Larson Davis System 824, Справочное руководство

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9/12/00 A -7
SEL Calculations
SEL is available for both the overall and current measure-
ments and is calculated using this formula:
Since the sample rate is 32 samples per second and SEL is
based on time in seconds, the log(32) is subtracted from the
log of the accumulation to perform a division by 32. All of
the SEL energy values in the analyzers utilize the Threshold
and Exchange Rate settings. Care should be taken when
modifying these settings since some standards or govern-
ments require SEL to be taken without a Threshold (set it to
zero) and with an Exchange Rate of 3 dB.
Dose and Projected Dose Calculations
Dose is a measure of Sound Exposure and is defined in
ANSI S1.25 Section 4.7 as:
where:
D(Q) is the percentage criterion exposure for exchange rate
Q
T
C
is the criterion sound duration = 8 hours
Logged into time history record at end of measurement interval (can be programmed for periods from 1/32nd of a
second to 255 minutes).
a. The display title within parenthesis () indicates the Model 820 display
location.
Variable Name Location
a
Settings
L
TWA
L
cal
k 10
L
s
( )
k
--------
s 1 =
n
∑








32
( )
log – log
•
+ =
D Q
( )
100
T
c
---------
 
 
10
L L
c
–
q
--------------
 
 
dt
0
T
∫
⋅
=