| 摘要 |
A system for controlling flow of gas in a continuous flow isotope ratio analyser comprising a measurement cell 9, a gas inlet line 1 and a gas outlet line 2 for providing gas into and from a measuring cell, and at least one switchable flow restriction on the gas inlet line for selectively controlling gas flow into the isotope ratio analyser. The switchable flow restriction is provided by a bypass gas line 3 which connects to the gas inlet line at a first junction 13 and a second junction 14, and a flow restriction 6 positioned upon the gas inlet line between the two junctions. The flow restriction may be a fixed flow controller, a mass flow controller or a proportional valve. The system may further comprise valves 7, 8 on the bypass line and on the gas inlet line between the two junctions. Ideally, a pressure sensor 17 in the cell is connected to a controller 18 which operates the system. The system may comprise several switchable flow restrictors in parallel (fig 3). A method for determining an isotope ratio by varying the flow rate between two non-zero flow rates which vary in a ratio of 2:1 to 20:1 is also disclosed. |
