Casella-cel CEL-281 Manual do Utilizador descarregar pdf (Página 30)

A Projected Sound Exposure can be calculated when a sample ex-

posure has been obtained over a period that is different from the stand-

ard eight hour working day.

For example if the exposure determined during a measured part of the

standard day is expected to continue for the remainder of the day, the

sample can be projected for the whole day as follows:

= E

(Pa h)

Where:

, = Measured exposure over sample

period T

in (Pa h),

d = Length of actual working day in hours,

= Exposure time of sample in hours.

The CEL-281 calculates both % dose and projected % dose values for

an eight hour day only.

The relationships between sound exposure (E

), noise dose (D) with

90 dB criterion, and daily sound exposure level (L

) for a normalised

eight hour working day are illustrated in Figure 1.

2.2.6 Distribution

This is a statistical determination of how often any particular event oc-

curs during a given survey found by dividing the total range of events re-

corded in a survey into separate events (or groups of similar events).

Such Statistical Distribution information is presented in the form of

a Histogram showing the number of times the event or group oc-

curred on a Frequency axis plotted against events or groups identified

on the other axis. Frequency is often replaced by Percentage Fre-

quency, which is the proportion of the total survey taken up by the

event.

Introduction_

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Casella-cel CEL-281 Manual do Utilizador Página 30