Phasensynchronisation zyklisch getakteter Baugruppen an seriellen Bussystemen

The state of the art to design automation systems is characterized by using fieldbus linked devices (e.g. sensors, drives, ...). Each single unit generates its own internal clock by means of quartz oscillators and timers. The relative phase shift of the sampling periods between different units is accidental and not constant, due to quartz oscillator tolerances and to an individual behavior after power-on. Given a possibility to read each actual phase position (timer value) repeatedly at common sampling points and to change the preset value, a selection of devices can be synchronized. The fieldbus system has to provide functions in order to sample data in different units at the same sample point, independent of its serial behaviour. This can be achieved by the Global Control Commands „Sync“ / „Freeze“ (PROFIBUS DP) or by similar broadcast mechanisms. The following publication shows an example for the synchronisation of digital drive units with practical measurements and it demonstrates the advantages in an application.