Stray light suppression circuit for light barrier arrangement

摘要

An oscillator (OS) produces a drive signal (AN) for a light source (LS) which is fed to a comparator (VE) with the reception signal (ES) produced by a light receiver (LE). The comparator produces a first logic signal when the drive and reception signals coincide and a second logic signal when they do not. The oscillator generates a scan signal (AB) with frequency an integral multiple of the drive signal frequency. Each scan signal pulse causes logic elements (NG,U1) to increment a first counter (Z1) when the first logic signal is generated. Further logic elements (U2) increment a second counter (Z2) when the second logic signal is generated. When at a first state, the first counter produces a first output signal which resets a memory element (SE). When at a defined second state, the second counter sets the memory element with a second signal. If the two counter signals occur simultaneously, both counters are reset.