Noise Measurements - BRUEL & KJAER 1022 Instructions And Applications

vibrations in buildings, machinery, ships, etc., can be measured. In Fig. 6.2a
a layout is shown, where the Type 3332 is be·ing used to automatically
record vibration measurements taken on the base of an electrical motor,
the Spectrometer allowing an analysis of the vibrations to be made. The
output from the Accelerometer is fed via the Preamplifier 1606 to the
CONDENSER MICROPHONE input of the Spectrometer. Information on the
calibration of the arrangement is given in the manual for the Type 1606.
Fig. 6.2b. shows a recording of the vibrations from a synchronous motor
which uses a 50 c/s mains supply. In this recording a 50 dB Range Potentio-
meter was used in the Level Recorder, 0 dB reference being equal to an
acceleration of 25 cm/sec2.
Noise Measurements.
Noise within factories, offices, cities, airports, etc. varies with the time of
day. Therefore it is a firm requirement that recordings of the noise should
be carried out over a conside· r able period of time as a single recording
taken at a particular instant would provide incorrect information.
Fig. 6.3 shows a recording taken of the noise level in a mechanical work-
shop over a selected period of time by using one of the WeighHng Networks
in the Spectrometer. As can be seen the noise level varies considerably with
time and a reliable analysis cannot be obtained by only taking a few
measurements. It is therefore necessary, when doing such a test, to record
continuously and then to stat· i stically assess the final re· s ult.
To measure, analyse and record such noise the Spectrometer
+
Level
Recorder (i.e. the receiving part of the AF Response and Spectrum Recorder
Type 3332) in combination with a B & K Condenser Microphone can be used.
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Fig. 6.3. Recording of the noise level in a mechanical workshop over a period
of time.
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