Norsonic nor140, Instructional Manual

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30
Chapter 5
Frequency analysis
Multispectrum is available as long as mini-
mum option 1 and 6 are installed. This is
treated in
Multispectrum measurements.
Statistics
If your instrument is equipped with the optional
extension 4 - statistics, the percentiles table will be
produced and there will be 8 percentiles for every
centre frequency. fail to produce values for all
percentile settings unless the measurement duration is
sufficiently long – see the
Missing percentiles
side bar
in this chapter for more on this.
Instruments with time profile installed
If your instrument has the time profile option installed,
you are able to see the time history for each filter
frequency. If you don’t require it, you should set the
resolution to the same value as the duration to keep the
instrument from logging the level as a function of time –
like the classic level recorders used to do.
Cf.
Enhanced time profile measurements, Basic
time profile measurements and Multispectrum meas-
urements
for details on logging the level vs. time with
or without the spectrum as a function of time.
Consider setting the time constant
If your instrument is not equipped with the optional
extension 5 – parallel time constants (see
Units
equipped with multiple time constants)
, you may
want to specify the time constant to be used in the
measurement.
The time constant is used for the SPL, the L
MAX
and
the L
MIN
measurements, but neither L
eq
nor L
E
make use
of it.
To set the time constant press the
TC
key until the
required time constant appears in the display. To see
this, be sure to operate the
FUNC
key until any of the
functions SPL, the L
MAX
or the L
MIN
appears in the
display first.
Setting C or Z as spectral weighting network
The Nor140 has three spectral weighting functions in
addition to the filter bands. These are A-weighting and
C- or Z-weighting. The Z-weighting is a replacement
for the previous Flat or Linear spectral weighting
functions.
The Z spectral weighting circuitry is flat within at
least 16 Hz to 16 kHz and is defined in the International
standard IEC 61672-1.
The Nor140 can make use of two of the three
spectral weighting functions simultaneously – viz. A-
weighting and Z- or C-weighting.
To specify whether to use Z- or C-weighting:
• Press
SETUP > 1
(instrument)
> 5
(2nd netw) and
navigate in the menu as usual.
The A-weighted value and the C- or Z-weighted value
will appear as extra bar graphs to the right of the spec-
trum in the display.