| abstract |
A gas analyzer for determining the concentration of the oxides of nitrogen in a sample gas is provided. The analyzer is particularly adapted for analyzing the exhaust from an internal combustion engine. In one embodiment, the analyzer comprises a sample chamber and a reference chamber. An arrangement is provided for delivering sample gas containing the lower oxide of nitrogen (NO) to the sample chamber and a quantity of ozone (O 3 ) for reacting with this oxide of nitrogen and producing a chemiluminescence. After the chemiluminescence is completed, the sample gas is discharged to the reference chamber. A sample photodiode is disposed adjacent to the sample chamber for receiving light emitted from the sample chamber and producing a sample signal representative of the total photoemissivity of the sample gas. A reference photodiode is disposed adjacent to the reference chamber for receiving light emitted from the reference chamber and providing a reference signal representative of the dark current of the photodiodes and the background photoemissivity of the sample gas. A circuit is provided for conditioning and substracting the sample signal and the reference signal to produce an output representative of the concentration of the oxide of nitrogen in the sample gas. Dilution air is mixed with the sample gas either in the instrument with a viscous metering technique or in a sample probe, mounted in the exhaust of the engine, with a sonic metering technique. In other embodiments, a single sample photodiode is used to measure the chemiluminescent reaction and determine the oxide of nitrogen content of the sample gas. |