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SL355-en-GB_V1.8 8/17
EXCHANGE RATE
Exchange rate is best illustrated by example, as follows: Since 100% DOSE = Criterion Level for 8
hours, a person would receive 50% DOSE in 4 hours if the noise level equals the Criterion Level
setting. Now consider a Criterion Level of 90dB, a noise measurement of 95dB (5dBA higher than
the Criterion Level), and an Exchange Rate of 5dB; in this example a 100% DOSE would be
received in only 4 hours. This is because with a 5dB Exchange Rate, a 5dB increase in sound
level is considered a doubling of the DOSE. Other Exchange Rates can be selected (3, 4, 5, or 6
db). Refer to the local regulations or standards for exchange rate, criterion level and threshold
settings.
FAST (F) SLOW (S) RESPONSE TIME
Set the response time to Fast (F) to capture quick bursts of sound such as discharging firearms,
fireworks, hammering, and other impulse noises. Use the Slow (S) setting if the noise under test is
more of a continuous drone or background din. The Slow setting is typically specified by OSHA
and MSHA standards for use in noise surveys.
THRESHOLD LEVEL
The threshold level is the sound level at which the meter begins to integrate noise into the
exposure test. For example, if the threshold level is set to 85dB, the meter will integrate all noise
that equals or exceeds 85 dB. Sound levels below this threshold would not be included in the
dose calculation.
TIME WEIGHTED AVERAGE (TWA)
TWA is the 8-hour projected average sound level based on data collected from the start of the test
up to the time the TWA is checked. TWA sound exposure is displayed in dB on the SL355
PEAK
When sound levels above 140dB are present, the meter displays the PK (and the ‘C’ or ‘Z’
weighting) symbols. The ‘C’ icon indicates ‘C’ frequency weighting and the ‘Z’ icon indicates flat
(or linear) peak where no frequency weighting is applied.
HIGH LEVEL INDICATOR
When sound levels above 115dB are present the meter displays the headphone
symbol.
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