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).
The following calculations are available for life data analyses:
Probability
Reliability
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.
Probability
of Failure
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.
Conditional
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%.
Conditional
Probability of Failure
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
Reliable
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.
BX%
Life
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.).
Mean
Life
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 software.
Mean
Remaining Life
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
Failure
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
Parameter
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.