Brüel & Kjær 2240 Guide De L'utilisateur page 24

18 Integrating-averaging Sound Level Meter Type 2240 – User Guide
Calibration
Calibration is an adjustment of your sound level meter to ensure correct measurement and
display values. This is necessary because the sensitivity of the microphone and the response of
the electronic circuitry can vary slightly over time or be affected by environmental conditions
such as temperature and humidity. Often, calibration is required by national and international
measurement standards. While you are not likely ever to experience a large drift or change in
sensititvity with Type 2240, it is nevertheless good practice to perform regular calibrations,
normally before each set of measurements.
Your instrument supports two types of calibration:
• acoustical calibration that calibrates all the instrument's components (microphone, preampli-
fier and electrical circuitry), wherein an acoustic signal of known magnitude and frequency is
applied
• electrical calibration that does not include calibration of the microphone and preamplifier
Acoustical Calibration
Acoustical calibration is the preferred calibration method, particulary when standards and regu-
lations require that a calibration is performed before a measurement.
To perform an acoustical calibration, use Brüel & Kjær Sound Level Calibrator Type 4231. It
provides a stable sound pressure at 1 kHz and has minimal susceptibility to environmental
factors. You use the calibrator's reference signal at 1 kHz to compare and adjust your sound
level meter in full, including microphone, preamplifier and electronic circuitry.
The procedure for performing an acoustical calibration is simple:
1) Stand away from loud sound sources that may interfere with the calibrator's signal.
2) Fit Sound Level Calibrator Type 4231 carefully onto the sound level meter and rest the
assembly on a table or other flat surface as shown in Fig.4.1.
Fig.4.1
Sound Level Calibrator
Type 4231 fitted onto your
sound level meter
Ensure that the calibrator fits snugly on the microphone.
Type 2240
030224