Crystal Instruments Spider - Page 242

Spider DSA User’s Manual
242
Frequency
Weighting
Filter
RMS
estimate &
Time
weighting
RPM or
Time
based?
RPM-based
buffer
Raw
data
Time-based
buffer
Figure 150. Time weighting sound level computation and storage against RPM or Time
The table below shows the symbols for the time-weighted sound level.
Symbol used for time
weighted value
Frequency Weighting
Z
A
B
C
Time
Weighting
F(Fast)
L
ZF
L
AF
L
BF
L
CF
S(Slow)
L
ZS
L
AS
L
BS
L
CS
I(Impulse)
L
ZI
L
AI
L
BI
L
CI
Custom
L
ZC
L
AC
L
BC
L
CC
Figure 151 Typical Measurement Values of SLM
Time Averaged Sound Levels
The Time averaged sound level is the output of frequency-weighting and then
time average operation. Time averaging uses a linear averaging operator. Figure
152illustrates the computation.