The fluidized bed signals can be decomposed into micro-scale, meso-scale and macro-scale by means of multi-resolution analysis, while how to perform the scale resolution accurately and convincingly still lacks appropriate criteria. In this study, the dual-channel fiber optical signals in the circulating fluidized bed were utilized to investigate the characteristic differences of correlation coefficients and time-delay between three scales. It's found that for two adjacent measurement signals there's good correlation and obvious time-delay at the meso-scale, characterizing the dynamic evolution of cluster structure, while high correlation and no time-delay at the macro-scale (apparatus scale), and no correlation at the micro-scale (discrete particles). Based on such analysis, the correlation time-delay function (CTF) f(tau r) was put forward as a scale resolution criterion to examine the characteristics of both correlation and time-delay between a pair of signals. Through analyzing the changes of f(tau r) with the level of decomposition signals, the raw fiber optical signals obtained from a pilot scale circulating fluidized bed (CFB) riser were effectively resolved into three scales. (C) 2018 Elsevier Ltd. All rights reserved.