The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Feb. 03, 1976
Filed:
Jan. 21, 1975
Gerold Brandli, Windisch, CH;
Pierre Keller, Baden, CH;
BBC Brown Boveri & Company Limited, Baden, CH;
Abstract
A method for contactless measurement of conductivity and/or temperature on metals by means of the eddy current effect induced within the metal by an alternating magnetic field produced by an excitation coil fed with alternating current arranged with its axis perpendicular to the surface of the metallic test specimen, there being in addition to the excitation coil a pair of measuring coils of equal radius arranged coaxially and symmetrically with respect to the excitation coil at each end respectively of the excitation coil and having an axial length substantially less than that of the excitation coil. The two measuring coils are connected electrically in series opposition and the phase angle between the current in the measuring coils and the current in the excitation coil is taken as an indication of the measured variable. In order to reduce the so-called 'lift-off' effect to a minimum and allow accurate contactless measurement such that substantial tolerances are permissible for the distance between the test specimen and measuring head which carries the coils, the radius between the excitation coil on the one hand, and the measuring coils on the other, is smaller than 1/4 or greater than 4, depending on whether the measuring coils are located respectively outside or inside the excitation coil, and the measuring head is at such a distance from the specimen surface that the phase angle between the excitation-coil signal and the measuring-coil signal exhibits a maximum.