The characteristic frequency band of acoustic emission (AE) in a stirred tank with respect to the behavior of particles movement was obtained by spectral analysis

wavelet transform and R/S analysis based on the mechanism of interaction between particles and the wall of tank.A criterion of slurry suspension height in the stirred tank was presented based on the relationship between the characteristic frequency band of acoustic emission from the particles-wall collisions with the height of the probing location in stirred tank.Slurry suspension height of stirred tank is the location where a sharp decrease of the AE energy on the characteristic frequency band or the ratio of the energy on the characteristic frequency band at one location to the average energy of the whole tank is observed.Experiments in the stirred tank with an inside diameter of 110 mm and different impellers in the system of glass beads and water showed that this criterion was useful for the online measurement of slurry suspension height.The average absolute relative deviation (AARD) was below 10% when the slurry suspension height determined with the AE technique was compared with ones by the method of visual observation.The criterion could meet the requirements of the online measurements of stirred tank.