Analog Signal Detection

Up to now, we have given a general theoretical development of the self-beat technique. As a practical illustration of the experimental apparatus used to detect autocorrelation functions in scattering experiments, the equipment currently used in our laboratory will now be described. While our treatment of the autocorrelation function has been in terms of an analog signal, the computer that measures this function is actually a digital device. This is based on the fact that it is also valid to count the scattered photons in order to calculate Ci(r) as the optical intensity signal is essentially determined by the number of photons that strike the photocathode per unit time. We have then... 

The most accurate measurements of peak areas are those obtained by means of electronic data reduction with integrators or computers. The vast majority of laboratories now have electronic or computer methods for determining peak areas. Two main features are required for electronic processing of chromatographic data accurate digitization of the analog signal and software. The software is required for the detection of peaks, correction for baseline drift, calculation of peak areas, retention times, and concentrations of components in the sample, and production of the final report.5... 

Peaks emerging from the size exclusion column were detected by refractive index and UV absorbance at 206 nm. Analog signals were digitized at a rate of 150 points per minute and in a remote location by a modcomp 7861 minicomputer, equipped with an analog input subsystem. 

Instrumental detection limit (IDL) protocols are used to determine when an analog signal is sufficiently different from the background noise to conclude that a measureable "real" signal has been observed. But IDL terminology and estimation protocols are not standard. 

As a rule, primary data are generated as analog signals either in a discrete or a continuous mode (Figure 1.1). For example, monitoring the intensity of optical radiation by means of a photocell provides a continuous signal. Weak radiation, however, could be monitored by detecting individual photons by a photomultiplier. 

There are many ways of utilizing this equipment to achieve optimal results. For analysis, the data in Tables 15-1,15-2,15-3, and 15-4 are used. It is also assumed that the SIS logic solver is programmed to detect out-of-range analog signals and send a diagnostic alarm. 

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