Personal sound meter for high-frequency sound

Status:

completed 08/2022

Aims:

Specific exposures to high-frequency auditory sound and ultrasound are beginning to emerge in an increasing number of occupational sectors. This applies, for example, to dentistry and all ultrasound workplaces (e.g. welding, gluing and cleaning operations). Most industrial applications have working frequencies between 20 and 40 kHz. It is not always possible to measure noise exposure at the workplace with a hand-held sound level meter or a hand-held ultrasonic level meter. In such cases, it is common to use a noise dosimeter worn on the body. These can be attached to the wearer and thus allow exposure detection even under challenging circumstances.

However, the standard requirements for commercially available dosimeters only cover audible frequencies up to and including 8 kHz. Institute for Occupational Safety and Health (IFA) tests have shown that the higher-frequency audible sound range between 8 and 16 kHz is often missed by dosimeters (unlike class 1 hand-held sound level meters) and that such devices are therefore unsuitable for measuring high-frequency noise exposure. The purpose of the project was to develop a prototype of a sound meter worn on the body, that is capable to detect high-frequency audible sound and low-frequency ultrasound up to 50 kHz with known measurement uncertainty, thus closing the gap in the exposure assessment mentioned above.

Activities/Methods:

The IFA was involved in the entire research and development of the new measuring device. This included defining and regularly reviewing requirements on the device and the test procedures, carrying out laboratory and field measurements and finally conducting functional tests on the finished device. In addition, a suitable testing and calibration unit was to be set up for the new measuring device at the IFA. The work that was carried out was based on the findings on measurement technology and measurement methods for airborne ultrasound obtained in the previous cooperation projects 4222 and 4223. In the current cooperation project 4239, a project financed by the German Federal Ministry for Economic Affairs and Energy (BMWi) under a funding programme called TransMeT (Transfer of Metrological Technologies), the IFA is benefiting from the metrological expertise of the National Metrology Institute of Germany (PTB, Physikalisch-Technische Bundesanstalt) and is a user of those metrological technologies.

Five prototypes of such a measuring device were to be created by the PTB from the IFA’s own material, and upon the completion of the project, they were to be available at the IFA for its own use and also for the metrological services of the accident insurance institutions. However, due to the restrictions and consequences of the Covid pandemic, the necessary components were not available, so that at the end of the project there was only an assembly manual for the device, the required peripherals and the firmware for operating the device. Any production of the actual devices therefore has to be postponed and will be carried out at the IFA with the help of the E-lab. The E-lab was brought into the project as soon as it emerged that the original project objective could not be reached.

Results:

Upon the completion of the project, a basic working prototype of a high-frequency and ultrasound dosimeter worn on the body will be available at the IFA. It will be able to simultaneously record measurands with relevance to occupational health and safety within the audible and ultrasonic frequency range of up to 50 kHz. This will include, in particular, continuous sound pressure levels in frequency weightings A and AU, peak sound pressure levels in frequency weightings C and Z as well as octave and 1/3 octave band levels. In addition, it will be possible to measure other parameters and levels, such as the air temperature, continuous sound pressure levels of ultrasonic frequencies and a single-event level (SEL). All of these may be of interest for research and special investigations, e.g. into accidents. The consequences of the Covid pandemic prevented the originally planned implementation of a prototype that would have been suitable for operational measurements, as essential components were not available or involved extremely long delivery times. The prototype measuring device that was developed in the project will therefore be modified by the IFA’s E-lab into a device that can be used for operational measurements, so that it can be made available to the metrological services of accident insurance institutions for operational measurements. It is not possible to anticipate when modification and production can proceed, as there are still key components requiring delivery times of a year or more.

The measuring device includes a comprehensive portable PC application that can be used for viewing and processing the recorded readings. In particular, the software makes it possible to export the (processed) measurement data to the OMEGA Noise software.

Furthermore, a feasibility study was carried out as part of a student thesis focusing on the calibration of the developed devices in the ultrasound range. With rental equipment, quality assurance requires that each device is calibrated whenever it is returned, making it important to access a readily available calibration facility. Also, as things are at present, such calibration work cannot be purchased from a service provider. The results of this study can also be used to adapt the IFA’s range of services to the changing needs of accident insurance institutions and to engage in research, development and standardisation.

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