How to Perform a Weibull Analysis – Data Preparation (Part 1 of 3)
Welcome to our three-part series about how to conduct a Weibull Analysis. Instead of showing tons of formulae, this series discusses essential steps you need to consider when performing the analysis, with some useful tips. Keep reading!
There are 4 steps to prepare life data:
- Determine the asset(s) to be analysed
- Determine the component failure mode for that asset(s)
- Obtain as much relevant life data as practical
- Classify life data
Step 1: Determine the asset(s) to be analysed
Step 2: Determine the component failure mode for that asset(s)
Step 3: Obtain as much relevant life data as practical
In order to make accurate predictions about the life of all products in the population, you need to gather as much relevant life data as practical. Good data, along with the appropriate model choice, usually results in good predictions.
Life data can be gathered from in-house/lab or field testing.
- In-house reliability test: such as testing during design, Qualification testing, Life tests, Quantitative accelerated life tests, Reliability growth tests.
- Field data: collected from call centres, warranty claims, inspection of returned items. Field data can be badly biased, however, it is more likely to reflect actual use (and abuse) conditions.
Step 4: Classify life data
Within censored data, it has 3 sub-types: right censored (suspended), Internal censored, and left censored data. Different data type requires different analysis methods, which is discussed in our next blog post.
The exact time-to-failure (TTF) for the unit is known (e.g., the unit failed at 300 hours of operation). Usually from highly structured lab testing or fully accessible field data with high failure rates.
Right Censored Data (aka Suspended Data)
The unit operated successfully for a known period of time and then continued (or could have continued) to operate for an additional unknown period of time (e.g., the unit was still operating at 300 hours of operation).
Interval Censored Data
The unit’s exact TTF is unknown but it failed at some point within an interval. (e.g. the unit failed between 300 hours and 400 hours).
Treat data as interval data if the granularity of the data is coarser than the desired results.
- If the desired result is in months and data points are in months as well, then consider the set to be complete data
- If the desired result is in days but data points are in months, then consider the set to be interval data
Left Censored Data
The unit’s exact TTF is only known to be before a certain time. (e.g., the unit failed between 0 hours and 300 hours).
Weibull Analysis Related Resources:
- How to Perform a Weibull Analysis – Data Preparation (Part 1 of 3) [THIS BLOG]
- How to Perform a Weibull Analysis – Lifetime Distribution Selection and Parameter Estimation (Part 2 of 3)
- How to Perform a Weibull Analysis – Validation of Results and Reliability Improvement (Part 3 of 3)
- The Quick Guide to Perform a Weibull Analysis [one-page infographic]
Weibull Analysis Software: ReliaSoft Weibull++ – Provide the most comprehensive toolset (e.g., distribution wizard) available for reliability life data analysis, calculated results, plots and reporting.