Patent GB-819252-A (GB)
Title: Analogue-to-digital converter
IPC: H03M1/00
Filed: 1955-10-26
Abstract: 819,252. Analogue-to-digital converters. UNITED AIRCRAFT CORPORATION. Oct. 26, 1955 [Oct. 26, 1954], No. 30560/55. Class, 40 (1). Relates to an apparatus for converting the relative movement between two members into a digital representation using the natural binary code. Rows of conductive elements are mounted on the first member, and the second member is provided with means for coupling an excitation voltage to the first row of elements, means being provided for deriving two complementary digital outputs from each row. Fig. 1 shows in developed form the arrangement of conductive segments on a disc which is driven by a shaft whose angular displacement is to be measured. An outermost circle of conductive segments 12, representing the least significant digit, are connected to a slip ring 14 by respective conductors 16, and a D.C. or pulse input is applied at 26 and bia a brush 28 to the segments 12 as they engage the brush, a corresponding output appearing at terminal 30 via slip ring 14, brush 22 and line 18. The segments 12 are of equal length and are separated by a distance equal to their length. The D.C. input at 26 is also applied to a D.C. inverting amplifier 36 arranged to have a gain of unity, the output of the amplifier 36 being applied to a D.C. summing. amplifier 42 of unity gain whose output is applied via line 20 to output terminal 32. The line 18 is also connected to the input of amplifier 42 and the arrangement is such that if brush 28 engages a segment 12 the resultant potential at terminal 32 is zero, representing " 0," and a potential appears at terminal 30, representing a " 1," and when the brush 28 is between adjacent segments 12, a " 1 " is represented at terminal 32 and a " 0 " at terminal 30. At all times one of the terminals 30, 32 has an output signal. but at no times do both have an output signal. The number of segments 12 is determined by the highest number it is required to represent in the binary code, and, as shown, the numbers 0 to 15 may be represented and eight segments 12 are required. The next digit is represented by segments 50, 58, alternate segments 50 being connected to a slip ring 54 and the remaining segments 58 to a slip ring 56. The length of a segment 50, 58 is slightly less than twice the length of a segment 12. A signal from the energized line 30, 32 is conducted via diode 66 or 68, and brush 62 or 64 to the segments 50, 58, the diodes preventing feedback to the unenergized line 30 or 32. The brushes 62, 64 are spaced by a distance equal to the length of a segment 12. Brushes 70, 72 connect slip rings 54, 56 to respective conductors 74, 76 and output terminals 82, 84, and a signal representing digit " 1 " appears on either 82 or 84, according to which brush 62 or 64 carries a signal, and which segment 50, 58 it engages, the other terminal 82, 84 carrying no output signal, representing a " 0." Similarly, the third digit is represented by segments 88, 96 connected to respective slip rings 92, 94. Each segment 88, 96 is slightly less than twice the length of a segment 50, 58. The output signal from line 74 or 76 is applied via diode 104 or 106 and brush 100 or 102 to segments 88, 96, an output signal appearing on a line 112 or 114 and output terminal 120 or 122 and its complement appearing on the other line. The spacing between brushes 100, 102 is approximately twice the spacing between brushes 62, 64, and is approximately equal to the length of segments 50, 58. The most significant digit is represented by segments 1.26, 134, the segment 126 being connected to a slip ring 130 and the segment 134 to a slip ring 132, and the length of the segments 126, 134 being approximately twice the length of segments 88, 96. The signal is fed via diodes 142, 144 and brushes 138, 140 to the segments 126, 134, the spacing of the brushes 138, 140 being approximately twice that between brushes 100, 102, an output signal appearing at one of the terminals 158, 160, and its complement at the other terminal. All brushes are electrically symmetrically disposed about a vertical line passing through the input brush 28. An output representing the angular displacement of the shaft in natural binary code is taken from terminals 32, 84, 122, and 160, or its complement may be taken from terminals 30, 82, 120 and 158. The arrangement allows for the misalignment of a brush with respect to a segment of Œ “ of the length of the segment before ambiguity is introduced. Two discs may be coupled together by suitable reduction gearing, Fig. 2 (not shown). In an alternative arrangement for pulse operation, Fig. 6 (not shown), the brushes are replaced by capacitive coupling.