B&K 2250 Light Manual do Utilizador descarregar pdf (Página 311)

APPENDIX E

Glossary

299

Xeq,T,mov

and L

eq,T,mov

: Moving (or sliding) X-weighted average (equivalent continuous noise level)

for the latest T minutes. Updated every second during measurement. The

parameter can be used to monitor the average noise level within T minutes,

for example, to monitor that the noise level during a music event doesn't

exceed a certain limit at any 15 minutes of observation time during the event.

The value is equal to L

Xeq

at the start of the measurement as long as the

elapsed time less than or equal to T. Two values with frequency weighting

X = A and C are measured simultaneously. ∆L

eq,T,mov

is calculated as the

difference between L

Ceq,T,mov

and L

Aeq,T,mov

Xeq,T,mov,max

and

L

eq,T,mov,max

The maximum of the L

Xeq,T,mov

values during the measurement, only taking

values into account where elapsed time is greater than or equal to T. Two

values with frequency weighting X = A and C are measured simultaneously.

∆L

eq,T,mov,max

is calculated as the difference between L

Ceq,T,mov,max

and

Aeq,T,mov,max

: The instantaneous time-weighted sound level, Lp, is available at any time.

‘A’ denotes that the A-frequency weighting is used. ‘F’ denotes that the Fast

time-weighting is used.

AFmax

: Maximum time-weighted sound level measured with A-frequency weighting

and Fast time weighting. It is the highest level of environmental noise

occurring during the measurement time. It is often used in conjunction with

another noise parameter (for example L

Aeq

) to ensure a single noise event

does not exceed a limit.

AFmin

: Minimum time-weighted sound level measured with A-frequency weighting

and Fast time weighting. It is the lowest level of environmental noise occurring

during the measurement time (time resolution is 1 s).

AF90.0

: The noise level exceeded for 90% of the measurement period with A-

frequency weighting and Fast time weighting. The level is based on statistical

analysis of a parameter (LAF or LAS) sampled at 10 ms intervals into 0.2 dB

wide classes. The percentage is user-definable.

An analysis of the statistical distributions of sound levels is a useful tool when

assessing noise. The analysis not only provides useful information about the

variability of noise levels, but is also prominent in many standards as the

basis for assessing background noise. For example, L

AF90

is used as an

indicator of background noise levels while L

AF10

or L

AF5

are sometimes used

to indicate the level of noise events.

A90.0

: The noise level exceeded for 90% of the measurement period with A-

frequency weighting. The level is based on statistical analysis of L

Aeq

sampled

at 1 s intervals into 0.2 dB wide classes. The percentage is user-definable.

AF(SPL)

: The Sound Pressure Level (maximum time-weighted sound level during the

latest second) is available at any time. 'A' denotes that the A frequency

weighting is used. ‘F’ denotes that the Fast time-weighting is used.

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