Plated sensor for monitoring corrosion or electroplating

• US 4,839,580 A
• Filed: 06/20/1988
• Issued: 06/13/1989
• Est. Priority Date: 01/21/1986
• Status: Expired due to Term

• Current Assignee: Clifford G. Moore, Herbert P. Silverman, James R. Bredow
• Original Assignee: Clifford G. Moore, Herbert P. Silverman, James R. Bredow
• Inventors: Moore, Clifford G., Silverman, Herbert P., Bredow, James R.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Harvey, Jack B.
• Application Number:
  US07/210,162
• Time in Patent Office: 358 Days
• Field of Search: 324/65 CR, 324/65 P, 324/71.2, 73/86, 427/8-10, 204/1 T, 204/14.1, 204/404, 338/13
• US Class Current: 324/699
• 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 of thickness of the substrate to thickness of the test coating, which ratio 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 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. 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.

2. The sensor of claim 1 wherein the thickness of said substrate is many times greater than the thickness of said test coating, said test coating thickness varying during operation of said sensor between a maximum wherein resistance of said test coating is substantially equal to resistance of said substrate and a smaller value wherein the resistance of said test coating is considerably greater than resistance of said substrate.

3. An electrical resistance sensor for monitoring electroplating 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 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.

4. An electrical resistance sensor for monitoring electroplating comprising:

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

a reference element protected from such bath, 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,

said electrolytic bath 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 bath in said substrate to flow in oppositely directed components in said substrate.

5. An electrical resistance sensor for monitoring plating in an electrolytic bath comprising:

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

a reference element protected from such bath, 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,

said electrolytic bath 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.

6. An electrical resistance sensor for monitoring plating in an electrolytic bath 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 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.

7. 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 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.

8. The sensor of claim 7 including means for effecting relative adjustment of said unidirectional conductive means.

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 reduced said adverse effects by causing the plating current to flow in oppositely directed components in the test element, said step of measuring resistance comprising plating the test element in the bath as the object is plated, and comparing resistance of the plated test element with a reference resistor to determine thickness of the plating on the test element.

10. A method of monitoring electrolytic plating of a plating material upon an object immersed in an electrolytic bath, said method comprising:

immersing in an electrolytic bath an electrode and an object to be plated with said plating material,

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

immersing in the electrolytic bath an electrically conductive test element substrate having an electrical resistivity considerably higher than the electrical resistivity of said plating material,

making a monitor connection between the plating power source and the test element substrate to cause plating current to flow in the test element and to cause said plating material to be plated upon said substrate as a plated coating on the substrate,

measuring resistance of the plated coated of the substrate,

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

reducing said adverse effects of the plating current on the measuring of resistance by causing plating current to flow in oppositely directed components in the test element substrate.

11. Apparatus for monitoring electroplating of a plating material upon an object in an electrolytic bath, said plating material having a relatively low electrical resistivity, said apparatus comprising:

a test element substrate formed of electrically conductive substrate material having a substrate resistivity, said substrate having a thickness substantially greater than the thickness of a coating to be electrically plated upon said object, the ratio of substrate resistivity to resistivity of the plating material being in the range of about 7/46 to 1/40.

12. The apparatus of claim 11 including means for causing current induced in the substrate by plating currents in the bath to flow in oppositely directed components in the substrate.

13. An electrical resistance sensor for monitoring the plating of an object in an electrolytic bath, said sensor comprising:

a substrate formed of an electrically conductive material, said bath inducing electrical current in said substrate that induces adverse effects upon measurement of resistance, said substrate adapted to be plated when immersed in said bath while an object immersed in the bath adjacent the substrate is also being plated, whereby measurement of resistance of the plating of the substrate will provide an indication of thickness of plating on an object in the bath, and

means connected with said substrate for suppressing said adverse effects of the electrical plating currents in the bath.

14. The sensor of claim 13 wherein said means for suppressing adverse effects comprises means for causing electrical currents induced in the substrate by the bath to flow in the substrate with equal and opposite components.

15. The sensor of claim 13 wherein said means for suppressing adverse effects comprises a center tap on the substrate.

16. An electrical resistance sensor for monitoring electroplating in an electrolytic bath, said sensor comprising:

a test element having a substrate adapted to be immersed in the electrolytic bath, whereby said test element substrate has a coating plated thereon by action of the electrolytic bath, said bath having electrical currents flowing therein,

a reference element protected from the bath,

means for comparing electrical resistance of the test element and reference element for determination of test element thickness, and

noise suppressing means connected to said test element substrate for reducing adverse effects of said electrical currents on said means for comparing, said means for comparing including means for determining thickness of the plating on said test element.

17. Apparatus for monitoring electroplating of an object immersed in an electrolytic bath, said apparatus comprising:

electrically conductive test and reference elements connected in series to one another, said test element comprising an electrically conductive substrate having an electrical resistivity considerably higher than the resistivity of the material to be plated on objects in the bath, said test element adapted to be immersed in the bath, said bath having current flowing therein that tends to generate noise current in the test element immersed therein,

means for applying an excitation potential to said test and reference elements,

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

noise suppressing means connected to said test element for reducing adverse effects of said noise current on measurement of resistance of said test and reference elements.

18. Apparatus for electrically monitoring progress of electroplating of a plating material upon an object in an electrolytic bath said apparatus comprising:

an electrically conductive test element adapted to be immersed in said electrolytic bath,

a reference element protected from the bath,

means for comparing electrical resistance of said test element and said reference element for determination of test element resistance,

said test element comprising a substrate formed of electrically conductive material having an electrical resistivity that is considerably higher than the electrical resistivity of said plating material,

said electrolytic bath causing said substrate to be plated with said plating material while an object immersed in the bath is also plated with said plating material,

said bath inducing electrical current in said substrate that adversely affects said means for comparing electrical resistance, and

means connected with the substrate for reducing adverse effects of said electrical current.

19. The apparatus of claim 18 wherein said means for reducing adverse effects comprises means connected with the substrate for causing electrical currents induced by the bath in the substrate to flow in oppositely directed components in the substrate.

20. The apparatus of claim 18 wherein said means for reducing adverse effects comprises a center tap on said substrate connected to a point of fixed potential.