Sound level meters measure acoustic noise levels in decibels (dB) and are essential for occupational noise exposure monitoring, environmental noise assessment, and product noise testing. Calibration verifies microphone sensitivity, frequency weighting accuracy, and overall measurement performance using acoustic calibrators and reference sound sources.
Inspect the microphone for physical damage, diaphragm contamination, and windscreen condition. Verify the display, controls, and battery. Check that the frequency weighting (A, C, Z) and time weighting (Fast, Slow) selections function correctly.
Attach a certified acoustic calibrator (typically 94 dB or 114 dB at 1 kHz) to the microphone. Record the as-found reading. The meter should agree with the calibrator's certified level within ±0.3 dB for Class 1 or ±0.5 dB for Class 2.
Using an electrostatic actuator or multifrequency sound source, verify the A-weighting, C-weighting, and Z-weighting (linear) responses at multiple frequencies (e.g., 31.5 Hz, 125 Hz, 500 Hz, 1 kHz, 4 kHz, 8 kHz). Compare to IEC 61672 tolerance limits.
At 1 kHz, verify the meter's linearity across its measurement range by applying sound pressure levels at 10 dB intervals from the noise floor to the maximum level. Record the error at each level.
Apply a tone burst of known duration and level to verify Fast and Slow time-weighting responses match the IEC 61672 exponential averaging specifications.
Record all measurements, reference standard certifications, and compliance with IEC 61672 class tolerances. Issue the calibration certificate and apply the calibration label.
Per IEC 61672 Class 1: A-weighted level tolerance is ±1.1 dB at 1 kHz and within specified limits at other frequencies. Overall level linearity must be within ±0.7 dB across the linear operating range. Class 2 allows wider tolerances (±1.4 dB at 1 kHz).
12 to 24 months; field calibration check before each use
Class 1 meters have tighter accuracy tolerances and wider frequency range than Class 2. Class 1 is required for precision environmental noise measurement and regulatory compliance. Class 2 is acceptable for general noise surveys and occupational screening. The IEC 61672 standard defines the tolerance limits for each class.
Best practice is to check the sound level meter with an acoustic calibrator before and after each measurement session. This field check verifies that the microphone and meter are functioning correctly. A deviation of more than ±0.5 dB from the calibrator level indicates a problem requiring investigation.
Yes, acoustic calibrators must be calibrated periodically (typically every 12-24 months) to ensure their output sound pressure level is accurate. An expired or out-of-tolerance calibrator will invalidate all sound level meter field checks performed with it.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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