Lower panel: These are the classical power and torque profiles that start with a dry mixing stage, rise steeply with binder solution addition, level off into a plateau, and then exhibit overgranulation stage.

The power and torque signals have similar shape and are strongly correlated. The pattern shows a plateau region where power consumption or torque is relatively stable.

Based on the theory by Leuenberger, useable granulates can be obtained in the region that starts from the peak of the signal derivative with respect to time and extends well into the plateau area.

The peak of the derivative indicates the inflection point of the signal. Prior to this point, a continuous binder solution addition may require variable quantities of liquid. After that point, the process is well defined and the amount of binder solution required to reach a desired endpoint may be more or less constant.

Upper Panel: Frequency Analysis of the signals. Power consumption and torque fluctuations are influenced by granule properties (particle size distribution, shape index, apparent density) and the granulation time. Fluctuation of power consumption and intensity of spectrum obtained by Fast Fourier Transfer (FFT) analysis can be used for end point determination.

Another interesting fact was reported recently by Terashita and co-workers who observed that when the end point region of a granulation is reached, the frequency distribution of a signal reaches a steady state.