Data analysis from downers requires a comprehensive methodology in order to set the data baseline. This analysis can be accomplished by using a mathematical approach based on solid mass balances and an iterative calculation. Each signal baseline is defined as X+n.sigma(x), where Xis the signal average; sigma(x) is the signal standard deviation; and "n" is a baseline parameter. By using this methodology, the noise resulting from secondary reflections is eliminated and all valuable data is kept in the time series. More than 500 experiments with >50 million data records were obtained using two independent gas-solid circulating fluidized bed downer units of 3 m height and two different diameters (2.54-cm and 5.08-cm ID). The solid used was a FCC catalyst with a mean particle diameter of 84.42 pm and a particle density of 1722 kg/m(3). Measurements were effected using a CREC-GS-Optiprobe, an optical sensor equipped with a GRIN lens. This lens focus radiation in a 118 +/- 34 mu m diameter highly irradiated volume, placed at 4.5 mm away from the sensor tip. CREC-GS-Optiprobe sensors do not require calibration and offer minimum intrusion. On the basis of the data obtained, this study reports a valuable methodology, applicable to downer units of different diameters. This leads for the two downers studied to particle clusters with very close asymmetric distributions. (C) 2016 Elsevier B.V. All rights reserved.