www.safetyandhealthmagazine.com/articles/gas-detector-10

Gas detector

January 1, 2011
The IR5500 Open Path Gas Detector provides continuous monitoring of combustible gas concentrations and features advanced infrared sensor technology with a single beam detection design, which improves accuracy and reduces drift. The IR5500 requires no tools for alignment at any range, and can be aligned without a scope at 100 meters or more. 
General Monitors