MIL-DTL-23659F
APPENDIX A
specified herein. System-specific levels in excess of those specified can be added to the
environmental sequence if beneficial, and must be applied during the type qualification phase of
system development. Provisions should be made in any hardware used as fixturing for the shock
and vibration tests to accommodate any ILI deformed by the 1.5 meter drop test.
A.7.6.9. Sensitivity Test and Analysis. This section provides some background information
on sensitivity test and analysis methods that are used for estimating the reliability and safety of
exploding foil initiators. Reliability and safety issues necessitate use of methodologies that can
assure consistency in derivation of these estimates. Accepted test and analysis methods for
estimating these parameters include the Langlie, Probit, One Shot Transformed Response and
Neyer D-Optimal Test methods. Although test and analysis are independent functions, each
unique test method is historically associated with a unique analysis technique. These methods
and techniques are commonly referred to as sensitivity tests and analyses. Because many ILI
have outputs that are not linearly linked to the input stimulus they require the specialized test and
analysis methods described here.
A.7.6.9.1. Objectives. The objective of sensitivity test and analysis methodologies used
should be assurance that estimates derived are as accurate and precise as possible. The
parameter to be estimated is the mean stimulus level at which some fraction of the samples of a
specific exploding foil initiator design will always function, in the case of an all-fire test, or not
function, in the case of a no-fire test. There are no methodologies capable of exact
determinations of this parameter. There are no non-destructive methods available to obtain the
data needed. The tests described here are usually considered as destructive in nature and
therefore, the test articles should not be re-used in the end item. The analysis portion of the
method computes estimated all-fire or no-fire rating. These estimated ratings are computed at a
specific reliability and confidence and are applicable to only the specific exploding foil initiator
design tested.
A.7.6.9.2. Sensitivity Test Limitations Tests. All methods used are small sample based.
Therefore error in the estimates will occur. Care must be exercised when choosing test stimulus
levels during the tests. If empirical data on the specific design is not available to assist selection
of test levels before start of the test then additional samples should be allocated to perform pre-
test evaluations. All of the methods used here assume the distribution of the threshold stimulus
levels is normal. It is simple to generalize this assumption and require that some functions, such
as a logarithm, of the threshold levels are normally distributed. None of the test methods will be
able to determine if even a relatively large percentage of the exploding foil initiators are duds,
that is, those that will not function at any voltage. Thus, threshold tests must always be backed
up with testing a sufficient quantity at an all-fire voltage.
A.7.6.9.3. Reliability and Confidence Levels Tests. For illustrative purposes in this example,
reliability and confidence level values of 0.99 and 95% upper confidence limit have been chosen.
This is literally interpreted to mean that 95% of the time such intervals are constructed, on
average, no more than 1 in 100 ILI will fail to function at the estimated all-fire rating. Users of
these computed values should be made aware that adding margin to estimated all-fire and no-fire
values is standard practice. Explosive system reliability assessments should therefore use the
minimum stimulus values that the ignition system delivers to the exploding foil initiator to assess
realistic system level reliability. Figure A-4 shows an example of a typical probability curve that
is obtained from analysis of sensitivity test data. The y-axis is plotted using probability scaling.
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