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ALTA Two-Stress Example

Stress Profile Example

ALTA Single-Stress Example

A manufacturer asks a team of engineers to determine, with a confidence level of 90%, whether a prototype device has a reliability of at least 90% at 6,000 hours. Since the life of the product under normal operating conditions is expected to be more than 15,000 hours, it is not feasible to test under these conditions and obtain results in an acceptable timeframe. So the engineers decide to run an accelerated test with a duration of 7,500 hours, by which time they expect that the majority of units will have failed. The normal operating temperature for this product is 323 K (50°C), and temperature is the only acceleration variable.

The data collected from the test for three different accelerated stress levels are shown next.

Stress Level (K) 393 408 423
Failure Time (Hr) 3850 3300 2750
4340 3720 3100
4760 4080 3400
5320 4560 3800
5740 4920 4100
6160 5280 4400
6580 5640 4700
7140 6120 5100
Did not fail 6840 5700
Did not fail Did not fail 6400

 

Click Calculate to display the results, as shown next.

The results show that the device’s estimated reliability at 6,000 hours is 99.09%. The lower one-sided 90% confidence bound is shown to be 90.61%. In other words, the test shows with 90% confidence that the device’s reliability a 6,000 hours is at least 90.61%, thus meeting the demands of the manufacturer.

 

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