Abstract: A detector for detecting a change in a fluid level and generating a digital signal uses a light source and a photodetector mounted diametrically on a tube in a predetermined location where a change in fluid level is to be detected. The circuit provides two stable output states or levels, one which corresponds to fluid not being in the tube between the light source such as an LED light and the photodetector and the other level when fluid is in the tube. In a particular application, the invention is utilized to monitor fluid level in a predetermined location of a manometer to shut off a radon remedial system and provide audio/and or visual alarms when there is a fluid level change which indicates that the radon remedial system is not operating effectively.

Abstract: A detector for detecting a change in a fluid level and generating a digital signal uses a light source and a photodetector mounted diametrically on a tube in a predetermined location where a change in fluid level is to be detected. The circuit provides two stable output states or levels, one which corresponds to fluid not being in the tube between the light source such as an LED light and the photodetector and the other level when fluid is in the tube. In a particular application, the invention is utilized to monitor fluid level in a predetermined location of a manometer to shut off a radon remedial system and provide audio/and or visual alarms when there is a fluid level change which indicates that the radon remedial system is not operating effectively.