NOVELTY - A portion of a hydrogen rich stream (HRS) is passed into a chamber having sensor(s). Sensor(s) in a chamber is regenerated by exposing to fresh air. Carbon monoxide concentration in HRS of a fuel cell reformer is determined by response of the sensor(s). HRS from the chamber is routed to the chamber, and sensor(s) are regenerated by exposure to fresh air.    USE - For measuring and removing carbon monoxide within the hydrogen rich stream of fixed and portable fuel cells, such as passenger cars, trucks, boats, air crafts and other vehicles, ships and power plants, for ammonia synthesis and other chemical processes.    ADVANTAGE - Service life of the fuel cell catalyst of the apparatus used for detecting and removing carbon monoxide is optimized and is protected. The concentration of carbon monoxide in the hydrogen rich stream is determined inexpensively and effectively using less power. The alarm systems prevent the danger of leakage of high concentration carbon monoxide. The detection system has carbon monoxide sensors which are control sensors, which reduce effects on environmental changes such as temperature and humidity.    DETAILED DESCRIPTION - A portion of a hydrogen rich stream (222) is passed into a chamber (255a) having sensor(s) (252) responsive with carbon monoxide (CO), when sensor(s) (252a) responsive to CO in a chamber (255b) is regenerated by exposing to fresh air. Concentration of CO in the hydrogen rich stream is determined by monitoring the response of sensors exposed to the hydrogen rich stream of a fuel cell reformer. The hydrogen rich stream is routed to the chamber (255b) and the sensor(s) in the chamber (255a) is exposed to fresh air and regenerated, when a predetermined CO saturation concentration is satisfied.    An INDEPENDENT CLAIM is included for an apparatus (210) for determining and measuring concentration of target gas within the hydrogen rich stream (HRS) of a fuel cell reformer. The apparatus has the chamber (255a) and chamber (255b) in communication with HRS and fresh air stream. The apparatus further has an equipment for selectively exposing the chambers to the HRS and fresh air stream. The chambers has sensors operating at predetermined saturation concentration. An equipment controller (260) controls the equipment used for exposing the chambers to the hydrogen rich and fresh air stream, and directs the HRS to the chamber previously exposed to fresh air.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of a dual carbon monoxide detection system with a controller to operate refrigeration and detection modes.    Sensing system (210)    Cooling heat exchanger (250)    Sensors (252, 252a)    Valves (254, 254a)    Sensor chambers (255a, 255b)    Controller (260)    Photon source (261, 261a)    Photodetector (262, 262a)