4.7μm Bandpass Filter

Context: This patent describes a remote sensing system designed to monitor industrial flares (the flames used to burn off waste gas in refineries) to ensure they are burning efficiently and complying with environmental regulations.

Usage of Filter: The system utilizes a specific bandpass filter (referred to as "Band 3") that transmits measuring light in the wavelength range of 4.7 µm to 4.8 µm.

Function: The filter is used to isolate the spectral emission signature of Carbon Monoxide (CO). While CO₂ is the product of complete combustion (monitored at ~4.3 µm), CO is the product of incomplete combustion.

Result: By measuring the radiance at 4.7 µm (CO) relative to the 4.3 µm (CO₂) and a background reference, the system can calculate the Combustion Efficiency (CE) in real-time. This allows plant operators to adjust steam or air injection to optimize the flare, preventing the release of toxic gases.

Context: A system for detecting hazardous gas leaks (like methane or other hydrocarbons) from a distance using active scanning.

Filter Usage: The patent describes the use of Resonant Cavity Infrared Detectors (RCIDs) and associated optical filtering effective at specific MWIR wavelengths, including 4.7 µm.

Function: In this configuration, the 4.7 µm filtering is often used as a reference channel or to detect secondary absorption features of gases like Nitrous Oxide (N2O) or Carbon Monoxide (CO) that may be present or acting as interferents.

Result: The use of this specific band allows for high-sensitivity discrimination between the target gas (e.g., Methane at 3.3 µm) and background noise or other combustion byproducts, reducing false alarms in industrial safety monitoring.