Patent GB-767521-A (GB)
Title: Improvements in electric analogue-computer devices
IPC: G06G7/28
Filed: 1954-03-18
Abstract: 767,521. Electric analogue calculating systems. SOC. D'ELECTRONIQUE ET D'AUTOMATISME. March 18, 1954 [March 19, 1953], No. 7958/54. Addition to 751,602. Class 37. In the electric analogue apparatus claimed and described in the parent Specification for simulating an arbitrary adjustable function whose characteristic is graphically reducible to a combination of elementary linear functions of predetermined positive or negative slopes joining predetermined co-ordinates individually represented by transfer networks each comprising two calibrated series impedances connecting a source of variable abscissa voltages to a common mixer amplifier producing the required analogue voltage, and a unidirectional shunt connecting the impedance junction to a variable voltage source limiting the variation of the appropriate linear function analogue voltage ; a series resistance is connected in the unidirectional shunt circuit of one or more transfer networks, causing the transfer characteristics to comprise a first linear portion through the origin with a first predetermined slope to a predetermined co-ordinate, followed by a second linear portion of a second predetermined slope commencing from the point at which the voltage limiting means becomes activated. Fig. 1 shows a transfer network wherein a variable analogue voltage x energizes a variable potentiometer 10 to apply a voltage x tan a<SP>1</SP> through equal series resistors 17, 18 of value R to the input of a common summation amplifier 22 having a feedback resistor 23 equal to 17, 18. The anode of a shunting diode 15 is connected through a resistor 100 of value R large compared with the diode resistance to the junction of resistors 17, 18, and its cathode is supplied with a limiting voltage y<SP>1</SP>=x<SP>1</SP> tan a<SP>1</SP> from potentiometer 9. The output voltage characteristic (Fig. 2) comprises a first linear portion OA representing y=x tan a<SP>1</SP> from origin to point (x<SP>1</SP>, x<SP>1</SP> tan a<SP>1</SP>) followed by a second linear portion AD representing y=x tan a<SP>2</SP>; it being shown that R = R<SP>1</SP> k/2(1-k) where k = tan a<SP>2</SP>/tan a<SP>1</SP> Fig. 4 shows a similar transfer network having a second shunt branch comprising a diode 115 whose anode is connected directly to the junction of resistors 17, 18 and whose cathode is returned to a reference voltage from potentiometer 119 representing y<SP>2</SP>(#y<SP>1</SP>)=x<SP>1</SP> tan a<SP>1</SP>+ (x<SP>2</SP> - x<SP>1</SP>) tan a<SP>2</SP>, whereby the second linear portion AD of the characteristic (Fig. 5) is limited at a point H corresponding to (x<SP>2</SP>, y<SP>2</SP>) and followed by a third linear portion HJ parallel to the abscissa at y=y<SP>2</SP>. In a modification (Fig. 6) the resistor 100 is subdivided into three series resistors 101, 102, 103 each large compared with a diode internal resistance, and two further diodes 215, 315 are provided having anodes connected to the junctions of resistors 102, 103 and 101, 102 respectively and cathodes connected to reference voltages y<SP>3</SP>=x<SP>3</SP> tan a<SP>3</SP> and y<SP>4</SP>=x<SP>4</SP> tan a<SP>4</SP> intermediate between y<SP>1 </SP>and y<SP>2</SP>. The overall transfer characteristic of the network (Fig. 7) then comprises linear portions OA from (o, o) to (x , y) of slope tan ax, AK from (x<SP>1</SP>, y<SP>1</SP>) to (x<SP>3</SP>, y<SP>3</SP>) of slope tan a<SP>3</SP>, KL from (x<SP>3</SP>, y<SP>3</SP>) to (x<SP>4</SP>,y<SP>4</SP>) of slope tan a<SP>4</SP>, LH from (x<SP>4</SP>, y<SP>4</SP>) to (x<SP>2</SP>, y<SP>2</SP>) of slope a<SP>2</SP> and HJ parallel to the abscissa at y=y<SP>2</SP>.