Performance Analysis of the CCD Pixel Binning Option in Particle-Image Velocimetry Measurements

This paper proposes convenient methods to increase the dynamic speed range in particle-image velocimetry (PIV) measurements, which employ a charge-coupled device (CCD) camera binning option. Although the binning procedure decreases spatial resolution along specified dimensions, its ability to increase the camera frame rate and preserve the field-of-view are important advantages, which need to be thoroughly investigated. In order to demonstrate the advantages of the CCD binning option, we have carried out experiments both on static images of in-plane particle displacements and on dynamic images of real-fluid flows. In the first experiment, we have analyzed static images of 0.5, 1, and 1.9 μm size fluorescent polystyrene microparticles placed on thick quartz glass plate and illuminated by high-power LED. The in-plane images were captured at various CCD binning options, the distance between particles was then calculated using cross-correlation analysis and a subpixel interpolation scheme based on a Gaussian filter. In the second experiment, the fluid flow in a 30 × 300 × 50 000 μm microchannel was recorded at various CCD binning modes, and then, evaluated using ensemble-averaged normalized cross-correlation analysis with Gaussian subpixel interpolation. Velocity profiles obtained at various CCD binning modes were compared with those obtained at the normal mode. Error analysis has shown that despite the loss of the spatial resolution, the advantages of pixel binning, specifically increased sensitivity and a total full-frame rate, can be useful in PIV measurements, especially in laminar-fluid flows.