Browse Prior Art Database

Thin Film Corrosion-Indicating Bridge

IP.com Disclosure Number: IPCOM000034786D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 227K

Publishing Venue

IBM

Related People

Long, TC: AUTHOR [+3]

Abstract

A thin film corrosion monitor is disclosed which operates on the Wheatstone bridge principle. By fabricating the resistive elements from an evaporated thin film, the performance of this device approaches that of an ideal Wheatstone bridge. The principal benefits of the thin film approach are: versatility (any metal or alloy which can be evaporated can be used as the corrosion sensor); a high degree of reproducibility (due to the use of a precision mask); sensitivity (due (Image Omitted) to the high line resistances attainable with thin films); and the minimization of undesirable thermal effects (no internal thermally induced EMFs).

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Thin Film Corrosion-Indicating Bridge

A thin film corrosion monitor is disclosed which operates on the Wheatstone bridge principle. By fabricating the resistive elements from an evaporated thin film, the performance of this device approaches that of an ideal Wheatstone bridge. The principal benefits of the thin film approach are: versatility (any metal or alloy which can be evaporated can be used as the corrosion sensor); a high degree of reproducibility (due to the use of a precision mask); sensitivity (due

(Image Omitted)

to the high line resistances attainable with thin films); and the minimization of undesirable thermal effects (no internal thermally induced EMFs). Another benefit of the thin film approach is that the thickness of the sensing elements can be tailored to the application, depending on the severity of the corrosive environment and the degree of sensitivity required by the investigator. A minimum of electronics is needed for operation; only a DC power source and a microvoltometer are required. The bridge offset voltage (V) is a function of the four resistance values of the bridge arms, and the bridge supply voltage
(E). For a standard DC Wheatstone bridge, in the special case where diagonally opposed arms have equal resistance, the offset voltage is (R-RO)

V = E ------ (1)

(R+RO) For the disclosed design, RO is a fixed resistance, and R is the corrosion sensing resistance, which increases in response to corrosion. The offset voltage can be simply expressed in terms of the corrosion film thickness: x

V = E ------ (2)

(2-x) where x is the ratio of the corrosion film thickness to the initial line thickness. For Equation (2) to be valid, the resistivity of each bridge arm must be the same at all times, and the initial dimensions of all four arms must be the same.

The first condition requires a close thermal linking of all four bridge arms, which is achieved with the monolithic thin film approach of the disclosed design. The second condition is met as a result of the dimensional accuracy which is achievable through the use of a precision mask. The thin film corrosion-indicating bridge consists of a four-lobed pattern of metal lines, with linewidth 52 micrometers. Diagonally opposed bridge arms are coated wit...