Patent GB-1014035-A (GB)
Title: Electrical goniometric system
Inventor: LEVY RALPH
IPC: H03M1/00
Filed: 1961-12-20
Abstract: 1,014,035. Electric selective signalling. MULLARD Ltd. Dec. 20, 1961, No. 45703/61. Heading G4H. In an electrical goniometric system comprising a chain of anglemeasuring discriminators of successively greater resolution, each discriminator is arranged to receive simultaneous electrical signals each of which is unidirectional (i.e. direct current) and the magnitudes of which are respectively proportional to the sine and cosine of an angle to be measured by the discriminator; each discriminator is arranged to determine, relative to a datum, the quadrant of a Cartesian representation in which the angle terminates; each discriminator except the first of the chain is arranged to operate with an expansion of four times the angular scale of the immediately preceding discriminator; and each discriminator is arranged to produce in binary digital form output signals indicative of the said quadrant, whereby the angle to be measured by the system can be indicated by the output signals from all the discriminators in the chain. If the input signals are X and Y, then the angle P = tan <SP>-1</SP> X - measured clockwise from the positive Y Y axis in Fig. 2, will lie in one of the four quadrants 1 1 -4 1 , the quadrant being determined uniquely by the signs of X and Y. This is done in logic unit L in Fig. 4, the outputs of which are the digits X 1 Y 1  representing the signs of X and Y. Signals X and Y are also fed to a unit K which produces outputs X 4  = sin 4P and Y 4  = cos 4P, and the signs of these signals similarly indicate in which of the quadrants I 4  - 4 4  within a quadrant I 1 -4 1  the angle P lies. Similarly the outputs of the first unit K are fed to a second unit K and unit L and to a third pair of units to produce outputs X 16 , Y 16  and X 64 , Y 64 . If discriminator 1 has a slight error so that a signal which should appear at 89 degrees (quadrant I 1 ) actually appears at 91 degrees (quadrant 2 1 ) the signal will appear in quadrant 4 4  at 356 degrees if the 4<SP>x</SP> discriminator is accurate. The system will record a signal in quadrant 2 1  and 4 4  which is an error of 90 degrees. Sucherrors are corrected by afeed back from unit L of the 4<SP>x</SP> discriminator to the unit L of the first discriminator, using the quantity Z 1  = 1Y 1 1 - 1X 1 1. The feedback obeys the rules (1) if Y 4  is positive, then (2) X 1 . Y 1  should equal Z 1  . X 4 ; if it does not, then (3) if Z 1  is positive, change X 1  only and if Z 1  is negative, change Y 1  only. The quantities Z 1 , Z 4 , Z 16  are used only internally for this correcting function, but the sign of Z 64  is used as an output signal. Thus the system produces nine binary digits which indicate the angle P in a binary code correct to one part in 256. Fig. 5 shows a diagram of a logic unit L to which input signals X and Y are fed. The moduli of signals X and Y are formed in units E, subtracted in unit D, and standardised in voltage in unit SZ to form Z 1 . Signals X and Y are standardized in units SX, SY, the signs only being retained, and then pass through units GX, GY which can be controlled to change or not to change these signs as required. The outputs of units G are taken to output terminals and are also multiplied in unit M to form X 1  . Y 1 . A second multiplying stage M receives X 4  from the next logic unit and Z 1  from SZ and produces X4 . Z1 which is compared with X 1  . Y 1  in unit C. If these products differ, then according to rule (2) the output of unit C is applied to sign splitter stage H which, provided Y 4  is positive (rule (1)), allows Z 1  from unit SZ to operate sign changer GX if positive or GY if negative (rule (3)). In another embodiment the discriminators are staggered, as illustrated in Fig. 6, so that the cardinal points of discriminator 1 occur at the centre positions of quadrant 1 of discriminator 4. Gross errors in discriminator 1 can therefore only occur when the signal falls in quadrant 1 4 ; the appearance of digits representing 1 4  may therefore be used to reject the quadrant digits of discriminator 1 and accept instead cardinal point digits determined by the signs of X - Y and 1X1 - 1Y1. The system may be used in a radio directionfinding arrangement, such as that described in Specification 999,620, or in a frequency measuring arrangement, such as that described in Specification 953,430. Specification 1,014,036 also is referred to.