Reliability HotWire

Reliability HotWire

Issue 116, October 2010

Tool Tips

*How can I change the data type for a Standard Folio in RGA 7?

Once you have created a Data Sheet in RGA 7’s Standard Folio, you cannot change the data type. For several data types, however, you can transfer the data set to a new Data Sheet that has been configured for a different data type. Transferring is available for the following data types:

  • Times-to-Failure Data - Multiple Systems
    • Concurrent Operating Times
    • Multiple Systems with Dates
    • Multiple Systems with Event Codes
  • Fielded Systems Data
    • Repairable Systems
    • Fleet

You can choose to transfer data from any of these data types to any other of these data types. To do this, choose Data > Transfer to New Data Type or click the Transfer to New Data Type icon on the Main page of the Standard Folio Control Panel.

The Transfer to New Data Type window will appear, allowing you to select a data type into which you would like to transfer the data from the current Data Sheet.

 When you make your selection and click OK, the new Data Sheet will be added to the current Folio.

 

*How can I evaluate the accelerated life test design recommended by ALTA’s test planning utility?

The accelerated test plan utility in ALTA 7 has options to help you evaluate the test design based on the conclusions you want to obtain from analyzing the test data. There are three factors you can manipulate to determine whether the design will meet your needs: confidence level, bounds ratio and sample size.

Bounds ratio is defined as the ratio between the upper and lower confidence bounds. It helps you determine the relative size of the variance of the B(X) life estimate you may obtain if you implement the test design and analyze the data that you record. The relationship between the bounds ratio, confidence level and sample size is summarized as follows:

  • The higher the required confidence level, the wider the confidence interval; therefore, a larger bounds ratio.
  • The larger the sample size, the narrower the confidence interval; therefore, a smaller bounds ratio.

Consider the sample test plan shown next. In the Control Panel on the right side of the result Folio, you can see that for a 90% confidence level and a sample size of 20, the calculated bounds ratio is approximately 3.53.

If the bounds ratio is determined to be too wide, then you have the option to either accept a lower confidence level or increase the sample size. You can experiment with different adjustments to find an acceptable solution. You also have the option to return to the test plan setup window, select a different test plan method and generate a new design that may be more suitable.

ALTA 7 also provides a simulation tool called SimuMatic® that you can use to visualize the confidence bounds associated with the bounds ratio presented in the test plans utility. The test plans utility uses an analytical solution that is based on the assumption of large sample size; the simulation tool does not make any assumptions about the sample size and thus may be preferred in the case of small sample sizes. For a comparison of the analytical solution vs. simulation results, see http://www.ReliaSoft.com/newsletter/v8i1/plans.htm.