Patent GB-877260-A (GB)
Title: Improvements in and relating to indicator apparatus
IPC: G01D5/245
Filed: 1958-04-17
Abstract: 877,260. Electric selective signalling. BUSCH-WERKE A. G. April 17, 1958. [April 18, 1957.] No. 12289/58. Class 40 (1) Apparatus for signalling the position of a moving member 1, Fig. 1, which carries a series of spaced reference marks comprises sensing means adapted to sense the marks during movement in both directions and to generate a pulse for each mark sensed, converter means connected to the sensing means which convert the pulses resulting from movement in one direction into first indicating signals and those from movement in the other direction, into second indicating signals and counting means connected in circuit with the converter receiving both sets of signals and adapted to sum the first signals and subtract the second to produce a final sum indicating the position of the member. The movable member may be the dial or scale of a weighing machine having a graduation pitch S. In a weighing operation the member first moves in one direction, swings back in the opposite direction and then perhaps oscillates before reaching a final position. There are two similar sensing devices for member 1, each having a screen 2, 6, lenses 4a, 4b and 8a, 8b, a lamp 3, 7 and a photo-cell 5, 9. The screens are formed with alternate black and transparent portions having similar dimensions to those of the scale 1. The light passing through transparent portions of a screen and member 1 generates a signal depending upon their relative positions, the screens being located as shown so as to register differently by a quarter of pitch S with the divisions scale 1. During movement of the scale cells 5 and 9 produce an identical train of pulses but they differ in phase by this displacement, “S, one pulse train leading in phase during movement in one direction and gagging by the same amount during movement in the other. This phase displacement is used to gate pulses to one line during forward movement and to another line during backward movement. The signals are passed by lines 13, 14 to triggers circuits 15, 16 each of which forms two sequences of positive rectangular pulses in anti-phase each having a duration equal to about half a period. These pulse trains appear on lines 18, 19 and 23, 24, the trains in the latter pair of lines differing by “S from the phase of the others. Lines 18, 19 pass their signals to differentiating circuits 20, 21 to produce trains of sharp, alternately positive and negative, pulses the two trains being in anti-phase. The signals from circuit 20 are applied to gates 25, 26 and those from circuit 21 to gates 27, 28. The outputs of gates 25 and 28 are combined on lead 30 and those of gates 26 and 27 are combined on lead 29. Gates 25 and 27 are opened by the rectangular pulses on lead 23 and gates 27 and 28 are opened by pulses on lead 24. The arrangement is such that positive pulses from devices 20, 21 can pass ,to lead 29 when the member 1 is moving in the forward direction and pulses arrive on lead 30 when the member 1 moves in the backward direction. In counting device 22 the pulses on lead 30 are subtracted from those on lead 29, the algebraic sum giving the number of scale divisions representing the final position of the member 1.