Visual observation of particle layer sediment at the vessel bottom by classical Zwietering's concept is the most known method for determining,just-suspended impeller speed. This method has many disadvantages which can be eliminated by new application of the electrochemical method (EDD) for observation of particle layer sediment on the vessel bottom and for identification of just off-bottom particle suspension state. The main goal of this paper is to demonstrate the applicability of an electrochemical method for determining the impeller speed for off-bottom particle suspension in a wide range of suspension concentrations. The results obtained from EDD measurements are compared with the results from visual observations.