Eddy Current Type Research Articles

Eddy-current mutual-inductance transducers with high-conductivity reference plates

The design considerations of mutual-inductance devices for use in noncontacting measurements of distance are studied with special emphasis on the eddy-current type utilizing “perfectly” conducting metal reference plates of infinite extent. The force on the plate due to the exciting current, typical schematic circuits used to detect the results, and the effects of rapid motion of the gauge are given. Since actual reference plates are not perfectly conducting nor infinitely extensive, some indications of the effects of finite conductivity and limited extent of reference plates are included.

Bibliography of Electric Couplings

This bibliography has been subdivided into groups covering the different types of electric couplings according to the definitions proposed by the AIEE Electric Coupling Subcommittee: Induction Couplings (Ship Propulsion Type Couplings & Eddy Current Type Couplings); Synchronous Couplings; Hysteresis Couplings; Magnetic-Friction Couplings; Magnetic-Particle Couplings. The titles have been classified into four major categories: General Theory - T; Research and Development - R; Design - D; Application - A. No attempt has been made to make the bibliography cover specific design details such as resistances, reactances, iron losses, and so forth. It is believed that for the present such references can be located in the general Bibliography of Rotating-Machinery, 1886-1947, AIEE Publication S32 (January 1950).

Abrasion Resistance of GR-S Vulcanizates

Abstract A method for determining the abrasion resistance properties of reinforced vulcanizates was required for evaluating new GR-S type elastomers and carbon blacks developed for use in automobile tire treads. In spite of the fact that past experiences revealed that most laboratory machines are unsatisfactory for testing GR-S vulcanizates, a program for evaluating several machines was undertaken. A Lambourn abrader similar to the one recently adopted by the British Standards Institution for testing elastomer vulcanizates appeared to be most promising, for which reason efforts were expended on constructing a similar machine. The abrader that was constructed and operated to simulate wear brought about by a tire slipping on road surfaces embodied the following four modifications of the British machine: 1. All parts and accessories were either obtained or fabricated in the United States. 2. The electrical eddy current type of brake used in the original Lambourn machine was replaced with a hydraulic, gear pump braking system. 3. Intermittent talcing of the test wheel during operation was specified. 4. A revolution counter equipped with a friction drive wheel, one foot in circumference, was installed to ride on the test wheel for the purpose of conveniently determining test run distances. The conditions for testing vulcanizates were standardized to obtain abrasion loss values that could be expressed in terms of loss in cubic centimeters per 3000 feet of running at 24 per cent slip. Adjustments were made in calculating abrasion ratings from volume loss values to bring them more in line with reported service test ratings.

Advanced Design—Original Features Embodied in New 160,000-Kw Oswego Steam Station

Abstract Advanced design is the keynote of the new 160,000-kw Oswego Station of the Niagara Hudson Power System. In the present paper, the many outstanding and original features incorporated in this two-unit, one-boiler-per-turbine plant are described and illustrated. Among these are the 80,000-kw single-spindle condensing turbine for 1250-psi 900-F steam; soot blowers which use 250-lb compressed air for the blowing medium to save 1250-lb steam, and which operate automatically in succession on a pre-selected schedule; electric couplings of the eddy-current type for control of fan speeds; pilot operation of boiler safety valves for obtaining better protection and reduced maintenance; acceleration of the main generator for synchronous-condenser operation by motorizing its direct-connected exciter.

Eddy Current Type Flaw Detectors for Non-Magnetic Metals

New developments in an eddy current type flaw detector are discussed. Several types of pick-up units, which contain the exciting coils for inducing eddy currents in the test material and pick-up coils for detecting changes in this eddy current pattern when a flaw is approached, are described. The electric power for the exciting current is supplied by a vacuum tube power oscillator at a frequency of 500 or 1000 cycles/second. The circuit for detecting the changes in the eddy current pattern employs vacuum tube bridge circuits sensitive to both amplitude and phase changes. The use of jigs to guide the pick-up unit, automatic scanning, and automatic recording is discussed.