B&K 2250 Light Instrukcja Użytkownika Pobierz pdf (Strona 162)

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Hand-held Analyzer Types 2250 and 2270 – User Manual

6) Steps 2 to 5 are automatically repeated a chosen number of times and the measured decays

are averaged together to reduce the uncertainty of the measurement.

7) The reverberation time spectra EDT, T20 and T30 are calculated and displayed on the screen.

The measurement can be in octaves or 1/3-octaves in parallel over a selectable frequency

range, allowing you to focus sound power on the relevant range. In each frequency band, the

decay is sampled 200 times each second, for reverberation times as long as 20 seconds.

You can enhance the signal-to-noise ratio by limiting the frequency range of the noise to cover

just a single frequency band, while keeping the output power constant. First, you make a

parallel measurement, then, if the signal-to-noise ratio is too low in a few bands (typically at

low frequencies) you select these bands for serial measurements. You can redo the

measurements including only these bands and merge the results with the parallel measurement.

Impulsive Excitation Method

With Impulsive Excitation, all you need to carry is Type 2250-F/2270-F, a tripod and a balloon

(or other impulsive source, such as a starting pistol). After you start the analyzer and pop the

balloon, the analyzer will start measuring, analyse the decay and display the RT spectrum and decay.

The single input range means that trial measurements are not necessary when using the impulsive

excitation method.

Fig.14.4

Typical RT measurement cycle for the impulsive excitation method

Fig.14.4 shows a typical RT measurement cycle performed by the analyzer, where the different

steps are described as follows:

1) After ‘Start’, the analyzer waits for the level to exceed the ‘Trigger Level’ (indicated on

the analyzer in three places by the “traffic light” giving a short green flash every second).

2) The impulse excitation is made, for example, a pistol is fired or a balloon is burst.

CAUTION: The use of hearing protection is highly recommended.

3) The impulse measurement is started 1 s before the level exceeds the ‘Trigger Level’.

Time

Trigger Level

Decay Time

Impulse measurement

Await Level

to exceed

Trigger Level

Start

Impulse

Excitation

Sound Level

060209

1 2 ... 157 158 159 160 161 162 163 164 165 166 167 ... 331 332

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