Automatic baseline compensator for optical absorption spectroscopy

Claim 1

In a dual beam spectrophotometer of the type including a monochromator and wavelength adjustment means for providing optical outputs from said monochromator at discrete wavelengths; means for providing a reference signal proportional to the intensity of the detected reference beam and a sample signal proportional to the intensity of the detected sample beam; means to combine said reference and sample signals to provide an electrical output indicative of the ratio or log 10 of the ratio of said signals, to thereby determine transmission or absorbance of a sample; and compensator means for adjusting the attenuation of at least one of said signals with respect to the other, to thereby establish a relatively flat baseline throughout the wavelength range of said spectrophotometer; the improvement wherein said compensator means comprises: attenuator means for adjustably attenuating at least one of said reference or sample signals; wavelength motor means for step-wise driving of said wavelength adjustment means, to provide a series of stepped discrete wavelength outputs from said monochromator; means for generating during a calibration run through the wavelength range of said spectrophotometer, an error signal indicative at each of the discrete wavelength outputs of said monochromator, of the presence and direction of an imbalance between said reference and sample signals; magnetic tape recorder means, including tape advance drive means incremently actuated to advance said tape in discrete steps, in synchronism with the incremental step-wise movement provided by said wavelength motor means; means for writing the information conveyed by said error signal on said tape during each discrete movement of said tape, as a single bit of a first readable level when said error signal indicates said imbalance is in said first direction, and as a single bit of a second readable level when said error signal indicates said imbalance is in said second direction, to enable recording of the information conveyed by said error signal during said calibration run, throughout the wavelength range of said spectrophotometer; means for integrating the stream of successive said bits and converting the integrated signal to an analog signal for controlling said attenuator means, to reduce, at the beginning of each stepwise change of wavelength, the imbalance of said reference and sample signals, and thereby flatten said baseline; and means for reading out the stream of successive bits on said tape during a sample run upon said spectrophotometer, and applying said read-out bit stream to said integrator to adjust said attenuating means during said sample run, to thereby duplicate the baseline adjustments effected during the writing of said bit stream upon said tape.