanced while a button is held, but not latched on. It is often used for
clearing jams, and loading new material
jump - a forced branch in a program
jumper - a short wire, or connector to make a permanent setting of hardware parameters.
K
k, K - specifies magnitudes. 1K = 1024, 1k = 1000 for computers, otherwise 1K = 1k = 1000. Note - this is
not universal, so double check the meanings when presented
Kelvin - temperature units that place 0 degrees at absolute zero. The magnitude of one degree is the same as
the Celsius scale
KiloBaud, KBaud, KB, Baud - a transmission rate for serial communications (e.g. RS-232C, TTY, RS-422)
A baud = 1bit/second, 1 Kilobaud = 1KBaud = 1KB = 1000 bits/second. In serial communication
each byte typically requires 11 bits, so the transmission rate is about 1Kbaud/11 = 91 Bytes per
second when using a 1KB transmission
Karnaugh maps - a method of graphically simplifying logic
kermit - a popular tool for transmitting binary and text files over text oriented connections, such as modems
or telnet sessions
keying - small tabs, prongs, or fillers are used to stop connectors from mating when they are improperly
oriented
kinematics/kinetics - is the measure of motion and forces of an object. This analysis is used to measure the
performance of objects under load and/or in motion.
L
label - a name associated with some point in a program to be used by branch instructions
ladder diagram - a form of circuit diagram normally used for electrical control systems
ladder logic - a programming language for PLCs that has been developed to look like relay diagrams from
the preceding technology of relay based controls
laminar flow - all of the particles of a fluid or gas are travelling in parallel. The complement to this is
turbulent flow
laptop - a small computer that can be used on your lap. It contains a monitor ad keyboard
LAN (Local Area Network) - a network that is typically less than 1km in distance. Transmission rates tend
to be high, and costs tend to be low
latch - an element that can have a certain input or output lock in. In PLCs these can hold an output on after
an initial pulse, such as a stop button
LCD (Liquid Crystal Display) - a fluid between two sheets of light can be polarized to block light. These are
commonly used in low power displays, but they require backlighting
leakage current - a small amount of current that will be present when a device is off
LED (Light Emitting Diode) - a semiconductor light that is based on a diode
LIFO (Last In First Out) - similar to FIFO, but the last item pushed onto the stack is the first pulled off
limit switch - a mechanical switch actuated by motion in a process
line printer - an old printer style that prints single lines of text. Most people will be familiar with dot matrix
style of line printers
linear - describes a mathematical characteristic of a system where the differential equations are simple linear
equations with coefficients
little-endian - transmission or storage of data when the least significant byte/bit comes first
load - In electrical system a load is an output that draws current and consumes power. In mechanical systems
it is a mass, or a device that consumes power, such as a turbine
load cell - a device for measuring large forces
logic - 1. the ability to make decisions based on given values. 2. digital circuitry
loop - part of a program that is executed repeatedly, or a cable that connects back to itself
low - a logic negative, or zero
LRC (Linear Redundancy Check) - a block check character
LSB (Least Significant Bit) - This is the bit with the smallest value in a binary number. for example if the
number 10 is converted to binary the result is 1010. The most significant bit is on the left side,
with a value of 8, and the least significant bit is on the right with a value of 1 - but it is not set in
this example
LSD (Least Significant Digit) - This is the least significant digit in a number, found on the right side of a
number when written out. For example, in the number $1,234,567 the digit 7 is the least
significant
LSI (Large Scale Integration) - an integrated circuit that contains thousands of elements
LVDT (Linear Variable Differential Transformer) - a device that can detect linear displacement of a central
sliding core in the transformer.
M
machine language - CPU instructions in numerical form
macro - a set of commands grouped for convenience
magnetic field - a field near flowing electrons that will induce other electrons nearby to flow in the opposite
direction
MAN (Metropolitan Area Network) - a network designed for municipal scale connections
manifold - 1. a connectors that splits the flow of fluid or gas. These are used commonly in hydraulic and
pneumatic systems. 2. a description for a geometry that does not have any infinitely small points
or lines of contact or separation. Most solid modelers deal only with manifold geometry
MAP (Manufacturers Automation Protocol) - a network type designed for the factory floor that was widely
promoted in the 1980s, but was never widely implemented due to high costs and complexity
mask - one binary word (or byte, etc) is used to block out, or add in digits to another binary number
mass flow rate - instead of measuring flow in terms of volume per unit of time we use mass per unit time
mass spectrometer - an instrument that identifies materials and relative proportions at the atomic level. This
is done by observing their deflection as passed through a magnetic field
master/slave - a control scheme where one computer will control one or more slaves. This scheme is used in
interfaces such as GPIB, but is increasingly being replaced with peer-to-peer and client/server
networks
mathematical models - of an object or system predict the performance variable values based upon certain
input conditions. Mathematical models are used during analysis and optimization procedures
matrix - an array of numbers
MB MByte, KB, KByte - a unit of memory commonly used for computers. 1 KiloByte = 1 KByte = 1 KB =
1024 bytes. 1 MegaByte = 1 MByte = 1MB = 1024*1024 bytes
MCR (Master Control Relay) - a relay that will shut down all power to a system
memory - binary numbers are often stored in memory for fast recall by computers. Inexpensive memory can
be purchased in a wide variety of configurations, and is often directly connected to the CPU
memory - memory stores binary (0,1) patterns that a computer can read or write as program or data. Various
types of memories can only be read, some memories lose their contents when power is off
RAM (Random Access Memory) - can be written to and read from quickly
It requires power to preserve the contents, and is often coupled with a
battery or capacitor when long term storage is required. Storage available
is over 1MByte
ROM (Read Only Memory) - Programs and data are permanently written
on this low cost ship. Storage available is over 1 MByte
EPROM (ELECTRICALLY Programmable Read Only Memory) - A program
can be written to this memory using a special programmer, and
erased with ultraviolet light. Storage available over 1MByte. After a program
is written, it does not require power for storage. These chips have
small windows for ultraviolet light
EEPROM/E2PROM (Electronically Erasable Programmable Read Only
Memory) - These chips can be erased and programmed while in use with
a computer, and store memory that is not sensitive to power. These can
be slower, more expensive and with lower capacity (measured in Kbytes)
than other memories. But, their permanent storage allows system configurations/
data to be stored indefinitely after a computer is turned off
memory map - a listing of the addresses of different locations in a computer memory. Very useful when
programming
menu - a multiple choice method of selecting program options
message - a short sequence of data passed between processes
microbar - a pressure unit (1 dyne per sq. cm)
microphone - an audio transducer (sensor) used for sound measurements
microprocessor - the central control chip in a computer. This chip will execute program instructions to direct
the computer
MILNET (MILitary NETwork) - began as part of ARPANET
MMI (Man Machine Interface) - a user interface terminal
mnemonic - a few characters that describe an operation. These allow a user to write programs in an intuitive
manner, and have them easily converted to CPU instructions
MODEM (MOdulator/DEModulator) - a device for bidirectional serial communications over phone lines,
etc
module - a part o a larger system that can be interchanged with others
monitor - an operation mode where the computer can be watched in detail from step to step. This can also
refer to a computer screen
motion detect flow meter - a fluid flow induces measurement
MRP (Material Requirements Planning) - a method for matching material required by jobs, to the equipment
available in the factory
MSD (Most Significant Digit) - the largest valued digit in a number (eg. 6 is the MSD in 63422). This is often
used for binary numbers
MTBF (Mean Time Between Failure) - the average time (hours usually) between the last repair of a product,
and the next expected failure
MTTR (Mean Time To Repair) - The average time that a device will out of use after failure before it is
repaired. This is related to the MTBF
multicast - a broadcast to some, but not necessarily all, hosts on a network
multiplexing - a way to efficiently use transmission media by having many signals run through one
conductor, or one signal split to run through multiple conductors and rejoined at the receiving
end
multiprocessor - a computer or system that uses more than one computer. Normally this term means a single
computer with more than one CPU. This scheme can be used to increase processing speed, or
increase reliability
multivibrator - a digital oscillator producing square or rectangular waveforms. |
