Patent GB-555182-A (GB)
Title: Improvements in and relating to measuring apparatus
IPC: G01B9/02
Filed: 1942-05-29
Abstract: 555,182. Magnetic tests. BRITISH THOMSON-HOUSTON CO., Ltd. May 29, 1942, No. 7325. Convention date, May 31, 1941. [Class 37] [Also in Groups XIX and XX] Magnetostriction is measured by projecting on to a viewing screen the light interference pattern caused by monochromatic light reflected from stationary and pivoted surfaces, the latter being moved by a lever system in which is arranged the sample of magnetic material to be tested, and also a similar compensating sample which is submitted to the temperature influence only. The sample 10 whose magnetostriction is to be measured is mounted from a stationary point 11 under tension of a weight 12. A magnetizing coil 13 surrounds the specimen and the change in length is transferred to a lever 14 pivoted at 15 having equal arms, and through a similar sample 10a to a second lever 17. The sample 10a has a non-inductive winding 16 which compensates for heating effect of winding 13 and the movement of lever 17 is due only to the magnetostriction. Secured to the free end of lever 17 is a transparent optically flat plate 19 having a partially reflecting under surface, below which is a stationary optically flat plate 20 having an upper reflecting surface. A monochromatic light source 21-a neon glow-lamp-supplies light through a ground glass plate 22. The wedge of air between the reflecting surfaces due to slight movement of lever 17 gives rise to dark interference lines wherever the separation between the surfaces is an odd number of quarter-wave lengths. A diagonal plate glass 23 reflects the returning light through a lens 24 to an observation screen 26. If, due to movement of the lever 17 the angle between the plates increases, the interference bands move to the left and are closer together. The parts may be so arranged and dimensioned that one dark and one bright line moving past a reference point 25 represents a change in length of the specimen 10 of one millionth of an inch. A scale on the flat 19 may be provided to facilitate the reading. In a modification both specimen 10a from flux leakage from the inductive of a balanced pivoted lever and the coils supported in casings of which the one surrounding 10a is of magnetic material to shield the specimen 10a from flux leakage from the inductive winding surrounding the specimen 10 which latter is surrounded with a casing of brass. In this form the reading is by a selenium cell which influences a counter. The Specification as open to inspection under Sect. 91 also describes the following. Fig. 11 (Cancelled) shows the invention applied to a calliper gauge. The top plate 56 is pivoted at 57 on an adjustable screw 58. It is allowed to engage a standard piece 60 by slacking off the screw 59. The screw 58 is now adjusted to obtain a convenient interference pattern on the screen and screw 59 raised, the lines passing a reference point being counted. A work piece to be gauged is substituted for the standard and the screw 59 lowered until the plate 56 engages the work the lines passing a reference point being counted. The difference between the two counts represent difference in size. In a further modification the free ends of the plates are provided with ball contacts to form an internal gauge. This subject-matter does not appear in the Specification as accepted.