| 摘要 |
A sample valve (20) for a synchronous detector working by means of modulating the dissolved substance alternately passes to a detector (40) a sample gas stream F1, which passes a modulator cell (13'), and a reference gas stream F2, which passes a compensating cell (12'). The sample valve (20) comprises a symmetrically constructed chamber (25) having inlets and outlets. A conventional switch (37) induces a control gas to enter the chamber alternately through one of two orifices (31 and 32) and to flow to outlet orifices (38 and 39) of the chamber which are opened and closed synchronously, so that the gas streams F1 and F2 are alternately fed to the detector (40) and discharged from the system. <IMAGE>
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