B&K 2250 Light Instrukcja Użytkownika Pobierz pdf (Strona 21)

Hand-held Analyzer Type 2250 –

Instruction Manual

3.5 Testing 1/1-octave-band and 1/3-octave-band Filters

When testing the octave-band filter sets according to IEC 61260, the rear ‘Input’ socket on Type 2250

should be used.

All tests according to IEC 61260 must be conducted with Spectrum frequency-weighting set to ‘Z’.

(Frequency Analysis Software BZ 7223 required.)

Note 1: When testing relative attenuation according to IEC 61260 paragraph 5.3, the input level must

be within 1 dB of the upper boundary of the Linear Operating Range. This could lead to overload

indications in the frequency range 1 to 8 kHz. These overload indications come from the A-frequency-

weighting filters and have no influence on the performance of the octave-band filter sets, as long as

there is no overload at 1 kHz. To reduce this phenomenon, it is advisable to conduct the test at 1 dB

below the upper boundary of the Linear Operating Range.

Note 2: In order to measure without any correction for sound field or windscreen, set Microphone Type

to Unknown for the transducer in use in the Transducers setup. (i.e., Transducers selected from the

Main Menu.) This will not affect the current calibration.

3.6 EMC test procedures

3.6.1 Signal Source for Immunity Test

The acoustic signal, which is used during the Immunity test, is applied to the microphone through a

½ ″ plastic hose (a normal water hose) – from a source outside the test room. In this way, the acoustic

source is not affected by the RF field. The source may be a normal entertainment earphone.

Fig.3.1

Setting up the

signal source for an

immunity test

To prevent the acoustic source from being affected by acoustic noise in the surroundings, the following

method can be used:

• Insert an acoustic attenuator in the hose close to the microphone, so that the sound pressure within the

greater part of the hose is held far above the surrounding sound level. The acoustic attenuator can eas-

ily be made from a short piece of metal tubing with an outer diameter of ½ ″. Squeeze a piece of paper

tissue into the tube, and compress it until the desired attenuation is obtained. Up to 40 to 60 dB of

acoustic attenuation can be obtained.

3.6.2 Reference Orientation

Fig.3.2 shows the reference orientation relative to the RF-emitter/receiver that is common to both

Emission and Immunity tests.

Microphone assembly

(windscreen removed)

Water hose

50 dB SPL inside

Acoustic

attenuator

Compacted

paper tissue

Water hose to

acoustic source

>90 dB SPL inside

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