3M eg3 Manuale Utente

60

    

Appendix B 

         Glossary of Terms 

Page   60 

  

To be sure the dosimeter is functioning within specified tolerance limits, it should be returned to the 

factory annually for a factory recalibration.  To verify that the dosimeter is measuring properly during 
normal use, field calibrations should be performed.  Pre-calibration is performed prior to any data being 

recorded by the dosimeter.  During a pre-calibration, the dosimeter level may be adjusted to match the 

calibrator output level.  Post-calibration is a simple verification that the instrument has remained in 
calibration throughout the measurement period. 

 

  

Measurements made in an area without sound reflections, diffractions and absorptions caused by 
nearby objects (including the operator).  Sound waves are free to spread out continuously, like ripples 

on a pond, without reflection.  When making free field measurements with a dosimeter set up for use 
as a sound level meter, the microphone is typically pointed directly at the sound source. 

 

The Occupational Safety and Health Administration (OSHA) and Mine Safety and Health Administration 
(MSHA) provide regulatory standards for hearing conservation programs.  In addition, the American 

Conference of Governmental Industrial Hygienists (ACGIH) provides industrial standards for hearing 
conservation programs. http://www.osha.gov/ , http://www.msha.gov/ , 

http://www.acgih.org/home.htm 
 

Unit of vibration frequency in cycles per second.

Lavg is the average sound level measured over the run time.  This becomes a bit confusing when 
thresholds are used.  Any sound below the threshold is not included in this average.   Remember that 

sound is measured in the logarithmic scale of decibels therefore the average cannot be computed by 
simply .adding the levels and dividing by the number of samples.  When averaging decibels, short 

durations of high levels can significantly contribute to the average level.  Example: Assume the 
threshold is set to 80 dB and the Exchange Rate is 5 dB (the settings of OSHA’s Hearing Conservation 

Amendment).  Consider taking a one-hour noise measurement in an office where the A-weighted 
sound level was typically between 50 dB and 70 dB.  If the sound level never exceeded the 80 dB 

threshold during the one hour period, then the Lavg would not indicate any reading at all.  If 80 dB 
was exceeded for only a few seconds due to a telephone ringing near the instrument, then only those 

seconds will contribute to the Lavg resulting in a level perhaps around 40 dB (notably lower than the 
actual levels in the environment). 

 
 

Daily personal noise exposure level.