Patent GB-410629-A (GB)
Title: Method of and apparatus for measuring mechanical forces, particularly for testing purposes
IPC: G01L3/10
Filed: 1933-06-27
Abstract: 410,629. Measuring forces. SIEMENS & HALSKE AKT.-GES., Siemenstadt, Berlin. June 27, 1933, Nos. 18258, 18259, 18260, and 18261. Convention dates, June 27, 1932, Nov. 26, 1932, Nov. 28, 1932, Jan. 11, 1933. [Class 106 (ii).] Comprises a device for measuring a mechanical force by determining the variations in permeability of a magnetic body subjected to the force in which the body forms a magnetic circuit consisting throughout of material of high permeability, the permanence of such parts of the magnetic body as are not subjected to the force being high in comparison with the permanence of the part subjected to the force. Fig. 1 shows a test body or test box consisting of a core 1<1> carrying an exciting winding 2 surrounded by a shell 1<11> rigidly mounted on the core. It is loaded as shown so that nearly all parts of the closed magnetic circuit are subjected to the load which is measured as shown in Fig. 20. The alternating current source 15 is connected through a resistance 16 to a bridge in the arms of which are connected respectively two rectifiers 17, 18 the exciting winding 2 and a reference resistance 19. A direct current measuring set 20 is connected on the diagonal branch of the bridge. The bridge is first balanced, the test box being under no load, by adjusting the resistance 19. The box is then placed under load the strain produced causing the impedance of the winding 2 to vary an amount corresponding to the load. Several forms of test box are described, for instance, in the box used in Fig. 20 only the nickel-iron core 1 which projects slightly from the shell is subjected to the load. The form shown in Fig. 1 may be used for torsion forces by coupling it in a line of shafting, and providing slip rings for the coil. A similar form comprises end pieces connected to the shaft and joined by a tube enclosing the coil which is on the shaft which forms part of the magnetic core. In the form shown in Fig. 4 only the shaft is strained, the shell being composed of two parts 3<1>, 3<11> coupled to the shaft and intermeshing with slight play. When the shaft is hollow, a reel-shaped part carrying the coil is inserted in the shaft and shrunk to it at the flanges. Several forms are described in which the box is built up of thin plates. In Fig. 6 the box consists of three thin walled tubes 1 insulated from one another with a central solid cylinder 29. Pressure pieces 30 are fitted and a built-up yoke 3 carries the coil. Fig. 13 shows in form which is given a predetermined tension bias. A tube 1 closed at the bottom 1<1> has inside it a second tube enclosing a spring 9 on which acts a piston on the end of a screw 11 screwed into the top end piece 8. By compressing the spring, the cylinder 1 is placed under tension. A preliminary compression may be arranged for by a suitable modification. In a further form of bridge circuit Fig. 21 the alternating current source 15 is connected through a transformer 23. The reference resistance 19 and coil 2 are connected between them and arranged as shown and the indicators 20 and a variable resistance 24 arranged between rectifiers 17, 18. A resistance 25 is connected on the other bridge arm between rectifiers 21, 22. In a further form a thermionic amplifying device is used.