• journal_title：Geophysics
• Contributor：C. R. Bruce
• Publisher：Society of Exploration Geophysicists
• Date：1967-
• Format：text/html
• Language：en
• Identifier：10.1190/1.1439898
• journal_abbrev：Geophysics
• issn：0016-8033
• volume：32
• issue：5
• firstpage：893
• section：Articles

This magnetometer uses magnetic shielding instead of a compensating coil to reduce ambient magnetic noise. Advantages of shielding include greater coupling to the specimen field, reduced stationary field at the specimen, lessened coherent noise from rotor magnetism, and a smaller coil size. The minimum detectable moment is 4 X 10 (super -7) emu. Specimen shape is either a 1 X 1 inch cylinder or a solid formed by the intersection of three mutually perpendicular cylinders. The functional principle is conventional but the electronic circuit is greatly simplified through mechanical design. Direction of magnetization is indicated directly on a scale on the sensing head after the sensing coil has been oriented to attain a null output on the phase sensitive detector. Then, by switching to a second optical band on the rotor, the reference phase is shifted 90 degrees and intensity is read on the phase-detector output meter. Operating frequency is 155 Hz. The instrument is calibrated by spinning a current loop of known characteristics in the specimen position. Three separate units--a sensing head, a control unit, and a power supply--compose the total system.