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Increased Sensitivity of Infrared Absorption Measurements by Computer Averaging

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Current infrared instrumentation permits the measurement of low concentrations or small quantities of material by electronic amplification of the signal and/or by utilizing infrared microscopes, beam condensers, and micro cells. It is now possible to achieve further sensitivity than permitted by these techniques. Using a computer of average transients (CAT) in conjunction with the spectrophotometer, a signal masked by noise can be increased with respect to the noise by a summation or averaging technique. In this method a region of the spectrum is scanned repetitively and the recorder input signal of each scan fed to the computer. A trigger circuit is utilized to synchronize the instrument and computer scans and provide a reference signal to the computer. The portion of the recorder input signal due to sample absorption is phase-locked to the reference signal, while the random component due to noise is not. When a number of input signals are added together, the phase-locked portions of the signal add arithmetically while the random noise adds out of phase and, therefore, tends to average out to zero. The improvement in the signal-to-noise ratio is proportional to the √N, where N is the number of scans summed. This technique has been applied recently to enhance the sensitivity of nuclear magnetic resonance and election spin resonance measurements (1).

Document Type: Short Communication


Affiliations: Pioneering Research Division U. S. Army Natick Laboratories Natick, Massachusetts

Publication date: November 1, 1964

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