Reference Library

What is Six Sigma?

Origins of Six Sigma

How Does It Work?


Six Sigma Methodology


Glossary of Terms


Glossary of Terms


Select the first letter of the word from the list above to jump to appropriate section of the glossary.

- A -

ABSCISSA - The horizontal axis of a graph.

ACCEPTANCE REGION ALPHA RISK - The region of values for which the null hypothesis is accepted.

ACCURACY-1. The degree to which an indicated value matches the actual value of a measured variable. 2. In process instrumentation, degree of conformity of an indicated value to a recognized accepted standard value, or ideal value.

A/D TRANSDUCER - A device that converts analog data into digital form.

ALGORITHM - 1. A prescribed set of well-defined rules or processes for the solution of a problem in a finite number of steps. 2. Detailed procedures for giving instructions to a computer.

ALPHA RISK - The probability of accepting the alternate hypothesis when, in reality, the null hypothesis is true.

ALTERNATE HYPOTHESIS - A tentative explanation which indicates that an event does not follow a chance distribution; a contrast to the null hypothesis.

ANALOG - The representation of numerical quantities by means of physical variables, such as translation, rotation, voltage, or resistance; contrasted with digital.

ANALOG SIGNAL - An analog signal is a continuously variable representation of a physical quantity, property, or condition such as pressure, flow, temperature, etc. The signal may be transmitted as pneumatic1 mechanical, or electrical energy.

APPLICATION MEMORY - The memory which stores the programmed instructions and data to control a specific machine or process. Application memory is often random access memory.

ARITHMETIC LOGIC BAUD RATE - A computer chip which computes mathematical functions.

ASSIGNABLE CAUSE - A source of variation which is non-random; a change in the source ("VITAL FEW" variables) will produce a significant change of some magnitude in the response (dependent variable), e.g., a correlation exists; the change may be due to an intermittent in-phase effect or a constant cause system which may or may not be highly predictable; an assignable cause is often signaled by an excessive number of data points outside a control limit and/or a non-random pattern within the control limits; an unnatural source of variation; most often economical to eliminate.

ASSIGNABLE VARIATIONS - Variations in data which can be attributed to specific causes.

ATMOSPHERIC PRESSURE - The barometric reading of pressure exerted by the atmosphere; at sea level 14.7 lb per sq in. or 29.92 in. of mercury.

ATTRIBUTE - A characteristic that may take on only one value, e.g. 0 or 1.

ATTRIBUTE DATA - Numerical information at the nominal level; subdivision is not conceptually meaningful; data which represents the frequency of occurrence within some discrete category, e.g., 42 solder shorts.

- B -

BACKGROUND VARIABLES - Variables which are of no experimental interest and are not held constant. Their effects are often assumed insignificant or negligible, or they are randomized to ensure that contamination of the primary response does not occur.

BACK-UP BATTERY - A battery which is available to maintain memory contents in the event of primary power failure.

BAUD RATE - The rate of a unit of signal speed equal to the number of code elements (pulses and spaces) per second or twice the number of pulses per second.

BETA RISK - The probability of accepting the null hypothesis when, in reality, the alternate hypothesis is true.

BIMETAL - A bonded laminate consisting of two strips of dissimilar metals; the bond is usually a stable metallic bond produced by coroiling or diffusion bonding; the composite material is used most often as an element for detecting temperature changes by means of differential thermal expansion in the two layers.

BIMETALLIC THERMOMETER ELEMENT - A temperature-sensitive strip of metal (or other configuration) made by mechanically bonding or mechanically joining two dissimilar strips of metal together in such a manner that small changes in temperature will cause the composite assembly to distort elastically and produce a predictable deflection; the element is designed to take advantage of the fact that different metals have different coefficients of thermal expansion.

BIT - The smallest unit of information that can be recognized by a computer.

BLACK BELT - The leader of the team responsible for applying the Six Sigma process.

BLOCKING VARIABLES - A relatively homogenous set of conditions within which different conditions of the primary variables are compared. Used to ensure that background variables do not contaminate the evaluation of primary variables.

- C -

CALIBRATION - Determination of the experimental relationship between the quantity being measured and the output of the device that measures it; where the quantity measured is obtained through a recognized standard of measurement.

CASCADE CONTROL - 1. A control system composed of two loops where the set point of one loop (the inner loop) is controlled by the output of the second loop (the outer loop). 2. A control technique that incorporates a master and a slave loop. The master loop control the primary control parameters and establishes the slave4oop set point. The purpose of the slave loop is to reduce the effect of disturbances on the primary control parameter and to improve the dynamic performance of the loop.

CAUSALITY - The principle that every change implies the operation of a cause.

CAUSATIVE - Effective as a cause.

CAUSE - That which produces an effect or brings about a change.

C CHARTS - Charts which display the number of defects per sample.

CHAMPION - Person responsible for the logistical and business aspects of a Six Sigma project. Champions select and scope projects that are aligned with the corporate strategy, choose and mentor the right people for the project, and remove barriers to ensure the highest levels of success.

CHARACTERISTIC - A definable or measurable feature of a process, product, or variable.

CELSIUS - A scale for temperature measurement based on the definition of 0 C and 100 C as the freezing point and the boiling point, respectively, of water at standard pressure.

CENTRAL TENDENCY - Numerical average, e.g., mean, median, and mode; center line on a statistical process control chart.

CENTER LINE - The line on a statistical process control chart which represents the characteristic's central tendency.

CENTIGRADE - A non-preferred term formerly used to designate the scale now referred to as the Celsius scale.

CENTRAL PROCESSING UNIT (CPU) - Made up of one or more microprocessors and associated components. The CPU controls system activities including interpretation and execution of programs. It has an arithmetic logic unit (ALU), timing and control circuitry, accumulator, scratch-pad memory, program counter, address stack, and instruction register.

CLASSIFICATION - Differentiation of variables.


CONFIDENCE LEVEL - The probability that a random variable x lies within a defined interval.

CONFIDENCE LIMITS - The two values that define the confidence interval.

CONFIGURATION - The arrangement of software-based function blocks in a controller. The configuration determines what functions the controller can perform and in what order.

CONFOUNDING - Allowing two or more variables to vary together so that it is impossible to separate their unique effects.

CONSUMERS RISK - Probability of accepting a lot when, in fact, the lot should have been rejected (see BETA RISK).

CONTINUOUS DATA - Numerical information at the interval of ratio level; subdivision is conceptually meaningful; can assume any number within an interval, e.g., 14.652 amps.

CONTINUOUS RANDOM VARIABLE - A random variable which can assume any value continuously in some specified interval.

CONTROL CHART - A graphical rendition of a characteristic's performance across time in relation to its natural limits and central tendency.

CONTROL SPECIFICATIONS - Specifications called for by the product being manufactured.

CONTROLLED VARIABLE - 1. The variable which the control system attempts to keep at the set point value. The set point may be constant or variable. 2. The part of a process you want to control (flow, level, temperature, pressure, etc.). 3. A process variable which is to be controlled at some desired value by means of manipulating another process variable.

CUTOFF POINT - The point which partitions the acceptance region from the reject region.

- D -

D/A TRANSDUCER - A device that converts a digital signal into a proportional analog voltage or current.

DASHBOARD - A set of metrics, usually not more than five or six, that provide an "at-a-glance" summary of a Six Sigma project's status. Every participant in a Six Sigma deployment -- from the CEO to a factory floor worker -- should have his or her own dashboard with function- and level-appropriate data summaries.

DATA - Factual information used as a basis for reasoning, discussion, or calculation; often refers to quantitative information.

DEGREES OF FREEDOM - The number of independent measurements available for estimating a population parameter

DENSITY - 1. A physical property of materials measured as mass per unit volume. 2. The weight of a substance for a specified volume at a definite temperature, for example, grams per cubic centimeter at 200C. 3. Closeness of texture or consistency.

DENSITY FUNCTION - The function which yields the probability that a particular random variable takes on any one of its possible values.

DEPENDENT VARIABLE - A Response Variable; e.g., y is the dependent or "Response" variable where Y=f (Xl. . . XN) variable.

DERIVATIVE CONTROL - In process instrumentation, control action in which the output is proportional to the rate of change of the input.

DEVIATION - The difference between the value of a specific variable and some desired value, usually a process set point.

DIFFERENTIAL PRESSURE - 1. The difference between the pressure at any two defined points. 2. The static pressure difference generated by the primary device when there is no difference in elevation between the upstream gage and the downstream gage.

DIFFERENTIAL PRESSURE TRANSMITTER - Any of several transducers designed to measure the pressure difference between two points in a process and transmit a signal proportional to this difference, without regard to the absolute pressure at either point.

DIGITAL SIGNAL - A discrete or discontinuous signal; often one whose various states are discrete intervals apart.

DISCRETE RANDOM VARIABLE - A random variable which can assume values only from a definite number of discrete values.

DISTRIBUTIONS - Tendency of large numbers of observations to group themselves around some central value with a certain amount of variation or "scatter" on either side.

- E -

EFFECT - That which was produced by a cause.

E/I TRANSDUCER - A device that linearly converts a voltage signal into a current signal.

ELBOW METER - A pipe elbow that is used as a flow measurement device by placing a pressure tap at both the inner and outer radii and measuring the pressure differential caused by the differences in flow velocity between the two flow paths.

ENERGY - The capacity of a body for doing work or its equivalent - it may be classified as potential or kinetic, depending on whether it is associated with bodies at rest or bodies in motion; or it may he classified as chemical, electrical, electromagnetic, electrochemical, mechanical, radiant, thermal, or vibrational or any other type, depending on its source or nature.

EXECUTION SEQUENCE NUMBER - The order in which the controller executes function blocks.

EXECUTIVE PROGRAM - The program in the PLC which contains instructions to direct the CPU in its execution of system activities.

EXPERIMENT - A test under defined conditions to determine an unknown effect; to illustrate or verify a known law; to test or establish a hypothesis.

EXPERIMENTAL ERROR - Variation in observations made under identical test conditions. Also called residual error. The amount of variation which cannot be attributed to the variables included in the experiment.

- F -

FACTORS - Independent variables.

FAHRENHEIT - A temperature scale in which the freezing point of pure water occurs at 32 F and the span between freezing point and boiling point of pure water at standard pressure is defined to be 180 scale divisions (180 degrees).

FEEDBACK - 1. Process signal used in control as a measure of response to control action. 2. The part of a closed loop system which automatically brings back information about the condition under control.

FEEDBACK CONTROL - An error driven control system in which the control signal to the actuators is proportional to the difference between a command signal from the process variable being controlled.

FEEDFORWARD CONTROL - A method of control that compensates for a disturbance before its effect is felt in the output. It is based on a model that relates the output to the input where the disturbance occurs. In distillation, the disturbances are usually feed rate and feed compositions. Steady-state feedforward models are usually combined with dynamic compensation functions to set the manipulative variables and combined with feedback adjustments (trim) to correct for control model-accuracy constraints.

FIBER OPTICS - A medium that uses light conducted through glass or plastic fibers for data transmission.

FIXED EFFECTS MODEL - Experimental treatments are specifically selected by the researcher. Conclusions only apply to the factor levels considered in the analysis. Inferences are restricted to the experimental levels.

FLOW - The movement of material in any direction.

FLOWRATE - The quantity of fluid that moves through a pipe or channel within a given period of time.

FLOWMETER - An instrument used to measure linear, nonlinear, or volumetric flow rate or discharge rate of a fluid flowing in a pipe. Also known as a fluid meter.

FLOWNOZZLE - A type of differential pressure producing element having a contoured entrance; characterized by its ability to be mounted between flanges and have a lower permanent pressure loss than an orifice plate.

FLUCTUATIONS - Variances in data, which are caused by a large number of, minute variations or differences.

FREQUENCY DISTRIBUTION- The pattern or shape formed by the group of measurements in a distribution.

FUNCTION BLOCKS - Programming tools that represent steps in a control strategy.

- G -

GAGE - (alternate spelling of Gauge) is a device or process by which measurements are taken.

Gage R&R - (Gage Repeatability and Reproducibility) this is a statistical tool that measures the accounts the amount of variation in the measurement system from the device used, the people taking the measurement, the interaction between the device and the person and the error seen from the parts.

GREEN BELT - An individual who supports the implementation and application of Six Sigma tools by way of participation on project teams.

- H -

HEAT - Energy that flows between bodies because of a difference in temperature; same as thermal energy.

HISTOGRAM - Vertical display of a population distribution in terms of frequencies; a formal method of plotting a frequency distribution.

HOMOGENEITY OF VARIANCE - The variances of the groups being contrasted are equal (as defined by statistical test of significant difference).

HUMAN FACTORS - Human capabilities and limitations to the design and organization of the work environment. Primarily attributed to errors, but also a consideration in the design of workflow and processes. The study of human factors can help identify operations susceptible to human error and improve working conditions to reduce fatigue and inattention.

HYDROSTATIC HEAD - The pressure created by the height of a liquid above a given point.

- I -

INDEPENDENT VARIABLE - A controlled variable; a variable whose value is independent of the value of another variable.

I/E TRANSDUCER - A device that linearly converts a current signal into a voltage signal.

I/O RACK MEMORY - Chassis for mounting computer I/O modules. May be local or remote from CPU/memory unit.

I/P TRANSDUCER - A device that linearly converts electric current into gas pressure.

INPUT MODULE - This module accepts analog or digital voltage and current signal from field devices. An analog-to-digital converter inside the module changes analog input signals into a digital format to be interpreted by the CPU. The input module also conditions the signal through sampling and filtering.

INSTABILITY - Unnaturally large fluctuations in a pattern.

INSTRUMENT - A device for measuring the value of an observable attribute; the device may merely indicate the observed value, or it may also record or control the value.

INSTRUMENTATION - Any system of instruments and associated devices used for detecting, signaling, observing, measuring, controlling, or communicating attributes of a physical object or process.

INTEGRAL CONTROL ACTION - Control action in which the output is proportional to the time integral of the input; i.e., the rate of change of output is proportional to the input.

INTERACTION - The tendency of two or more variables to produce an effect in combination which neither variable would produce if acting alone.

INTERNAL ENERGY - Ability of a working fluid to do its work based on the arrangement and motion of its molecules.

INTERVAL - Numeric categories with equal units of measure but no absolute zero point, i.e., quality scale or index.

- K -

KELVIN - Metric unit for thermodynamic temperature. An absolute temperature scale in which the zero point is defined as absolute zero (the point where all spontaneous molecular activity ceases) and the scale divisions are equal to the scale divisions in the Celsius system; in the Kelvin system, the scale divisions are not referred to as degrees as they are in other temperature measurement systems but as kelvins; 0 C equals approximately 273.16 K.

KINETIC ENERGY - The energy of a working fluid caused by its motion

- L -

LASER - Light Amplification by Stimulated Emission of Radiation. It is a source of EM radiation generally in the IR, visible, or UV bands and is characterized by small divergence, coherence, monochromaticity, and high collimation.

LATENT HEAT - Heat that does not cause a temperature change.

LED - Light Emitting Diode.

LIMIT FUNCTION - Action which sets a high or low limit on any signal within the controller.

LINE CHARTS - Charts used to track the performance without relationship to process capability or control limits.

LOWER CONTROL LIMIT - A horizontal dotted line plotted on a control chart which represents the lower process limit capabilities of a process.

- M -

MANIPULATED VARIABLE - 1. In a process that is desired to regulate some condition, a quantity or a condition that is altered by the control in order to initiate a change in the value of the regulated condition. 2. The part of the process which is adjusted to close the gap between the set point and the controlled variable.

MANOMETER - A gage for measuring pressure or a pressure difference between two fluid chambers. A U-tube manometer consists of two legs, each containing a liquid of known specific gravity.

MASS - Amount of matter an object contains.

MASS FLOWRATE - The mass of fluid moving through a pipe or channel within a given period of time.

MASTER BLACK BELT - A teacher and mentor of Black Belts. Provides support, reviews projects, and undertakes larger scale projects.

MEASURED VARIABLE - 1. The physical quantity, property, or condition which is to be measured. Common measured variables are temperatures, pressure, rate of flow, thickness, speed, etc. 2. The pan of the process that is monitored to determine the actual condition of the controlled variable.

MEMORY - Any form of computer data storage, including main memory and mass storage, in which data can be read and written; in its strictest sense, memory refers to main memory.

MICROPROCESSOR - A large-scale integrated circuit that has all the functions of a computer, except memory and input/output systems. The IC thus includes the instruction set, ALU, registers and control functions.

MIXED EFFECTS MODEL - Contains elements of both the fixed and random effects models.

MODULARITY - The degree to which a system of programs is developed in relatively independent components, some of which may be eliminated if a reduced version of the program is acceptable.

MULTILOOP CONTROL - A control scheme that incorporates more than one feedback loop in order to ensure more precise control.

- N -

NOMINAL - Unordered categories which indicate membership or non-membership with no implication of quantity, i.e., assembly area number one, part numbers, etc.

NONCONFORMING UNIT - A unit which does not conform to one or more specifications, standards, and/or requirements.

NONCONFORMITY - A condition within a unit which does not conform to some specific specification, standard, and/or requirement; often referred to as a defect; any given nonconforming unit can have the potential for more than one nonconformity.

NONVOLATILE MEMORY OUTPUT MODULE - Computer memory that retains data when power is removed.

NORMAL DISTRIBUTION - A continuous, symmetrical density function characterized by a bell-shaped curve, e.g., distribution of sampling averages.

NULL HYPOTHESIS - A tentative explanation which indicates that a chance distribution is operating; a contrast to the null hypothesis.

- O -

OFFSET - A constant and steady state of deviation of the measured variable from the set point.

ONE-SIDED ALTERNATIVE -The value of a parameter which has an upper bound or a lower bound, but not both.

ORDINAL - Ordered categories (ranking) with no information about distance between each category, i.e., rank ordering of several measurements of an output parameter

ORDINATE - The vertical axis of a graph.

ORIFICE - A calibrated opening in a plate inserted in a fluid stream for measuring velocity of flow.

OUTPUT MODULE - This module may contain a digital-to-analog converter. Signals from this module go to the final control element which makes the required change to the process.

- P -

PARAMETER - A constant defining a particular property of the density function of a variable.

PARETO DIAGRAM - A chart which ranks, or places in order, common occurrences.

PARITY - The use of a self-checking code in a computer employing binary digits in which the total number of l's or 0's in each permissible code expression is always even or always odd.

P CHARTS - Charts used to plot percent defectives in a sample.

PERIPHERAL DEVICE - Any device, distinct from the central processor, that can provide input to or accept output from the computer.

PERTURBATION - A non-random disturbance.

POPULATION - A group of similar items from which a sample is drawn. Often referred to as the universe.

POTENTIAL ENERGY - Energy related to the position or height above a place to which fluid could possibly flow.

POWER OF AN EXPERIMENT - The probability of rejecting the null hypothesis when it is false and accepting the alternate hypothesis when it is true.

POWER SUPPLY - The device within a computer that converts external AC power to internal DC voltage.

PRECISION - The degree of reproducibility among several independent measurements of the same true value.

PRESSURE - Measure of applied force compared with the area over which the force is exerted.

PRESSURE MEASUREMENT - Any method of determining internal force per unit area in a process vessel, tank, or piping system due to fluid or compressed gas; this includes measurement of static or dynamic pressure, or absolute (total) or gage (total minus atmospheric) pressure, in any system of units.

PREVENTION - The practice of eliminating unwanted variation a priori (before the fact), e.g., predicting a future condition from a control chart and then applying corrective action before the predicted event transpires.

PRIMARY CONTROL VARIABLES - The major independent variables used in the experiment.

PROBABILITY - The chance of something happening; the percent or number of occurrences over a large number of trials.

PROBABILITY OF AN EVENT - The number of successful events divided by the total number of trials.

PROBLEM - A deviation from a specified standard.

PROBLEM SOLVING - The process of solving problems; the isolation and control of those conditions which generate or facilitate the creation of undesirable symptoms.

PROCESS - A particular method of doing something, generally involving a number of steps or operations. A physical or chemical change of matter or conversion of energy, for example, a change in pressure, temperature, speed, electrical potential, et cetera.

PROCESS AVERAGE - The central tendency of a given process characteristic across a given amount of time or at a specific point in time.


PROCESS CONTROL CHART - Any of a number of various types of graphs upon which data are plotted against specific control limits.

PROCESS MANAGEMENT - The cycle of continuous review, re-examination and renewal of fundamental work processes that contribute to an organization's performance and productivity. Itself a continual process, process management must at all times challenge a process' fit with other processes, and may result in radical change to work methods and practices.

PROCESS SPREAD - The range of values which a given process characteristic displays; this particular term most often applies to the range but may also encompass the variance. The spread may be based on a set of data collected at a specific point in time or may reflect the variability across a given amount of time.

PRODUCERS RISK - Probability of rejecting a lot when, in fact, the lot should have been accepted (see ALPHA RISK).

PROJECT - A problem. usually calling for planned action.

PROGRAMMABLE LOGIC CONTROLLER (PLC) - A microprocessor-based industrial control system. It communicates with other process control components through data links. It is used in process control for simple switching tasks, PID control, complex data manipulation, arithmetic operations, timing and process and machine control.

PROPORTIONAL BAND - The change in input required to produce a full range change in output due to proportional control action. The preferred term is proportional gain.

PROPORTIONAL CONTROL - A control mode in which there is a continual linear relationship between the deviation computer in the controller, the signal of the controller, and the position of the final control element.

PROPORTIONAL GAIN - The ratio of change in output due to proportional control action to the change in input.

PROPORTIONAL, INTEGRAL , DERIVATIVE CONTROL (PID) - A combination of proportional, integral, and derivative control actions.

PSI - Abbreviation for pounds per square inch.

PSIA - Abbreviation for pounds per square inch, absolute.

PSIG - Abbreviation for pounds per square inch, gage.

- R -

R CHARTS - Plot of the difference between the highest and lowest in a sample. Range control chart.

RANDOM - Selecting a sample so each item in the population has an equal chance of being selected; lack of predictability; without pattern.

RANDOM ACCESS MEMORY (RAM) - This is memory that can be written into or read from and allows access to any address within the memory. RAM is volatile in that contents are lost when the power is switched off.

RANDOM CAUSE - A source of variation which is random; a change in the source ("trivial many" variables) will not produce a highly predictable change in the response (dependent variable), e.g., a correlation does not exist; any individual source of variation results in a small amount of variation in the response; cannot be economically eliminated from a process; an inherent natural source of variation.

RANDOM EFFECTS MODEL - Experimental treatments are a random sample from a larger population of treatments. Conclusions can be extended to the population. Interference's are not restricted to the experimental levels.

RANDOMNESS - A condition in which any individual event in a set of events has the same mathematical probability of occurrence as all other events within the specified set, i.e., individual events are not predictable even though they may collectively belong to a definable distribution.

RANDOM SAMPLE - One or more samples randomly selected from the universe (population).

RANDOM VARIABLE - A variable which can assume any value from a set of possible values.

RANDOM VARIATIONS - Variations in data which result from causes which cannot be pinpointed or controlled.

RANGE - The difference between the highest and lowest values in a set of values or "subgroup."

RANKINE - An absolute temperature scale in which the zero point is defined as absolute zero (the point where all spontaneous molecular activity ceases) and the scale divisions are equal to the scaled divisions in the Fahrenheit system; 0 F equals approximately 459.69.

RANKS - Values assigned to items in a sample to determine their relative occurrence in a population.

RATIO - Numeric scale which has an absolute zero point and equal units of measure throughout, i.e., measurements of an output parameter, i.e., amps.

RATIO CONTROL - A control mode which is used to proportionally blend two of more raw materials.

RATIO CONTROLLER - A controller that maintains a predetermined ratio between two or more variables.

READ ONLY MEMORY (ROM) - Storage containing data that cannot be changed by computer instruction, but required alteration of construction circuits; therefore, data that is non-erasable and reusable, or fixed.

REJECT REGION - The region of values for which the alternate hypothesis is accepted.

REMOTE - In data processing, a term used to refer to any devices that are not located near the main computer.

REPLICATION - Observations made under identical test conditions.

ROBUST - The condition or state in which a response parameter exhibits hermetically to external cause of a nonrandom nature; i.e., impervious to perturbing influence.

REPRESENTATIVE SAMPLE - A sample which accurately reflects a specific condition or set of conditions within the universe.

RESEARCH - Critical and exhaustive investigation or experimentation having for its aim the revision of accepted conclusions in the light of newly discovered facts.


RESISTANCE - The opposition to the flow of electricity in an electric circuit measured in ohms.

RESISTANCE TEMPERATURE DETECTOR - A component of a resistance thermometer that consists of a material whose electrical resistance is a known function of temperature.

RESPONSE TIME - 1. The time required for the absolute value of the difference between the output and its final value to become and remain less than a specified amount, following the application of a step input or disturbance. 2. The time required for the output to first reach a definite value after the application of a step input or disturbance. 3. The time it takes for a controlled variable to react to a change in input.

RTD - A temperature transducer that provides temperature information as the change in resistance of a metal wire element, often platinum, as a function of temperature.

- S -

SAMPLE - One or more observations drawn from a larger collection of observations or universe (population).

SCAN TIME - The time required for the CPU to read all inputs, execute the control program and update all local and remote I/Os.

SCATTER DIAGRAMS - Charts which allow the study of correlation, e.g., the relationship between two variables.

SELF-DIAGNOSTIC MESSAGES - Allow the controller to locate internal and some external faults.

SELF-TUNING - A mode which continuously adjusts the tuning parameters as the process characteristics change.

SENSIBLE HEAT - Heat that causes a temperature change.

SENSOR - A generic name for a device that detects either the absolute value of a physical quantity or a change in value of the quantity and converts the measurement into a useful input signal for an indicating or recording instrument.

SET POINT - An input variable, which sets the desired value of the controlled variable. The input variable may be manually set, automatically set or programmed. It is expressed in the same units as the controlled variable.

SIGNAL - The event or phenomenon that conveys data from one point to another.

SIGNAL CONDITIONING - Processing the form or mode of a signal so as to make it intelligible to or compatible with any given device.

SINGLE-LOOP CONTROL - In a process, one variable is controlled with either an analog or a digital controller.

SIX SIGMA - Sigma is a letter in the Greek alphabet. The term "sigma" is used to designate the distribution or spread about the mean (average) of any process or procedure.

For a business or manufacturing process, the sigma value is a metric that indicates how well that process is performing. The higher the sigma value, the better. Sigma measures the capability of the process to perform defect-free-work. A defect is anything that results in customer dissatisfaction.

Sigma is a statistical unit of measure which reflects process capability. The sigma scale of measure is perfectly correlated to such characteristics as defects-per-unit, parts-per million defective, and the probability of a failure/error. Meaning no more than 3.4 parts per Million.


SQUARE ROOT EXTRACTOR - A component within the controller that receives a signal representing a non-linear process. The signal is linearized so that it can be correctly interpreted by the instrument.

STABLE PROCESS - A process which is free of assignable causes, e.g., in statistical control.

STANDARD DEVIATION - A statistical index of variability which describes the spread.

STATISTICAL CONTROL - A quantitative condition which describes a process that is free of assignable/special causes of variation, e.g., variation in the central tendency and variance. Such a condition is most often evidenced on a control chart, i.e., a control chart which displays an absence of nonrandom variation.

STATISTICAL PROCESS CONTROL - The application of statistical methods and procedures relative to a process and a given set of standards.

SUBGROUP - A logical grouping of objects or events which displays only random event-to-event variations, e.g., the objects or events are grouped to create homogenous groups free of assignable or special causes. By virtue of the minimum within group variability, any change in the central tendency or variance of the universe will be reflected in the "subgroup-to-subgroup' variability.

SYMPTOM - That which serves as evidence of something not seen.

SYSTEM - That which is connected according to a scheme.

SYSTEM MEMORY - The memory which stores programs and data associated with the controller operation. System memory is often read-only memory.

SYSTEMATIC VARIABLES - A pattern which displays predictable tendencies.

- T -

TEMPERATURE - Indication of how hot or cold a substance is.

TEST OF SIGNIFICANCE - A procedure to determine whether a quantity subjected to random variation differs from a postulated value by an amount greater than that due to random variation alone.

THEORY - A plausible or scientifically acceptable general principle offered to explain phenomena.

THERMISTOR - A temperature transducer constructed from semiconductor material and for which temperature is converted into a resistance, usually with negative slope and highly nonlinear. Its usual applications are as a nonlinear circuit element (either alone or in combination with a heater), as a temperature compensator in a measurement circuit, or as a temperature measurement element.

THERMOCOUPLE - A temperature measuring instrument that develops voltage when heated based on the combined thermoelectric effect between two electrically connected conductors (usually wires) of dissimilar composition and the temperature difference between the connection (hot junction) and the other end of the conductors (cold junction).

TRANSDUCER - Any device or component that converts an input signal of one form to an output signal of another form-for instance, a piezoelectric transducer converts pressure waves into electrical signals, or vice versa.

TRANSMITTER - A transducer which responds to a measured variable by means of a sensing element and converts it to a standardized transmission signal which is a function only of the measurement.

TUNING - The use of various techniques involving adjustments to both hardware and software to improve the operating efficiency of a computer system.

TWO-POSITION ACTION - A type of control-system action that involves positioning the final control device in either of two fixed positions without permitting it to stop at any intermediate position.

TWO-SIDED ALTERNATIVE - The values of a parameter which designate an upper and lower bound.



- U -

UNNATURAL PATTERN - Any pattern in which a significant number of the measurements do not group them-selves around a center line; when the pattern is unnatural, it means that outside disturbances are present and are affecting the process.

UPPER CONTROL LIMIT - A horizontal line on a control chart (usually dotted) which represents the upper limits of process capability.

USER PROGRAM - The program loaded into a PLC which contains the instructions to run the process or machine. The user program contains instructions that indicate what each output should be, based on the status of one or more specified inputs.

- V -

VARIABLE - A characteristic that may take on different values.

VARIABLES DATA - Numerical measurements made at the interval or ratio level; quantitative data, e.g., ohms, voltage, diameter; subdivisions of the measurement scale are conceptually meaningful, e.g., 1.6478 volts.

VARIATION - Any quantifiable difference between individual measurements; such differences can be classified as being due to common causes (random) or special causes (assignable).

VOICE OF THE BUSINESS – The stated mission, goals and business objectives of an organization. This collection of specific, documented statements of intent are the guidelines by which linkages are established between Six Sigma projects and targeted levels of improvement. The Voice of the Business should outline exactly what it is the business does, as well as how the business intents to accomplish its mission. Combined with the Voice of the Customer, the Voice of the Business plays an important role in defining potential Six Sigma projects.

VOICE OF THE CUSTOMER – A systematic, institutionalized approach for eliciting and analyzing customers’ requirements, expectations, level of satisfaction and areas of concern. Typically, a Voice of the Customer effort includes facilitated focus groups, individual interviews, surveys. The Voice of the Customer is a key data source in the Project Selection process.

VENTURI TUBE - A primary differential pressure producing device having a cone section approach to a throat and a longer cone discharge section. Used for high volume flow at low pressure loss.

VOLATILE MEMORY - Memory whose contents are lost when the power is switched off.

VOLUME - 1. The three-dimensional space occupied by an object. 2. A measure of capacity for a tank or other container in standard units.

VOLUMETRIC FLOWRATE - The volumes of fluid moving through a pipe or channel within a given period of time.

VORTEX SHEDDING FLOWMETER - A device that uses differential pressure variations associated with the forming and shedding of vortices in a stream of fluid flowing past a standard flow obstruction to actuate a sealed detector at a frequency that is proportional to vortex shedding, which, in turn, provides an output signal directly related to flow rate.

- W X Y Z -

WET LEG - The liquid-filled, low-side impulse line in a differential pressure measuring system.

WORKING FLUID - Fluid that does the work for a system.

X & R CHARTS - A control chart which is a representation of process capability over time; displays the variability in the process average and range across time.

YELLOW BELT - A Yellow Belt is any employee who has received introductory training in the fundamentals of Six Sigma. The Yellow Belt gathers data, participates in problem-solving exercises and adds their personal experiences to the exploration process. Yellow Belts should have basic high school level math and reading skills.

Z-SCORES - Sometimes called ?standard scores,? Z-Scores are a special application of the transformation rules. The Z score for an item indicates how far, and in what direction, that item deviates from its distribution’s mean, expressed in units of its distribution’s standard deviation. The z score transformation is especially useful when seeking to compare the relative standings of items from distributions with different means and/or different standard deviations.

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