Patent GB-943644-A (GB)
Title: Method and device for integrating deflections of measuring instruments variable withtime
IPC: G01D1/04
Filed: 1960-11-21
Abstract: 943, 644. Electric selective signalling systems. SCHOLVEN-CHEMIE A. G. Nov. 21, 1960 [Nov. 21, 1959; April 2, 1960], No. 39915/60. Heading G4H. [Also in Division G1] A variable, represented by the deflection of a measuring instrument, is integrated by repeatedly scanning the amplitude of deflection so that each momentary deflection corresponds to a proportionate time interval during each scan, and constantfrequency pulses are supplied to a counter only during these time intervals throughout the period of integration. The invention is described in its application to gas chromatography analysis, in which the successive peaks of a signal define successive integration periods, and is primarily concerned with apparatus for representing the angular position of the output shaft of a measuring instrument by a train of pulses. In a first embodiment, Fig. 1, a beam of light from a source 1 is reflected by a mirror 5 which is continuously rotated by motor 6. The rotating beam reflected by conical mirror 8 scans circumferentially arranged apertures in a mask 12, and the chopped, rotating beam then falls on a shutter 13, the angular aperture of which is determined by the position of shaft 15 of the measuring instrument. Thus the number of light pulses transmitted by shutter 13 depends on the momentary value of the measured variable, and these pulses are reflected by conical mirror 9 and rotating mirror 7 onto photo-cell 11. The pulses from photo-cell 11 are counted over the integration period and may be used to provide a printed record. Separate counters may be provided for successive peaks of the measured variable. In a second embodiment, Fig. 7 (not shown) shaft 15 positions a photo-cell relative to a fixed photo-cell and the arrangement is scanned by an aperture in a rotating disc to give signals corresponding in their time of occurrence to the zero position of shaft 15 and its momentary position, these signals being used to gate a train of pulses to a counter. In a third embodiment, Fig. 8, the shaft of the measuring instrument carries a mask 116 having an aperture 117 so as to project a beam of light of variable angular extent on to a photoconductive ring on disc 121. Disc 123 having an aperture 124 is rotated by motor 122 so as to pass pulses from generator 105 through the photoconductive ring on disc 121 to counter 107 for a period determined by the position of the shaft. Yet another embodiment, Fig. 9 (not shown) operates on a similar principle to that of Fig. 7, but employs fixed and movable mirrors which reflect beams of light on to fixed photo-cells to produce differentially timed signals representing the measured quantity. Range changing. The shaft of the instrument actuates limit switches to vary the attenuation of the signal applied to the instrument by factors of two, and to vary the number of binary stages in the counter accordingly. Errors in the counter which would occur owing to the finite response time of the instrument after a range-changing operation are compensated by delaying the changeover of the counting stages by a time dependent on the response time of the instrument. Remaining errors in the count during the ascending side of a peak are substantially cancelled by errors of opposite sign occurring during the descending side of the peak.