<title>High-precision laser vibrometers based on digital Doppler signal processing</title>

Abstract

Recent developments in the field of digital signal processing (DSP) hardware and affordable powerful PC platforms enable the realisation of a new generation of laser-Doppler vibrometers, providing outstanding measurement accuracy and resolution. The paper presents both PC based and DSP based solutions for digital Doppler signal processing, utilized within the latest vibrometer models introduced by Polytec GmbH, Waldbroim. It is shown, that heterodyne interferometer technology in combination with high-speed AID conversion and numerical demodulation methods provides superior accuracy and resolution in a wide amplitude and frequency range. Depending on the particular application, either PC based systems or plug-in DSP decoder modules are the preferred solution. Advantages and tradeoffs of both ways are analysed. In addition to digital decoding technology, the presented systems make use of digital signal transmission via a standard S/P-DIF interface, commonly known from digital-audio equipment. This interface allows distortion-free signal recording on digital media and signal acquisition without expensive A/D boards. Based on the described technology, a primary calibration system for accelerometers has been developed in a cooperation project. The aim of this paper is the demonstration of digital signal processing as a powerful alternative to analog technology, that will advance measurement accuracy of future laser-Doppler vibrometers.