ALTA Test Plan Utility

The ALTA Test Plan utility is a planning tool that helps you design a one-stress or two-stress accelerated life test that will yield the closest possible estimate of product life under normal operating conditions. It generates a test plan with recommendations for what stress levels should be used in the test and how many units should be tested at each stress level.

Follow the steps outlined below to generate a recommended test plan.

Create a new Test Plan folio by choosing Insert > Tools > ALTA Test Plan.

From the Number of Simultaneous Stresses drop-down list, choose whether you will be designing a test that applies only one type of stress during the test, or a combination of two stresses applied simultaneously (e.g., temperature and humidity).
From the Test Plan Type drop-down list, choose an appropriate test plan. The test plan level is the number of stress levels that the plan recommends (e.g., a 3 level plan will recommend subjecting some units to a low stress level, some to a mid level and the rest to a high level). Test plans may also differ according to how they allocate the units to stress levels. Your specified test plan will minimize the variance on the value you enter in the BX Life Estimate Sought field. See ALTA Test Plan Types for details on each test plan.
In the BX% Life Estimate Sought field, enter (as a percentage) the BX% life that you intend to estimate from the test (e.g., for the B10 life, you would enter 10).

In the Available Test Time field, enter the duration of the accelerated life test you are planning. (The duration can be entered in any unit of time, but you must use the same time unit throughout the utility.)
From the Unit Allocation drop-down list, choose Show Allocations as % if you do not want to specify the total number of units that will be available for testing. In this case, the test plan will only display the percentage of the available units that should be allocated to each stress level.

If you want the test plan to display both the percentage and the quantity of test units allocated to each stress level, choose Show Allocations as Qty and then enter the total number of units that will be available in the Number of Units Available field.

From the Lifetime Distribution drop-down list, select the distribution that describes your product's life behavior. You can select Weibull and enter the shape parameter in the Beta field, or select Lognormal and enter the shape parameter in the Std field.

Tip: If your product's underlying life distribution is exponential, select Weibull from the Life Distribution drop-down list and enter 1 in the Beta field. This is equivalent to using an exponential distribution.

Next, in the Stress 1 area, choose the appropriate Life-Stress Relationship from the drop-down list. Then enter the stress level at normal use conditions in the Use Stress Value field. In the Maximum Stress Value field, enter the maximum stress level that could be applied during the test without introducing failure modes that would not occur under normal use conditions. Repeat these steps for Stress 2 if you selected to design a two-stress test.
In order to provide reasonable recommendations for the stress levels to be used in the test, the software must estimate a life-stress relationship for your product. The utility will estimate a life-stress relationship using the values you enter in the Probabilities of Failure (%) area. Each probability of failure is for the time you entered in the Available Test Time field and at the stress level described.
- For example, if you specified a test time of 100 and one of the fields in this area is P(Time, Use Stress 1, Maximum Stress 2), then you should enter the estimated probability of failure for the product at time = 100, where the product experiences Stress 1 at the specified use stress value and Stress 2 at the specified maximum stress value.
Click Calculate to generate the recommended test plan. The Test Plan Results sheet will appear. See Test Plan Results Sheet for information on how to read the results and evaluate the plan. You can further evaluate the recommended plan by using the utility's control panel.