# Open Path Detection #detection-technology #sensor #system-design Open path gas detection systems detect gas clouds over distances using infrared beams, providing area coverage rather than point detection. ## Principle - IR beam transmitted from source to receiver - Gas cloud absorbs IR radiation - Reduction in received signal indicates gas presence - Measures gas concentration along beam path (LELm) ## Advantages - Area coverage (not just point detection) - Detects gas clouds between source and receiver - Can cover large areas with fewer detectors - Effective for perimeter monitoring ## Applications - Perimeter monitoring - Large area coverage - Pipeline monitoring - Tank farm protection - Fence line monitoring ## Limitations - Requires clear line of sight - Affected by weather conditions - Beam alignment critical - More complex installation - Higher cost than point detectors ## Measurement Units - LELm (Lower Explosive Limit meters) - Concentration × path length - Different from point detector units (%LEL) ## Installation Considerations - Beam alignment - Height above ground - Protection from damage - Weather protection - Regular maintenance and testing ## Related Concepts - [[IR Absorption]] - [[Gas Detector Placement]]