PRIMARY ACCELERATION MEASUREMENT USING FRINGE COUNTING WITH HETERODYNE INTERFEROMETRY

Thomas Bruns, Frank Blume, Henrik Volkers

Abstract

The application of heterodyne interferometry with direct access to the frequency modulated signal was deemed unfeasible for low frequency vibration measurement, because of the trade-off between a carrier frequency and modulation bandwidth in the MHz range calling for high sampling rates on the one hand, and the low vibration frequency calling for long measuring times on the other hand. Data acquisition systems with the necessary amount of sample memory are expensive and the CPU time needed for the appropriate data processing becomes prohibitive at very low vibration frequencies.<BR />PTB recently developed a new method related to the classic homodyne fringe counting, which reduces the sampling rates for the interferometer signal to ranges related to the spectral contents of the vibration motion. <BR />The new method of heterodyne fringe counting is capable of magnitude and phase response measurements. The contribution describes the methodology and discusses some of its distinctive features and possible pitfalls.

Keywords

heterodyne laser interferometry, primary accelerometer calibration, fringe counting

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IMEKO-TC22-2014-004.pdf

DOI

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IMEKO TC

TC22 - Vibration Measurement

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