7.19 S

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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.