TSI Quest EDGE EG-4P, Руководство пользователя

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B-2 The Edge Personal Noise Dosimeter Model EG-4P User Manual
Combining Noise
sources Because sound levels are measured in decibels they cannot be simply added
together. A sound level of 90 dB plus 90 dB does not yield 180 dB but rather
93 dB. The procedure for mathematically determining a combined level of sound
from independent measurements made for two noise sources is given below.
1. Make independent measurements for both noise sources, where each exists
without the presence of the other.
2. Determine the decibel difference between these two measurements.
3. Find that difference on the x -axis of the figure below.
4. Find the point on the curve directly above this difference.
5. Read the corresponding value on the y -axis for that point (the Amount to Add).
6. Add this value to the larger of the two measurements.
Example : Independent measurements for the two noise sources yielded levels of
90 dB and 91 dB. For a difference of 1 dB, the correction factor taken from the
curve below is 2.5 dB. Therefore the combined level when these two sound
sources are present in the measurement area at the same time 93.5 dB.
Crest Factor Crest Factor is the ratio of the instantaneous peak value of a wave to its RMS
value. This is a performance specification of a meter’s ability to process signals
that have peaks that are substantially higher than their RMS averages.
Criterion Level (CL) Criterion level is the average SPL that will result in a 100% dose over the Criterion
time, usually 8 hours. The Criterion Level is typically set by a regulating agency,
such as OSHA, and is not usually applicable for community noise monitoring.
Examples: OSHA mandates the Criterion Level (maximum allowable accumulated
noise exposure) to be 90 dB for 8 hours. For an 8-hour sample, an average level
(Lavg) of 90 dB will result in 100% dose. For the OSHA HEARING
CONSERVATION AMENDMENT, the “action level” is 85 dB for 8 hours. This
would result in a 50% dose reading. Note that the Criterion Level has not changed.
(If the Criterion Level were changed to 85 dB then an 8-hour average of 85 dB
would result in 100% dose.)
Criterion Time The time over which the Criterion Level is established, generally 8 hours.
Decibel (dB)
Sound Level Meters use the decibel as the unit of measure known as Sound
Pressure Level (SPL). SPL uses the ratio between a reference level of
20 microPascals (.00002 Pascals) and the level being measured. SPL = 20 log
(measured level/reference level). Example: the SPL for 1 Pascal is 20 log
(1 Pascal/.00002 Pascal) = 94 dB 20 microPascals (.00002 Pascals) is considered
the average threshold of hearing. A whisper is about 20 dB. A normal conversation
is typically from 60 to 70 dB, and a noisy factory from 90 to 100 dB. Loud thunder
is approximately 110 dB, and 120 dB borders on the threshold of pain.