Reliability HotWire: eMagazine for the Reliability Professional
Reliability HotWire

Issue 53, July 2005

Tool Tips

*In RCM++, how can I indicate that certain maintenance tasks should be performed together?

The Maintenance Task Packaging window allows you to group tasks into maintenance packages for the most efficient allocation of resources.

 

You can add or edit maintenance packages by clicking Add Package or Edit Package, which opens the Maintenance Package Properties window, as shown next.

Once you have added a maintenance package, you can add tasks to it manually by dragging them from the Individual Tasks area. This area displays all master (i.e. non-linked) tasks that have not yet been assigned to a package.

You can also automatically assign tasks to packages by specifying criteria for automatic task packaging in the Maintenance Packaging Properties window. Clicking Auto-Package Tasks in the Maintenance Task Packaging window will assign all unpackaged tasks with assigned intervals from 170 to 190 hours to this maintenance package. Note that if a task fits assignment criteria for more than one package, it will be assigned to the first package in the list for which it qualifies.

Chapter 9 in the RCM++ Users Guide provides more information on maintenance task packaging.

*What are the main differences between Xfmea Standard and Xfmea Enterprise?

Both Xfmea Standard and Xfmea Enterprise provide comprehensive support for FMEA/FMECA and related analyses.

Xfmea Standard stores data in individual Access databases located on the user's computer or a shared network drive. This does not require any special IT infrastructure/support and the user can work on the analysis "off-line" (e.g. from a laptop computer at a remote location). However, there are limitations to the amount of data that can be stored in a single database and the number of users who can simultaneously access the same database.

Xfmea Enterprise stores data in a SQL-Server database that has been configured on the organization's network. This is a much more robust database that can store a large amount of data and support simultaneous access by a large number of users. Due to the centralized data storage, Xfmea Enterprise is able to provide some additional features that are not available in Xfmea Standard, such as automatic login based on Windows NT authentication; a personalized "Portal" that provides quick access to projects, actions and messages of interest to the specific user; expanded actions management capabilities; more options to control the access levels of individual users, etc. (For specific details, see http://Xfmea.ReliaSoft.com/enterprise.) However, this implementation requires the IT infrastructure/support for SQL-Server and users must export their data to Xfmea Standard if they want to work on the analysis "off-line."

For more information, visit http://Xfmea.ReliaSoft.com/enterprise/compare.htm.

* How do I obtain goodness of fit results in Weibull++?

Select Show Other and then Goodness of Fit Results from the Data menu to open the Goodness-of-Fit Results window. This window shows the results of the Kolmogorov-Smirnov, correlation coefficient and Chi-Squared tests, as shown below.

Both the KS and Chi-Squared tests return the probability that the respective critical value is less than the calculated value. High values, close to one, indicate that there is a significant difference between the theoretical distribution and this data set.

 

The correlation coefficient returns a measure of the linear fit of the regression line to the plotted data. It is not available if MLE is used.

 

Special Note: Depending on the sample size used, the Chi-Squared and KS tests will return different results. For KS, DCRIT becomes smaller as the sample size increases, thus increasing the probability that DCRIT < D. On the other hand, the Chi-Squared test is really not valid for smaller sample sizes; a minimum sample size of 35 is required for results to be valid.

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