Sri International

Donald J Eckstrom

Robert J Vidmar

Walter G Chestnut

Joseph J Eash

An apparatus for measuring isotopic ratios provides four separate optical paths for separate measurement of each of two isotopes relative to a reference signal, using spectrally resolved infrared radiation. The design permits the measurements to be made accurately without significant time lags between measurements, and without interchanging of cells or filters.

NDIR apparatus and method for measuring isotopic ratios in gaseous

A system (20) for broadband electromagnetic absorption in an anechoic chamber (22) has walls (24) of the chamber (22) forming a sealed space. A plurality of ionization sources (30) are mounted on an inside surface of the walls (24), facing the sealed space (28), with a spacing to give one ionization source/m.sup.2 of chamber (22) surface. An electron beam source (32) is connected to the ionization sources (30). A source (36) of helium gas is connected to supply the helium to the space (28). An electronic unit (42) under test is inside the anechoic chamber, and is connected to a test system (44). The test system (44) is also connected to the electron beam source (32). The ionization sources (30) generate a helium plasma in the space (28) by pulsed operation of the electron beam source (32). Timing signals are supplied by the synchronizer (52) to electron-beam source (32) and to the test system (44), so that test signals are supplied by the test system (44) to the unit (42) under test and outputs from the unit (42) are supplied to the test system (44) during an approximately 200 .mu.second low-noise portion of the helium plasma afterglow following energization of the ionization sources (30). Electromagnetic waves generated by the unit (42) in the chamber (22) during the test are absorbed by the helium plasma, so that the outputs from the unit (42) do not include any substantial interference from reflected electromagnetic waves in the chamber (22).

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Portola Valley, CA, United States of America

Donald J Eckstrom