Noise Monitors and Meters

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Sound level meters

Description and Applications
The sound level meter is a lightweight instrument for the measurement of sound pressure level (SPL) in decibels. All ANSI-approved meters meet minimum requirements that include an A-weighted network, a slow-response meter characteristic, and a fully graduated scale with measurements ranging from 80 to 130 dBA. The Type II meter is most frequently used. Applications are in worker exposure and noise evaluations.

Octave Band Analyzer
Some sound level meters may have an octave or one-third octave band filter attached or integrated into the instrument. The filters are used to analyze the frequency content of noise. They are also valuable for the calibration of audiometers and to determine the suitability of various types of noise control.

Calibration
In normal operation, calibration of the instrument usually requires only checking. Prior to and immediately after taking measurements, it is a good practice to check, using a calibrator, the ability of the sound level instrument to correctly measure sound levels. As long as the sound level readout is within 0.2 dB of the known source, it is suggested that no adjustments to the calibration pot be made. If large fluctuations in the level occur (more than 1 dB), then either the calibrator or the instrument may have a problem.


Special Considerations

Always check the batteries prior to use. Use the microphone windscreen to protect the microphone when the wearer will be outdoors or in dusty or dirty areas. (The windscreen will not protect the microphone from rain or extreme humidity.)
Never use any other type of covering over the microphone (e.g., plastic bag or plastic wrap) to protect it from moisture. These materials will distort the noise pickup, and the readings will be invalid.
Never try to clean a microphone, particularly with compressed air, since damage is likely to result. Although dirt and exposure will damage microphones, regular use of an acoustical calibrator will detect such damage so that the microphones can be replaced.
Remove the batteries from any meter that will be stored for more than 5 days. Protect meters from extreme heat and humidity.
Maintenance
No field maintenance is required other than replacement of batteries.

Personal dosimeters

Description and Applications
These meters can be worn by personnel to obtain individual readings of noise exposure. Typical dosimeters consist of a pocket-sized monitor with remote microphone and an indicator for readout of exposure data. Some have a preset threshold; others have a selector switch that may be preset. It is also possible to select the threshold, criterion level, and exchange rate on many dosimeters.

Calibration
Field calibrate at the measurement site according to the manufacturer's instructions both before and after each use. Use an acoustical calibrator that was designed to be used with the particular model noise dosimeter being used.

Special Considerations

Always check the batteries prior to use. Be very careful with the microphone cable. Never kink, stretch, pinch, or otherwise damage the cable.
Use the microphone windscreen to protect the microphone when the wearer will be outdoors or in dusty or dirty areas. (The windscreen will not protect the microphone from rain or extreme humidity.)
Never use any type of covering over the microphone (e.g., plastic bag or plastic wrap) to protect it from moisture. Such materials will distort the noise pickup, and the readings will be invalid.
Never try to clean a microphone, particularly with compressed air, since damage is likely to result. Although dirt and exposure to industrial environments will damage the microphones, regular use of an acoustical calibrator will detect such damage so that microphones can be replaced.
Remove the batteries when the dosimeter will be stored for more than 5 days. Protect dosimeters from extreme heat and humidity.
Maintenance
No field maintenance is required other than replacement of batteries.

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