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9 Options for
Options for optimising measurement results
9
Options for optimizing measurement results
The ability to detect a leak depends on the correct calculation of
the time difference. In cases where the leak noises are strong
enough and there are no external sources of noise, the time dif-
ference displayed after just a few averaging procedures (4 to 16)
should suffice.
But what can you do when a “nice” incisive peak just will not
form? The following advice cannot of course replace the practice
and experience required for difficult cases, but it can provide an
insight. Regardless of this, however, you must always remember:
when the leak noises do not reach the microphones with enough
intensity, correlation is not possible.
9.1
Changing the number of averaging procedures
If the result is still unsatisfactory after the initial averagings, you
can increase the number of averagings as often as you wish. The
result will improve because the calculation can be based on ad-
ditional information over the progression of the leak noise. From
experience, however, the result does not improve any further after
64 to 128 averagings.
9.2
Using filters
Use the possibilities offered by mathematical filters. Unfortunately
universal “formulae” can rarely be given. Only your own experi
-
ence and trial and error will result in success.
Usually it is only recommended to select frequency ranges for
the CCF in which the coherence function has a significant exces
-
sive increase compared to the surrounding area, in other words,
features a “hump”.
Single frequencies from various sources of interference produce
a continuously sinusoidal CCF. They can be identified in the
spectra as a sharp line.
