Patent GB-1077871-A (GB)
Title: Improvements in or relating to circuits for generating electrical signals representing trigonometrical functions
Inventor: BILLIN JAMES JOHN
IPC: G06G7/22
Filed: 1963-04-30
Abstract: 1,077,871. Electric selective signalling; electric analogue calculating. ELECTRIC & MUSICAL INDUSTRIES Ltd. April 10, 1964 [April 30, 1963], No. 16888/63. Addition to 1,024,831. Headings G4G and G4H. In a circuit for deriving electrical signals proportional to the sine and cosine of an angle by the addition of terms involving trigonometrical functions of partial angles which together equal the desired angle, the trigonometrical functions are set up on tapped transformers by means of a switching circuit as described in Specification 1,024,831. The 360 degree period is divided into 2000 units of 0À18 degrees, the desired angle being defined by a decimal number. The partial angles A, B and C consist of the thousands and hundreds digits, the tens digit and the units digit respectively. The equations used to derive the desired signals are:- K being cos C divided by cos B which is approximately equal to 1. A reference supply of 1000 cycles per second is applied between terminals (1 and 2, Fig. 1, not shown). Terminal (1) is connected to the centre of primary windings (3 and 5) of transformers (4 and 6). Terminal (2) is connected to either side of winding (3) through transistors (7, 8) and to either side of winding (5) through transistors (9, 10). These transistors are rendered conducting according to the quadrant in which the deserved angle A lies. If the angle A is between 0 and 180 degrees terminal (11) is energized. If between 180 and 360 degrees terminal (15) is energized. The four gates (13, 14, 17 and 18) respond to signals indicating that the angle A lies in the four quadrants 0-90 degrees, 90-180 degrees, 180-270 degrees and 270- 360 degrees, respectively. The reference voltage on terminals (1, 2) is applied to different combinations of the half windings (3 and 5). For example for an angle between 0-90 degrees the signal on terminal (11) enables transistor (7) and gate (13), opened by a signal from one of the selector leads (41A-41E) via a diode (43), enables transistor (10) so that the input reference voltage is applied to the left-hand part of winding (5) and the right-hand part of winding (3). Sign reversals are made in the other three quadrants. The secondary winding (25) of transformer (4) has five tappings one of which can be selected by enabling one of the transistors 26A-26E). These give from left to right sin 9 degrees, sin 27 degrees, sin 45 degrees, sin 63 degrees and 81 degrees. Winding (36) is a mirror image giving cosine values of these angles. When one of the selector terminals (41A-41J) is energized appropriate ones of the five transistors are enabled for both the sine and cosine windings, the polarities of the energization of the primary windings being selected by terminals (11 and 15) and by gates (13, 14, 17 and 18) as described above. Transformers (28 and 39) have primaries connected to receive values sin A and cos A respectively. The tappings of the secondary windings (44, 45) are selected by a signal on one of ten terminals (49A-49J) indicating the angle B. The outputs, representing cos A.tan B and sin A. tan B are applied to windings (46, 47) of transformers (30, 35). Transformers (52, 54) have tappings representing tan C which are selected via transistors (57A-57J and 58A-58J) by a signal on one of leads (60A-60J). The output across terminals (31, 32) which is applied to primary (51) is the desired value K sin (A+B +C). The product of this with tan C is fed back to winding (46) and added to cos A and sin A tan B, so as to produce between terminals (32 and 33) the signal K cos (A+B+C) according to the original equation. This signal is fed back in the same way to form K sin (A+B+C). In a modification the value of tan C is set up to an accuracy of one in a hundred steps, there being ten steps on one secondary winding and ten steps of one tenth the size on another secondary winding on the same transformer.