Abstract:
A rapid scan spectrum identifier fur use in identifying infrared spectrum of the output of a gas chromatograph to identify its absorption characteristics and includes an infrared source and beam splitter, a double beam chopper for alternately sending the infrared beam through a sample or reference gas cell mounted in a suitable furnace, the output of which is recombined and analyzed by a monochromator having a narrow output passband of energy detected by a rapid response detector, the output of which is processed by suitable electronic circuitry to provide a readout. The monochromator is of the scanning type in which a grating is synchronously scanned with a circular variable filter so that the first order output of the grating is selectively passed and higher orders rejected by the filter. The sample and reference gas cell furnace assembly utilizes specially constructed sample and reference gas cells symmetrically mounted in a furnace arrangement for maintaining input gas streams at equal temperatures within each cell and above the temperature of condensation of the sample under investigation. The beam chopper contains associated photoelectronics for physically determining the location of a chopping blade to thereby provide gating signals for indicating the presence at the detector of a sample, reference, or a background signals. These grating signals are used in sample and hold circuits to convert an essentially digitally sampled output into a relatively smooth continuous curve indicative of the absorption of the sample so that the readout represents the sample absorption characteristics corrected for reference for the carrier gas and background effects. The instrument is designed to operate with scan rates of approximately 6 and 30 seconds.
Abstract:
A monochromator having a corner mirror scanning wheel and a fixed baffle adjacent the scanning wheel to vary the effective height of an exit slit. The height profile of the baffle is adapted to selectively vary the radiant energy passed through this exit slit at different wavelengths so as to provide the desired balance among resolution, signal-to-noise ratio and the dynamic range of the background signal over the scanned portion of the spectrum.