Instruction Manual

Sound Level Meter Types 2245 – Instruction Manual Page 37 of 110
For acoustic calibration the Brüel & Kjær Sound Level Calibrator Type 4231 shall be
used and selected in System settings >Advanced settings > Calibration >
Calibrator.
The adjustment data according to IEC 61672-1 paragraph 5.2.4 for Microphone Type
4966 with Sound Calibrator Type 4231 is 93.85 dB for the 94 dB setting of the calibrator.
This value is build into the software when Microphone Type 4966 and Calibrator Type
4231 is selected in the user interface.
3.3.2 Electrical Substitute for Microphones
For electrical tests, the Electrical Substitute for Microphones shall be used and the
instrument shall be calibrated by keying in the Sensitivity using the following procedure:
1) To obtain a BNC Type electrical input, replace the microphone with a WA-0302-B,
15 pF, fitted with a 10–32 UNF to BNC Adapter, UA-0245.
2) In System settings >Advanced settings > Service mode select Enabled.
3) In System settings >Advanced settings > Microphones select the microphone
used for the tests and select Edit > Sensitivity > Yes.
4) Adjust Sensitivity to 43.35 mV/Pa. This corresponds to the Microphone Type 4966's
nominal Open Circuit Sensitivity (50.00 mV/Pa), attenuated by the build in
microphone preamplifier’s nominal attenuation (1.24 dB).
5) Connect an electrical sinusoidal signal with a frequency of 1 kHz to the Electrical
Substitute for Microphones and adjust the amplitude of this signal until L
ZF
(or L
CF
)
displays 94.00 dB in the normal measurement screen. This electrical amplitude is
the 94.00 dB reference signal for the electrical tests. The amplitude will typically be
51.9 mV. This is due to the attenuation of the Electrical Substitute for Microphones
together with the preamplifier (nominally 1.54 dB).
This procedure calibrates the sound level meter to a calibration that corresponds to the
calibration you would get if the sound level meter were fitted with a microphone with
the nominal Open Circuit Sensitivity.
The electrical input obtained in this way has a maximum input level of ±16.9 V
Peak
and
no damage will occur for signals up to ±20 V
Peak
.
All electrical inputs can be short-circuited when needed for test.
3.4 Wi-Fi and Bluetooth during tests
Bluetooth is only used for paring devises (transferring IP address) for Wi-Fi. Therefore,
it is not relevant during tests.
Wi-Fi should be turned on as a Hotspot during tests using the following procedure:
Set System settings >Network settings > Wi-Fi settings to Hotspot
3.5 Mounting for Acoustical Tests
For acoustical tests, it is important that the test rig for mounting the sound level meter
to be tested is designed to minimise the influence of reflections to a level that is
comparatively smaller than the test parameter’s maximum Expanded Uncertainties of
Measurement. This has to be demonstrated with a good, known laboratory
microphone.