Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1989-12-14
1991-05-21
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324232, 324233, 324234, G01B 710, G01N 2772, G01R 3312
Patent
active
050178695
ABSTRACT:
An apparatus for measuring the thickness of a coating on a substrate has a bridge circuit including four coils. One coil is placed near the coated substrate and another placed near an uncoated substrate of the same material. An oscillator is connected to the bridge circuit and frequency sweeps, e.g. from 10 KHz to 10 MHz. Phase differences between the voltages induced in the coils are detected to determine conductivity changes with frequency. A method for measuring coating thickness comprises generating variable frequency eddy current in coated and uncoated substrates of the same material and comparing the generated eddy current.
REFERENCES:
patent: 2916694 (1959-12-01), Hanysz et al.
patent: 3407352 (1968-10-01), Smith
patent: 3441840 (1969-04-01), Randle
patent: 3878457 (1975-04-01), Rodgers
patent: 4752739 (1988-06-01), Wang
patent: 4893079 (1990-01-01), Kustra et al.
Hanysz, Eugene A.; Swept Frequency Eddy-Current Device to Measure Overlay Thickness, The Review of Scientific Instruments; vol. 29, No. 5, May 1958 pp. 411-415.
Davis Jr. James C.
General Electric Company
Strecker Gerard R.
Webb II Paul R.
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