Patent GB-1018199-A (GB)
Abstract: 1,018,199. Potentiometer voltage measurement; recording apparatus. HEWLETT-PACKARD CO. Jan. 8, 1964 [Jan. 24, 1963], No. 942/64. Headings G1J and G1U. In the electromechanical recording system a flexible belt 13 encircling rotatable wheels 9, 11 carries spaced styli 14, 15, 16 traversing a recording chart 17 carried by an earthed drum 19. The belt also has a pair of apertures 21, 23 for each of the styli, so disposed as to identify the end of the traversal of one stylus and the start of the traversal of the next by producing an impulse at the output of a photo-sensitive element 27 when any aperture is aligned with the illumination path thereof. Each such pulse is amplified and applied over pulse separator and gate 31 either to an input of ramp binary 35 or to sampling switch 39. The ramp binary output is passed to switch 41 of ramp generator 43 and to a time varying signal generator 45 of ramp slope regulator 47 and to the pulse separator and gate. The ramp generator output is applied to an input of each of a series of amplitude comparators 49, 51 &c. and to an input of ramp comparator 53 also receiving a reference voltage from source 55, and the comparator output is connected to the remaining input of the ramp binary 35.The outputs of comparators 49, 51 &c. are combined, shaped at 59, amplified, and applied to wheel 9 and belt 13, while the individual outputs are gated at 63, 65 &c. under control of contacts of switch 73 operated by drum 19, to the input of indicator circuit 69 whose output excites the pulse width control of pulse shaper 59. In operation, the wheels 9, 11 are motor rotated at a constant angular velocity subject to line frequency variations, and styli 14, 15, 16 are successively traversed at constant velocity over chart 17, which is motor driven at predetermined rate. On alignment of stylus e.g. 15 at the chart edge, aperture 23 illuminates element 27 to produce a pulse, changing over pulse separator and gate 31 to apply the next pulse from element 27 to the sampling switch 39, and energizing the ramp binary 35, which in turn pulses open the switch 41 of ramp generator 43, which operates as a Miller integrator supplied from terminal 50 to produce a positive to negative going voltage which is compared with input N at comparator 49 to yield a pulse at equality which is shaped, amplified, and applied to stylus 15 to mark the chart by spark discharge so that the displacement of the mark from the start of the sweep represents the amplitude. Similar marks indicate the inputs N-1, N-2 &c. to other comparators during the sweep cycle, and several input channels may be located at predetermined positions of the chart by superimposing appropriate unidirectional bias voltages. The ramp voltage is also applied to the ramp comparator 53, and at a predetermined relationship with the reference voltage, a pulse is applied to ramp binary 35, which returns to its initial state and pulses switch 41 to terminate the output of the ramp generator 43 and also pulses operative the signal generator 45 to yield a signal increasing rapidly with time, which commences either before or after the transversal of the chart by the stylus, in dependence on variation of the stylus speed from its speed during the preceding cycle. On completion of the chart traverse, element 27 produces a pulse in response to light admitted by aperture 21 of belt 13, which is amplified and passes through pulse separator and gate 31 to sampling switch 39, which briefly samples the signal from generator 45 to represent the time interval between the end of the ramp voltage and the end of the stylus sweep, which is zero if the linear displacement of the stylus is to bear a constant relation to the instantaneous ramp voltage irrespective of the stylus velocity. The sample pulse at the end of a stylus sweep is integrated to a steady signal combined with the supply voltage at 50 to determine the slope of the ramp voltage during the succeeding stylus sweep, so that variations of the stylus velocity or ramp voltage slope during a stylus sweep varies the timing of the pulse marking the end of the sweep, and thus the slope of the ramp voltage during the next succeeding sweep. The pulses from the amplitude comparators 49, 51 &c. are passed through gates 63, 65 to the indicator circuit 69; the gates being opened in timed sequence by switch 73 driven from the chart drum to admit equality pulses to increase the width of the pulse derived from shaper 59 to a duration determined by the time for which the indicator circuit 69 remains in a single operative state, and thus widens the corresponding recording pulse, which appears on the relevant trace on the chart, and is identified by alignment with one of a series of numbers on the recording chart identifying the appropriate signal channel.