Environmental Engineering Reference
In-Depth Information
Units of running time
-1
Running-in
period
Ageing period
Normal service period
Operating time
1. 8
Changes of FR
λ
(
t
).
measures
P
(
t
),
f
(
t
) or λ(
t
), determines the law of the random variable which
is chosen depending on the properties of the object, its working conditions
and the nature of failures.
Formulation of the problem of statistical processing of test results
and determination of reliability indcators.
The results of tests of
non-renewable
N
identical objects yield the statistical sample - a set of
operating times (in any units) to failure of each of
N
test objects. Sampling
characterises the random value of the operating time to failure of the object
T
= {
t
}.
The law of distribution of
T
must be selected and the correctness of the
choice of appropriate criteria verified.
Selection of the distribution is based on approximations (smoothing) of
the experimental data on operating time to failure which must be presented
in the most compact graphical form. The approximating function is selected
on the basis of the hypothesis put forward by the researcher. Experimental
data can confirm or not confirm the validity of a hypothesis with different
probability. Therefore, it is necessary to answer the question: are the results
of an experiment in agreement with the hypothesis that the random value of
operating time is governed by the distribution law selected on the basis of
the experiment? The answer to this question given by result of calculations
using specific criteria.
The algorithm for data processing and calculation of reliability
indicators.
Formation of a statistical series
With a large number of test objects the set of the operating time values
{...,
t
i
, ...} is a cumbersome and insufficiently visual form of expressing
the random variable
T
. Therefore, for brevity and clarity, the sample is
represented in the graphical representation of a statistical series - the
histogram of the operating time to failure. For this purpose it is necessary
to:
- set the operating time interval [
t
min
,
t
max
] and its length
ξ= −
tt t
min
,
max
where
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