Svantek SVAN 979, User Manual

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SVAN 979 User Manual - Appendixes
APPENDIX D. DEFINITIONS AND FORMULAE OF MEASURED VALUES
D.1. S
OUND
L
EVEL
M
ETER
D.1.1 Basic terms and definitions (SLM mode)
T current time period of the measurement in seconds.
1
T
the last second of the measurement.
e
T
exposure time in seconds (time period during which a person is exposed to the action of noise).
This parameter can be set in the
Exposure Time setup ( Measurement menu). The available
values are from 1 minute to 12 hours with 1 minute step.
h 8
T
time period equal to 8 hours (28 800 seconds).

exponential time constant in seconds for the giving time-weighting. Three time constant are
available:
Slow (1000 ms), Fast (125 ms), Impulse (35 ms, but on falling values a longer time
constant of 1500 ms is applied).
W frequency-weighting filter ( A , C, B , Z , U , AU or LF ).
( )
t p
W
instantaneous frequency-weighted sound pressure with the weighting filter W . Sound pressure
is expressed in pascals (Pa).
( )
t p
W

instantaneous frequency and time-weighted
sound pressure
with the weighting filter W and
time constant

calculated from the equation:
( ) ( )
( )

 −
  =

 − −


t
/ t
d e p
1
t p
2
W W
where:

– variable of integration.
( )
t r
instantaneous sound pressure depends on the
<RMS Integration> parameter:
( )
( )
( )



=
=

=
Exp n Integratio RMS
Lin n Integratio RMS
t p
t p
t r
W
W
0
p
the reference value (20

Pa).
( )
x log
represents the logarithm of x to the base 10.