Accelerated Life Testing Data Analysis
Fitting the ALTA Model
ALTA provides all the tools and options you will need for accelerated life testing data analysis. It is designed for use with complete (time-to-failure), right censored (suspended), interval or left censored data. Data can be entered individually or in groups.
ALTA Standard gives you a choice of the following life-stress relationships:
- Arrhenius: a single stress model typically used when temperature is the accelerated stress.
- Eyring: a single stress model typically used when temperature or humidity is the accelerated stress.
- Inverse Power Law (IPL): a single stress model typically used with a non-thermal stress, such as vibration, voltage or temperature cycling.
- Temperature-Humidity: a double-Arrhenius model that is typically used when temperature and humidity are the acceleration variables.
- Temperature-Nonthermal: a combination of the Arrhenius and IPL relationships that is typically used when one stress is temperature and the other is non-thermal (e.g., voltage).
In addition, ALTA PRO offers four other models for more advanced applications:
- Generalized Eyring: a variation of the Eyring relationship that is typically used when both temperature and humidity are accelerated.
- Proportional Hazards: analyzes data with up to 8 stress types using the Exponential relationship for each stress. It also allows the use of zero as a stress value, which enables the analysis of data with indicator variables (e.g., 0 = on/off and 1 = continuous operation).
- General Log-Linear: supports the analysis of data with up to 8 stress types and provides the flexibility of specifying the life-stress relationship (Arrhenius, Inverse Power Law or Exponential) for each stress.
- Cumulative Damage: analyzes data with up to 8 stress types and/or situations where the stress varies with time, and also provides the flexibility of specifying the life-stress relationship for each stress.
You can select to combine these life-stress relationships with an underlying Weibull, Exponential or Lognormal life distribution. If you are not sure which is appropriate for a given data set, the convenient Distribution Wizard automatically performs multiple goodness-of-fit tests in order to rank the available distributions.
Maximum Likelihood Estimation (MLE) is used for all parameter calculations. ALTA also provides Fisher Matrix confidence bounds for parameters, calculated results and plots.
Calculated Results and Plots
The software provides a complete array of Calculated Results and Plots based on the analysis. For accelerated life testing data analysis, this includes:
- Reliability or probability of failure
- Reliable life (i.e., time for a given reliability, also called "warranty time")
- BX% life (i.e., time for a given unreliability)
- Mean life
- Failure rate
- Acceleration factor
- Probability plots and pdf plots
- Life vs. stress, acceleration factor vs. stress, and standard deviation vs. stress plots
- Residuals plots
- Three-dimensional surface plots such as reliability vs. time vs. stress
The Quick Calculation Pad (QCP) has been updated and redesigned in the Synthesis version. The new interface provides a "Calculation Log" that works like a paper roll in an adding machine, allowing you to record the results from a series of different calculations and then copy/paste the information as needed.