BRUEL & KJAER 2245 - Linear Operating Range; Measurement Range; Octave Band Time Constants

Sound Level Meter Types 2245 – Instruction Manual Page 63 of 110
4.11.3 Linear Operating Range
Linear Operating Range according to the international standard IEC 61260, for electrical
input, for all filters in the filter banks:
Table 4.11 Linear Operating Range
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.
Table 4.12 Measurement Range
4.11.5 Octave Band Time Constants
At low centre frequencies, the B*T product for time weightings becomes too small to
give statistically 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 frequencies (and corresponding bandwidths). See
Table 4.13 and Table 4.14.
Table 4.13 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
-
20, 16, 12.5
1000
2000
Table 4.14 Octave band Slow Time Constants
1/1-octave
Centre Frequency
(Hz)
1/3-octave
Centre Frequency
(Hz)
Time Constant
(ms)
Averaging Time
(ms)
≥16
≥12.5
1000 (Slow)
2000 (Slow)
Upper Limit
(dB)
Lower Limit
1/1-octave
(dB)
Lower Limit
1/3-octave
(dB)
141.2 21.2 22.1
1/1-octave
(dB)
1/3-octave
(dB)
141.2 - 21.2 141.2 - 22.1