Svantek SVAN 979 - Statistical Levels - Lnn Definition

361
SVAN 979 User Manual - Appendixes
Ovl
Percentage of the overloaded input signal, which occurred during the current time period of the
measurement (T)
Peak
Maximum absolute value of the signal calculated
for the given T
( )
tamaxPeak
WT
=
P–P
Peak-to-peak (P-P) result is the difference
between highest and lowest value of the signal
calculated for the given T
( )
( )
( )
( )
ta,0minta,0maxPP
WTWT
−=−
Max
Maximal value of the time-weighted signal for
current time period of the measurement (T)
( )
( )
tamaxMax
W
T

=
RMS
RMS (root mean square) result for current time
period of the measurement (T)
( )

=
T
0
2
dttv
T
1
RMS
D.3. STATISTICAL LEVELS – LNN DEFINITION
The noise level L(t) is the continuous random variable. The
probability that the temporary noise level L(t) belongs to the interval
LL,L
kk
+
is called the class density and it can be expressed
by the equation:
( )
 
PtLLtLLP
n
1i
ikkk

=
=+
where:
i
t
- time intervals, in which the noise
level
( )
LL,LtL
kk
+
occurs,
L
- so-called class interval or
distribution class of the series,
P
- total observation period.
In case when the class interval approaches infinity, the probability of L(t) tends to the probability of
k
L
. In practice,
L
value is strictly determined, and it depends mainly on the dynamics of the measurements performed in the
instrument. There are 120 classes in the instrument and the width of each class is equal to 1 dB. The histogram
is the set of the class density values calculated for all classes.
The statistical distribution function, which determines the
probability (expressed in %) of the noise occurrence on the level
equal or less than
LL
k
+
is given by the formulae:
( )
 
( )

=
=
j
1k
kj
LPLtLP
The cumulative density function, expressed by the equation:
is directly used to determine so-called statistical levels LN% or
position parameters of the distribution.
( )
 
( )
 
jj
LtLP1LtLP −=
The LN% is the certain boundary level surpassed by the temporary noise level values in not more than N% of
the observation period.