APPARATUS FOR ANALYSING SIGNALS COMPRISING EXCURSIONS FROM A NOMINALLY CONSTANT BACKGROUND LEVEL

摘要

1,214,153. Selective signalling. NATIONAL RESEARCH DEVELOPMENT CORP. 31 July, 1968 [31 July, 1967], No. 35130/67. Heading G4H. [Also in Division G1] In a circuit for obtaining a signal free of baseline drift from a signal V, Fig. 3 (e.g. from a chromatogram), having base-line drift, the signal V is differentiated and when the derivative V 1 exceeds a pre-set threshold level found by experiment to be just larger the maximum rate of base-line drift, a signal V 3 is produced which causes the input signal V to be inverted and clamped, V 4 , at its value at that instant, which clamped signal V 4 is added to the input signal V to produce a signal V 5 substantially free of base-line drift. As described, the derivative signal V 1 , produced by a circuit 21, Fig. 2, is rectified, 22, before being applied to a threshold circuit 23 set just higher than the maximum rate of base-line drift, and the output signal V 3 is used to control a circuit which inverts and clamps the input signal V, the output of which, V 4 , is added, 25, to the input signal V to produce the required signal V 5 . The trough in the rectified signal V 2 identifies the peak of the input signal and is particularly useful when two adjacent peaks occur without an intermediate return to the base-line. So that such overlapping peaks may be detected, the output signal V 5 is applied to a threshold circuit 26 the output V 6 from which only falls to a low level when the signal V 5 falls below a threshold level, and this signal V 6 is also applied to the threshold circuit 23 so that its output, having gone high because the derivative signal V 1 has exceeded the maximum rate of base-line drift, remains high until the signal V 5 falls to below its threshold. In a modification (Fig. 5, not shown) a second derivative is used in place of the first derivative. The Specification also outlines a system for digitizing any peaks in the output signal V 5 , using the rectified signal V 2 to identify them, and for integrating the signal V 5 for the duration of signal V 3 to find the area under each peak or multiple peak.