We intend to keep this glossary growing, and will add new terms on an ongoing basis. If you cannot find a specific term, or would like to suggest an addition to the glossary, please contact us at support@relex.com, attention "Relex Glossary."

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 Access, Microsoft A database software program created by Microsoft. The Relex CAD Import/ExportWizardTM is completely compatible with Microsoft Access files, able to import information from, and export data to, the Microsoft Access format. Active Device A discrete component whose operation involves the activity of a semiconductor junction. Some examples include integrated circuits and transistors. Arrhenius A model used for user-defined parts in the Relex Reliability Prediction Software. The Arrhenius equation models the effect of temperature on reliability. ASCII American Standard Code for Information Interchange. A universal file format for text files. The Relex CAD Import/ExportWizardTM is completely compatible with ASCII files, able to import information from, and export data to, the ASCII format. Assembly A level of organization used in the Relex System Tree. Availability The probability that a system is operational when called upon to perform its function. The numerical value of availability is expressed as a probability from 0 to 1. Availability calculations take into account both the failures and the repairs of the system. Back to Top

B Bellcore TR-332 (Telcordia SR-332) MTBF Calculations Also now known as Telcordia GR-332, is a reliability prediction standard developed by Bellcore Communications Research (Bellcore) for telecommunications companies, but later adopted by many other organizations. Bellcore, which previously was the telecommunications research arm of the Regional Bell Operating Companies (RBOCs), is now known as Telcordia Technologies. The Bellcore Reliability Prediction Procedure (RPP) document provides mathematical reliability models for nearly all types of electrical and electronic components. These reliability models are based on parameters of the components such as number of transistors, power dissipation, and environmental factors. Results from Bellcore TR-332 (Telcordia SR-332) are provided as both a failure rate and as an MTBF (Mean Time Between Failures) where the MTBF is the mathematical inverse of the failure rate for components with exponential distributions. Bill of Materials (BOM) Fixed-format ASCII files where each piece of information appears between certain columns. The Relex CAD Import/ExportWizardTM is completely compatible with BOM files, able to import information from, and export data to, the BOM format. Bitmap A common graphics format. Both Relex RBD and the Relex Visual Report Designer accept bitmap images. Burn-in The process of operating devices or equipment often under accelerated voltage, temperature, or load in order to screen out infant mortality failures. Back to Top

C CAD Import/ExportWizardTM A feature included in Relex Reliability Studio. It enables you to import and export information between Relex Project files and various spreadsheet, word processing, and database file formats. CAFTA (Also known as CAFTA for Windows.) A software program designed to generate fault tree analyses. Relex Fault Tree supports the conversion of CAFTA for Windows files into the Relex Fault Tree format. CAGE Commercial and Government Entity Code. Normally a 5 digit code. CNET 93 A reliability standard developed by France Telecom© that provides reliability models for a wide range of components. CNET 93 is a comprehensive model similar to MIL-HDBK-217, which provides a detailed stress analysis. Common Cause Failure Group An event or mechanism that can cause two or more failures simultaneously is called a common cause. The failures are referred to as common cause failures. Relex Fault Tree will recognize a common cause failure group of up to 4 events for any single common cause. It also enables you to create a common cause failure group file, to organize your common cause failure information. Correlation File A file which stores the table correlating your in-house part numbers to part numbers in the Relex-supplied parts libraries. Cost Analysis Analyzing the cost of a product or system over its entire lifetime, including design, development, and replacement costs. Relex Life Cycle Cost (LCC) enables users to perform cost analyses, using a Cost Breakdown Structure (CBS) tree, factoring in alternatives, time intervals, and other variables. Criticality A relative measure of the consequence of a particular failure mode and its frequency of occurrence. The criticality value is used to rank failure modes when performing a FMECA. Criticality Matrix A graphical representation of the failure mode and effects, usually graphed as probability of occurrence vs. severity level. The Relex FMEA Wizard enables users to configure the X and Y axes of the criticality matrix when setting up Project files to receive FMEA information. Back to Top

D DBF Files (Also known as dBASE files.) A standard file format that can be generated from many different databases and spreadsheet programs. The Relex CAD Import/ExportWizardTM is completely compatible with DBF files, able to import information from, and export data to, the DBF format. Defaults File A file which stores default values for the parameters for the various types of parts. If certain part parameters are left blank or defined as zero, Relex will default these parameters to the values in the Defaults file. If values are not specified for the parameters, Relex will use its own built-in defaults. Delimited Files Files in which the different data fields are set apart by a delimiting character (usually a comma). The Relex CAD Import/ExportWizardTM is completely compatible with delimited files, able to import information from, and export data to, a delimited file format. Derating File A file in which maximum stress levels for the various types of parts are stored. Derating files are used to set an upper limit for electrical and thermal stresses on each part type. By keeping devices operating at or below the maximum derated level, reliability can be improved. Design FMEA A failure modes effects analysis that studies how a system design reacts to various failure modes. The Relex FMEA software module supports design FMEAs. Device Any electrical part (e.g., integrated circuit, diode, resistor) with distinct electrical characteristics. Distribution Methods Relex RBD and Relex Weibull support several failure rate distributions. Users can select from these multiple distributions to provide the best fit for failure data analyses. Distribution Parameters Each failure distribution requires the definition of distribution parameters in order to properly analyze reliability data. These parameters vary with the specific failure distributions in use, and can include the mean, standard deviation, characteristic life, shape factor, lower and upper bound, among others. Duty Cycle Used when computing failure rates based on active and dormant settings. The duty cycle is equal to the percentage of total time the item or system is in the active environment. Back to Top

E Estimation Methods Used in Relex Weibull to help determine the truest possible values for the data set and the parameters of the failure data analysis. The software supports the following choices: Benard, Binomial, Mean, Hazen, Benard Special, Binomial Special, Mean Special, Hazen Special, Maximum Likelihood, and Modified Maximum Likelihood. Event Tree Analysis A process designed to determine the probability of an event based on the outcomes of each event in the chronological sequence leading up to it. The Relex Event Tree module can be used to analyze safety and mission-oriented systems, as well as continuously operating systems, to calculate the probability of an initiating event. Excel, Microsoft A spreadsheet software package created by Microsoft. The Relex CAD Import/ExportWizardTM is completely compatible with Microsoft Excel files, able to import information from, and export data to, the Microsoft Excel format. Exponential Distribution Probably the most widely known and used distribution in reliability evaluation of systems. The most important factor for it to be applicable is that the hazard rate should be constant. Exponential distribution is frequently used for the analysis of time-dependent data when the rate at which events occur does not vary. Back to Top

F Failure Data Analysis A type of reliability analysis used to study a variety of fields, practices, and disciplines, including mechanical, chemical, electrical, electronic, materials, and human failures. It is useful for maintenance planning, developing cost-effective replacement strategies, spare parts forecasting, and warranty analysis. The Relex Weibull module provides extensive failure data analysis capabilities. Failure Mode and Effect Analysis (FMEA) An inductive, bottoms-up method of analyzing system design and performance. At the core of a FMEA is the determination of the effects of various types of failures on a system. Various standards such as SAE J1739, AIAG Potential Failure Mode and Effects Analysis, as well as documents from Ford, Chrysler, and GM, provide instructions and formats on performing FMEAs. Failure Mode, Effects and Criticality Analysis (FMECA) An inductive, bottoms-up method of analyzing system design and performance. At the core of a FMECA is the determination of the effects of various types of failures on a system. A criticality factor, assigned to each failure mode, allows ranking the most severe failure modes and the ones most likely to occur. The analyst may then target these failure modes in order to reduce their probability of occurrence. MIL-STD-1629 provides instructions and formats for performing FMECAs. Failure Rate The number of failures experienced or expected for a device divided by the total equipment operating time. For constant failure rate items, i.e. exponentially distributed failures, the failure rate is the numerical inverse of the mean time between failures (MTBF). Fault Tree Analysis A deductive, top-down method of analyzing system design and performance. It involves specifying a top event to analyze, followed by identifying all of the associated elements in the system that could cause that top event to occur. Fault tree analyses are generally performed graphically using a logical structure of AND and OR gates. Sometimes certain elements, or basic events, may need to occur together in order for that top event to occur. In this case, these events would be arranged under an AND gate, meaning that all of the basic events would need to occur to trigger the top event. If the basic events alone would trigger the top event, then they would be grouped under an OR gate. The entire system as well as human interactions would be analyzed when performing a fault tree analysis. FIN file (Also known as Fault equivalence Identification Number.) Files that are based on the concept of fault equivalence groups. A fault equivalence group contains the failure consequences of the failure mode, i.e. the local effect, next effect, end effect, severity, and other consequences of a failure. FIN Definition files facilitate the grouping together of failure modes that exhibit identical consequences. FIN files are useful in FMEA and FMECA calculations. First-Year Multiplier Ratio of the first-year failure rate to the steady-state failure rate. FITS (Also known as failures in time.) Describes the failure rate when the units are in failures per billion hours. FoxPro A common database program. The Relex CAD Import/ExportWizardTM is completely compatible with FoxPro files, able to import information from, and export data to, the FoxPro format. FRACAS (Also known as Failure Reporting, Analysis, and Corrective Action System.) A closed-loop system that consists of identifying failures, analyzing the causes of those failures by performing a failure analysis, deciding corrective actions, and implementing those corrective actions back into the design and/or manufacturing process. A good FRACAS system is essential to healthy reliability improvement. Back to Top

G Gumbel- (Lower) An extreme minimum value failure distribution, similar to the Weibull distribution. The Gumbel distribution is related to Weibull since Gumbel is a Type I lower extreme value and Weibull is a Type III (lower). Gumbel+ (Upper) An extreme maximum value failure distribution. Gumbel+ (Upper) is a Type I upper extreme value. Back to Top

H HRD5 A reliability standard developed by British Telecommunications plc© that also provides models for a wide range of components. In general, HRD5 is similar to CNET 93, but provides simpler models and requires fewer data parameters for analysis. Hybrid A component in a relatively large package that contains other parts mounted on a substrate. Back to Top

J JPEG A common graphics format. The Relex Visual Report Designer accepts JPEG images. Junction An object used in reliability block diagrams to join multiple connectors together such as in parallel or redundant configurations. Junctions can be set in series, parallel operating, or standby operation. Back to Top

K Keyword A free format ASCII file that has keywords for each field of information. The Relex CAD Import/ExportWizardTM is completely compatible with keyword files, able to import information from, and export data to, the keyword format. Back to Top

L Lambda-Tau Calculation A calculation method used to determine availability or short-term reliability when the age of a component or system is unknown or indeterminate. Relex Fault Tree supports multiple methods of Lambda-Tau calculations. In all methods, Lambda signifies the failure rate of the system or component. Tau can represent the inspection interval, repair time, or mission time of the system. Life Cycle Cost (LCC) A method of analyzing the cost of a piece of equipment over its entire life, including development costs, production costs, warranty costs, repair costs, and disposal costs. Relex Life Cycle Cost (LCC) enables users to perform cost analyses, using a Cost Breakdown Structure (CBS) tree, factoring in alternatives, time intervals, and other variables. Lognormal Distribution A failure distribution similar to the Normal distribution except that the logarithm of the values of random variables, rather than the values themselves, are assumed to be normally distributed. Thus all values are positive and the distribution is skewed to the left. LSAR files (Also known as Logistics Support Analysis Records.) Text files that conform to MIL-STD-1388 2B. Relex Reliability Studio can automatically export reliability data into the LSAR format. Lotus A database or look-up table that contains standard parts and their associated part parameters. The Relex CAD Import/ExportWizardTM is completely compatible with Lotus files, able to import information from, and export data to, the Lotus format. Back to Top

M Macros Programs used to automate tedious or time-consuming tasks. Relex Reliability Studio provides complete support for macros, including a macro editor, and ready-made macros to use as reference when creating custom macros. Maintainability Prediction The measure of the ability of an item to be retained in or restored to a specified condition when skilled personnel perform the maintenance. The Relex Maintainability Prediction module enables you to generate numerous maintainability parameters, including mean time to repair (MTTR), mean maintenance man-hours per repair (MMH/Repair), and many others. Mean Time Between Failures (MTBF) The mean time expected between failures, typically measured in hours. MTBF is a statistical value and is meant to be the mean over a long period of time and large number of units. For constant failure rate systems, MTBF is the inverse of the failure rate. If failure rate is in failures/million hours, MTBF = 1,000,000 / Failure Rate for components with exponential distributions. Technically MTBF should be used only in reference to repairable items, while MTTF (Mean Time to Failure) should be used for non-repairable items, but MTBF is commonly used for both repairable and non-repairable items. Mean Time to Failure (MTTF) The mean time expected to the first failure of a piece of equipment. It is a statistical value and is meant to be the mean over a long period of time and large number of units. For constant failure rate systems, MTTF is the inverse of the failure rate. If failure rate is in failures/million hours, MTTF = 1,000,000 / Failure Rate for components with exponential distributions. Technically MTBF should be used only in reference to repairable items, while MTTF should be used for non-repairable items, but MTBF is commonly used for both repairable and non-repairable items. Mean Time to Repair (MTTR) The total amount of time spent performing all corrective maintenance repairs divided by the total number of those repairs. Measures of Reliability When performing a reliability prediction analysis, there are several calculated values that provide measures of reliability. These values include failure rate, mean time between failures (MTBF), reliability and availability. Mentor Graphics Mentor Graphics provides digital and analog design, circuit simulation, board layout and other engineering software tools. The Relex CAD Import/ExportWizardTM is completely compatible with Mentor Graphics files, able to import information from, and export data to, the Mentor Graphics format. Methods (Also referred to as Calculation Methods.) An additional tool that can be used in the analysis of Relex Reliability Prediction calculations. Calculation Methods can be used to take into account burn-in, laboratory, and test data when calculating failure rate and MTBF for a system. The Calculation Methods used by Relex are based on those outlined in the "Bellcore Reliability Prediction Procedure for Electronic Equipment", but in Relex they can be used for both Bellcore and MIL-HDBK-217 calculations. MIL-HDBK-217 A reliability prediction standard originally developed for defense and aerospace related organizations, but later adopted by many commercial and industrial companies. Many times referred to simply as 217, MIL-HDBK-217 includes mathematical reliability models for nearly all types of electrical and electronic components. These reliability models are based on parameters of the components such as number of pins, number of transistors, power dissipation, and environmental factors. Results from MIL-HDBK-217 are provided as both a failure rate and as an MTBF (Mean Time Between Failures) where the MTBF is the mathematical inverse of the failure rate. MIL-HDBK-472 The accepted industry standard for maintainability prediction analysis. The Relex Maintainability Prediction software module supports MIL-HDBK-472 Procedures 2, 5A and 5B, and generic maintenance procedures. MIL-STD-1629 A long recognized standard that describes a method of performing Failure Mode, Effects, and Criticality Analyses. It is used by government, military, and commercial organizations worldwide. MIL-STD-1629 provides calculations for criticality that allows ranking of failure modes dependent on severity classification. The Relex FMEA/FMECA software module supports the calculations included in MIL-STD-1629. Modes File Contains the associated potential modes of failure and the percentage of time that each mode of failure occurs for a specified part type. It provides centralized storage for all failure modes of all part types. Modes files are typically used for piece-part FMEAs. Monte Carlo Simulation A simulation method used by Relex RBD when calculating complex reliability block diagrams. A Monte Carlo Simulation will perform random tests on the specified system in order to provide an analysis of the overall reliability and availability of the system. The result of these simulations will determine the reliability and availability of the RBD model. Back to Top

N Net Present Value (Also known as NPV.) The cost of a product or system calculated in the present-day currency. Relex Life Cycle Cost (LCC) enables NPV calculations, to determine if a particular cost would be better incurred in the present year, or at a future date when costs may be lower. Normal Distribution An important and widely-used distribution in the field of statistics and probability. All Normal distributions are symmetric, and the mean and standard deviation values are used as its two distribution parameters. Back to Top

O Operating Environment Environment of the selected item in the Relex hierarchical display (tree). When the operating environment is selected for the top level of the tree, it serves as the environment for all levels below it. If an environment is selected in the Properties of a lower level item, that selection overrides the environment at the higher level. OrCAD Provides digital and analog design, circuit simulation, board layout and other engineering software tools. Back to Top

P Paradox A popular database program. The Relex CAD Import/ExportWizardTM is completely compatible with Paradox files, able to import information from, and export data to, the Paradox format. Parallel Operating A type of redundancy recognized in the Relex RBD software module. Parallel Operating describes a redundancy of several items performing the same task, but all redundant systems or components are fully operational at all times. In a parallel operating environment, not all units are required for successful operation. Parts Libraries The Relex Reliability Prediction software module provides vast libraries containing data on commercial and military parts, including diodes, transistors, integrated circuits, resistors, capacitors, and nonelectronic parts. These libraries can be searched using the powerful SQL search engine. Information from these parts libraries can be included in Relex Project files. Passive Device A discrete component that is not active, where an active component is one whose operation involves the activity of a semiconductor junction. Resistors and capacitors are examples of passive devices. Pi Factors Variables used in reliability prediction equations. Probabilistic Risk Assessment (Also known as PRA.) Provides a systematic approach for transforming failures, termed initiating events, into risk profiles. A PSA, Probability Safety Assessment, generally deals with issues that are safety related, while a PRA may deal with other non-safety issues. The results of the PRA or PSA provide the resulting probabilities of each risk. Process FMEA A Failure Modes and Effects Analysis that studies how failure in the manufacturing or service process affects the system operation. The Relex FMEA software module supports process FMEAs. Project File Relex Project files are the main storage area for your analysis information. Project files are the primary file type and can contain a hierarchical outline of the system being analyzed, parts lists for the assemblies within the system, and details regarding the assemblies and components in the system. Back to Top

Q QuestLink Relex Software has forged a partnership with QuestLink Technology, Inc. to provide Relex users with access to the extensive component database found at QuestLink's web site. This functionality is built into the Library Browse feature of Relex. When you select a part in the parts library and click the "QuestLink" button, Relex automatically launches your web browsing software, accesses the QuestLink web site, and displays the data for that specific part. Back to Top

R Rayleigh Distribution A special case of the Weibull failure distribution where the Beta (slope) value is known to equal 2. Redundancy The existence of more than one piece of equipment, any of which could perform a given function. These multiple pieces of equipment are used to help improve the reliability and availability of the system. Redundancy is generally expressed as the number of pieces of equipment required and the total number available. For example, 2 out of 3 means that there are a total of 3 pieces of equipment and 2 pieces are required for proper operation of the system. Reliability The ability of an item to perform a required function under stated conditions for a stated period of time. The numerical value of reliability is expressed as a probability from 0 to 1 and is also sometimes known as the probability of mission success. Reliability is the probability, assuming the system was operating at time zero, that it continues to operate until time t. Reliability Allocations Performed early in a design to allocate a given failure rate or MTBF goal across the equipment in the system. Various weights are assigned to each piece of equipment during the reliability allocations process. Reliability Analysis A method of analyzing a system design evaluating reliability-related issues. The goal is to improve the field reliability of the system. Reliability Block Diagram (RBD) A visual representation of a system that contains redundancy in its elements. Redundancy is used for mission critical functions where a single-point failure is not acceptable and reliability needs to be improved. Generally represented in a graphical manner, a simple RBD model may be calculated using analytical solutions, while a more complex RBD may be calculated using a Monte Carlo simulation. Results may include reliability, availability, failure rate, and MTBF. Reliability Calculations Performed in order to quantify the reliability of a piece of hardware or software prior to and during development and production. Reliability Centered Maintenance (RCM) Methodology used to define a maintenance program while having reliability as an input to the decision making process. Originally developed by the aviation industry and known as MSG-3 (Maintenance Steering Group), Reliability Centered Maintenance or RCM has since been adopted by many different industries. Reliability Prediction A primary component of reliability analysis is referred to as the failure rate, or the number of failures expected during a certain period of time. Calculation of equipment failure rate, and the related MTBF (Mean Time Between Failures), is the basis of performing a reliability prediction analysis. Reliability Software A general term that may be used to describe software that performs reliability predictions per MIL-HDBK-217 and Bellcore, FMEA and FMECA analysis, reliability block diagram analysis, fault tree analysis, event tree analysis, and Weibull (failure data) analysis. Reliability software packages may also be used in FRACAS systems, life cycle cost analyses, and maintainability predictions. Risk Priority Number (RPN) Used in FMEA analysis to rank the importance of different types of failure. RPN = Severity x Occurrence x Detection Back to Top

S SAE Society of Automotive Engineers. Organization that developed the SAE ARP5580 that outlines a general approach for FMEA analysis. The Relex FMEA/FMECA software module supports the SAE ARP 5580 FMEA/FMECA standards. Sensitivity Analysis Used in life cycle cost (LCC) analyses to determine how robust a particular alternative is, and how sensitive the overall cost is to certain variables. Series A type of redundancy recognized by Relex in the Relex RBD. Series describes a redundancy of several items performing the same task, but all redundant systems or components are fully operational at all times and are required for successful operation. Single Point Failure Used to describe an item that, if failed, would cause a failure of the system. Software Reliability A method of analyzing and predicting the reliability of a piece of software. There are many methods available to quantify the reliability of software. Software reliability is a relatively new field of study, compared to hardware reliability. SPICE (Also known as Simulation Program with Integrated Circuit Emphasis.) A circuit simulation technology from Berkeley, California. SPICE has been developed into software products for sale from software manufacturers such as Intusoft and OrCAD among others. Standby Nonoperating A type of redundancy recognized by Relex in the Relex RBD software module. Standby Nonoperating describes a redundancy of several items performing the same task, but all redundant systems or components are not fully operational at all times. Only those that are required are in an "on" state. In a Standby Nonoperating environment, not all units are required for successful operation. Steady-State Failure Rate The constant failure rate after one year of operation. System Tree A hierarchical system of organization used in Relex for organizing assemblies and parts. Back to Top

T Tasks, Basic A simple, one-step procedure. When tasks are created and stored for use in a maintainability prediction, they generally include a description and an associated time along with other fields that may be available for further definition of the task. The Relex Maintainability Prediction software module includes a Tasks file of standard maintenance tasks based on the tasks and repair times from MIL-HDBK-472. It also allows the creation of user-defined Tasks files. Tasks, Super (Also known as a maintenance action.) A collection of basic tasks which have been combined together to represent a larger task. For example, replacing a video card could be classified as a super task. It would include several of the following basic tasks: removal of screw, removal of card, replacement of card. and replacement of screw. The Relex Maintainability Prediction software module includes a Tasks file of standard maintenance tasks based on the tasks and repair times from MIL-HDBK-472. It also allows the creation of user-defined Tasks files. Telcordia Relex Reliability Studio supports the updated version of the Bellcore TR-332 standard, renamed Telcordia Issue 1. The latest version, "Reliability Prediction Procedure for Electronic Equipment - A Telcordia Technologies Special Report," SR-332, Issue 1, May 2001, updates the calculation models, and serves as the update to Bellcore Issue 6. Time-Independent Distribution Displays the probability that a unit will not operate properly. This probability remains constant, and does not change with time. It is the unreliability or unavailability of the unit in question. Types of Redundancies There are generally three different types of configurations that would be used in system design. These configuration types are: Series, Parallel Operating, and Standby Non-Operating. Back to Top

U Uniform Distribution The simplest of all failure distributions. it can be interpreted as meaning that the random variable can only exist in the range A to B (lower to upper) and that the probability of occurrence is directly proportional to the interval length. Unit An assembly of devices (e.g., circuit pack, module, plug-in, racks, and power supplies). User-Defined Values Files Allows user to create custom environments, quality levels, categories and subcategories. Once a User-Defined Values file is enabled in a Project file, the environments, quality levels, categories and subcategories defined in the User-Defined Values file can be used within the Project file. Back to Top

V Value-Added File Offers additional flexibility to Relex Reliability Studio. Value-Added files can range from Library files and Correlation files (which store data regarding components) to Derating and Default files (which provide more control over the handling and review of data). Back to Top

W WeiBayes A special case of the Weibull failure distribution where the Beta (slope) value can be defined by the user. Weibull Distribution A failure distribution that is very useful in reliability activities because it can be used to model many other life distributions. By adjusting the beta factor, or shape parameter, of the Weibull distribution, it can be made to model a decreasing, constant, or increasing hazard rate. The Weibull distribution provides reasonably accurate failure analysis and failure forecasts with extremely small samples. Word, Microsoft A word processing software program created by Microsoft. The Relex CAD Import/ExportWizardTM is completely compatible with Microsoft Word files, able to import information from, and export data to, the Microsoft Word format. WYSIWYG An acronym for "What You See Is What You Get." It describes a screen format that displays information (text, graphics, etc.) very similarly to the final output. The Relex Visual Report Designer employs a WYSIWYG interface, which makes it much easier to design, edit, and visualize reliability reports. Back to Top