[en] The Optical Fiducial Volume Trigger system (OFVT) has been developed for use with the Rapid Cycling Bubble Chamber (RCBC), serving as a vertex detector in the European Hybrid Spectrometer (EHS). Its purpose is to decide whether an interaction took place within the useful (fiducial) volume of the chamber. In this way it complements the main interaction trigger which lacks the necessary accuracy of vertex localisation. The system can reduce the cost of film material, film treatment and scanning by up to 60%, the precise saving being dependent on the experimental conditions. The principle of the optical track detection by linear diode arrays is described, as well as details of the hardware construction. The properties of the system are discussed on the basis of results from the first run with RCBC. (orig.)

[en] The European Hybrid Spectrometer is described in its preliminary version for the NA16 charm experiment. The performance of the small hydrogen bubble chamber LEBC and the detectors of the spectrometer is discussed. In particular the combination of the bubble chamber information with the spectrometer data is described in detail. The track reconstruction efficiency is 90%. The precision with which vertices seen in the bubble chamber are reconstructed is around 10 μm and the two track resolution is 40 μm. Therefore very complex event configurations, in particular charm particle decays, can be reconstructed correctly. (orig.)