Abstract: An ionic transducer for measuring the transit time of stream of ionized particles produced at an emission station and flowing towards a receiving station, which is used for controlling the richness of the air-fuel mixture fed into an internal combustion engine. At the receiving station is disposed a receiving device including a receiving grid on which a signal is induced upon passage of the ionized stream of particles. The receiving grid is situated between two other grids connected to ground and serving as shielding and airflow stream stabilizer. The several grids are movable and adjustable with respect to the direction of the stream of ionized particles.