Microphone calibration service for airborne ultrasound

Technical ultrasound is increasingly used in many fields of industry. The accompanying airborne noise - produced on purpose or as by-product - gives reason to a growing number of noise measurements at the ultrasound frequencies beyond the audible range of hearing. These are for example the assessment of noise immission at working sites and the noise emission of products for safety guidelines. A general problem of such measurements is the lack of traceability of the measuring instruments at high frequencies beyond 20 kHz. Especially the acoustical calibration of the microphone used was not possible up to now. More recently, the primary calibration of special microphones at ultrasound frequencies has become available at DFM in Danemark. Now, a secondary calibration service has been implemented at PTB to connect measurement systems of end users to the new primary standard. By use of a classical substitution procedure, a combination of a 1/4-inch measurement microphone and an adapter to 1/2-inch preamplifiers can be traced back to a primary transfer standard up to 100 kHz. The secondary calibration procedure presented is the last link in the metrological traceability chain to create working standards for airborne ultrasound measurements. The new service is now available at PTB.