In many applications, a light curtain is used to detect the intrusion of a human (or other protected object) into the danger zone. After detecting the interruption of the light curtain, a safety function is activated to bring the danger zone into a safe state (nonhuman). If the space taken by the light curtain is at the same time a working space, it is necessary to distinguish whether the light curtain interrupt is caused by man or material (material flows cannot cause the dangerous zone to be

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... ut into a safe state). There are several ways how to achieve this resolution, but additional (optional) sensors are commonly used. The paper deals with the parameters of additional sensors and how to connect them to the achieved Safety Integrity Level (SIL) of the safety functions realized by the help of the light curtain.