A report on an investigation of a commutated magnetometer detector
Badger, Algernon S
Pfeiffer, Paul E.
Master of Science
The subject of this investigation is a commutated rotating coil magnetometer element. One detector with quadrature sets of brushes could be used to align a second element with the total earth's field. It was lay contention that a commutated detector with a suitable filter and contact-modulated d-c amplifier would reduce the noise and stray pick-up considerably over existing design and simplify the application of a servomechanism as well. In order to determine the feasibility of such a device, the design and construction of the commutated detector, filter and contact-modulated amplifier were necessary. The armature consisted of 39 coils of 150 turns each of enameled no. 34 B. & S. copper wire spaced by fiber separators protruding from a luclte core. The Incite cylinder and copper coffiautator were force fit on a brass shaft supported by non-magnetic copper-beryllium ball bearings, Son-magnetic brush rigging and supports were used with the brush rig mounted so it could be rotated and the angular deflection read on a scale. An aluminum pulley was mounted on the shaft to drive the armature by means of a long cord belt and an oscillograph drive motor. Data taken to evaluate the relation between brush axis angle and output voltage of the amplifier. The axis of the armature was placed perpendicular to the horizontal component of the earth’s field and the rotor driven at 1600 RPM. Readings were taken of the amplifier output voltage and angular scale deflection over the Interval from zero output to saturation voltage on both sides of the zero position. These readings were checked and rechecked over a period of thirty minutes with no difference observed greater than the possible error in scale readings. The results of the data show clearly that the output voltage is linear with the angular change over the small interval near zero output. The magnitude of voltage developed at the 0.3535 degree limits desired is much greater than the inherent noise and is easily capable of controlling a servo system.