Patent GB-938755-A (GB)
Title: Carrier signal attenuation as a function of two variables
IPC: G06G7/30
Filed: 1961-09-21
Abstract: 938,755. Electric analogue calculating. BENDIX CORPORATION. Sept. 21, 1961 [Sept. 27, 1960], No. 33907/61. Class 37. Apparatus varying amplitude of a signal as a function of two variables, e.g. for modifying system gain of flight control apparatus as a predetermined function of Mach and altitude includes a first device for generating electric signals representing discrete step values of a first variable, a set of function generators corresponding to respective step values of such first variable, each of which produces an electric signal which is a predetermined non-linear function of a second variable ; the nature of such function being separately imposed for each generator in accordance with the selected step value, a variable attentuator receiving the input signal to attenuate the amplitude thereof by a variable factor as a function of a control signal, and a gate arrangement controlled by the signals from the first device for applying the attenuator as control signal, the output of a particular function generator corresponding to the step value produced by the first device. Plural functions: Z=F 1 X Z=F 2 X Z=F 3 X Z=F 4 X where X is e.g. Mach and Z is e.g. the gain of a control channel for an aircraft are plotted for discrete values Y 1 , Y 2 , Y 3 , Y 4  of e.g. altitude γ on three dimensional co-ordinates (Fig. 1) and it is shown that if d y  is the interval between discrete values of Y the value of Z at intermediate value y between discrete values Y 1 , Y 2  of y at which Z=A=F 1 X and Z=B=F 2 X is given   by Z (A+B)  = A(1 -Y/dY) + B(Y/dY) (Fig. 2, not shown). Similar considerations apply to interpolation between discrete values Y 2 , Y 3  and Y 3 , Y 4  of y. In Fig. 3 an alternating carrier signal E i  is applied to cascaded linear attenuators 11, 13 and 10, 12 of the kind described in Specification 932,509, and the output 12 is applied to control attenuator 13 to produce an output signal E 0 . A direct signal E x  representing independent variable X energizes function generators 20, 21, 22, 23 containing slope shaping and summation networks to produce analog currents <SP>1</SP>f1, I f2 , I f3 , I f4  of functions F 1 X F 2 X, F 3 X, F 4 X to AND gates G 1 , G 2 , G 3 , G 4 ; the outputs of G 1 , G 3  energizing a control winding of attenuator 10 and those of G 2 , G 4  energizing a control winding of attenuator 11. A commutator 30 of the kind described in Specification 933,361 comprises a shaft 31 responsive to variable Y rotating opaque disc 32 having a transparent area 35 of overlapping concentric segments 33a, 33b, 33c, 33d whereby light from a source is passed simultaneously through two adjacent segments to energize corresponding pairs of photo-sensitive elements 34, 35, 36, 37 controlling ON-OFF networks 38, 39, 40, 41 whose outputs feed discrete step signals P 1 , P 2 , P 3 , P 4  to gates G 1 , G 2 , G 3 , G 4  in adjacent pairs (Fig. 4). Shaft 31 is geared with ratio 0 to rotate ganged circular D.C. energized linear potentiometers 42, 43 providing symmetrically increasing and decreasing resistance over 360 degrees rotation and having 180 degrees spaced sliders, # being the displacement of shaft 31 to transport segment 33b, 33c, or 33d across the light beam to provide a discrete step signal ; thus representing traversal from Y 1  to Y 3  or Y 2  to Y 4  during which potentiometers 42, 43 produce oppositely phased triangular current signals I 2 , I 3  (Fig. 4) applied to control windings of attenuators 12, 13 respectively. The output E 3  of attenuator 12 is given by E 3 =K(I 2 )E 1  and that of attenuator 13 by E 0 =[K(I 3 )E 2 +E 3 ]=[K(I 3 )E 2 +K(I 2 )E 1 ] and since AND gates G 1  to G 4  are opened on successive discrete values of Y to control attenuators 10, 11 by successive pairs of functions of X so that E 1 =F 1 X or F 3 X and Eg= F 2 X or F 4 X, the output voltage E 0  is equivalent Y Y to A(1--)+B(-) or to the required interdy dy polated value of Z. In a modification (Fig. 5), since Z A+B = Y A+(B-A)- the signal E i  is applied to dY cascaded attenuators 50, 51 and to single attenuator 52 whose output E 5  controls attenuator 51. As before a direct voltage E x  energizes function generators 20, 21, 22, 23 to energize AND gates G 5  with function signal I f1 ; gates G 6 , G 7  with function signal I f2 ; gates G 8 , G 9  with function signals I f3  and gate G 10  with function signal I f4 ; while a photo-electric commutator 53 applies discrete Y step signals P 5 , P 6 , P 7  to gates G 5 , G 6 ; G 7 , G 8 ; G 9 , G 10  respectively in response to the angular position of the disc, driven in response to variable Y. Interconnected outputs of G 6 , G 8 , G 10  control attenuator 50 in opposition to the interconnected outputs of G 5 , G 7 , G 9  which also control attentuator 52, while a 360 degrees D.C. energized potentiometer 55 controls attenuator 51 in response to the input shaft of commutator 53 through gearing of ratio 0 by generating a sawtooth current waveform I 4  (Fig. 6) synchronized with successive Y step signals. The output signal E 0 =K(If 1 )Ei+K(If 2 ) - (If 1 )EiI 4    corresponds to Z A+B =A+(B - A) Y/dY and   other interpolated values of Z may be similarly obtained. It is stated that the carrier signal E i  may be attenuated by continuous transfer function of an independent variable X and discrete step functions of a further independent variable Y. In a further modification (Fig. 7, not shown), the X signal E x  is selectively applied to generators of X function signals I f1 , I f2 , I f3 , I f4  through respective AND gates controlled from the commutator device and the signals I f1 , I f3  and I f2 , I f4  are combined in pairs to control attenuators yielding signals E 1 , E 2  for treatment as in Fig. 3.