Built by Stanford Research Systems, the QMS200 atmospheric pressure gas analyzer is a complete system that is designed to sample a gas stream at atmospheric pressure and preform a mass spectroscopic analysis on that stream. The heart of the unit is a quadripole residual gas analyzer with a 1-200AMU sensitivity. Pressure reduction between the sampling port and the RGA is accomplished via capillary tube and a differential pumping system. Most of the gas stream bypasses the RGA, so that the sampling flow rate is on the order of 1~10 ml/min. This particular QMS200 also has provision for direct access to the RGA from a high vacuum system, allowing dual use as a dedicated RGA.