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7 Menu
Since the energy of the reflected noise signals is generally ex
-
tremely low, it is recommended to use this procedure only in special
cases. If the pipe contains gases, the chances may be better.
If Auto correlation is used, the location of the reflection point must
be known.
The auto correlation function (ACF) always runs symmetrically. Only
the negative range of the auto correlation (delta t < 0) is significant.
7.6.6
Sampling frequency
The continuous time signal of the used channels is sampled and
digitised with a particular frequency, the sampling frequency.
The lower the sampling frequency, the less time is required for calcu
-
lating the averaging processes. However, the used sampling theorem
demands a sampling frequency which is at least twice as high as the
highest frequency contained in the signal! Setting the sampling fre-
quency too low may lead to faulty measurements. For this reason, it
is recommended to decrease the sampling frequency only in special
cases, e.g., if extreme low-frequency noise is to be measured.
If Automatic is selected, the sampling frequency is set to its maxi
-
mum height.
If you want to define the setting manually, select Direct. You can
then change the sampling frequency with the arrow keys.
All following measurements are performed with this sampling
frequency.
7.6.7
Table
In this menu, you can select two different sound velocity tables.
They differ in subranges.
Sound velocity 1:
Particularly good experiences in France
Sound velocity 2:
International validity
Sound velocity 3: This function is not available
7.6.8
Standard values
All parameters in the
Parameter menu of the
SeCorr 08
are re-
set to the respective
standard values. This also includes those
parameters which remain stored after switching off the device.
The set
language is not changed.