Plated sensor for monitoring corrosion or electroplating

• US 4,755,744 A
• Filed: 01/21/1986
• Issued: 07/05/1988
• Est. Priority Date: 01/21/1986
• Status: Expired due to Term

• Current Assignee: Rohrback Corporation
• Original Assignee: Rohrback Corporation
• Inventors: Silverman, Herbert P., Bredow, James R., Moore, Clifford G.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): BROWN, THEATRICE
• Application Number:
  US06/021,013
• Time in Patent Office: 896 Days
• Field of Search: 324/65 CR, 324/65 P, 324/71.2, 73/86, 338/13, 427/8-10, 204/1 T, 204/14.1, 204/404
• US Class Current: 324/700
• CPC Class Codes: G01N 17/00 Investigating resistance of materials to the weather, to corrosion, or to light
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00

Abstract

A high sensitivity electroplating or corrosion sensor and method for sensing employing a relatively strong, self-supporting electrically conductive substrate of high resistivity and a test coating that is electroplated directly onto the substrate. For corrosion monitoring, a test element of the sensor is formed of a thick, high resistivity substrate, such as stainless steel, upon which is electroplated a thin test coating of material to be tested in a corrosive environment. For many applications, the ratio of resistivity of the substrate to resistivity of the test coating is substantially equal to the ratio thickness of the substrate to thickness of the test coating, which ratios may be about 40 to 1. The sensor may be employed in the monitoring of electroplating by immersing the stainless steel substrate in the electrolytic bath with the object to be plated and measuring the decreasing parallel resistance of the substrate and coating that is plated upon the substrate during a plating of the object. To decrease resistance measuring noise due to currents generated in the plating or corrosion sensor by external currents, the power supply is connected to the sensor substrate to cause equal and opposite current components to flow in the substrate.

Claims

1. A corrosion monitoring probe including an electrical resistance sensor, said sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished,

a reference element protected from such environment, and

means for comparing electrical resistances of said elements for determination of test element thickness,

said test element comprising a substrate formed of electrically conductive material having a relatively high electrical resistivity, and an electrically conductive test coating on said substrate, said test coating having an electrical resistivity considerably less than said substrate resistivity, wherein the ratio of substrate thickness to test coating thickness at the start of probe life is approximately the same as the ratio of substrate resistivity to coating resistivity.

2. A sensor for monitoring electroplating of an object immersed in an electrolytic bath with an electrode, said object and electrode being connected in a plating circuit having a plating power source, said sensor comprising:

an electrically conductive substrate adapted to be immersed in said bath and to be plated as said object is plated, said substrate being subject to plating current caused to flow therein by said electrolytic bath,

means for measuring electrical resistance of said substrate, said means for measuring being adversely affected by plating current flowing in said substrate, and

means for reducing adverse effects of said plating current on said means for measuring, said means for reducing adverse effects of said plating current comprising unidirectional conducting means for coupling opposite ends of said substrate to each other and to said power source.

3. A method of monitoring corrosion of a fluid environment comprising the steps of

mounting an electrically conductive substrate and an electrically conductive reference element in a sensor body with said reference element protected from an environment in which said sensor is to be immersed and with said substrate positioned for exposure to such environment,

electroplating a conductive test coating on said substrate, said substrate having a greater resistivity and a greater thickness than said test coating,

said step of electroplating comprising plating said test coating upon said substrate to a thickness at which the resistance of the test coating is about equal to the resistance of said substrate,

exposing said test coating to said environment to cause corrosion of said test coating and decrease of its thickness to a thickness at which the resistance of the test coating is greater than the resistance of said substrate, and

comparing the combined resistance of said substrate and test coating with the resistance of said reference element.

4. The method of claim 3 wherein said step of mounting comprises the steps of positioning the substrate to extend through an apertured header, and sealing and electrically insulating said substrate to said header with a fused sealant before said step of electroplating.

5. The method of claim 3 including the step of connecting a reference conductor in parallel with said reference element, said reference conductor having the same resistance as said first mentioned resistance of said test coating.

6. An electrical resistance sensor comprising:

a substrate formed of electrically conductive substrate material having a substrate resistivity and having a substrate thickness sufficient to enable said sensor to be self-supporting,

an electrically conductive test material electroplated on the substrate, said test material having a resistivity substantially less than said substrate resistivity and a thickness substantially less than said substrate thickness, and

a center tap on said substrate connected to a point of fixed potential.

7. An electrical resistance sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished,

a reference element protected from such environment, and

means for comparing electrical resistances of said elements for determination of test element thickness,

said test element comprising a substrate formed of electrically conductive material having a relatively high electrical resistivity, and an electrically conductive test coating on said substrate, said test coating having an electrical resistivity considerably less than said substrate resistivity,

said environment inducing electrical current in said substrate that adversely affects said means for comparing electrical resistance, and means connected with said substrate for reducing adverse effects of said electrical current,

said means connected with said substrate comprising means for connecting said substrate to cause electrical current induced by said environment in said substrate to flow in oppositely directed components in said substrate.

8. An electrical resistance sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished,

a reference element protected from such environment, and

means for comparing electrical resistances of said elements for determination of test element thickness,

said test element comprising a substrate formed of electrically conductive material having a relatively high electrical resistivity, and an electrically conductive test coating on said substrate, said test coating having an electrical resistivity considerably less than said substrate resistivity,

said environment inducing electrical current in said substrate that adversely affects said means for comparing electrical resistance, and means connected with said substrate for reducing adverse effects of said electrical current,

said means for reducing adverse effects of said electrical current comprising a center tap on said substrate connected to a point of fixed potential.

9. A method of monitoring electrolytic plating comprising

immersing an electrode and an object to be plated in an electrolytic bath,

making a plating connection between a plating power source and the object and electrode to cause plating current to flow in the object,

immersing an electrically conductive test element in the electrolytic bath,

making a monitor connection between the plating power source and the test element to cause plating current to flow in the test element,

measuring resistance of said test element,

the plating current in the test element tending to cause adverse effects on the measuring of resistance, and

making the monitor connection at a selected region of the test element so as to reduce said adverse effects by causing the plating current to flow in oppositely directed components in the test element.

10. The method of claim 9 including the step of causing plating current to flow in the test element in substantially equal and opposite components by making the monitor connection to a central region of the test element.

11. The method of claim 9 including the step of causing the plating current to flow in the test element in substantially equal and opposite components by making the monitor connection between the plating power source and first and second mutually spaced regions on said test element.

12. An electrical resistance sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished,

a reference element protected from such environment,

means for comparing electrical resistances of said elements for determination of test element thickness,

said test element comprising a substrate formed of electrically conductive material having a relatively high electrical resistivity, and an electrically conductive test coating on said substrate, said test coating having an electrical resistivity considerably less than said substrate resistivity, and

a noise suppressing lead connected to said test element,

said noise suppressing lead comprising a center tap on said test element.

13. An electrical resistance sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished,

a reference element protected from such environment, means for comparing electrical resistances of said elements for determination of test element thickness,

said test element comprising a substrate formed of electrically conductive material having a relatively high electrical resistivity, and an electrically conductive test coating on said substrate, said test coating having an electrical resistivity considerably less than said substrate resistivity, and a noise suppressing lead connected to said test element,

said noise suppressing lead comprising first and second undirectional conductive means connected to opposite ends of said test element.

14. An electrical resistance sensor comprising:

a substrate formed of electrically conductive substrate material having a substrate resistivity and having a substrate thickness sufficient to enable said sensor to be self-supporting,

an electrically conductive test material electroplated directly on the substrate, said test material having a resistivity substantially less than said substrate resistivity and a thickness substantially less than said substrate thickness, and

a noise suppressing lead connected to said test element, said noise suppressing lead comprising a center tap on said test element.

15. An electrical resistance sensor comprising:

a substrate formed of electrically conductive substrate material having a substrate resistivity and having a substrate thickness sufficient to enable said sensor to be self-supporting,

an electrically conductive test material electroplated directed on the substrate, said test material having a resistivity substantially less than said substrate resistivity and a thickness substantially less than said substrate thickness, and

a noise suppressing lead connected to said test element, said noise suppressing lead comprising first and second unidirectional conductive means connected to opposite ends of said test element.

16. The method of monitoring corrosion of a fluid environment comprising the steps of:

mounting an electrically conductive substrate and an electrically conductive reference element in a sensor body with said reference element protected from an environment in which said sensor is to be immersed and with said substrate positioned for exposure to such environment,

electroplating a conductive test coating on said substrate, said substrate having a greater resistivity and a greater thickness than said test coating,

said step of electroplating comprising plating said test coating upon said substrate to a thickness at which the resistance of the test coating is about equal to the resistance of said substrate,

exposing said test coating to said environment to cause corrosion of said test coating and decrease of its thickness to a thickness at which the resistance of the test coating is greater than the resistance of said substrate,

comparing the combined resistance of said substrate and test coating with the resistance of said reference element, and

connecting a center tap between said substrate and a point of fixed potential.

17. The method of monitoring corrosion of a fluid environment comprising the steps of:

mounting an electrically conductive substrate and an electrically conductive reference element in a sensor body with said reference element protected from an environment in which said sensor is to be immersed and with said substrate positioned for exposure to such environment,

electroplating a conductive test coating on said substrate, said substrate having a greater resistivity and a greater thickness than said test coating,

said step of electroplating comprising plating said test coating upon said substrate to a thickness at which the resistance of the test coating is about equal to the resistance of said substrate,

exposing said test coating to said environment to cause corrosion of said test coating and decrease of its thickness to a thickness at which the resistance of the test coating is greater than the resistance of said substrate,

comparing the combined resistance of said substrate and test coating with the resistance of said reference element, and

forming first and second unidirectional conductive paths between opposite ends of said substrate and a point of fixed potential.

18. An electrical resistance sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished and in which electrical currents are flowing,

a reference element protected from such environment, means for comparing electrical resistances of said elements for determination of test element thickness,

noise suppressing means connected to said test element for reducing adverse effects of said electrical currents on said means for comparing,

said noise suppressing means comprising a center tap connected to said test element.

19. An electrical resistance sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished and in which electrical currents are flowing,

a reference element protected from such environment,

means for comparing electrical resistances of said elements for determination of test element thickness,

noise suppressing means connected to said test element for reducing adverse effects of said electrical currents on said means for comparing,

said noise suppressing means comprising unidirectional conducting means connected to opposite ends of said test element.

20. In combination with a vessel that confines a fluid in which electrical currents flow, an electrical resistance sensor comprising:

a test element immersed in said fluid and being subject to noise currents induced therein by said electrical currents which flow in said fluid,

means for measuring electrical resistance of said test element, and

noise suppressing means connected between said test element and a point of fixed potential for causing components of noise currents therein to flow in mutually opposite directions in said test element, thereby reducing adverse effects of said electrical currents upon said means for measuring.

21. In combination with a vessel that confines a fluid in which electrical currents flow, and electrical resistance sensor comprising:

a test element immersed in said fluid,

means for measuring electrical resistance of said test element, and

noise suppressing means connected between said test element and a point of fixed potential for reducing adverse effects of said electrical currents upon said means for measuring,

said noise suppressing means comprising a center tap on said test element.

22. In combination with a vessel that confines a fluid of which corrosive tendencies are to be monitored, an electrical resistance corrosion sensor comprising:

a test element immersed in said fluid,

means for measuring electrical resistance of said test element,

said fluid having electric current flowing therein that tends to adversely effect said means for measuring, and

means for reducing adverse effects of said electric current on said means for measuring comprising means for providing an electrically conductive path between a point intermediate the ends of said test element and said vessel.

23. In combination with a vessel that confines a fluid of which corrosive tendencies are to be monitored, an electrical resistance corrosion sensor comprising:

a test element immersed in said fluid,

means for measuring electrical resistance of said test element,

said fluid having electric current flowing therein that tends to adversely effect said means for measuring,

means for reducing adverse effects of said electric current on said means for measuring comprising means for providing an electrically conductive path between said test element and said vessel,

said means for providing an electrically conductive path comprising a center tap on said test element.

24. An electrical resistance sensor comprising:

electrically conductive test and reference elements connected in series to one another, said test element adapted to be exposed to an environment in which a measurement is to be made, said environment having current flowing therein that tends to generate noise current in the test element exposed to such environment,

means for applying an excitation potential to said elements,

measurement leads connected to said elements for measuring resistance of said test and reference elements, and

noise suppressing means connected to said test element for causing noise current components to flow in mutually opposite directions in said test element, thereby decreasing net noise current in said test element.

25. An electrical resistance sensor comprising:

electrically conductive test and reference elements connected in series to one another, said test element adapted to be exposed to an environment in which a measurement is to be made, said environment having current flowing therein that tends to generate noise current in the test element exposed to such environment,

means for applying an excitation potential to said elements,

measurement leads connected to said elements for measuring resistance of said test and reference elements, and

noise suppressing means connected to said test element for decreasing net noise current in said test element,

said noise suppressing means comprising a center tap on said test element adapted to be connected to a point of fixed potential.

26. An electrical resistance sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished,

a reference element protected from such environment, and

means for comparing electrical resistances of said elements for determination of test element thickness,

said test element comprising a substrate formed of electrically conductive material having a relatively high electrical resistivity, and an electrically conductive test coating on said substrate, said test coating having an electrical resistivity considerably less than said substrate resistivity,

said environment inducing electrical current in said substrate that adversely affects said means for comparing electrical resistance, and means connected with said substrate for reducing adverse effects of said electrical current,

said substrate being a self-supporting, highstrength material that is substantially uniform throughout its thickness and having an exterior surface, said test coating being electroplated directly on said material over all of said exterior surface,

said means connected with said substrate comprising means for connecting said substrate to cause electrical current induced by said environment in said substrate to flow in oppositely directed components in said substrate.

27. An electrical resistance sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished,

a reference element protected from such environment, and

means for comparing electrical resistances of said elements for determination of test element thickness,

said test element comprising a substrate formed of electrically conductive material having a relatively high electrical resistivity, and an electrically conductive test coating on said substrate, said test coating having an electrical resistivity considerably less than said substrate resistivity,

said environment inducing electrical current in said substrate that adversely affects said means for comparing electrical resistance, and means connected with said substrate for reducing adverse effects of said electrical current,

said substrate being a self-supporting, high-strength material that is substantially uniform throughout its thickness and having an exterior surface, said test coating being electroplated directly on said material over all of said exterior surface,

said means for reducing adverse effects of said electrical current comprising a center tap on said substrate connected to a point of fixed potential.

28. A resistance probe for use in monitoring electrolytic plating of an object immersed in an electrolytic bath and connected to a plating power source, said probe comprising:

an electrically conductive test element adapted to be immersed in the electrolytic bath with the object to be plated,

means for electrically connecting resistance measuring apparatus to first and second points on said test element, and

means for electrically connecting the plating power source to said test element between said first and second points.

29. An electrical resistance sensor comprising a test element adapted to be exposed to an environment in which monitoring is the be accomplished and in which electrical currents are flowing, a reference element protected from such environment, means for comparing electrical resistances of said elements for determination of test element thickness, and noise suppressing means connected to said test element for reducing adverse effects of said electrical currents on said means for comparing,

wherein said means for comparing includes measuring means connected to first and second points of said test element, and wherein said noise suppressing means includes means connected to said test element at a point between said first and second points.

30. An electrical resistance sensor comprising:

a test element adapted to be exposed to an environment in which monitoring is to be accomplished,

a reference element protected from such environment, and

means for comparing electrical resistance of said elements for determination of test element thickness,

said test element comprising a substrate formed of electrically conductive material having a relatively high electrical resistivity and a relatively large cross sectional area, and an electrically conductive test coating on said substrate, said test coating having an electrical resistivity and cross sectional area considerably less than said substrate resistivity and cross sectional area,

wherein said test element substrate is formed substantially entirely of said material.

31. An electrical resistance sensor comprising:

a substrate formed of electrically conductive substrate material having a substrate resistivity and having a substrate thickness sufficient to enable said sensor to be self-supporting,

an electrically conductive test material electroplated on the substrate, said test material having a resistivity substantially less than said substrate resistivity and a thickness substantially less than said substrate thickness,

the ratio of substrate resistivity to test material resistivity being in the range of about seven to forty-six.

32. An electrical resistance sensor comprising:

a substrate formed of electrically conductive substrate material having a substrate resistivity and having a substrate thickness sufficient to enable said sensor to be self-supporting,

an electrically conductive test material electroplated on the substrate, said test material having a resistivity substantially less than said substrate resistivity and a thickness substantially less than said substrate thickness,

each of (a) the ratio of substrate resistivity to test material resistivity and (b) the ratio of substrate thickness to test coating thickness before the sensor has been used, being about forty to one.