Patent GB-688549-A (GB)
Title: Improvements relating to graph-plotting apparatus
Inventor: HAYNES FRANK GRENVILLE
IPC: G01D9/28
Filed: 1950-03-22
Abstract: 688,549. Electric indicating systems. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Dec. 11, 1950 [March 22, 1950], No. 7184/50. Class 40 (i) [Also in Group XXXVI] Apparatus for plotting a graph connecting two variables comprises two self-balancing potentiometer units wherein two representative voltages are respectively compared with reference voltages derived therefrom and the difference voltages each deflect a galvanometer to initiate automatic potentiometer adjustment to rebalance the corresponding voltages, which adjustments respectively displace at the same time a recording pen and a chart table in mutually perpendicular directions to graph the unknown variables. In Fig. 1 a motor 1 drives a shaft 3 to intermittently operate through cams and gears a mechanical detector 4 of a self-balancing potentiometer unit 5 wherein the unbalance between one unknown voltage to be measured and a reference voltage from a fixed contact engaging a rotary potentiometer slidewire (not shown) deflects a galvanometer 6, whose pointer is cyclically contacted by a feeler mechanism operated. by the rotating shaft to initiate rotation of the slidewire in the direction of balance, the cycle being repeated until balance is obtained. A second similar self-balancing potentiometer unit 5' is operated by shaft 3 through coupling 7 in synchronism with unit 5 to balance a second unknown voltage. The rebalancing displacement of the slidewire of unit 5 operates a spring and pulley drive to deflect a pen 8 along the Y axis proportionately to the first unknown, and the displacement of the slidwire of unit 5' similarly deflects a chart table 9 along the X axis proportionately to the second unknown so that a graph relating to the two quantities is drawn. A standardizing unit 10 is driven by shaft 3 to cyclically compare the voltage. drop across a fixed resistance in the potentiometer energization circuit with the voltage of a standard cell and thus automatically readjust the current to a standard value. To graph either of the unknowns against time, a roll chart driven through gearing from the shaft 3 is traversed by a recording pen 8<SP>1</SP> which may be selectively linked mechanically with the deflections of the pen 8 or the chart table 9 Fig. 2 (not shown). Nonlinearity between the quantity to be measured and the corresponding voltage applied to the apparatus is compensated by a cam arrangement. Fig. 3 (not shown) as described in Specification 688,609, for mechanically shifting the appropriate potentiometer contact relatively to the slidewire during the rebalancing movement so that the rotation of the slidewire relative to a fixed point is proportional to the change in the unknown. and a strictly linear graph is recorded. The apparatus is particularly applicable to the graphing of linear expansion with heat, in which a thermocouple output is connected to unit 5 to deflect pen 8 while the potentiometer of a remote reading' micrometer of the kind described in Specification 645,833 is connected in bridge with the potentiometer slidewire of unit 5<SP>1</SP> to deflect the chart table 9.