B&K 2250 Light Manuel d'utilisateur télécharger pdf (Page 25)

Hand-held Analyzer Type 2250 –

Instruction Manual

4.4 Reference Conditions for Acoustic Calibration

Reference range: Only one range exists and this is the reference range

Reference sound pressure level: 94.00 dB re 20 µPa

Reference frequency: 1kHz

4.5 Microphone

Microphone Type 4189 and Preamplifier Type ZC 0032:

Type: Prepolarized Free-field ½ ″ Condenser Microphone

Nominal Open Circuit Sensitivity: 50 mV/Pa, (corresponding to –26 dB re 1 V/Pa) ± 1.5 dB

Capacitance: 13 pF (at 250 Hz)

Nominal preamplifier attenuation: 0.25 dB

Extension cables between Type ZC0032 and Type 2250: Up to 100 m without affecting measure-

ments. Note: EMC is only tested with a 10 m cable (AO 0442)

Microphone reference point: The centre of the front surface of the microphone protection grid. With

UA 1404 mounted, this point can be difficult to find. Therefore, it is marked on the windscreen

Reference direction of sound incidence: See Fig.4.14 to Fig.4.15

4.6 Frequency Response

The frequency responses are given in tabular form in Appendix A and in graphical form in this section.

The Expanded Uncertainties of Measurement in the tables are the two-sigma limits maintained in the

Brüel & Kjær production for the specific product. This means that the correct value lies in the range of

the measured value plus/minus the Expanded Uncertainties of Measurement with a probability of 95%.

Note: This range is not related to the production spread. The range is for a specific typical unit. The

factory acceptance tests at Brüel & Kjær ensure that the ranges for all units are within the IEC 61672–1

limits.

The IEC 61672–1 limits, reduced by the Maximum Expanded Uncertainties of Measurement from Ap-

pendix A of IEC 61672–1, are also drawn in the graphs. These Maximum Expanded Uncertainties of

Measurement are the maximum uncertainties that a test organisation may have on its measurements

when it performs conformance tests according to IEC 61672.

4.6.1 Electrical Frequency Responses

The electrical frequency response depends on the selected frequency weighting, see Fig.4.1.

The Z-weighted electrical frequency response is given in the "Electrical Response" column of the

appropriate tables of Table A.2 to Table A.9 in Appendix A.

The electrical frequency responses are valid both for introduction of the electrical signal through the

recommended means to substitute the microphone with an electrical input facility (see section 3.4) and

for the rear ‘Input’ socket.

Z-weighted frequency range: ±0.15dB, 11Hz to 22kHz

Extended low frequency range: ±0.15dB, 4Hz to 22kHz

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B&K 2250 Light Manuel d'utilisateur Page 25