Patent GB-280890-A (GB)
Title: Improvements in and relating to means for recording indications at a distance electrically
IPC: G01R11/00
Filed: 1927-10-31
Abstract: 280,890. British Thomson-Houston Co., Ltd., (Assignees of Pratt, W. H., and Price, D. R.). Nov. 16, 1926, [Convention date]. Transmitting actuation to counters.-In a method of indicating at a distance the speed of rotation of a rotary element, such as the spindle of a watt-hour meter, arranged to produce impulses at a rate dependent upon its speed, an impulse-receiving mechanism is arranged to produce a continuous rotary motion proportional to the average impulse rate. Consecutive impulses impart equal predetermined rotary motions to different members, differentials being used to convert the different rotary motions into a continuous rotary motion dependent upon the average impulse rate. A magnetic drag motor compensated for change of temperature is used to convert the continuous rotary motion into a steady proportional deflection, the motor being driven by a resilient free-wheel connection which allows the motor to overrun the rotary motion. The impulses may be produced by a single meter, or by a series of independent meters, in which case the final indication is a summation of the series of indications. In the arrangement shown in Fig. 1, a steady indication is given on the dial 13 proportional to the average rate of the impulses produced by the rotation of the watt-hour meter 10. The closure of contact 12 at each rotation of the meter causes magnet 14 to move the ratchetdriven arm 16 from one position to the next, momentary currents passing over the contacts 17, 17a, 17b, &c. to the relays 18, 18a, 18b, &c. which close the circuits of motors 23, 23a, 23b, &c arranged to make one complete revolution and then come to rest. The shaft of each motor has a conducting disc 28 with an insulating part 29 normally engaged by a brush 30. The motor circuit is momentarily closed by the relay and is maintained by the disc 28 until the part 29 comes beneath the brush. The eight motors corresponding to the eight contacts engaged by the arm 16 thus rotate successively through one revolution, the rotations overlapping more or less according to the rate of the impulses. The eight rotary movements thus produced are added up by seven differentials 27, 31, 32, 33, &c., the shaft 35 thus being driven at a speed proportional to the instantaneous sum of the speeds of the eight motors. The rotations of the shaft 35 may be integrated at 13'. In order to smooth out any remaining irregularities in the movement the shaft 35 drives the indicator 13 through a resilient one-way drive 36 and a magnetic drag motor 37 of considerable inertia, the pointer 46 being biassed by a spring 45. The apparatus. may be used to sum up the indications from a number of meters; the lower four motors may be' driven from a four-contact distributor, such as 14, 16, from one meter, and the upper four motors from a similar distributor and the other meter. Or each motor may be associated with an individual meter. In a modification instead of using eight independent motors, a single motor 50, Fig. 2, may be successively connected to the various differentials in driving relation with this motor for a predetermined motion period. The main drive shaft 51 has four gears 54 each of which is adapted to drive one side of two differentials located on opposite sides of the gears 54. Thus the upper gear 54 drives the upper sides of the differentials 55, 56 while the next gear 54 drives the lower sides of the same differentials. Differential 59 adds the movements of 56, 61, 58 adds the movements of 55, 60, and 57 adds the movements of 58, 59, the shaft of 57 being connected through a resilient one-way drive 38, 39 and magnetic drag motor 87 to the indicator 46. The driving gears of the differentials 55, 56. 60, 61 are brought successively into gear with the shaft 51 by a series of staggered fingers 71 on geared shafts 72, 73, rotated step by step by a magnet 77 responsive to the metering impulses. (The connection between the armature 92, Fig. 3, of this magnet and the driving pawl 95 is such that the major portion of the work is done in the final stage of the armature movement when the magnetic pull is strongest. The link-shaped pawl 95 is pivoted to a lever 96 connected by a link 98 to the armature, the pawl and link being connected by a spring 99). In order that it may be given a single complete rotation, the driving gear 63 of the first differentials is formed with a plain part 64 normally opposite the gear 51 and is provided with a gear sector 65 pivoted at right angles to the axis of rotation. The teeth of the sector 65 are above the plain section of the gear 63 and normally above the gear 54. When a cam 68 is engaged by a finger 71 on the shaft 72, say, a pin 67 on the sector is disengaged and allows the sector to be rotated by a spring 69 about its pivot 73, so that its teeth engage the gear 54. The sector 65, gear 63, and cam 66 are then rotated as a unit, the teeth of gear 63 engaging gear 54 to complete the rotation, the cam 66 acting on cam 68 to restore the sector 65 to its normal position before the rotation is complete. The magnetic drag motor shown in Fig. 2 is compensated for changes in temperature. The drive shaft 86, Figs. 2 and 5, carries an inner bar magnet 87 and an outer magnetic structure 88 between which extends a cylindrical member 89 of conducting material in which eddy currents are set up. To compensate for changes in the resistance of the member 89 with temperature, the poles of the magnet 87 are shunted by bars 90, which have a negative temperature coefficient of permeability.