Svantek SV 977D - Page 351

351
SV 977D User Manual - Appendixes
APPENDIX D. DEFINITIONS AND FORMULAE OF MEASURED VALUES
D.1. SOUND LEVEL METER
D.1.1 Basic terms and definitions (SLM mode)
T
current time period of the measurement in seconds.
1
T
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.
h8
T
time period equal to 8 hours (28 800 seconds).

exponential time constant in seconds for the given 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).
( )
tp
W
instantaneous frequency-weighted sound pressure with the weighting filter W. Sound
pressure is expressed in pascals (Pa).
( )
tp
W 
instantaneous frequency and time-
weighted sound pressure with the
weighting filter W and time constant

calculated from the equation:
( ) ( )
( )

−
  =
 − −


t
/t
dep
1
tp
2
WW
where:

– variable of integration.
( )
tr
instantaneous sound pressure depended
on the RMS Integration parameter:
( )
( )
( )



=
=

=
Exp nIntegratioRMS
Lin nIntegratioRMS
tp
tp
tr
W
W
0
p
reference value (20 Pa).
( )
xlog
logarithm of x to the base 10.