An internal vibrator for vibrating a plastic material such as concrete has a measuring device for determining certain operating parameters, e.g. for measuring the motion of a vibrating cylinder in which a device for generating vibrations is accommodated or a power consumption or speed of an electromotor belonging to the device for generating vibrations. Two acceleration sensors that are able to detect the acceleration values for the vibrating cylinder in the concrete to be vibrated are also suitable since this enables conclusions to be made about the result of the vibration. The measuring values of the acceleration sensor and a power measuring device are evaluated by an evaluation circuit and can be conveyed to the user via a display.