Accuracy evaluation on linear measurement through opto-electronic plethysmograph

Abstract

Opto-electronic plethysmograph (OEP) is a motion analysis device able to measure chest wal l motion and volume variation by surface measurement. The estimation is obtained through displacements measurements of markers placed on the thorax. Therefore OEP accuracy on markers' displacement measurements may play a role in the volume's measurement. The aim of present work is to evaluate OEP accuracy in the estimation of linear displacements, taking into account the contribution due of number of cameras, markers size and displacement magni tude. A linear DC-motor was used to move the marker fixed on its shaft. Trials have been carried out varying 1) marker size (diameters of 6 mm and 12 mm) , 2) cameras number (2, 4, and 6) and 3) the magni tude of displacements ( from 10 μm up to 200 μm). Number of cameras and marker size do not seem to play a crucial role as far as it concerns accuracy on linear displacements. The relative percentage uncertainty decreases from 10% to 6% for marker A, increasing number of cameras from 2 to 6; for marker B, the percentage relative error decreases from 17% to 10%, increasing number of cameras from 2 to 4. Moreover, OEP shows a discrimination threshold of 30 μm.