B&K 2250 Light Uživatelský manuál stáhnout pdf (Strana 18)

CHAPTER 2

Measured Quantities and Parameters

The symbols used on the screen of Type 2250 for equivalent continuous I-weighted sound levels are

(for A, C and Z frequency-weighting):

AIeq

, L

CIeq

, L

ZIeq

Peak Sound Level

The peak sound level, L

xpeak

(T), is defined as twenty times the logarithm to base ten of the ratio of the

greatest absolute instantaneous sound pressure, p

(t), within a time interval starting at t =T and ending

at t =T +

∆t, to the reference sound pressure, p

, instantaneous sound pressure being obtained with a

frequency weighting, x, where:

• x is A for A-weighted, C for C-weighted or Z for Z-weighted

• p

(t) is the x frequency-weighted instantaneous sound pressure

• p

is the reference sound pressure, equal to 20 µPa

• T is the start time of the measurement, indicated as Start Time

•

∆t is the measuring period, indicated as Elapsed Time

The maximum peak sound level is expressed in decibels (dB).

The symbols used on the screen of Type 2250 for peak sound levels are (for A, C and Z frequency-

weighting):

Apeak

, L

Cpeak

, L

Zpeak

2.5.4 Spectrum Measurements

Note: These measurements require Frequency Analysis Software BZ 7223.

The definition of the measured quantities is the same as for the broadband measurements.

At low frequency bands the exponential time constants for Fast-weighting are modified to get a reason-

able B*T product, see section 4.11.5.

2.5.5 Instantaneous Spectrum Measurements

Note: These measurements require Frequency Analysis Software BZ 7223.

The Instantaneous Spectrum Measurements can measure instantaneous time-weighted sound level L

where:

• x is A for A-weighted, C for C-weighted or Z for Z-weighted

• y is F for Fast-weighted or S for Slow-weighted

Overload is common to the broadband measurements.

No Under-Range is indicated.

2.5.6 Timed Spectrum Measurements

Note: These measurements require Frequency Analysis Software BZ 7223.

The Timed Spectrum Measurements can measure minimum time-weighted sound level, L

xymin

, maxi-

mum time-weighted sound level, L

xymax

, and equivalent continuous sound level, L

xeq

, where:

• x is A for A-weighted, C for C-weighted or Z for Z-weighted

• y is F for Fast-weighted or S for Slow-weighted

Latched Overload and Overload Percentage is common to the broadband measurements.

No Under-Range is indicated.

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