Patent ID: 7263823

Claim:
A system for measuring NOx content of exhaust gas produced by an internal combustion engine, the system comprising: a bypass conduit having a first end fluidly coupled to an exhaust pipe of the engine, a second end open to ambient air and a third end fluidly coupled to the exhaust pipe downstream, relative to the exhaust pipe, of a junction of the exhaust pipe with the first end of the bypass conduit, with the second end of the bypass conduit open to ambient air between the first and third ends; a first valve positioned in-line with the bypass conduit; a second valve positioned inline with the bypass conduit; a NOx sensor fluidly coupled to the bypass conduit between the first and second valves, the NOx sensor producing a NOx signal indicative of a NOx content of exhaust gas flowing thereby; and a control circuit controlling the first valve to an open position to allow exhaust gas to flow past the NOx sensor when measurement of the NOx content is desired, and otherwise controlling the valve to a closed position to inhibit exhaust gas flow past the NOx sensor.