Design of digital filters for frequency weightings required for risk assessments of workers exposed to vibration

Abstract

Many workers are exposed to vibration in their industrial environment. Vibration can be transmitted through a vehicle seat or a hand-held power tool. Excessive vibration exposure may cause health problems and therefore it is important that the worker's vibration exposure is assessed, which may require measurement by the equipment manufacturer or the employer. Human exposure to vibration may be measured using accelerometers; however, weighting filters are required to correlate the physical vibration measurements to the human's response to vibration. ISO 2631, BS 6841 and ISO 5349-1 describe suitable weighting filters, but do not explain how to implement them for digitally recorded acceleration data. ISO 8041 Annex C suggests a method but does not provide a solution. By using the bilinear transform, it is possible to transform the analogue equations given in the standards into digital filters. This paper describes the implementation of the weighting filters as digital IIR (Infinite Impulse Response) filters and provides all the necessary formulae to directly calculate the filter coefficients for any sampling frequency. Thus, the filters in the standards can be implemented in any numerical software.