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II) in comparative tests the structure is representative of the
real circumstances.
The structure defines the adequacy of the test. The quantity
or the sample size of the input and its accuracy influence the
extent and the confidence level of a test.
b) The auxiliary devices should be adapted to the function or struc
ture of the system components to which the test applies. Such
devices should be calibrated; their accuracy must be higher
than the required accuracy of the component being tested.
Standard inputs and auxiliary devices can be used in combina
tion. Both must be specially prepared for a test; the preparation
depends on the testing process.
4.4. Definition of testing process
The structure of a testing process is conditioned by the objectives,
environments, configuration of the system itself and by the means
for execution. The approach is different for the detective and the
comparative tests.
In detective tests, the configuration of the system or of operations
concerned should be defined as accurately as possible. For this
purpose it is convenient to construct a functional diagram.
Then the probable sources of error or disturbances can be studied
and their effect on the output can be estimated. The analysis is
based on the knowledge from experience, on physical understanding
of the phenomena involved, and sometimes on experimental
research. All the significant sources of error must be considered, and
they can be classified into groups with similar effects on the output.
The result of such an analysis is the mathematical model, which
will be discussed in more detail under "data processing". The
designing of a testing process and the establishment of the mathem
atical model for data processing is carried out simultaneously. The
structure of the testing process should reflect the mathematical
model and vise versa.
For the detection of instrument errors, the principle of maximum
response to these errors should be applied. This can be achieved
e.g. by:
I) the choice of an appropriate input structure and sample size,
II) making use of sensitive auxiliary devices,
III) the choice of convenient values for the system parameters,
IV) variation of system parameters during the test (between
the successive phases of the test),
V) selection of critical ranges and/or directions,
VI) applying a convenient technique of operation, etc. (e.g.
backlash, tracking error, straightness.
