Ultrasound level meter for practical use in occupational health and safety

A measuring system for airborne ultrasound is being developed within the scope of a technology transfer program. This system is specially dedicated to the practical application of measuring noise for occupational health and safety purposes. It will allow the determination and assessment of risks represented by widespread ultrasonic machines which can cause very high sound pressure levels.

The number of workplaces exposed to airborne ultrasound is constantly increasing due to the growing incidence of ultrasonic technologies such as ultrasonic welding, cleaning and cutting. The German Occupational Health and Safety Regulation on Noise and Vibrations [1] demands that all actual and potential risks due to noise at the workplace be assessed, which includes the measurement of ultrasound. Currently available sound level meters are, however, poorly suited to measuring sound in this frequency range. Consequently, entities such as professional associations cannot fully fulfill their tasks with regard to the risk assessment of exposed workplaces. Within the scope of the TransMeT program, PTB is therefore developing a sound level measuring system that covers not only the range of audible sound, but also the ultrasonic frequency range. Our partner (and direct user of the measuring system) is the Institut für Arbeitsschutz (IFA) of the Deutsche Gesetzliche Unfallversicherung (DGUV) [2].

For the development of the ultrasound-measuring system, numerous requirements must be taken into account; these are derived from IEC 61672 standard "Sound level meters" [3] and from the envisaged application field at workplaces that are exposed to ultrasound. For example, the electromagnetic compatibility of the system must be guaranteed to ensure that the measurement is not biased by strong electromagnetic fields as are encountered at some industrial sites. Moreover, the measuring range should be selected in such a way that the very high sound level pressures occurring locally at workplaces that are exposed to ultrasound can be detected. Due to its short wavelengths, the spreading of ultrasound can be hindered by very small obstacles. This must be taken into account when using microphone protection facilities or supports in order to disturb the sound field to be measured as little as possible.

The first prototype of the ultrasound level meter (Fig. 1) consists of a notebook, an analog-to-digital converter, a power module, a preamplifier and a 1/4-inch condenser microphone cartridge. A battery may be used as the power supply unit for the system, hereby enabling mobile applications.

 Fig. 1: Prototype of the ultrasound level meter

To compute, display and record the sound levels, a software program has been implemented in the programming language Python; this is controlled via a graphic user interface. Besides the real-time indication of the sound level/time evolution and of the frequency spectrum, it also allows the most diverse level measurands to be recorded and saved for later evaluation.

The system is not only being developed, but also being tested as to whether it can live up to the special requirements in practical application. For this purpose, PTB's various specialized measuring set-ups for the testing of sound level meters within the scope of type approvals will be used. The measuring system will then be complemented with a calibration procedure and a measurement method which still have to be developed.

In the short term, engineers working in occupational health and safety will be provided with a concrete tool to determine and assess the exposure to noise due to airborne ultrasound at workplaces in accordance with the requirements of the relevant standards. In the long run, the findings obtained from the development of the measuring system can be used in standardization and for the development and commercialization of improved systems.

Literature:

[1] Verordnung zum Schutz der Beschäftigten vor Gefährdungen durch Lärm und Vibrationen (Lärm- und Vibrations-Arbeitsschutzverordnung - LärmVibrationsArbSchV)
[2] http://www.dguv.de/ifa/index.jsp
[3] DIN EN 61672-1:2013: Elektroakustik – Schallpegelmesser – Teil 1: Anforderungen

Contact person:

Moritz Wächtler, FB 1.6, AG 1.62, E-Mail: moritz.waechtler(at)ptb.de