Quick Answer
Sound level meter (SLM) calibration uses a NABL-calibrated acoustic reference calibrator (pistonphone or sound level calibrator) to verify the SLM's sensitivity at 1 kHz reference frequency (typically 94 dB SPL or 114 dB SPL), per IEC 61672-2 and GPCB requirements.
Key Takeaways
- SLM calibration uses an acoustic calibrator (pistonphone) generating 94 dB or 114 dB at 1 kHz.
- Calibration per IEC 61672-2 for Type 1 (precision) and Type 2 (general purpose) sound level meters.
- GPCB and CPCB require NABL-calibrated SLMs for ambient noise and industrial noise monitoring.
- Calibration includes frequency response, linearity, and weighting network (A, C, Z) verification.
- Prism calibrates SLMs used for occupational noise exposure (OSHA, IS 9779) and environmental monitoring.
Sound Level Meter Calibration Procedure
Field Calibration Check
Use acoustic calibrator (pistonphone, 94 dB / 1 kHz) at start and end of each monitoring session. Adjust SLM sensitivity if deviation > ±0.5 dB.
Laboratory Electro-Acoustic Calibration
Full laboratory calibration using precision sound source in an anechoic environment. Verify: sensitivity, frequency response (20 Hz–12.5 kHz), A/C/Z weighting, time constants (Fast, Slow, Impulse).
Linearity Check
Verify linearity of SLM at 60 dB, 80 dB, 94 dB, 110 dB SPL.
Certificate Issue
Issue NABL certificate with SLM sensitivity correction, frequency response data, and expanded uncertainty (typically ±0.5 dB).
GPCB Noise Compliance Monitoring — Gujarat Requirements
Gujarat Pollution Control Board (GPCB) and CPCB require industries to monitor ambient noise levels per Environment (Protection) Rules 1986. Industrial areas: day 75 dB(A), night 70 dB(A). Commercial areas: day 65 dB(A), night 55 dB(A). Residential: day 55 dB(A), night 45 dB(A). NABL-calibrated SLMs are required for monitoring data to be accepted in GPCB compliance reports.
Frequently Asked Questions
What is an acoustic calibrator and why is it needed?
An acoustic calibrator (pistonphone or cavity-type calibrator) generates a precisely known sound pressure level (94 dB or 114 dB) at 1 kHz when coupled to the SLM's microphone. It is used to verify and adjust the SLM's sensitivity before and after each monitoring session. The calibrator itself must be NABL-calibrated annually.
What type of SLMs does Prism calibrate?
Prism calibrates Type 1 and Type 2 sound level meters (per IEC 61672-1) from all major brands: Brüel & Kjær, Larson Davis, Cirrus Research, PCE Instruments, Extech, and TES.
Is NABL SLM calibration required for GPCB noise monitoring?
Yes. GPCB requires noise monitoring data to be collected with calibrated instruments. NABL calibration certificates are the accepted form of calibration evidence for GPCB compliance submissions.
How often should sound level meters be calibrated?
Annual NABL calibration is required. Field calibration checks with a pistonphone before and after each monitoring session are also mandatory.
Does Prism calibrate personal noise dosimeters?
Yes. Prism calibrates personal noise dosimeters used for occupational noise exposure monitoring per IS 9779 and OSHA 1910.95.
Written by
Er. Parthiv Kinariwala
Managing Director · Prism Calibration Centre · NABL CC-2480 · Ahmedabad
Er. Parthiv Kinariwala founded Prism Calibration Centre in 2004 and has over 20 years of hands-on experience in calibration engineering, NABL accreditation, and industrial compliance. His team performs 10,000+ calibrations annually from the Vatva GIDC laboratory, serving 5000+ industries across Gujarat.
Prism Calibration Centre — Vatva GIDC, Ahmedabad
Prism Calibration Centre
F-101, Rudraksh Complex 2, Phase 3, GIDC Vatva, Near Jasoda Nagar Cross Road, Ahmedabad — 382445, Gujarat, India
Phone: +91 98245 26444
Email: info@prismcalibration.com
NABL: CC-2480 · ISO/IEC 17025:2017
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