Example: Solving product blockages and adhesions in silos. Electric external vibrators generate non-directional, circular vibrations. To drive chutes, screens, or vibration tables, external vibrators are synchronized in pairs and used in opposite directions to achieve a directed vibration. With an optional frequency converter, the vibration frequency and force can be adjusted and optimized for the specific process. Structure and mode of operation: Electric external vibrators are motors with unbalanced weights mounted on both ends of their shafts. The unbalance discs, and thus the working torque, centrifugal force, and amplitude of vibration, are adjustable.