The SCL has developed a new calibration service for working grade microphones with constant current line drive (CCLD) preamplifiers in accordance with International Standard IEC 61094-5:2016. Unlike the traditional polarisation voltage supported preamplifier, the CCLD preamplifier gives output signals in the form of voltage modulation in the constant current power supply line. It is commonly used for multichannel acoustic measurements such as workplace noise assessment.

Apart from the new calibration service, the SCL also upgraded its calibration services for sound level meters and laboratory grade microphones in accordance with the latest versions of the international standards IEC 61672-3:2013 and IEC 61094-2:2009 respectively. New requirements for evaluation of the stability performance of sound level meters and a new method of calculation of acoustic transfer impedance based on a broadband approach for laboratory grade microphones were introduced in these new versions of the international standards.

In January 2017, these new and extended calibration services were assessed by overseas peer reviewer Dr. Huang Yu Chung, Chairman of the Technical Committee for Acoustics, Ultrasound and Vibration (TCAUV) of the Asia Pacific Metrology Programme (APMP), under the HOKLAS accreditation. The range of calibration of a working grade microphone with CCLD preamplifier is from 63 Hz to 12.5 kHz, with a best measurement uncertainty of 0.07 dB. The range of calibration of a laboratory grade microphone is from 20 Hz to 25 kHz, with a best measurement uncertainty of 0.04 dB. For more information about SCL’s acoustics related calibration services, please visit the SCL website at www.itc.gov.hk/scl.