Larson Davis System 824, Reference Manual

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7-16 824 Reference Manual 11/8/00
exposure level every time the exposure duration is cut in
half. This setting provides the following four options:
The formulas for TWA can be found
in Appendix A of this manual.
3dB - The default 3dB option is the most commonly
used and results in the L
eq
time weighted average.
(When a threshold of 0 is used.) It is used internation-
ally and for measurements that comply with U.S.
Environmental Protection Agency (EPA) regulations.
4dB
-
The 4dB option results in the L
DOD
time
weighted average which is used for measurements
that comply with U.S. Department of Defense (DOD)
regulations.
5dB
-
The 5dB option results in the L
OSHA
time
weighted average which is used for measurements
that comply with U.S. Occupational Safety and
Health Administration (OSHA) regulations.
6dB
-
The 6dB option results in the L
Avg
time
weighted average which is merely a convenient rep-
resentation of the long-term average noise level as
opposed to the RMS noise level.
Ovll Threshold - (LOG)
This setting affects the System 824’s
primary or overall buffer. The Ovll Threshold setting sets the threshold for computing
the overall time weighted average (TWA).
As per the requirements of various regulatory agencies, only
those sound levels which are above a certain threshold level
are used when computing the TWA. Accordingly, this set-
ting can take on any integer value within the following
range:
0 - 255 dB
For hearing conservation measurements, set the threshold to
80dB. For most community noise measurements, set the
threshold to 0 dB. (When set to 0, all levels are included)
Ovll Criterion - (LOG)
The Ovll Criterion setting sets the TWA level which consti-
tutes 100% dose for the overall measurement. The 100%
dose occurs if a person is exposed to that level for the crite-
rion time. Accordingly, this setting can take on any integer
value within the following range: