Patent GB-219640-A (GB)
Title: Improved method of and apparatus for electro-magnetic testing of metals
IPC: G01N27/80
Filed: 1924-02-12
Abstract: 219,640. American Chain Co., Inc., (Assignees of Forest, A. V. de). July 24,1923, [Convention date]. Magnetic tests; inductances and time constants, measuring. -The physical properties of metals are ascertained from their magnetic and electrical properties by determining the effects of a specimen on the reactance of an alternating current testing circuit at different values of the initial reactance. As shown in Fig. 1 a solenoid A, fixed resistances R', R<6>, and a variable resistance R<4> form the arms of a wheatstone bridge supplied with alternating or other variable current from a source E through a variable inductance D, variable resistance R<2>, and ammeter I. The galvanometer G is preferably of the type having a coil M movable in the field of a solid or laminated electromagnet H supplied with alternating current through an adjustable inductance D<1>, adjustable resistance R<3> and ammeter I<I>. Balance is obtained with a standard specimen and with the specimen to be tested inserted in the solenoid A, the difference in the resistance R<4> required for balance being a measure of the combined effect on the reactance of the coil A of the magnetic properties and eddycurrent losses of the specimen. The test is then repeated with different values of the inductance D, the results enabling the magnetic properties of the specimen to be differentiated from the eddy-current losses. The variable re;istance R<4> of the wheatstone bridge may be replaced by a variable inductance. In the modification shown in Fig. 3 a solenoid comprising primary and secondary windings A, B is employed, the primary winding A being in the main circuit and the secondary winding B forming one of the arms of the bridge. A condenser' C' is connected as shown. Balance is obtained by means of a slider P co-operating with a slide-wire S. In the galvanometer circuit is a condenser C which can be short-circuited by a key K. Balance is obtained with the key K closed and a standard specimen in the solenoid A, B. This is then replaced by the specimen to be tested and balance again obtained. The reactance of the galvanometer circuit is then altered by opening the key K, and a second test is made. A deflection method instead of a null method may be employed, in which case the secondary winding B is in series with the condenser C and moving coil M. Alternatively two solenoids each with a primary and a secondary winding may be employed. Readings are taken with standard specimens in both solenoids and with one replaced by the specimen to be tested. In another modification two similar solenoids, one containing a standard specimen and one the specimen under test, form two arms of a wheatstone bridge, of which the other two arms are formed by a slidewire. In the arrangement shown in rig. 7 two solenoids having primary windings A. A' and secondary windings B, B<1> are employed. A slidewire resistance S is connected in parallel with the primary windings A, A<1>, a slider P being connected to their junction. A second slide-wire resistance S<1> is connected in parallel with the secondary windings B, B<1>. A standard snecimen is placed in the solenoid A, B and the specimen under test in the solenoid A<1>, B<1>, positions of the sliders P, P<1> being found for balance with the key K open and closed. A second galvanometer may be connected in, the lead L. In place of the solenoids A, B, A<1>, B<1>, U-shaped electromagnets having primary and secondary windings may be employed, the standard and test specimens forming armatures.