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Magnetic Reluctance Film Thickness Gauge

IP.com Disclosure Number: IPCOM000074135D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Hoel, JE: AUTHOR

Abstract

This system measures the thickness of chromium plating on ferrous substrates, by employing the plating-substrate composite as an element of variable reluctance in a magnetic flux circuit. Variations in the flux coupling distance X to the ferrous substrate will induce corresponding changes in the magnitude of the magnetic flux in the circuit. The flux magnitude, which has a one-to-one correspondence with the plating thickness X, is converted to a voltage pulse by the circuit shown at A and given a limit test. If the plating thickness exceeds predefined limits, a signal is generated which indicates a reject condition. This signal can also be used to initiate compensatory action in process control applications.

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Magnetic Reluctance Film Thickness Gauge

This system measures the thickness of chromium plating on ferrous substrates, by employing the plating-substrate composite as an element of variable reluctance in a magnetic flux circuit. Variations in the flux coupling distance X to the ferrous substrate will induce corresponding changes in the magnitude of the magnetic flux in the circuit. The flux magnitude, which has a one-to-one correspondence with the plating thickness X, is converted to a voltage pulse by the circuit shown at A and given a limit test. If the plating thickness exceeds predefined limits, a signal is generated which indicates a reject condition. This signal can also be used to initiate compensatory action in process control applications.

It can be shown that the detectable flux phi(X) can be approximately expressed as in equation:

(Image Omitted)

where M(s) and M(d) is the magnetomotive force of the input oscillator and the detection circuit, respectively, R(g) is the reluctance of the air gap, A(cr) and A(fe) is the average cross-sectional area of the flux in the chromium and ferrous medium, respectively, S(fe) is the average path length for the flux through the ferrous medium, mu(cr) and mu(fe) are the magnetic permeability of the chromium and ferrous material, respectively, X is the thickness of the chromium film, and C is a constant of proportionality. The success of the measurement depends on the invariance of those parameters in the equation whic...