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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
S
safety margin - a factor of safety between calculated maximums and rated maximums
SCADA (Supervisory Control And Data Acquisition) - computer remote monitoring and control of
processes
scan-time - the time required for a PLC to perform one pass of the ladder logic
schematic - an abstract drawing showing components in a design as simple figures. The figures drawn are
often the essential functional elements that must be considered in engineering calculations
scintillation - when some materials are high by high energy particles visible light or electromagnetic
radiation is produced
SCR (Silicon Controlled Rectifier) - a semiconductor that can switch AC loads
SDLC (Synchronous Data-Link Control) - IBM oriented data flow protocol with error checking
self-diagnosis - a self check sequence performed by many operation critical devices
sensitivity - the ability of a system to detect a change
sensor - a device that is externally connected to survey electrical or mechanical phenomena, and convert
them to electrical or digital values for control or monitoring of systems
serial communication - elements are sent one after another. This method reduces cabling costs, but typically
also reduces speed, etc
serial design - is the traditional design method. The steps in the design are performed in serial sequence. For
example, first the geometry is specified, then the analysis is performed, and finally the
manufacturability is evaluated
servo - a device that will take a desired operation input and amplify the power
session layer - an OSI network model layer
setpoint - a desired value for a controlled system
shield - a grounded conducting barrier that steps the propagation of electromagnetic waves
Siemens - a measure of electrical conductivity
signal conditioning - to prepare an input signal for use in a device through filtering, amplification,
integration, differentiation, etc
simplex - single direction communication at any one time
simulation - a model of the product/process/etc is used to estimate the performance. This step comes before
the more costly implementation steps that must follow
single-discipline team - a team assembled for a single purpose
single pole - a switch or relay that can only be opened or closed. See also single pole
single throw - a switch that will only switch one line. This is the simplest configuration
sinking - using a device that when active will allow current to flow through it to ground. This is
complimented by sourcing
SLIP (Serial Line internet Protocol) - a method to run the internet Protocol (IP) over serial lines, such as
modem connections
slip-ring - a connector that allows indefinite rotations, but maintains electrical contacts for passing power
and electrical signals
slurry - a liquid with suspended particles
SMTP (Simple Mail Transfer Protocol) - the basic connection protocol for passing mail on the internet
snubber - a circuit that suppresses a sudden spike in voltage or current so that it will not damage other
devices
software - a program, often stored on non-permanent media
solenoid - an actuator that uses a magnetic coil, and a lump of ferrous material. When the coil is energized a
linear motion will occur
solid state - circuitry constructed entirely of semiconductors, and passive devices. (i.e., no gas as in tubes)
sonar - sound waves are emitted and travel through gas/liquid. they are reflected by solid objects, and then
detects back at the source. The travel time determines the distance to the object
sound - vibrations in the air travel as waves. As these waves strike the human ear, or other surfaces, the
compression, and rarefaction of the air induces vibrations. In humans these vibrations induce
perceived sound, in mechanical devices they manifest as distributed forces
sound absorption - as sound energy travels through, or reflects off a surface it must induce motion of the
propagating medium. This induced motion will result in losses, largely heat, that will reduce the
amplitude of the sound
sound analyzer - measurements can be made by setting the instrument for a certain bandwidth, and centre
frequency. The measurement then encompasses the values over that range
sound level - a legally useful measure of sound, weighted for the human ear. Use dBA, dBB, dBC values
sound level meter - an instrument for measuring sound exposure values
source - an element in a system that supplies energy
sourcing - an output that when active will allow current to flow from a voltage source out to a device. It is
complimented by sinking
specific gravity - the ratio between the density of a liquid/solid and water or a gas and air
spectrometer - determines the index of refraction of materials
spectrophotometer - measures the intensities of light at different points in the spectrum
spectrum - any periodic (and random) signal can be described as a collection of frequencies using a
spectrum. The spectrum uses signal power, or intensity, plotted against frequency
spherical wave - a wave travels outward as if on the surface of an expanding sphere, starting from a point
source
SQL (Structured Query Language) - a standard language for interrogating relational databases
standing wave - if a wave travels from a source, and is reflected back such that it arrives back at the source
in phase, it can undergo superposition, and effectively amplify the sound from the source
static head - the hydrostatic pressure at the bottom of a water tank
steady state - describes a system response after a long period of time. In other words the transient effects
have had time to dissipate
STEP (Standard for the Exchange of Product model data) - a standard that will allow transfer of solid model
data (as well as others) between dissimilar CAD systems
step response - a typical test of system behavior that uses a sudden step input change with a measured
response
stoichiometry - the general field that deals with balancing chemical equations
strain gauge - a wire mounted on a surface that will be stretched as the surface is strained. As the wire is
stretched, the cross section is reduced, and the proportional change in resistance can be measured
to estimate strain
strut - a two force structural member
subroutine - a reusable segment of a program that is called repeatedly
substrate - the base piece of a semiconductor that the layers are added to
switching - refers to devices that are purely on or off. Clearly this calls for discrete state devices
synchronous - two or more events happen at predictable times
synchronous motor - an AC motor. These motors tend to keep a near constant speed regardless of load
syntax error - an error that is fundamentally wrong in a language
synthesis - is the specification of values for the design variables. The engineer synthesizes a design and then
evaluates its performance using analysis
system - a complex collection of components that performs a set of functions.
T
T1 - a 1.54 Mbps network data link
T3 - a 45 Mbps network data link. This can be done with parallel T1 lines and packet switching
tap - a connection to a power line
tare - the ratio between unloaded and loaded weights
TCP (Transmission Control Protocol) - a transport layer protocol that ensures reliable data communication
when using IP communications. The protocol is connection oriented, with full duplex streams
tee - a tap into a larger line that does not add any special compensation, or conditioning. These connectors
often have a T-shape
telnet - a standard method for logging into remote computers and having access if connect by a dumb
terminal
temperature - the heat stored in an object. The relationship between temperature and energy content is
specific to a material and is called the specific heat
temperature dependence - as temperature varies, so do physical properties of materials. This makes many
devices sensitive to temperatures
thermal conductivity - the ability of a material to transfer heat energy
thermal gradient - the change in temperature as we move through a material
thermal lag - a delay between the time heat energy is applied and the time it arrives at the load
thermistor - a resistance based temperature measurement device
thermocouple - a device using joined metals that will generate a junction potential at different temperatures,
used for temperature measurement
thermopiles - a series of thermocouples in series
thermoresistors - a category including RTDs and thermistors
throughput - the speed that actual data is transmitted/processed, etc
through beam - a beam is projected over an opening. If the beam is broken the sensor is activated
thumbwheel - a mechanical switch with multiple positions that allow digits to be entered directly
TIFF (Tagged Image File Format) - an image format best suited to scanned pictures, such as Fax
transmissions
time-division multiplex - a circuit is switched between different devices for communication
time-proportional control - the amount of power delivered to an AC device is varied by changing the number
of cycles delivered in a fixed period of time
timer - a device that can be set to have events happen at predetermined times
titration - a procedure for determining the strength of a solution using a reagent for detection. A chemical is
added at a slow rate until the reagent detects a change
toggle switch - a switch with a large lever used for easy reviews of switch settings, and easy grasping
token - an indicator of control. Often when a process receives a token it can operate, when it is done it gives
it up
TOP (Technical Office Protocol) - a network protocol designed for offices. It was promoted in conjunction
with MAP in the 1980s, but never became widely used
top-down design - a design is done by first laying out the most abstract functions, and then filling in more of
the details as they are required
topology - 1. The layout of a network. 2. a mathematical topic describing the connection of geometric
entities. This is used for B-Rep models
torque - a moment or twisting action about an axis
torus - a donut shape
toroidal core - a torus shaped magnetic core to increase magnetic conductivity
TPDDI (Twisted Pair Distributed Data Interface) - counter rotating token ring network connected with
twisted pair medium
TQC (Total Quality Control) - a philosophical approach to developing quality methods that reach all levels
and aspects of a company
transceiver (transmitter receiver) - a device to electrically interface between the computer network card, and
the physical network medium. Packet collision hardware is present in these devices
transducer - a device that will convert energy from one form to another at proportional levels
transformations - include translation, rotation, and scaling of objects mathematically using matrix algebra
Transformations are used to move objects around in a scene
transformer - two separate coils wound about a common magnetic coil. Used for changing voltage, current
and resistance levels
transient - a system response that occurs because of a change. These effects dissipate quickly and we are left
with a steady state response
transmission path - a system component that is used for transmitting energy
transport layer - an OSI network model layer
TRIAC (TRIode Alternating Current) - a semiconductor switch suited to AC power
true - a logic positive, high, or 1
truth table - an exhaustive list of all possible logical input states, and the logical results
TTL (Transistor Transistor Logic) - a high speed for of transistor logic
TTY - a teletype terminal
turbine - a device that generates a rotational motion using gas or fluid pressure on fan blades or vanes
turbulent flow - fluids moving past an object, or changing direction will start to flow unevenly. This will
occur when the Reynold’s number exceeds 4000
twisted pair - a scheme where wires are twisted to reduce the effects of EMI so that they may be used at
higher frequencies. This is casually used to refer to 10b2 ethernet
TXD (Transmitted Data) - an output line for serial data transmission. It will be connected to an RXD input
on a receiving station.
U
UART (Universal Asynchronous Receiver/Transmitter) - UDP (User Datagram Protocol) - a connectionless method for transmitting packets to other hosts on the network. It is seen as a counterpart to TCP
ultrasonic - sound or vibration at a frequency above that of the ear (> 16KHz typ.)
ultraviolet - light with a frequency above the visible spectrum
UNIX - a very powerful operating system used on most high end and mid-range computers. The predecessor
was Multics. This operating system was developed at AT & T, and grew up in the academic
environment. As a result a wealth of public domain software has been developed, and the
operating system is very well debugged
UPS (Uninterruptable Power Supply) -
user friendly - a design scheme that simplifies interaction so that no knowledge is needed to operate a device
and errors are easy to recover from. It is also a marketing term that is badly misused
user interfaces - are the means of communicating with the computer. For CAD applications, a graphical
interface is usually preferred. User friendliness is a measure of the ease of use of a program and
implies a good user interface
UUCP (Unix to Unix Copy Program) - a common communication method between UNIX systems.
V
Vac - a voltage that is AC
vacuum - a pressure that is below another pressure
vane - a blade that can be extended to provide a good mechanical contact and/or seal
variable - a changeable location in memory
varistor - voltage applied changes resistance
valve - a system component for opening and closing mass/energy flow paths. An example is a water faucet
or transistor
vapor - a gas
variable - it is typically a value that will change or can be changed. see also constant
VDT (Video Display Terminal) - also known as a dumb terminal
velocity - a rate of change or speed
Venturi - an effect that uses an orifice in a flow to generate a differential pressure. These devices can
generate small vacuums
viscosity - when moved a fluid will have some resistance proportional to internal friction. This determines
how fast a liquid will flow
viscosity index - when heated fluid viscosity will decrease, this number is the relative rate of change with
respect to temperature
VLSI (Very Large Scale Integration) - a measure of chip density. This indicates that there are over
100,000(?) transistors on a single integrated circuit. Modern microprocessors commonly have
millions of transistors
volt - a unit of electrical potential
voltage rating - the range or a maximum/minimum limit that is required to prevent damage, and ensure
normal operation. Some devices will work outside these ranges, but not all will, so the limits
should be observed for good designs
volume - the size of a region of space or quantity of fluid
volatile memory - most memory will lose its contents when power is removed, making it volatile
vortex - a swirling pattern in fluid flow
vortex shedding - a solid object in a flow stream might cause vortices. These vortices will travel with the
flow and appear to be shed.
W
watchdog timer - a timer that expects to receive a pulse every fraction of a second. If a pulse is not received, it assumes the system is not operating normally, and a shutdown procedure is activated
watt - a unit of power that is commonly used for electrical systems, but applies to all
wavelength - the physical distance occupied by one cycle of a wave in a propagating medium
word - 1. a unit of 16 bits or two bytes. 2. a term used to describe a binary number in a computer (not limited
to 16 bits)
work - the transfer of energy
write - a digital value is stored in a memory location
WYSIWYG (What You See Is What You Get) - newer software allows users to review things on the screen
before printing. In WYSIWYG mode, the layout on the screen matches the paper version exactly
X
X.25- a packet switching standard by the CCITT
X.400 - a message handling system standard by the CCITT
X.500 - a directory services standard by the CCITT
X rays - very high frequency electromagnetic waves
X Windows - a window driven interface system that works over networks. The system was developed at
MIT, and is quickly becoming the standard windowed interface. Personal computer
manufacturers are slowly evolving their windowed operating systems towards X-Windows like
standards. This standard only specifies low level details, higher level standards have been
developed: Motif, and Openlook
XFER - transfer
XMIT - transmit
xmodem - a popular protocol for transmitting files over text based connections. compression and error
checking are included.
Y
ymodem - a popular protocol for transmitting files over text based connections. compression and error
checking are included.
Z
zmodem - a protocol for transmitting data over text based connections.
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