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Views on the Edge
Definitions of data log values and views
19
Views on the Edge
Explanation
L
TWA
Time-weighted average
- is the sound level (in dB) that is accumulated for any time
period but with its average level computed over an 8-hour period. TWA is usually
measured with A-weighting, Slow response, and a 5dB exchange rate.
All sound levels at or above the threshold level (cutoff level) are averaged
into the calculations relating to noise exposure. TWA is calculated with no
cutoff, with cutoff 1 (typically 80dB), or with cutoff 2 (typically 90dB).
If the time period is less than 8 hours, the TWA will be less than the LAvg. If
the time period is more than 8 hours, the TWA will be more than the LAvg.
L
AE
Sound Exposure Level (SEL)
–
The sound exposure level averages the sampled
sound over a one second period. Assuming the sampled run time to be greater than
one second, SEL is the equivalent one-second noise that would be equal in energy to
the noise that was sampled. SEL is typically measured using a 3dB exchange rate
without a threshold. (L
AE
is not used by OSHA.)
Dose
Dose
- Related to the Criterion Level, a dose reading of 100% is the maximum
allowable exposure to accumulated noise. For OSHA, 100% dose occurs for an
average sound level of 90 dB over an 8 hour period (or any equivalent exposure).
(Please see Glossary of Terms for more details).
Projected Dose
(Pdose)
Projected Dose –
this is similar to Dose. However, instead of an 8 hour period, a
specific hour is entered. (See dose for more information.)
UL
Upper Limit -
is the amount of time that the sound level exceeds a preset level (the
Upper Limit).
L
C-AAVG
It is the result of subtracting an A-weighted L
AVG
from a simultaneously collected C-
weighted L
AVG
. This value is used to determine the following equation:
Estimated Exposure (dBA) = Workplace Noise Level (dBA) – (NRR- L
C-AAVG
)
Time Response
(Fast, Slow)
Typically, noise is not constant. Using a response of Slow or Fast simply smoothes the
noise fluctuation and makes the sound level easier to work with.
Slow
– 1 second (1,000 milliseconds)
Fast
– 0.125 second (125 milliseconds)
RT
Run Time -
The overall time of your noise study.
Weighting
(A, C)
A and C weighting are types of frequency filters that cover the frequency range of
human hearing (20Hz to 20 kHz).
“A” weightin
g
- The “A” weighted filter attempts to make the dosimeter respond
closer to the way the human ear hears. It attenuates the frequencies below
several hundred hertz as well as the high frequencies above six thousand hertz.
“A” weighted measurements are often reported as dBA.
“C” weighting
provides a fairly flat frequency response with only slight attenuation of
the very high and very low frequencies. “C” weighting is intended to represent how the
ear perceives sound at high decibel levels and is often used as a “flat” response when
LINEAR is not available. “C” weighted measurements are often reported as dBC.
Table 3-1: Dosimeter parameters and definitions (continued)
Summary of Contents for Edge eg5
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Page 58: ...49 Appendix A Edge Block Diagram Analog Board ...
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Page 68: ...59 Appendix C Appendix C Measurement equations APPENDIX C ...