THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

9.8 Proper Procedures for Using the Sound Level Meter 185Figure 9.8. Block diagram of the principal elements of a sound level meter.Periodically, every 6 months to a year depending on frequency and rigor ofusage, both the SLM and the calibrator should be rechecked with calibration instrumentswhich, in turn, have been calibrated periodically in a manner traceableto direct comparison with the standards set up by the U. S. National Institute ofScience and Technology (NIST) or the appropriate standards bureau in anothernation. Updated certifications of calibration are necessary for both SLM and itscalibrator as proof of the accuracy and reliability of the measurement devices.While executing measurements and entering data, one should also record sufficientinformation to identify all measuring instruments at a later date should theFigure 9.9. Cross section of an oscillator-driven sound level calibrator. This model producesan 1-kHz tone at a SPL of 94 dB. (Courtesy of Brüel & Kjær.)