The Honeywell LLE Series liquid level sensors offer a reliable solution for single-point liquid level detection in various industrial applications. These sensors utilize a unique design with an LED and phototransistor sealed within a plastic dome, ensuring total internal reflection for a normally high output. When liquid covers the dome, the refractive index changes, reducing light reaching the phototransistor and causing the output to switch low. Proper fluid selection is crucial, and Honeywell recommends freon and alcohol-based solvents. Users should verify compatibility with polysulphone before use. These sensors are suitable for a wide range of applications requiring non-invasive liquid level monitoring.