Loss of optical input circuit

Abstract From the Canadian patent

A loss of optical input detector is disclosed disposed to receive a signal voltage from a fiber-optic receiver indicating that the optical input has dropped below a preset threshold. The detector includes a voltage follower connected to the fiber-optic receiver which passes to the detector circuit the signal voltage. A comparator circuit receives the signal voltage and compares it to a reference voltage. When the signal voltage is greater than the reference voltage the comparator produces and applies to an alarm circuit a positive voltage signal. This positive voltage signal turns on the alarm circuit. The alarm circuit provides a visual alarm indication and a logic signal to a controller …