Process for calibrating a gas metering instrument

Claim 1

A process to form a calibrating gas, comprising providing the test chamber with a gas inlet duct for receiving a flushing gas into the chamber and a gas outlet duct for removing gas from the chamber, providing a feed pump in the gas outlet duct for moving gas out of the test chamber through the gas outlet duct which also draws flushing gas into the test chamber through the gas inlet duct, activating the feed pump at a selected known rate and for a selected predetermined time period to draw gas out of the test chamber through the gas outlet duct and draw flushing gas into the test chamber through the gas inlet duct to flush all but the flushing gas from the test chamber, deactivating the feed pump after the selected predetermined time period to stop the passage of flushing gas, and thereafter feeding into the test chamber a known metered amount of a liquid calibrating substance using a delivery metering pump, the calibrating substance being supplied from a reservoir containing the liquid calibrating substance by the metering pump, controlling the metering pump and the feed pump at known selected rates, the calibrating substance being fed into the test chamber producing a mixture with the flushing gas in the test chamber to form the calibrating gas.