Patent GB-939277-A (GB)
Title: Computers
IPC: G06G7/75
Filed: 1961-09-22
Abstract: 939,277. Electric analogue calculating. E. I. DU PONT DE NEMOURS & CO. Sept. 22, 1961 [Sept. 22. 1960], No. 34012/61. Class 37. Electric analogue computer determining   approximately the difference function F S <SP>1</SP>a - F R <SP>1</SP>a) where F S  F R  are numerical quantities and the exponent a lies between 2 and 5; comprising potentiometric means generating a first electrical signal representing where C 2  is a constant; and means for inserting a second input signal representing (F S -F R ) into potentiometric means responsive to the first signal whereby a third electrical signal is generated representing the product which when multiplied by a further constant approximates the required difference function. A computer for evaluating the expression (F S <SP>1/a</SP> - F R <SP>1/a</SP>) where F S , R R  are numerical quantities and a varies between 2 and 5 by the relationship where C 1 , C 2  are constants and E is an error function varying approximately linearly with either side of the equation when E is omitted; e.g. in colour co-ordinate computation where 1/a specifically = <SP>1</SP>/ 3  for evaluation of colour difference co-ordinates given by #L=25.29 (F SG <SP>1</SP>/ 3 -F KQ <SP>1</SP>/ 3 ) (2) #a= 106 [(F SR /<SP>1</SP>/ 3  F RR / <SP>1</SP>/ 3 ) (F SG <SP>1</SP>/ 3  F RG <SP>1</SP>/ 3 )] (3) #b= 42.34 [(F SG <SP>1</SP>/ 3  - F RG <SP>1</SP>/ 3 ) - (F SB <SP>1</SP>/ 3  - F RB <SP>1</SP>/ 3 )] (4) in the cube root colour co-ordinate system set forth in the Jnl. Optical Society of America, Vol. 48, No. 10, at pages 736-740, where F SG , F RG  are the sample and reference reflectances or transmissions with a green filter measured on a colorimeter of the kind described in U.S.A. Specification 2,774,276. F SR , F RR  are the sample and reference reflectances or transmissions with a red filter. F SB , F RB  are the sample and reference reflectances or transmissions with a blue filter, and the red-prime factors F SR  # 0.8 F SR  + 0.2 F SB  F RR / # 0.8 F RR  + 0.2 F RB  by definition and L defines lightness, a defines red/greenness, b defines yellow/blueness, while # L  = L S  - L R  # For samples S and #a=a S  - a R  # references S and #b=b S  - b R  # references R. #b=b S -b R  # A computing unit (Fig. 1) comprises an A.C. energized resistance potentiometer R 1  whose slider circuit to earth is loaded by resistance R 2  to feed resistance potentiometer R 3  whose slider circuit to input is loaded by resistance R 4 . The sliders are ganged for operation by hand wheel 24 and register 25 responsive to reflectance value F S  to produce an overall output shown to be proportional to at terminal 5. A further loaded potentiometer stage may be added for higher accuracy. Design formulµ are given. Reflectance values F S , F R  from hand wheels and registers 24, 25; 32, 34 (Fig. 2) are fed to differential 31 to produce a mechanical output (Fs - FR) on shaft 35; the shaft of hand wheel 32 being locked while hand wheel 24 is rotated. Shaft 35 adjusts potentiometer 40 (Fig. 4) across the earth centre tapped secondary of transformer 39 energized from the slider 45 of 10 turn potentiometer Rd in series with resistances Rc, Re loaded by resistance R 4  (corresponding to potentiometer R 3  in Fig. 1) which is energized from slider 44 of 10 turn potentiometer Ra in series with resistance Rb and loaded with resistance R 2  (corresponding to potentiometer R 1  in Fig. 1); the sliders 44, 45 being operated through 10 : 1 reduction gear from hand wheels 24, 32. The output at slider 40 represents in magnitude and phase sense and is applied to one grid of a double triode V 1  (Fig. 5) of a conventional null detector tube with cathode load R K  and reference voltage input to the other grid from potentiometer R 2  energized from earth centre-tapped secondary of transformer 51 fed from potentiometer R H  in series with variable resistance R D  ; fed in turn from potentiometer R A  energized from transformer 20 (Fig. 4). Sliders 49 of R H  and 13 of R Q  are operated over shaft connection 48 for manual balance at which it is shown that or where Xm represents an error function the settings of R A  and R D  being adjustable for calibration; the error function correction term being generated by the potentiometer R H  (Fig. 5) ganged to balance potentiometer R Q . The cathode voltage of V 1  is amplified at 57 and chopped by vibrator 61 energized by winding 65 to excite centre-zero phase sensitive voltmeter 60 whose null indicates the balance point at which the position of shaft 48 represents (F S <SP>1/3</SP> - F R <SP>1/3</SP>) to a high degree of accuracy. The generalised determination of (FS<SP>1/3</SP> - F R <SP>1/3</SP>) above permits the computation using two channels of #L and #b in equations (2) and (4) above, but computation of #a necessitates a preliminary calculation since FR'=0.8 F R + 0.2 F B . Figs. 6, 7 show schematic computing arrangements incorporating the above networks. In Fig. 6 reflectance factors F RG  and F SG  are entered by hand wheels 71, 72 into 100 turn registers 73 and 74 and into differential 75; the F RG  input being locked by brake 70 while F SG  is entered. The differential output 76 adjusts " Green " potentiometer 77 or Rp (Fig. 4) proportionally to (F SG  - F RG ) to derive a voltage indicative of (F SG  - F RG )f 1 (F SG )f 2 (F SG ). Hand wheel 72 rotates through a 10: 1 stepdown 78 the ganged contacts of " Green " potentiometers 79, 80 or Ra, Rd (Fig. 4) to derive voltages indicative of f 1 (F SG ) and f 2 (F SG ). Hand wheel 84 enters reflectance factor F RR  into 100 turn register 85 and hand wheel 86 enters reflectance factor F SR  into register 87. The inputs are also supplied to differential 89 with a brake 88 locking the F RR  input during entry of the F SR  input, and the output representing (F SB  - F RR ) over shaft 90 is supplied to a differential 94 over 1:1.6 stepdown 93 with a brake 91 holding the input in storage without alteration. Hand wheel 86 also enters F SR  into differential 99 over 1: 1.6 stepdown 98 where it is held in storage. Hand wheel 102 enters reflectance factor F RG  to register 103 and differential 107, and the input is locked by brake 104, Hand wheel 105 introduces reflectance factor F SB  to register 106 and to differential 107 whose output (F SB  - F RB ) adjusts the " Blue " potentiometer R D  (Fig. 4) or 109. The hand wheel also operates " Blue " potentiometers Ra, Rd (Fig. 4) or 111, 112 over a 10: 1 stepdown 110. The output (F SB  - F RB ) from differential 107 is entered to differential 94 over 2.5: 1 stepdown 116 and input F SB  is entered to differential 99 over 2.5: 1 stepdown 118. The output of differential 94 rotates shaft 19 proportionately to (F SR / - F RR /)=0.8(F SR -F RR )+0.2(F SB -F RB ) to adjust the corresponding potentiometer R p  (Fig. 4) or 120. Similarly, the output of differential 99 proportional to F SR <SP>1</SP>=0.8F SR +0.2F SB  rotates shaft 121 over 10: 1 stepdown 122 to adjust ganged corresponding potentiometers Ra, Rd (Fig. 4) or 123, 124. Computation channels of the kind shown in Fig. 4 are provided for each of the Rp potentiometers and are switched successively to a null balance device of the kind shown in Fig. 5 having three correspondingly switchable rebalancing networks adjustable in succession for null balance with the three computation channels by three hand wheels 129, 147, 138 (Fig. 7) corresponding to #b, A L , and #a which adjust corresponding potentiometers 131, 132; 149,150; 139, 140; in the positions R Q /, R H  (Fig. 5) for blue, green and red-prime factors S B , S G  and S R <SP>1</SP> corresponding to (F SB 1/3-F RB 1/3), (F SG 1/3- F RG 1/3), (F SR 1/3-F RR / 1/3). Initially, the green computing channel is switched to the null detector with the rebalance voltage from the potentiometers 149, 150 in conjunction. Hand wheel 147 is turned for meter null and S G = (F SG 1/3 - F RG 1/3) which is fed negatively to #a differential 143 and displayed on #L register 151 as one of the required co-ordinates, where it is held by brake 152. The register incorporates multiplying coefficient 25.29 [Equation (2)]. Next the red prime channel is switched to the null detector, with the rebalance voltage derived from potentiometers 139, 140 in conjunction. Hand wheel 138 is adjusted for null and S R /=(F SR / 1/3-F RR / 1/3) which is fed positively to differential 143 held by brake 142. Finally, the blue channel is switched to the null detector with the rebalance voltage derived from potentiometers 131, 132 in conjunction. Hand wheel 129 is adjusted for null and S B =(F SB 1/3 -F RB 1/3) is fed negatively to #b differential 134 and held by brake 133. A 2: 1 reduction is introduced by both differentials so that their outputs are proportional to and to These are respectively transmitted through 1: 3.3 stepdown 156 to #b output register 157 and through 1: 8.4 stepdown 158 to #a output register 159, while AL output register 151 is driven directly from hand wheel 147 and held by brake 152. The apparatus is mounted in a housing (Fig. 8) having hand wheels 71, 72, 84, 86, 102, 105 entering sample and reference reflectance values for green, red, and blue with corresponding register dials 74, 73; 87, 85; 106, 103 mounted on a panel having indicator lamps 166 indicating operative connection of the registers. A selector switch 169 connects the reference or sample network of a given channel in circuit and a selector switch 170 operates the brakes, indicator lamps, and switching of each function generator and its reference voltage network in conjunction with the common null detector whose meter 60 is mounted on the panel. Readout hand wheels 129, 147, 138 having register dials 157 for #b, 151 for #L and 159 for #a with operative indicator lamps 171 are adjustable for balance. A calibration and computation procedure is described.