Patent GB-889021-A (GB)
Title: Improvements in or relating to the testing of synchronous electromagnetic data transmission devices
Inventor: HIBBITT ALEC ENNEVER WILLIAM
IPC: G08C19/48
Filed: 1957-08-22
Abstract: 889,021. Testing synchronous electrodynamic devices; measuring time intervals. MUIRHEAD & CO. Ltd. June 6, 1958 [Aug. 23, 1957], No. 26551/57. Class 37. In apparatus testing synchronous electromagnetic devices for the angular spacing of the magnetic axes of the rotor and stator coils, motor means drive the rotor at a speed determined by a relatively high-frequency alternating supply also energizing master and slave counters, energizing means excite the rotor from a relatively low-frequency alternating supply, and detector means respond to the occurrence of successive null voltages in the stator windings to produce pulses operative to switch the counting means, which indicate the angular displacement of the rotor. A transmission device under test having a triple wound stator and a single wound rotor energized from an A.C. supply of e.g. 50 c.p.s. is located (Fig. 5) with its stator 21 in the bore 20 of base 19, and the shaft 27 of rotor 24 mounted in bearings for geared rotation by synchronous motor 28. The stator windings are connected at S1, S2, S3 (Fig. 4), to a phantom star network of equal resistances SN; the three points and the star point of which are connected to rotary switches SW1, SW2, whereby input leads 29, 30 and 291, 301 are respectively and selectively connectable to any pair of points of the star network. Initially, motor 28 is connected to an A.C. supply of e.g. 1000 c.p.s. by a power switch (not shown) and drives rotor 24 to rotate 30 degrees in the period of 10,000 cycles, and starting switch 59 is closed to pulse multivibrator 42, which sets electronic relay 41 in its off position. Multivibrator 56 is also pulsed to direct an input pulse solely to multivibrator 57, which is also pulsed together with multivibrator 58 from switch 59 so that the former is " on " and the latter is " off." Relay 61 is simultaneously pulsed to reset the 0-10,000 slave electronic counter 47 to zero and relay 63 is operated to reset the 0-10,000 master electronic counter 45 to zero. Switches SW1, SW2 are set so that input leads 29, 30 are connected to points of the star network SN at which a first voltage null will occur, and input leads 291, 301 are connected to those points at which a second voltage null will occur, nominally after 30 degrees rotation of the shaft of the test device (Figs. 1 to 3, not shown). The input leads are respectively connected over amplifiers 31, 311, 32, 321 to harmonic filters 33, 34 and 331, 341 which supply further amplifiers 35, 351, 36, 361, energizing phase-sensitive detectors 37, 371 operative to generate direct voltages reversing their polarities when the in-phase components of the input voltages are zero, whereby the effects of parasitic quadrature voltages are eliminated. The direct voltages are amplified at 38, 381, and differentiated at 39, 391 to produce alternate positive and negative going pulses at the polarity reversely, converted to trains of negative pulses in pulse reverser 40, 401. At the first voltage null of the test device, pulse reverser 401 changes over multivibrator 42 to operate relay 41 and apply the 1000 c.p.s. supply to relays 43, 44 and to master counter 45 which registers. Multivibrator 57 being " on," relay 43 is operated so that the supply is connected over squaring circuit 46 to 0-10,000 slave counter 47 which also registers. After a count of 5000 cycles (i.e. after 15 degrees rotor rotation) master counter 45 emits a pulse which is amplified at 52 to operate relay 53 which excites operating gear 54 to step rotary switches SW1, SW2, SW3, SW4 by one position, whereby SW2 disconnects input leads 29, 30 and reconnects these to points at which a third voltage null will appear after a further 30 degrees rotation (Figs. 1 to 3, not shown), and SW4 operates relay 62 to zeroize slave counter 49. Assuming the error in the test device is such that the angle between nulls exceeds 30 degrees, master counter 45 resets to zero after 10,000 cycles corresponding to 30 degrees, and pulses multivibrator 56 through differentiator 55 to change over and pulse multivibrator 58 to " on," whereby relay 44 is energized and the 1000 c.p.s. supply excites slave counter 49 over squaring circuit 48, while multivibrator 57 remains " on " and slave counter 47 continues to count. When the rotor is positioned so that a voltage null occurs between leads 29, 30 pulse reverser 40 impulses multivibrator 57 to " off " whereby relay 43 is released and slave counter 47 is de-energized to stop and display the number of cycles counted since it was zeroized simultaneously with master counter 45; representing the electrical error of the stator of the test device at the position of the first voltage null. Master counter 45 again impulses after counting a further 5000 cycles to step swtiches SW1, SW2, SW3, SW4 whereby SW1, SW2 recorrect input leads 29, 30 to the points at which a fourth null occurs, while SW3 resets slave counter 47 to zero. Assuming the electrical error at the position of the second voltage null exceeds 60 degrees from the starting null, a null voltage occurs at input leads 29, 30 before master counter 45 has registered 10,000. Pulse reverser 401 impulses multivibrator 58 which changes over to " off " to release relay 44 and arrests slave counter 49 to display a count of less than 10,000; the difference between such count and 10,000 representing the electrical error of angle. Slave counter 47 is operative until the master counter 45 has registered 10,000 and then impulses the multivibrator 56 which changes over and impulses multivibrator 57 to change over into its "on" position. Relay 43 now operates counter 47, which counts cycles simultaneously with master counter 45. The sequence continues as described until a series of tests of electrical angular error has been effected at 30 degrees intervals over a 360 degrees rotation of the rotor. The slave counters 47, 49 may operate a printer 70 recording the results. The apparatus is adaptable to test devices having triple wound rotors, or double wound stators and/or rotors, and the phantom star network SN is replaceable by a delta network (Fig. 6, not shown), comprising two equal fixed resistances and an equal tapped resistance; a voltage null occurring between the junction of the fixed resistance and a flying lead engaging the tapped resistance at angular intervals of less than 30 degrees depending on the tapping selection.