Q: How can I find out about your software validation and QA practices?

A: Refer to our Statement Regarding Standard Software Validation & QA Practices, which presents our software validation and quality assurance practices.

Q: Can I open files created by one ReliaSoft software product in another ReliaSoft product. For example, can I open Weibull++ files in ALTA and/or ALTA files in Weibull++?

A: ALTA 6 and ALTA 6 PRO provide the ability to open files created in Weibull++ 5.0 (*.wdf) or Weibull++ 6 (*.rw6). Simply select Open from the File menu. In the Open Previously Saved File window, select Weibull++ File (*.wdf, *.rw6) from the Files of type drop-down menu. Locate the Weibull++ file that you wish to open in ALTA and click Open. If the Weibull++ files contain interval censored data, you will be prompted to specify how the data will be treated in ALTA. 

Weibull++ 6 provides the ability to open files created in ALTA 1.0 (*.adf) or ALTA 6/ALTA 6 PRO (*.ra6). Follow the procedure described above for Weibull++ and select ALTA File (*.ADF, *.RA6) from the Files of type drop-down menu. The data in the stress column(s) in ALTA will be placed into the Subset ID column in the Weibull++ folio.

This procedure opens only the data folios from the other application. Plots and general spreadsheets will not be transferred. This functionality is not available in ALTA 1.0 or Weibull++ 5.0.

In addition to the ability to open files created by other applications, ALTA 6, ALTA 6 PRO and BlockSim provide more integration with Weibull++. You can transfer data from ALTA to Weibull++ for further analysis and attach the Weibull++ analysis to the ALTA folio. You can also use Weibull++ to compute the life distribution and parameters (failure or repair) of a block in BlockSim.  

Q: Are special pricing options available if I purchase ReliaSoft software and attend a training seminar? 

A: Yes. ReliaSoft provides special "bundled" pricing options for users who purchase both software and training. Complete details are available at http://www.ReliaSoft.com/bundles.htm.

Q: Can I share plots from ReliaSoft applications with colleagues who do not have the applications installed on their computers? 

A: Weibull++ and ALTA have a built-in graphics editing application called RS Draw. RS Draw can be accessed by selecting the Edit Plot command from the Plot Options menu, or by clicking the RS Draw icon on the toolbar. You can edit and annotate plots in RS Draw and then save them in the Windows metafile format (*.wmf). In BlockSim, you can select Export Plot Graphic from the Tools menu or Plot Sheet shortcut menu to export the plot as a metafile. Metafile graphics can be transmitted via e-mail or other mechanism and can also be imported or pasted into other applications such as Microsoft Word or PowerPoint.

You can also copy a plot in Weibull++, ALTA or BlockSim and paste it into another application like Microsoft Word or Excel. In addition to copying the plot graphic, in some cases, you have the option to copy/paste the data that was used to create the plot. The data can then be pasted into Excel with the Paste Special command. 

Q: How do I get the latest software updates? 

A: An integral part of ReliaSoft's continuous improvement process involves issuing updates for all of our products to address technology changes, functionality requests and/or issue resolutions. Same version software updates (i.e. same major version number such as 6.X.X) are made available to all licensed users free of charge. We encourage you to update your product when a new update is released. 

Service releases are available via the ReliaSoft.com Web site. Consult the product home page for the product of interest or consult the Reliability Software Downloads table for updated information. 

Q: Where can I get information on the theory behind the calculations and analyses being performed in ReliaSoft applications?

A: In addition to the software User's Guide, ReliaSoft's standard software packages come with an additional reference text that explains the theory and background of the calculations being performed by the particular application. Many users have found these reference texts to be an invaluable tool for increasing their understanding of the concepts behind the reliability analyses they regularly perform. These texts can also be purchased separately from the software. For ordering information, see http://www.ReliaSoft.com/RSPub.htm. 

Additionally, ReliaSoft provides free on-line versions of some of these reference texts that can be accessed from ReliaSoft's reliability engineering resources Web site at http://www.weibull.com. These include:

• Life Data Analysis Reference (for use with Weibull++) - http://www.weibull.com/lifedatawebcontents.htm
• Accelerated Testing Reference (for use with ALTA) - http://www.weibull.com/acceltestwebcontents.htm
• Reliability Growth Reference (for use with RG) - http://www.weibull.com/relgrowthwebcontents.htm

A: There are some shortcuts available in Weibull++ and ALTA for speeding up the data entry process. 

In a Data Entry Spreadsheet that is configured for grouped data entry, it is not necessary to enter a value for the "Number in Group" if the value is 1. Weibull++ and ALTA will automatically insert the value of 1 for the cells that are left blank in the "Number in Group" column. 

Another shortcut can be used when a "State F or S" column is displayed in the Data Entry Spreadsheet. In this case, the cells in the "Time Failed" column can be entered first. When a positive value is entered, Weibull++ and ALTA automatically insert an "F" in the corresponding "State F or S" column position. When a negative value is entered, the applications automatically insert an "S" in the "State F or S" column. For example, for a right censored item at 100 hrs, type "–100" in the "Time Failed" column. An "S" will automatically be inserted into the "State F or S" column.

These applications also provide a variety of copy/paste and import capabilities to obtain data from existing data sources.

Q: Can I display the locations of suspensions on my probability plots?

Q: How do I remove the Program ID from the plots in Weibull++ and ALTA?

A: The Program ID appears in the upper left corner of plots in Weibull++ and ALTA, and contains information about the software and ReliaSoft. Your selection for the Print Program ID on Plot option from the Plot page of the User Setup determines whether this text will be displayed in each new plot you create.

Q: What is the DRT (Design of Reliability Tests/Testing) utility in Weibull++ and how can it be used?

A: The Weibull++ DRT utility allows you to determine the required numbers of units and/or test time required to demonstrate a certain reliability result. It is a useful tool when you need to evaluate the number of units, the test time required under a certain testing scenario or the reliability and confidence that can be demonstrated if such a scenario is actually implemented. The utility uses the binomial distribution (and in Weibull++ 6, the reliability equation) to perform the required calculations.

Both Weibull++ 5.0 and Weibull++ 6 include this utility. The enhanced utility in Weibull++ 6 automates some processes that previously required some "legwork" on the part of the user. Also, there is added functionality for test design for units with an assumed exponential distribution.

Q: How are the points on the probability plot determined in Weibull++?

A: Weibull++ 5.0 uses median ranks to calculate the points for the plot. Weibull++ 6 uses median ranks or Kaplan-Meier estimates. For a more detailed discussion of the use of median ranks for plotting, see ReliaSoft's Life Data Analysis Reference on the following topics. The reference is also available in an on-line version on weibull.com.

Q: When using the Tests of Comparison utility (Comparison Wizard) in Weibull++, is it applicable to change the lower limit to something other than zero on the Setup tab?

A: No, the lower limit should be equal to zero. The tests of comparison utility has been designed to compare data sets over their entire life spans, starting at time t=0.

Q: Why doesn't the calculated MLE line track the data points on my probability plot in Weibull++?

A: The reason that the fitted MLE model does not track the data points is due to differences in the way the plot and the MLE model are generated. The probability plot incorporates estimates of the unreliability in order to provide y-axis values to go with the failure times on the x-axis. In Weibull++, these unreliability estimates are provided by median ranks or Kaplan-Meier estimates. The maximum likelihood estimator (MLE) method of parameter estimation only uses the failure and suspension (x-axis) data when generating the unreliability model. Consequently, the fitted model may not necessarily track the data points on the plot. However, this does not mean that the model or the plot is "wrong," just that they were generated using two different methods.

Q: How can I show information from more than one data set on one plot in Weibull++?

A: Weibull++ Folios that contain more than one data set can easily display data from multiple sources using the Multiple Plot Sheet feature. Once the data sets of interest have been entered and analyzed, you can insert a Multiple Plot Sheet by making a selection from the Folio menu, pressing the hotkey combination Ctrl+M, or clicking the Multiple Plot Sheet icon in the toolbar.

In the Multiple Plot Sheet, simply select the data sheets that will appear in the plot and specify the rest of the plot properties. In order to be available for inclusion in a Multiple Plot Sheet the data sheet must have been calculated and, for probability plots, the data sheets must have been calculated with the same distribution. For example, if you have a data set that has been analyzed using the lognormal distribution, it cannot be displayed on a Weibull probability plot. This is because probability plots are constructed specifically for one type of distribution. 

The ALTA software also provides Multiple Plot Sheet functionality.

Q: How do I avoid having borders on my printed plots in Weibull++?

A: In both Weibull++ 5.0 and Weibull++ 6, you can de-select the Print Outline on Plot by Default option from the Plot page of the User Setup window.

Q: In Weibull++, what does the "Use True 3-P MLE on Weibull" option do?  

Q: Is there a way that I can display probability scales on the probability plots in Weibull++? 

A: Probability scales allow the user to read parameter estimate values directly from the probability plot. To toggle this feature on or off in Weibull++, select Show Probability Scales from the Plot Options menu or the Plot Sheet shortcut menu (accessible by right-clicking inside the plot area). This will show the probability scales appropriate to the selected distribution on the probability plot.

Q: How can I determine the confidence bounds on parameter estimates in Weibull++?  

Q: When entering temperature values into ALTA, on what temperature scale should the values be based?

A: If you are entering temperature values for the stress, you should enter the values in an absolute scale, i.e. Kelvin or Rankine. If the values are not in absolute scale, proper results will not be returned.

Q: How is thermal cycling handled in ALTA 1.0?

A: All of the models available within ALTA 1.0 deal with constant stress, i.e. stress that does not change over time. However, in temperature cycling you can cautiously use the change in temperature per cycle as the stress level in a constant stress model as defined by the Coffin Manson relationship. For a more detailed discussion, consult ReliaSoft's Accelerated Testing Reference, which is also available in an on-line version on weibull.com. The Coffin Manson relationship is covered on pages 164-167 of the reference (revised July 2001 and distributed with ALTA 6--pages 155-158 in the original reference distributed with ALTA 1.0). 

The ALTA 6 PRO software provides the cumulative damage (cumulative exposure) life-stress relationship model for analysis of data with time-varying stress profiles.

Q: What life-stress relationships and life distributions are available in ALTA?

A: All versions of the ALTA software provide the Weibull, lognormal and exponential life distributions.

Q: How is the activation energy, E_A, handled within the Arrhenius model in ALTA?

A: The Arrhenius reaction rate equation is given by:

• R is the speed of the reaction
• A is an unknown thermal constant
• E_A is the activation energy (eV)
• k is the Boltzman's constant (8.617385E-05 eV/K)

The Arrhenius life-stress relationship is given by:

   (1)

• L represents a quantifiable life measure
• V represents the stress level
• C is an unknown parameter
• B is the other unknown parameter

Depending on the application, B may be replaced by B = E_A/k. Note however that in this formulation, the activation energy must be known a priori and this is rarely the case. Therefore, the activation energy is treated as unknown and is included within the parameter B. It can be seen in Eqn. (1) that B has the same properties as the activation energy. B is a measure of the effect that the stress has on the life.

For a more detailed discussion, consult ReliaSoft's Accelerated Testing Reference, which is also available in an on-line version on weibull.com. The parameter B is covered on page 89 of the reference (revised July 2001 and distributed with ALTA 6--page 81 in the original reference). 

Q: What do I need to know before analyzing data from an accelerated life test with more than one type of stress in ALTA? 

A: Before analyzing data with more than one stress type (e.g. temperature and humidity), there must be an "overlap" of the stress levels in order to be able to fit a multiple stress life-stress relationship. This is because a relationship between the stress levels and the failure behavior of the product needs to be established. For example, consider a situation where Stress 1 has levels A and B and Stress 2 has levels X and Y. If the failure information is only collected where the stress levels are at A and X and at B and Y, a mathematical relationship between the two stress types and reliability cannot be obtained. The same failure data will have to be collected at a stress combination of A and Y or B and X in order to obtain a solution for the data set. If you attempt to analyze a non-cross-referenced data set in ALTA with a multiple stress model (such as the temperature-humidity and temperature-nonthermal models in ALTA 1.0 and ALTA 6 and the proportional hazards and general log-linear models in ALTA 6 PRO), a message box will inform you that such an analysis is not possible. 

Q: What do the parameters B and C represent in ALTA?

A: The parameters B and C are used by ALTA for the Arrhenius and temperature-nonthermal life-stress relationships. The application returns values for these variables along with the shape parameter for the selected distribution (beta for Weibull or standard deviation for lognormal). However, it is much more difficult to glean information about the test items from the B and C parameters than from the shape parameter.

Essentially, B and C are just variables for which ALTA solves in order to determine the relationship between stress and life; it is difficult to draw any conclusions about the behavior of the products based on the values of these parameters. However, you can get an indication of the nature of the relationship between life and stress from the parameter B. The sign of the B parameter indicates in which direction the life-stress relationship lies. If B is positive, the life of the product decreases with increasing stress. If B is negative, the life of the product increases with increasing stress (an unusual but by no means impossible situation). Similarly, the magnitude of the B parameter can indicate how quickly the life of the product changes with stress; values with larger magnitudes indicate that the life of the product is more sensitive to the stress. However, all of this is relative and one cannot draw any conclusions based on the value of B alone. The parameter C does not impart any useful information at all, it is merely a variable that ALTA solves for in order to complete the analysis.

Q: Is there a quick way to specify stress profiles in ALTA 6 PRO?

Q: Does BlockSim handle k-out-of-n parallel redundancy configurations?

A: Yes. This functionality is controlled by the use and configuration of the nodes in BlockSim. Lines going out from units in parallel can end in a node. A node is a block that usually has no failure characteristics (although they can be assigned failure characteristics in BlockSim). Double-click the node block to open the Node Properties window, where you can assign how many paths out of the parallel units must be functioning in order for that part of the system to operate. In this way, k paths out of n units can be assigned.

Q: How can I repeat the results I get when performing simulations in BlockSim?

A: The reliability and maintainability simulations in BlockSim rely on a random number generator to perform the analyses. Consequently, if you perform consecutive analyses on the same system without specifying a seed for the random number generator, the results will differ each time you run the simulation. If repeatable results are desired, be sure to select the Use Seed option on the Maintainability or Reliability tab of the Reliability/Maintainability Simulation window and specify the value to be used as the seed.

Q: In BlockSim, how can I simultaneously change the values of more than one block in the RBD? 

A: In order to change the values in more than one block, highlight the collection of blocks of interest. This can be accomplished either by dragging a box around the group of blocks you want to change, or by clicking the individual blocks while simultaneously holding down the Ctrl key. Double-click the highlighted blocks to begin editing (a message box will pop up to inform you that you are changing the values of more than one block). Note that once the changes have been entered, the blocks will have the same values for all parameters, even parameters that were not changed during the editing process.

Q: How do I obtain component failure and repair information for RBD blocks in BlockSim?

A: The recommended way to obtain failure and repair information is through empirical testing. This may be through in-house testing of components and parts or from information supplied by the vendor. ReliaSoft takes the position that this type of directly-obtained component information is the best way to represent the failure and repair characteristics of the components, and consequently will produce the best results for the system-level analysis. 

However, ReliaSoft recognizes that this information may not always be available for those who wish to perform a system reliability analysis. This may be due to a lack of affordable parts for testing early in the development process or simply due to the desire to "blue sky" and play around with potential design configurations without having to undergo costly testing procedures. Consequently, BlockSim can also import generic failure rates from the PRISM database developed by the Reliability Analysis Center (RAC). The RAC PRISM software has the next generation of electronic component failure rate models and a comprehensive searchable database of observed field failure rates modeled after RAC's successful NPRD and EPRD data book series. The PRISM concept accounts for the myriad of factors that can influence system reliability, combining all those factors into an integrated system reliability assessment resource. For more information about BlockSim's integration with PRISM, see http://BlockSim.Reliasoft.com/prism.htm.

Q: How can I quickly insert identical units in series in a BlockSim reliability block diagram?

A: Identical blocks in series can be inserted automatically using BlockSim's Add Block to Diagram command. Simply select an existing block in the diagram and select Add Block to Diagram from the Diagram menu or click the icon.

A new block, with the same style and properties as the selected block, will be created in the diagram. The new block will be placed to the right of the original block and connected with a relationship line.

Q: How can I copy a portion of a reliability block diagram (RBD) into the same diagram sheet in BlockSim?

A: Entire RBDs or sections of RBDs can be copied and pasted into the same diagram sheet in BlockSim simply by clicking the diagram sheet outside the blocks and dragging an outline around the section of interest. This will highlight a group of blocks that can be copied by selecting Copy from the Edit menu or by pressing Ctrl+C. By selecting Paste from the Edit menu or pressing Ctrl+V, the entire section of blocks (with connections) will be pasted back into the same diagram sheet and additional blocks and connections can be inserted to link this portion of the diagram with the original section of blocks.  

Q: Is there an easy way to align the blocks in BlockSim?

A: BlockSim's Align Objects tool allows you to align selected blocks in relation to the top, middle, bottom, left, center or right sides of the blocks. 

In addition, the Diagram Setup window provides the Snap to Grid option, which automatically aligns the blocks in the diagram sheet to a grid. To access the Diagram Setup, press Ctrl+D or select Diagram Setup from the Diagram menu or Diagram Sheet shortcut menu. The Diagram Setup also allows you to hide or display grid lines in the diagram sheet and change other aspects of the appearance of the diagram.

Q: Can I have circular references in my BlockSim reliability block diagram (RBD)?

A: Circular references are not allowed in BlockSim. The software uses a methodology called the Path Tracing Method in order to evaluate the reliability of the system in the RBD. The Path Tracing Method requires that each RBD has one starting block and one ending block. It then calculates all of the "paths" from the starting block to the ending block that would allow the system to function. For this reason, circular references are not allowed, as it would result in an infinite number of paths through the system. Note: Issue 2 of the Reliability HotWire eMagazine presents a more detailed discussion of methods to determine the reliability of complex systems.

In some circumstances, it may be possible to work around the problem of circular references by splitting blocks, or creating an input block and an output block, which represent two different functions of the same component.

Q: Why do I receive an error message when I export my Xfmea project to an XML file and then try to open the XML file in BlockSim?

A: This question is answered under Xfmea and FMEA/FMECA Analysis.

Q: What models are included with RG 1.0?

A: RG 1.0 provides the following models:

• Duane

• N.H.P.P. (AMSAA)

• Lloyd-Lipow

• Standard Gompertz

• Modified Gompertz

• Logistic

These models are described in more detail in ReliaSoft's Reliability Growth Reference, which is also available in an on-line version on weibull.com.

 

MPC 3 and MSG-3 Systems and Powerplant Analysis

Product Home

Q: What are the requirements for defining system configurations in MPC 3?

A: MPC 3's System Hierarchy has been designed to fit the Air Transport Association (ATA) definitions for aircraft groups, systems and subsystems (described in the document ATA iSpec 2200: Aircraft Systems). Therefore, the following constraints apply:

• There is a maximum of four levels in the system hierarchy: system, subsystem, sub-subsystem and part.
• The system numbers are intended to be based on the ATA iSpec2200 where, for example, 21 represents Air Conditioning, 23 represents Communications, 34 represents Navigation and so on.
• The subsystem numbers are intended to be identified in multiples of ten (i.e. 10, 20, 30, 40, etc.) based on the ATA iSpec2200 where, for example, 21-10 represents the Compression subsystem of the Air Conditioning system and 34-30 represents the Landing and Taxiing Aids subsystem of the Navigation system and so on.
• The subsubsystem numbers are intended to be defined within the range specified by the subsystem. For example, for any subsystem #10, the numbers 11 through 19 are valid to define the sub-subsystems.
• The "ATA Number" that is presented in the print-ready reports will consist of four (or more) numbers, in which the first two numbers are determined by the system, the third number is determined by the subsystem, the fourth number is determined by the sub-subsystem. Two or more additional numbers may be used to represent parts. For example, the ATA# 231500 represents the following system configuration:
  • System = 23 Communications
  • Subsystem = 10 Speech Communications
  • Sub-Subsystem = 15 SATCOM
• In CRV 3.0.11, ReliaSoft added the ability to use the "extended" MSI number format in print-ready report output. If this option is selected on the Report Properties page of the User Setup, the first two numbers are determined by the system, the third and fourth numbers are determined by the subsystem and the fifth and sixth numbers are determined by the sub-subsystem. For the example given above, this would be 231015.

Q: Why are the MSI selection questions disabled in MPC 3?

A: The MSI selection questions are available only at the lowest level of the system hierarchy; answers made at that level are then "rolled up" to the higher levels. If, for example, you have a hierarchy with a system, a subsystem and a sub-subsystem, MSI selection questions will be available only for the sub-subsystem. If you have assigned one or more parts below that sub-subsystem, however, the selection questions will be available only for those parts and the answers to the questions will apply at all levels above the parts. This is based on the assumption that if any component of an assembly poses, for instance, a safety risk, then the entire assembly also poses a safety risk, and so on. A Yes answer for any question for any part will identify the subsubsystem as a Maintenance Significant Item in the software and in the report output.

Q: Which FMEA/FMECA standards does Xfmea support?

A: Xfmea supports the following major industry standards for FMEA/FMECA reporting:

• SAE J1739
• AIAG FMEA-3
• MIL-STD-1629A

In addition, Xfmea provides extensive customization capabilities to allow you to customize the interface and reports to fit your own specific procedures.

Q: In Xfmea Standard, why are the Add and Delete buttons disabled in the Profiles/Libraries Management window? I am also unable to edit any of the profiles.

A: This will occur if the active library is Read-Only for the user. To test this, go to the Other page of the User Setup and determine the location/filename for the active library file (*.lib). Then determine whether the user has Read/Write access to this file. If not, give the user Read/Write access (e.g. place the file in a directory that the user has Read/Write access to and/or open the Properties window for the file and de-select the Read-only option) or choose a different library to be active.

Q: Why do I receive an error message when I export my Xfmea project to an XML file and then try to open the XML file in BlockSim?

A: You will receive an error message in BlockSim when you try to open an XML file that was created in Xfmea if at least two higher level items in the Xfmea project have the same name. This is because any item that has one or more sub-items is represented as a subdiagram in BlockSim and the diagram names in BlockSim must be unique. This will also occur if the project and a higher level item have the same name because the project is also represented as a diagram in BlockSim.

When you receive this error message in BlockSim, you will be asked if you want to see the error report. Click Yes so you can identify the errors in the XML file. You may be prompted to enter a path for the word processor that will display the error report. Type the pathname for an application on your computer that can open a text file (e.g. Notepad, WordPad, etc.). For example, enter C:\Windows\System32\Notepad.exe. (Please note that if this is not a valid pathname/filename on your computer, then the report will not open.) Click OK. The report will automatically open in the specified application with a list of the errors that have been found in the XML file. You can then go back to your Xfmea project and correct these errors, export the revised project to XML and then open the XML file in BlockSim.