Abstract: A dual sensor system for measuring the presence of a wide range of water vapor concentration in an atmosphere. A first sensor for measuring higher levels of water vapor concentration and a second sensor for measuring lower levels of water vapor concentration. A pair of three way valves operable to provide two flow paths for the atmosphere, a first path including both the first and second sensors, and a second path including only the second sensor. An electronic control arrangement for indicating the water vapor levels in the atmosphere and for providing an electronic signal to actuate the pair of three way valves.

Abstract: A sensor system and method for measuring very low levels of a particular gas in an atmosphere which initially has high level of the gas. A pair of sensors of the particular gas are provided, one of which senses high levels of the particular gas and the other of which senses very low levels. The sensor which senses very low levels of the gas is not exposed to the atmosphere until the gas level has reached a low level, thereby enabling it to more quickly respond to further reduction in the gas.