GB732790A - Improvements relating to the analysis of scientific data - Google Patents

Abstract

732,790. Photo-electric curve reading devices. T.M.M. (RESEARCH), Ltd., BAMFORD, H., and WITCOMBE, L. May 26, 1953 [May 26, 1952], No. 13251/52. Class 40 (3). In apparatus for producing an electrical output in accordance with the ordinate of a trace on a chart, the chart is scanned by a light spot the interception of the spot by the trace being used to produce an output related in frequency or amplitude to the ordinate of the trace on the chart. As shown (Fig. 1) the trace 2 is carried on a continuously moving chart, a light spot produced by a cathode-ray tube 4 and lens 3 oscillating across the chart in a path at right angles to the chart movement. The image of the spot is received by a photo-electric cell 5 which feeds a control signal into a time base generator 6 deflecting the spot. The arrangement is such that the spot moves vertically until it intersects the trace when the sudden reduction of light reaching the photo-cell is used to reset the trace. Thus the rate of resetting is a measure of the amplitude of the trace ordinate while the value which the deflecting time base voltage has reached also represents this ordinate. Circuit (Fig. 2).-Reduction of the light reaching photo-cell 5 by interception of the flying spot by the trace triggers a thyratron 10 discharging condenser 12 (previously charged through resistor 11) through the thyratron. The thyratron cuts off and the condenser recharges, the potential developed at the positive plate of condenser 12 being used to deflect the spot which is thus reset each time the thyratron fires. The repetition frequency of pulses developed across a resistor 16 in the thyratron cathode circuit is a measure of trace amplitude while the current in cathode follower valve 14 depends on the instantaneous value of the time base deflecting voltage. Hence a series of pulses are produced across the cathode resistor of valve 14 and the output obtained through a low-pass filter circuit 15 is a reproduction of the trace. In modifications the spot is arranged to travel the full width of the screen at constant frequency so that an impulse is obtained as the spot passes the trace in both directions, the impulse causing an electronic switch to produce pulses of width inversely proportional to the ordinates. Alternatively impulses may be obtained as the spot passes, first a datum line and then the trace so as to cause the electronic switch to produce pulses of width proportional to the ordinates. Again, the switch may start a pulse when the spot passes the trace in the upward direction and stop it when the spot next crosses the trace, the width of the pulses thus depending on the slope of the trace.