सीएसआईआर-राष्ट्रीय भौतिक प्रयोगशाला

CSIR-National Physical Laboratory

Acoustics & Vibration Metrology

CSIR-National Physical Laboratory has a strong base in R&D in the area of Acoustics and Ultrasonics. The calibration and other facilities available in the area are comparable with facilities in other countries. CSIR-National Physical Laboratory, New Delhi, being the National Measurement Institute (NMI) of India, has the statutory obligation to establish, maintain and upgrade the national standards of measurement and calibration facilities for different parameters.

It is equipped with advanced instrumentation for measurement of sound and vibration and calibration of electro-acoustic equipments such as ‘Norsonic’ Sound Level Analyzer, ‘Pimento’ Vibration Analyzer, ‘Grass’ Sound Intensity Probe and specialized Reverberation and Anechoic Chambers for carrying out sound insulation and absorption studies of materials and diagnosing machinery noise. Apex level calibration and testing services and technical advisory consultancy in architectural acoustics are provided to the industry and institution of the country. R&D work is going on in applied acoustics and building acoustics.

The new facility of primary vibration calibration standard in extended frequency range of 0.1 Hz to 20 kHz had been established. The new microphone calibration standard facility using insert voltage technique was also established for the calibration of acoustic calibrators and microphones which has reduced the uncertainty in calibration to a level at par with other NMIs of APMP region.

The measurement of ultrasonic propagation parameters such as velocity and attenuation, acoustic field parameters such as sound pressure, intensity, power, vibration amplitude, noise and vibration is done at the highest accuracy. CSIR-NPL has works on the development of measurement techniques using ultrasonics. It has, for example, already developed techniques for assessment of parallelism between faces of an opaque block, quality evaluation of ultrasonic blocks, measurement of ultrasonic velocity in membrane, attenuation measurement without invoking diffraction correction, ultrasonic C-scan of rods providing 3-D map, detection of subtle changes on surface of marble stone, theoretical modeling for determining moisture content in composite material, acoustic impedance of liquids etc.

A number of instruments have also been developed such as ultrasonic interferometer, ultrasonic immersion and contact transducers for NDT and medical applications, pellicle with 98% transmission coefficient, calibration blocks for surface wave and creeping wave probes, piezoelectric pressure transducer, ultrasonic blind aid, displacement transducer, ultrasonic atomizer, fish tag, directional hydrophone etc.

CSIR-NPL maintains primary standards, viz. the standard of sound pressure, vibration amplitude and ultrasonic power. The primary standard of sound pressure (Fig. 1a) is maintained through absolute calibration of standard condenser microphones in coupler cavity by the reciprocity technique in the frequency range 31.5 Hz to 25 kHz with an expanded uncertainty of ± 0.17 dB. The primary standard of vibration amplitude (Fig. 1b) is maintained through absolute calibration of standard accelerometer by Laser interferometer technique in the frequency range 5 to 5000 Hz with accuracy better than ± 1.2 %. The new facility of primary low vibration calibration standard in extended frequency range of 0.1 Hz to 20 kHz had been established (Fig. 1c). The primary standard of ultrasonic power (Fig. 1d) is maintained through absolute calibration of standard power transducer by electronic radiation force microbalance system in frequency range 1.0 MHz to 10 MHz and for power range from 0.01 to 10 W with accuracy better than ± 9%. The accuracy of primary standards is verified periodically through participation in Key–comparison exercises with leading NMIs in the world.

The primary standard transducers are calibrated by absolute method while secondary and measurement transducers are calibrated by comparison and transfer standard method respectively. The latest international standard 16063-11 specifies three calibration methods based on laser interferometer viz., Fringe counting method (FCM), Minimum point method (MPM) and Sine approximation method (SAM). The FCM can be used for sensitivity calibration in the frequency 1 to 800 Hz. The MPM is intended for sensitivity calibration in the frequency range 800Hz to 10 kHz. The SAM covers the frequency range 1Hz to 10 kHz and additionally makes it possible to measure the phase lag between the mechanical input and the accelerometer output voltage. The accuracy of transfer standards like sound level calibrator (± 0.15 dB) and vibration level calibrator (± 1.5 %) is determined with the help of transducers calibrated by absolute methods. The working standards like measurement microphones and accelerometers are calibrated with the help of transfer standards with an overall expanded uncertainty of ± 0.3 dB for microphones and ± 2.0 % for accelerometers. The field / in – situ measurements are carried out with the help of sound and vibration level meters which themselves are calibrated with the help of transfer standards (spot checking).

Consultancy is also provided in the setting up of the acoustic facility, noise and vibration abatement, building acoustics and for particular NDT problems.

Fig. 1a: Primary Microphone Calibration Standard using Reciprocity Technique

Fig. 1b: Primary Vibration Calibration Standard using Laser Interferometer

Fig. 1c: Primary Low Frequency Vibration Calibration Standard

Fig. 1d: Primary Standard for Ultrasonic Power Measurement using Radiation Force Balance (RFB)

A. Parameters Covered

1. Sound Pressure

2. Vibration Amplitude (Displacement, Velocity & Acceleration)

3. Sound Power

4. Sound Transmission Loss

5. Sound Absorption Coefficient

B. Facilities Available in the Section (Items Calibrated)

Standards & Measurement Microphones, Sound Level Meters, Loudspeakers, Standard & Measurement Accelerometers, Vibration Meters, Sound Level calibrators, Reference Sound Sources, Sound Absorbing Material, Sound Insulation Material, Crackers Noise, Noise & Vibration Measurement and Analysis.

Parameters CoveredCalibration Facilities available forRange and uncertainty (Expanded) at k = 2 and 95%
Sound PressureStandard and Measurement Microphone, Sound Level Meter, Sound Level Calibrators, Pistonphone40-160 dB (20 Hz-25 kHz) ±0.05-0.17 dB
Vibrational amplitude (Displacement, Velocity, Acceleration)Standard and Measurement Accelerometers, Vibration Meters, Accelerometer Calibrator

Displacement: 0.001 – 10 mm (5 Hz-100 kHz)

Velocity: 0.01 – 1000 mm/s

Acceleration: 0.10 – 1000 mm/s 2 ± 1.0 %

Sound PowerReference Sound Sources, Miscellaneous Noise Sources40-160 dB (31.5 Hz – 20 kHz) ±1.0 dB
Ultrasonic PowerRadiation Force Balance1 mW to 1 W (1 MHz – 15 MHz) ± 4.5%
Sound Transmission Class (STC)Sound Insulation Materials± 1.0 dB (100 Hz – 4 kHz)
Noise Reduction Coefficient (NRC)Sound Absorbing Materials± 5% (100 Hz – 4 kHz)
Noise and Vibration Measurement & AnalysisFire Crackers, Multipurpose Halls, Recording Theaters, Ground Vibrations, Machinery Noise40-160 dB(20 Hz – 25 kHz) ±1.0 dB

. Standards Used

Primary Standards

  • Primary standard of sound pressure is maintained through absolute calibration of LS1P & LS2P laboratory standard microphones in coupler cavity by Reciprocity Technique (IEC