B&K 2250 Light Instrukcja Użytkownika Pobierz pdf (Strona 52)

CHAPTER 4

Specifications

Below the Lower Limit, the Level Linearity Error is less than or equal to the error found in Fig.2.1

with L

inh

set to the Lower Limit – 11.5 dB.

4.11.4 Measurement Range

Measurement Range according to the International Standard IEC 61260 is the difference between the

Upper Limit of the Linear Operating Range on the least sensitive level range and the Lower Limit of

the Linear Operating Range on the most sensitive level range.

On Type 2250, the Measurement Range equals the Linear Operating Range, because the instrument

only has one range.

4.11.5 Octave Band Time Constants

At low centre frequencies, the B*T product for Fast time-weighting becomes too small to give statisti-

cally reliable measurements. To overcome this, the Fast time constant (125 ms) and the Slow time

constant (1000 ms) are replaced by progressively longer time constants with decreasing centre frequen-

cies (and corresponding bandwidths).

Table 4.11 shows the Fast time constants for the full range of octave bands.

Table 4.12 shows the Slow time constants for the full range of octave bands:

For a white Gaussian signal and for 1/1-octave centre frequencies from 8 Hz to 63 Hz, these time

constants give a maximum relative standard deviation of approximately 1.5 dB. For 1/3-octave centre

frequencies from 6.3 Hz to 160 Hz, these time constants give a maximum relative standard deviation of

approximately 2 dB.

4.12 Influence from the Operating Environment

The temperature and humidity specifications are given provided that no condensation inside the instru-

mentation results from the combination.

Excessive condensation may cause permanent damage to the instrumentation.

Table 4.10

Linear Operating

Range

Upper Limit

(dB)

Lower Limit 1/1-Octave

(dB)

Lower Limit 1/3-Octave

(dB)

140 25.9 22.1

Table 4.11

Octave band Fast

Time Constants

1/1-Octave

Centre Frequency

(Hz)

1/3-Octave

Centre Frequency

(Hz)

Time Constant

(ms)

Averaging Time

(ms)

≥ 63 ≥100 125 (Fast) 250 (Fast)

31.5 80, 63, 50 250 500

16 40, 31.5, 25 500 1000

8 20, 16, 12.5 1000 2000

– 10, 8, 6.3 2000 4000

Table 4.12

Octave band Slow

Time Constants

1/1-Octave

Centre Frequency

(Hz)

1/3-Octave

Centre Frequency

(Hz)

Time Constant

(ms)

Averaging Time

(ms)

≥ 8 ≥12.5 1000 (Slow) 2000 (Slow)

– 10, 8, 6.3 2000 4000

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