Svantek SV 971A, Руководство пользователя

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SV 971A User Manual
– Appendixes
289
E Amount of the acoustical energy received
by the worker.
 
10
LEQ
2
o
10 p
3600
s T
E
 =
E_8h The E_8h result (Exposition in 8 hours)
represents the amount of the acoustical
energy received by the worker during 8
hours. The E_8h result is expressed in the
linear units [Pa
2
h].
 
10
LEQ
2
o
10 p h 8 h 8 _ E
  =
PTC Peak Threshold Counter
– the number of the overpasses of the Threshold Level by
Lpeak result. This result is incremented in 100 ms intervals.
PTP
PTC result expressed in percent.
ULT Upper Limit Time -
time that SPL exceeded the “ULT Threshold Level” set during
configuration.
TWA Time Weighted Average is the average A-
weighted sound level for a nominal 8-hour
workday with Time Weighting S and
Exchange Rate 5.
TWA is usually
measured with A-weighting and Slow
response detector type. TWA is calculated
from the measured LAV (taking Threshold
Level into account) and a Reference time
of 8 h. Mainly used in the USA for
assessing the noise exposure for a worker
during a workday.
•
Sound levels at or above the
THRESHOLD LEVEL are averaged
into the calculations relating to noise
exposure.
TWA is calculated with no
threshold level, or with threshold level
(typically 80dB or 90dB)
•
In case the time period is below 8 hours,
the
TWA is less than the LAV
In case the time period is more than 8
hours, the
TWA is greater than the LAV
PrTWA
Projected Time Weighted Average is calculated from the measured LAV (taking
THRESHOLD LEVEL into account) and the exposure time.
Lc-a The C-A measurement is an Leq that
enhances the low-frequency components
of the sound signal. It is the result of
subtracting an A-weighted LAeq from a
simultaneously collected C-weighted Leq Lc-a = LCeq - LAeq
D.4 S
TATISTICAL LEVELS
–
L
N DEFINITION
The noise level L(t) is the continuous random variable. The
probability that the temporary noise level L(t) belongs to the
interval
L L , L
k k
 +
is called the class density and it can be
expressed by the equation:
( )
 
P t L L t L L P
n
1 i
i k k k

=
 =  +  
where:
i
t

- time intervals, in which the noise
level
( )
L L , L t L
k k
 + 
occurs,
L

- so-called class interval or
distribution class of the series,
P - total observation period.