An apparatus and method are adapted for analyzing exhaust emissions by using a small fraction of a continuously-extracted exhaust sample combined with a pollutant-free diluent through a system of critical flow orifices at a predetermined and precisely controlled flow ratio. A small quantity of gas...http://www.google.ca/patents/US5756360?utm_source=gb-gplus-sharePatent US5756360 - Method and apparatus for providing diluted gas to exhaust emission analyzer 
