Patent GB-676088-A (GB)
Title: A ferromagnetic hysteresis potentiometer
IPC: G01R33/12
Filed: 1951-02-15
Abstract: 676,088. Magnetic measurements. ASPDEN, H. Feb. 15, 1951, No. 3706/51. Class 37. [Also in Group XXXVII] A potentiometer and switch device is so arranged that hysteresis loss may be measured directly, without recourse to graphical methods. Fig. 1 shows a typical hysteresis curve for a specimen of ferro-magnetic material showing the change in flux-density B when the magnetising force H is varied from A to C and back to A. The points D, F indicate the value of B for the same value of the magnetising current when this is being varied from A to C and from C to A respectively, DF being the difference between these values. The specimen Q, Fig. 8, s wound with a magnetising winding M and a search coil P. A source of potential E is connected through an impedance Z to the magnetising coil M. The search coil P is connected through a switch S to a heavily damped ballistic galvanometer G without restoring means. By traversing the loop through the portion DCF a permanent deflection proportional to DF is obtained on the galvanometer. The switch S is then opened while the loop is traversed from F to A and from A to the next one of a series of points D as shown in Fig. 9, the whole range of current change being divided into an even number of equal sections. The switch S is then closed and the loop traversed through the portion DCF, thereby adding to the previous deflection a deflection proportional to the value of the new intercept DF. This process is repeated throughout the loop, so that a deflection is obtained proportional to the sum of the intercepts DF, which is proportional to the area of the loop. Fig. 10 shows the circuit diagram of a potentiometer box corresponding to the impedance Z, Fig. 8, for causing the magnetizing current to vary through twelve successive cycles in one operation. A circle of studs 1 ... 72 are connected as shown to terminals A, B and resistances a ... f, certain studs 3, 5, 9, 11 &c. being isolated. Mounted for rotation on a spindle at the centre of the ring of studs is a switch arm, Fig. 11, carrying a contact L, which engages with the studs 1 ... 72, and a contact K connected to the contact L and engaging a brass ring V. The connections to the magnetising coil M, search coil P, and galvanometer G are shown in Fig. 12, a source of voltage - E, negative to O, and a source +E, positive to O, being connected to the terminals AB. The ring V is connected to a terminal C to which one end of the magnet ising coil M is connected. A resistance X in series with the coil M brings the total resistance to that for which the potentiometer is designed, e.g. 5 ohms. One complete rotation of the arm makes the current changes necessary to carry out the series of cycles to obtain the sum of the intercepts DF shown in Fig. 9. The switch S, Fig. 8, is replaced by terminals F, J on the potentiometer box. A second ring of twentyfour studs, a brass ring W, Fig. 11, and a bridging contact N connect F, J directly only while the current is changing between its maximum negative value and the intermediate value, the studs in this ring being connected together and to the terminal J. When the device is used to study displaced loops an extra magnetising circuit may be used. In a modification a toroidal resistance is employed having a contact arm Y, Fig. 13. The galvanometer G is connected and disconnected at the correct instants by a switch shown in Fig. 14. A screw L rotates through one revolution for each revolution of the contact arm. A threaded boss B is mounted on the screw L and is prevented from rotating by an arm A engaging a slot in a cylindrical surface C. A member D is rotatably mounted on the boss B and has an attachment H which engages a slot in the screw L. As the screw L rotates the boss B moves axially while the member D rotates with the screw and carries with it an attached contact arm K, which sweeps round and brushes the surface C, moving along the length of the cylinder as it does so. A lead T is connected to the galvanometer circuit. Part of the cylindrical surface C is metallic and part non-metallic, the metallic part being shaped to give connection and disconnection between the arm K and the lead T at the required times. In a modification, Fig. 16, the cylinder C is replaced by a solid cylinder Q geared to rotate at the same speed as the screw L.