Optical sensing measurement system - responds to rapid intensity changes and suppresses low change rates using filtering comparator

摘要

The optical measurement system i.e. for detecting the presence of a vehicle uses a sensor producing an output signal dependent on the light it receives and operates independently of light source variations caused by obscuring dirt etc. It operates economically and reliably and is easily installed and reacts to system light intensity increases but not to ambient intensity changes. Two varying threshold signals (US1,US2) are dependent on the sensor output signal (USi). One is greater and one less than the sensor signal by a given voltage level. Theshold signal variations faster than a defined rate of change are suppressed by low pass filters (5,6) whose outputs are compared with the sensor signal by comparators (7,8). A sensor light variation is only indicated when the sensor signal exceeds the upper or falls below the lower rate limited threshold.