Gas flow control system for an analytical instrument

Claim 1

In an instrument for measuring analytically the amount of a gaseous constituent in a gaseous sample mixture by introducing the gaseous sample mixture into a reaction chamber and measuring a characteristic of the gaseous constituent within the reaction chamber, a flow control system for maintaining accurate flow of the gaseous sample mixture into the reaction chamber comprising an upstream flow restricting device and a downstream flow restricting device in series with each other for conducting the gaseous sample mixture to the reaction chamber, bypass flow means connected to the junction of the upstream flow restricting device with the downstream flow restricting device, said bypass flow means including a bypass pump for drawing off a portion of the gaseous sample mixture that has passed through the upstream flow restricting device and regulating means responsive to the pressure difference between the junction of the flow rEstricting devices and the reaction chamber for regulating the pressure at the junction of the flow restricting devices, and an exhaust pump connected to the reaction chamber for drawing gaseous sample mixture from the junction of the flow restricting devices through the downstream flow restricting device and into the reaction chamber.