Patent US 3,961,898

The invention concerns an automatic continuous-flow fluid analyzer of the pe wherein a stream of fluid, segmented by air bubbles or other separating medium inert to the fluid to be analyzed, passes through a colorimeter flow cell. The bubble artifact is eliminated from the photoconductor signal while allowing the signal produced from the fluid segment to remain intact. This is accomplished by means of a signal comparator which operates as a digitally controlled differentiator, but could alternatively be a purely analog differentiator. The signal comparator through continual signal comparisons momentarily samples and stores a photoconductor output. For a finite period of time, the stored value is compared with all subsequent succeeding photoconductor output signals. If any signal that follows varies outside a preset range from the stored value, the comparator logic concludes that an air bubble is passing and the output to the recorder is not changed. The recorder continues to record from the signal in the memory means at all times. If the signal that follows remains constant as compared to the stored value, the comparator logic concludes that a fluid segment is in the flow cell and the signal at that time is transferred to the memory means and to the recorder.