QCP Calculations for Life Data Analysis

Weibull++ includes a Quick Calculation Pad (QCP) for computing useful life data analysis metrics. You can access the QCP by clicking its icon on the Main page of the control panel.

To perform a calculation, select the appropriate option and enter any required inputs in the Input area, then click Calculate. For more detailed information on how to use the QCP in general, see Quick Calculation Pad (QCP).

Probability

Calculates the probability that a new product will operate without failure for a given period of time. Enter the time at which you wish to calculate the reliability in the Mission End Time field. The mission is assumed to start at time = 0.

For example, a reliability of 90% for a mission end time of 3 years means that if 100 identical units are fielded, then 90 of them will still be operating at the end of 3 years.

Calculates the probability that a new product will be failed in a given period of time. Enter the time at which you wish to calculate the probability of failure in the Mission End Time field. The mission is assumed to start at time = 0.

Probability of failure is also known as unreliability, and it is the inverse of the reliability. For example, a probability of failure of 10% for a mission end time of 3 years is equivalent to a 90% reliability.

Calculates the probability that a product will successfully operate at a specific time interval given that it has operated successfully up to a specified time. Enter the start time of the interval in the Mission Start Time field and enter the duration of the interval in the Mission Additional Time field.

For example, a product may have a reliability of 90% for 3 years. If the product has operated for 2 years without failure, the conditional reliability for an additional year (for a total of 3 years of operation) may be 95%.

Calculates the probability that a product will be failed at a specific time interval given that it has not failed up to a specified time. Enter the start time of the interval in the Mission Start Time field and enter the duration of the interval in the Mission Additional Time field.

For example, a product may have a 10% probability of failure for 3 years. If the product has operated for 2 years without failure, the conditional probability of failure for an additional year (for a total of 3 years of operation) may be 5%.

Life

Calculates the estimated time at which a specified reliability value will be achieved. Enter the reliability goal in the Required Reliability field. For example, a goal of 90% reliability with a reliable life of 4 years means that if 100 identical units are fielded, then 90 of them will be still be operating at the end of 4 years.

Calculates the estimated time at which a specified probability of failure will be achieved. Enter the probability of failure in the BX% Life At field. For example, a B10 life of 4 years means that 10% of the fielded units are expected to be failed at the end of 4 years of operation (note that this is equivalent to a 90% reliability with a reliable life of 4 years).

Note: In the early days of reliability engineering, bearing manufacturers used the term "B10 life" to refer to the time by which 10% of the components would fail. Keeping with tradition, ReliaSoft retained this nomenclature but replaced "10" with "X," since the software allows you to get this information at any percentage point and not just at 10% (e.g., B1, B5, etc.).

Calculates the average time at which a product is expected to operate before failure. In the Weibull++ life data folio, the mean life is the mean time to failure (MTTF) based on the fitted model.

Note: The term mean time to failure (MTTF) is used as a metric for the analysis of non-repairable components. In the Weibull++ life data folio, all data are assumed to come from non-repairable components that are independent and identically distributed (i.i.d.). On the other hand, the term mean time between failures (MTBF) is used as a metric in repairable systems analysis, where the same system may fail and be repaired multiple times. To analyze simple repairable system data in Weibull++, use the recurrent event data analysis (RDA) folios.

For more complex repairable system analyses, see ReliaSoft’s BlockSim and RGA software.

Calculates the expected remaining life given that the product, component or system has survived to time t. Enter the time at which you wish to calculate the mean remaining life in the Mission End Time field.

Rate

Calculates the instantaneous number of failures per unit time that can be expected at a certain time given that a unit survives to that age. Enter the time at which you wish to calculate the failure rate in the Mission End Time field.

For example, a failure rate of 0.01 at 100 hours means that each unit that survives to 100 hours has approximately a 1% probability of failure in the next hour.

Bounds

Calculates the specified bounds on the parameter estimates, allowing you to quantify the amount of uncertainty in those estimates. This option is available only when you have specified the type of confidence bounds to use from the Bounds drop-down list. When you click Calculate, the Results Window will open to display the estimated parameters and their bounds.