| 摘要 |
1499164 Testing super-conductors SIEMENS AG 30 June 1975 [1 July 1974] 27591/75 Headings G1N and G1U Apparatus for testing an elongate conductor consisting at least partly of super-conductor material, comprises: means for generating an applied magnetic field; means for passing the conductor, while the super-conductor material is in the superconducting state, lengthwise along a path transverse to the applied magnetic field; and means located adjacent the path for monitoring the magnetic field generated by currents induced in the conductor. A tape 12 having a super-conductive core is passed round and under a roller 18 of diameter e.g. 40 mm located in a liquid-helium cryostat, so that at its lowest point it is travelling substantially transversely to the region of maximum flux density of a super-conducting electromagnet 16 also located in the cryostat. Secondary magnetic fields generated by eddy currents induced in the tape 12 are detected by a Hall plate 19, or preferably by two Hall plates on respectively opposite sides of the tape, the Hall e.m.f. due to the primary applied magnetic field being backed off in electronic apparatus (24), Fig.2 (not shown). A curve plotted by a chart printer (25) thus represents the secondary magnetic field due to eddy currents induced in the tape 12. The magnetic flux density is e.g. 2-5 tesla; and the tape speed is so chosen (e.g. 1 metre/min) that the induced current attains the critical value corresponding to the applied flux density everywhere within the super-conducting portion. Thus the recorder graph comprises a steady component due to the mean critical current, with superimposed noise due to surface irregularities of the tape, any flaws in the super-conductive portion being represented by negative spikes. Further coils 23, 23, may be included to superimpose either monotonic or alternating variations on the applied flux, to investigate variations of critical current with applied flux. If an alternating variation is applied, then phase-sensitive detection may advantageously be used to separate timedependent effects such as those due to ohmic resistance in normally-conductive portions of the tape. |
