QCP Calculations for Accelerated Life Testing
For life-stress data only.
Accelerated Life Testing includes a Quick Calculation Pad (QCP)
for computing useful 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 accelerated life
testing data analysis:
Probability
Reliability
Calculates the probability that a
new product will operate without failure for a given period
of time at the stress level specified in the Stress
field. 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 at the
stress level specified in the Stress
field. 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 and at the stress level specified in the Stress
field. 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 it operates at a stress
level of 10 volts. 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 and at the stress
level specified in the Stress
field. 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 it operates at a
stress level of 10 volts. 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 at the stress
level specified in the Stress
field. 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 at
the stress level specified in the Stress
field. Enter the probability of failure in the BX%
Life At field. For example, a B10 life of 4 years means
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 life, B5 life, etc.).
Mean
Life
Calculates the average time at which
a product is expected to operate before failure at the
stress level specified in the Stress
field. In the life-stress 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 Accelerated Life Testing life-stress 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. Simple repairable system data
can be analyzed in Weibull++ using the Recurrent
Event Data Analysis (RDA) folio.
For more complex repairable system analyses, see ReliaSoft’s
BlockSim.
Mean
Remaining Life
Calculates the expected remaining
life given that the product, component or system has survived
to time t at the
stress level specified in the Stress
field. 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 and at the stress level specified in the Stress
field, 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 and at a stress level of 10 volts means that
each unit that survives to 100 hours has approximately a 1%
probability of failure in the next hour.
Acceleration
Acceleration
Factor
Calculates the ratio of the product's
use level life to its life at an accelerated stress level.
For example, if the product has a life of 100 hours at the
use stress level, and it has a life of 50 hours at an accelerated
level, then the acceleration factor at the specified stress
levels would be 2. Click the arrow in the Stress
field to enter the use level stress values for every stress
that was used to calculate the data sheet. Click the arrow
in the Accelerated Stress
field to enter the accelerated stress values.
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.