The invention relates to an ultrasonic sensor system, especially for controlling a resistance welding process. Said system comprises at least one receiver which is used to detect the ultrasonic signals from the area to be examined. At least two piezoelectric sensors (31, 32) are used as a receiver and are arranged in such a way that their polarization direction vectors indicate various directions, said vectors being projected in a plane perpendicular in relation to the propagation direction of an ultrasonic wave to be detected.