Patent GB-768296-A (GB)
Title: Improvements in or relating to an apparatus for measuring, or producing a response related to the torque in an electrical machine
IPC: G01R33/07
Filed: 1955-01-13
Abstract: 768,296. Electric measuring systems. SIEMENS - SCHUCKERTWERKE AKT. - GES. Jan. 13, 1955 [Jan. 13, 1954; Feb. 10, 1954; Feb. 26. 1954; Feb. 26, 1954; March 4, 1954; April 17, 1954; April 17, 1954; Oct. 30, 1954], No. 1144/55. Class 40 (1). [Also in Groups XXXV and XXXVII] Apparatus for measuring the torque of an electric motor for indicating or control purposes comprises a semi-conductor body transversely located in the magnetic field of the motor and fed with the armature current in a perpendicular direction, whereby a Hall effect voltage is produced in the third perpendicular direction whose magnitude is proportional to the torque produced by the motor. As shown for a D.C. series-wound machine 106 (Fig. 7), the semiconductor body 110 is located between a field pole and the armature, so that the flux passes transversely through it, and an E.M.F. proportional to the armature current is obtained from a series resistor 111 to be fed in at terminals 101, 102 located at the axially opposing edges of the body 110, whereby the Hall voltage appearing at terminals 103, 104 on the other opposing edges is proportional to the torque, and may be used to control full load relay 113, operating a warning lamp 115; and over-load relay 114 which can trip the main switch 112. The longitudinal current through the semi-conductor body 110 may alternatively be obtained through a D.C. transformer comprising an A.C. energized coil wound on a core having a further winding carrying the motor armature current, whereby the impedance of and the current in the A.C. winding is proportional to the D.C. load current, and is rectified before being fed to the semi-conductor body 110. To indicate the power output of the machine, the Hall voltage torque signal obtained from a semi-conductor body 210. (Fig. 9), as described above is multiplied by a speed signal obtained from a tacho-generator 215 driven by the motor (not shown), in a wattmeter-type instrument, or in a multiplier comprising a choke 220 whose energizing winding 221 is fed by the tacho-generator 215, and which has a further semi-conductor body 219 located in an air gap in the iron circuit, fed with the torque signal from semi-conductor 210 at terminals 205, 206 to produce a further Hall voltage at terminals 207, 208 indicative of their product and representing the power output. Alternatively the torque and speed signals may feed the field and armature of a motor driving a meter pointer through a clutch which is energized separately for each operation, so that the total work done during each operation may be determined. In an embodiment for maintaining a constant tension in steel strip rolling apparatus (Fig. 12), the strip, initially on a reel 309, is fed between rolls 325, 326 to a reel 328. The rolls 325, 326 are driven at constant speed by motor 310; the reel 328 is driven by a motor 311; the reel 309 is located on a shaft carrying a motor 312 which acts as a generator brake when strip is being fed in the direction shown, the functions of motors 311, 312 being reversed when the direction of winding is reversed. The torque output signal of motor 311 is combined with the speed signal produced by a tacho-generator 322 in a second semi-conductor device 319 to obtain a voltage at terminals 307, 308 representative of the work done by motor 311, which is compared at resistor 324 with a voltage from tacho-generator 323 driven by the motor 310, any difference being applied to the control grid 315 of a mercury arc rectifier 314 feeding the armature of motor 311, whereby the winding speed of reel 328 is adjusted to that consistent with a constant tension in the strip. To avoid inaccuracies due to armature reaction the torque-measuring semi-conductor element may be mounted on the rotating armature, connections being made through a combination of slip-rings and commutators, or the load current may be tapped off directly from an adjacent armature conductor. A plurality of seriesconnected, torque-measuring semi-conductor 'elements may be used, located either axially or circumferentially or both on the surface of the armature. Alternatively, to avoid the effects of variable armature reaction, variable speed and variable temperature, the magnetic condition under the pole of a motor 501 (Fig. 15), may be reproduced in a static magnetic core 503, the main flux being produced by a winding 508 in series with the field winding 502, the semi-conductor body 505 being located in a gap 504 and fed with a proportionate armature current from shunt resistor 506, the complete magnetic conditions being simulated by the addition of a saturable leg 509 and a yoke 510 separated by an adjustable insulating strip 511, and auxiliary winding 512 short-circuited through a resistor 513. To determine the torque output of an A.C. motor the semiconductor element is located 90 degrees electrically from the field winding whose current is being fed to the semi-conductor body, so that its instantaneous magnetic flux is that produced by the instantaneous current through it, which therefore bear the correct phase relationship.