| 摘要 |
PURPOSE:To prevent malinformation by detecting heat rays from a warning beam area with two nearby differential pyroelectric type infrared sensors, and generating a warning when a signal exceeding threshold value and then a larger signal is detected. CONSTITUTION:Heat rays from a body to be detected which crosses the warning beam area are detected by the photodetection part 16 composed of two pyroelectric type infrared sensors 14 and 15 which are connected together nearly in series having the opposite polarities through a reflecting mirror. When the body crosses the area vertically, only the sensor 14 generates a differential waveform signal firstly; and the differential signal between differential waveform signals of the sensors 14 and 15 is generated as a detection signal having a large amplitude and the opposite polarity and further only the sensor 15 generates a differential waveform signal. Those signals are outputted to an output terminal 20 through a field effect transistor 18 to generate a warning signal only when the 1st signal exceeds the threshold value and a larger signal is outputted within a specific time.
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