PHOTOELECTRIC SENSOR HAVING SELF-DIAGNOSTIC FUNCTION

PURPOSE: To generate a self-diagnosis signal without fail irrespective of the speed of movement of an object of detection when a light reception level is in an unstable region. CONSTITUTION: Light is projected into a monitoring space from a light-emitting element 11 and a reflected light on an object l is received by a photodetector 21. When a light reception level in the photodetector 21 is in an unstable region wherein it is higher than a stable light-interception level and lower than a stable light-entrance level, a self-diagnosis signal is outputted from a self- diagnostic circuit 30. The self-diagnostic circuit 30 delivers rectangular wave signals which show a first output value outputted when the light reception level in the photodetector 21 is the stable light-interception level or below or the stable light-entrance level or above and a second output value being different from the first output value repeatedly and alternately in a set period, and it generates the first output value at the time point when the light reception level enters the unstable region.