Innovations in Eddy Current
        Technology
    by Curtis Desselles




       Blythe McCarthy - Freer Gallery
Valuable information about cultural materials
   is not always visible to the naked eye.




Tattoodjj, “Statue of Prometh...
Northwestern State University & NCPTT are
continuing research into use of eddy current testing
               on cultural ...
Without nondestructive testing, cultural information
                  will be lost.




        Corroded Penny - www.wild...
By making affordable eddy current instruments,
preservationists can have access to the technology.




           Eddy Cur...
Affordable eddy current instruments can be used to
             analyze cultural materials.




            Eddy Current T...
Eddy Currents have been used in a variety of
       nondestructive applications.




       Adam Hoke, an aviation mainten...
Eddy currents were discovered in 1851 by Foucault.




            Léon Foucault (1819-1868), Wikipedia.
Applications of eddy currents include detection of
 cracks, discontinuities, flaws, and thicknesses.




   Measuring pain...
Testing for Cracks - NDT Resource Center
Voltage
 is a measurement of the energy
  contained within an electric
  field, or an electric circuit, at a
  given poin...
Current
 a flow of electricity through a
  conductor, measured in
  amperes
Resistance
 a material's opposition to the
  flow of electric current,
  measured in ohms
Capacitance
 a capacitor is an electronic
  component used for storing
  charge and energy, measured
  in farads
Inductance
 a measure of the reaction of
  electrical components
  (especially coils) to changes in
  current flow by cre...
Conductance
 a measure of a material's ability
  to conduct electric charge; the
  reciprocal of the resistance,
  measur...
Impedance
 the total effective resistance in
  an electric circuit to the flow of
  an alternating current
Reactance
 opposition to the flow of
  alternating current caused by
  the inductance and capacitance
  in a circuit rath...
What are eddy currents?




     Eddy Currents - NDT Resource Center
Eddy currents are analogous to a flowing stream.




        EDDIES IN THE OYASHIO CURRENT, G. K. Vallis, Princeton Univer...
Similarly, eddy currents can be created in metals.




              Drawing Courtesy of Curtis Desselles
Here are the steps to construct an
affordable eddy current analyzer.




         Chichen Itza - Travelblog.org
Eddy currents can be created in the follow way in
                 cultural materials.

• Create an alternating current (A...
A Complete Eddy Current
    Analyzer Circuit
Magnet wire is used to constructed for use as
                  probes.




            Magnet Wire RadioShack® - $5.99
Coil Construction - 30 Gauge Magnet Wire




 Photographs Courtesy of Curtis Desselles and Jason Church
Determine the inductance value with an LCR meter.




            LCR Meter - Photograph Courtesy of Curtis Desselles
Use a square or sine wave to excite the LC circuit




         LC Circuit - Drawing Courtesy of Curtis Desselles
Circuitry is built to excite the LC circuit to resonance




             Propeller Demo Board - Parallax, Inc.
The frequency of the square or sine wave must
match the resonant frequency of the LC circuit.




          L = Inductance...
Once at resonance, the voltage and current across
            the coil is at its maximum.




              Drawing Courte...
The AC voltage is converted to DC using a diode
        and it is stored in a capacitor.
We then convert the analog signal to a digital signal
                  using an ADC.




                                ...
Using Microsoft Visual Basic an algorithm was
   created to convert the data to a bitmap.
Once the eddy current analyzer is built and
 calibrated, metal artifacts were tested.




         Reference Samples - Fre...
Four Techniques used in Eddy Current Analysis


• Identification of defects in metals.
• Identification and conductivity.
...
Four Techniques used in Eddy Current Analysis
      “Identification of defects in metals”
• Eddy Current Parameter
   ●
  ...
Four Techniques used in Eddy Current Analysis
      “Identification of defects in metals”
• Phase Lag
   ●
       Three de...
Four Techniques used in Eddy Current Analysis
      “Identification of defects in metals”
• Phase Lag
      ●
          Th...
Four Techniques used in Eddy Current Analysis
      “Identification of defects in metals”
• Methodology
   ●
       Set fr...
Four Techniques used in Eddy Current Analysis
      “Identification of defects in metals”
                   Case Study


...
Four Techniques used in Eddy Current Analysis
        “Identification and Conductivity”
• Eddy Current Parameter
  ●
    L...
XL




                      R
     Screen capture of id measurements
        Black is baseline conductivity
Four Techniques used in Eddy Current Analysis
         “Identification and Conductivity”
• Lift-Off
    ●
        Zero pro...
“Identification and Conductivity”
Four Techniques used in Eddy Current Analysis
         “Thickness Measurements”
• Eddy Current Parameter
• Lift-Off
   ●
 ...
Four Techniques used in Eddy Current Analysis
         “Thickness Measurements”
Lift-Off




              Drawing Courtes...
Four Techniques used in Eddy Current Analysis
            “Recovery of Hallmarks”
• Eddy Current Parameter
  ●
    Phase l...
Four Techniques used in Eddy Current Analysis
           “Recovery of Hallmarks”




              Lead Bale Seal, Los Ada...
Building the Instrument
How do we get from this…
…to this
 Pre-drill Holes to Later Insert Electrical
  Components
 Copy Circuit
  Design to
  Copper
  Circuit Board
 Use Sharpie
  Marker for
  Layout
Completed Circuit Diagram
 Etch Copper Board in Ferric Chloride
  Sharpie Ink Acts as a Resist
Periodic Agitation Speeds the Process
Solder on the Components
560 pf Capacitor

↓
        ↑
 RCA Coil Inlet
Rectifier Diode


          ↓
     ↑
.1 µf Capacitor
741 IC 8pin Chip 100 mega ohm Resistor


          ↓↓  ×
                  ↑
               1 mega ohm Resistor
ADC0831 Analog to Digital Converter


            ↓
   ↑
Wires to Serial Port
Coil Construction - 30 Gauge Magnet Wire
Coil Construction - 30 Gauge Magnet Wire


Iron Ferrite Core




                                        ↓
               ...
Future Directions
   iPhone Applications
   Tomographic Layers
   Database of Standard Parameters
   Better Resolution
iPhone Applications
Eddy Current Imaging
Database of Standard
    Parameters
Conclusion
• These case studies show the potential of the affordable
eddy current instrument.
• As cultural resources age ...
Acknowledgements


• Northwestern State University of Louisiana (NSU)
• National Center for Preservation Technology and Tr...
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Eddy Current Metal Testing for Conservation

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This powerpoint was presented as part of a workshop on Eddy Current Testing for Conservation at the annual metting of the AIC on May 19, 2009 Los Angeles, CA.

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Eddy Current Metal Testing for Conservation

  1. 1. Innovations in Eddy Current Technology by Curtis Desselles Blythe McCarthy - Freer Gallery
  2. 2. Valuable information about cultural materials is not always visible to the naked eye. Tattoodjj, “Statue of Prometheus”, June 8, 2008, online image, Flickr. Rockefeller Center, NY. Opacity, “statue of Bastet, gilded bronze, Late Period”, March 8, 2009, online image, flickr.
  3. 3. Northwestern State University & NCPTT are continuing research into use of eddy current testing on cultural heritage. NCPTT, Photograph courtesy of Jason Church
  4. 4. Without nondestructive testing, cultural information will be lost. Corroded Penny - www.wildbell.com/.../ 2008/05/img_9834.jpg
  5. 5. By making affordable eddy current instruments, preservationists can have access to the technology. Eddy Current Testing, Freer Gallery
  6. 6. Affordable eddy current instruments can be used to analyze cultural materials. Eddy Current Testing, Freer Gallery
  7. 7. Eddy Currents have been used in a variety of nondestructive applications. Adam Hoke, an aviation maintenance technician with the U.S. Coast Guard, inspects the belly of a Boeing 737 using an eddy current scanner. (Photo by Randy Montoya) Sandia Labs.
  8. 8. Eddy currents were discovered in 1851 by Foucault. Léon Foucault (1819-1868), Wikipedia.
  9. 9. Applications of eddy currents include detection of cracks, discontinuities, flaws, and thicknesses. Measuring paint thickness - NDT Resource Center
  10. 10. Testing for Cracks - NDT Resource Center
  11. 11. Voltage  is a measurement of the energy contained within an electric field, or an electric circuit, at a given point, measured in volts
  12. 12. Current  a flow of electricity through a conductor, measured in amperes
  13. 13. Resistance  a material's opposition to the flow of electric current, measured in ohms
  14. 14. Capacitance  a capacitor is an electronic component used for storing charge and energy, measured in farads
  15. 15. Inductance  a measure of the reaction of electrical components (especially coils) to changes in current flow by creating a magnetic field and inducing a voltage. Its unit is the henry
  16. 16. Conductance  a measure of a material's ability to conduct electric charge; the reciprocal of the resistance, measures in Siemens
  17. 17. Impedance  the total effective resistance in an electric circuit to the flow of an alternating current
  18. 18. Reactance  opposition to the flow of alternating current caused by the inductance and capacitance in a circuit rather than by resistance.
  19. 19. What are eddy currents? Eddy Currents - NDT Resource Center
  20. 20. Eddy currents are analogous to a flowing stream. EDDIES IN THE OYASHIO CURRENT, G. K. Vallis, Princeton University
  21. 21. Similarly, eddy currents can be created in metals. Drawing Courtesy of Curtis Desselles
  22. 22. Here are the steps to construct an affordable eddy current analyzer. Chichen Itza - Travelblog.org
  23. 23. Eddy currents can be created in the follow way in cultural materials. • Create an alternating current (AC) in the form of a square or sine wave (excite circuit). • Excite a series LC circuit (coil and capacitor) who’s resonant frequency matches that of the excite circuit. • Bring the probe(s) (coil) near the metal to be tested. • Convert the voltage across the probe(s) to direct current (DC) using a diode. • Divide and store the voltage to a capacitor. • Measure the voltage in the capacitor using an analog to digital converter (ADC) ADC0831.
  24. 24. A Complete Eddy Current Analyzer Circuit
  25. 25. Magnet wire is used to constructed for use as probes. Magnet Wire RadioShack® - $5.99
  26. 26. Coil Construction - 30 Gauge Magnet Wire Photographs Courtesy of Curtis Desselles and Jason Church
  27. 27. Determine the inductance value with an LCR meter. LCR Meter - Photograph Courtesy of Curtis Desselles
  28. 28. Use a square or sine wave to excite the LC circuit LC Circuit - Drawing Courtesy of Curtis Desselles
  29. 29. Circuitry is built to excite the LC circuit to resonance Propeller Demo Board - Parallax, Inc.
  30. 30. The frequency of the square or sine wave must match the resonant frequency of the LC circuit. L = Inductance in Henries C = Capacitance in Farads
  31. 31. Once at resonance, the voltage and current across the coil is at its maximum. Drawing Courtesy of Curtis Desselles
  32. 32. The AC voltage is converted to DC using a diode and it is stored in a capacitor.
  33. 33. We then convert the analog signal to a digital signal using an ADC. ADC0831 - Parallax Inc. ADC PBasic code - Curtis Desselles
  34. 34. Using Microsoft Visual Basic an algorithm was created to convert the data to a bitmap.
  35. 35. Once the eddy current analyzer is built and calibrated, metal artifacts were tested. Reference Samples - Freer Gallery
  36. 36. Four Techniques used in Eddy Current Analysis • Identification of defects in metals. • Identification and conductivity. • Thickness determination on gilded or coated surfaces. • Hallmark recovery on metal objects. Photographs Courtesy of Jason Church
  37. 37. Four Techniques used in Eddy Current Analysis “Identification of defects in metals” • Eddy Current Parameter ● Phase lag is the shift in time between the eddy current response from a disruption on the surface and a disruption at some distance below the surface. Drawing Courtesy of Curtis Desselles
  38. 38. Four Techniques used in Eddy Current Analysis “Identification of defects in metals” • Phase Lag ● Three defects at different depths and frequencies R B G Drawing Courtesy of Curtis Desselles - 50 KHz
  39. 39. Four Techniques used in Eddy Current Analysis “Identification of defects in metals” • Phase Lag ● Three defects at different depths and frequencies A B G Drawing Courtesy of Curtis Desselles - 300 KHz
  40. 40. Four Techniques used in Eddy Current Analysis “Identification of defects in metals” • Methodology ● Set frequency to 150 KHz ● Bring probe within 1 mm from test surface ● Scan object from left to right in a slow but steady manner ● Results appear on laptop screen ● High frequency ● Lower depth penetration and higher resolution ● Low frequency ● Greater depth penetration and lower resolution
  41. 41. Four Techniques used in Eddy Current Analysis “Identification of defects in metals” Case Study Aluminum (1mm) - 158.5 KHz Screen Capture - 158.5 KHz
  42. 42. Four Techniques used in Eddy Current Analysis “Identification and Conductivity” • Eddy Current Parameter ● Lift-off - This technique usually involves zeroing out a probe (coil) in air. Then placing the probe in contact with the sample surface. For nonmagnetic materials, the change in impedance of the coil can be correlated directly to the conductivity of the material. ● Resistance v. inductive reactance
  43. 43. XL R Screen capture of id measurements Black is baseline conductivity
  44. 44. Four Techniques used in Eddy Current Analysis “Identification and Conductivity” • Lift-Off ● Zero probe ● Touch probe to sample ● Lift off in a slow and steady manner ● Touch probe to sample ● Results will appear on screen Photograph Courtesy of Jason Church
  45. 45. “Identification and Conductivity”
  46. 46. Four Techniques used in Eddy Current Analysis “Thickness Measurements” • Eddy Current Parameter • Lift-Off ● Zero probe ● Touch probe to sample ● Lift off (1 mm) in a slow and steady manner ● Scan left to right ● Results will appear on screen
  47. 47. Four Techniques used in Eddy Current Analysis “Thickness Measurements” Lift-Off Drawing Courtesy of Curtis Desselles
  48. 48. Four Techniques used in Eddy Current Analysis “Recovery of Hallmarks” • Eddy Current Parameter ● Phase lag is the shift in time between the eddy current response from a disruption on the surface and a disruption at some distance below the surface. ● Touch probe to sample ● Scan left to right ● Repeat scanning of entire object ● Results will appear on screen
  49. 49. Four Techniques used in Eddy Current Analysis “Recovery of Hallmarks” Lead Bale Seal, Los Adaes, Williamson Museum, NSU Scan of handle area
  50. 50. Building the Instrument
  51. 51. How do we get from this…
  52. 52. …to this
  53. 53.  Pre-drill Holes to Later Insert Electrical Components
  54. 54.  Copy Circuit Design to Copper Circuit Board  Use Sharpie Marker for Layout
  55. 55. Completed Circuit Diagram
  56. 56.  Etch Copper Board in Ferric Chloride Sharpie Ink Acts as a Resist
  57. 57. Periodic Agitation Speeds the Process
  58. 58. Solder on the Components
  59. 59. 560 pf Capacitor ↓ ↑ RCA Coil Inlet
  60. 60. Rectifier Diode ↓ ↑ .1 µf Capacitor
  61. 61. 741 IC 8pin Chip 100 mega ohm Resistor ↓↓ × ↑ 1 mega ohm Resistor
  62. 62. ADC0831 Analog to Digital Converter ↓ ↑ Wires to Serial Port
  63. 63. Coil Construction - 30 Gauge Magnet Wire
  64. 64. Coil Construction - 30 Gauge Magnet Wire Iron Ferrite Core ↓ RCA Output ↓
  65. 65. Future Directions  iPhone Applications  Tomographic Layers  Database of Standard Parameters  Better Resolution
  66. 66. iPhone Applications
  67. 67. Eddy Current Imaging
  68. 68. Database of Standard Parameters
  69. 69. Conclusion • These case studies show the potential of the affordable eddy current instrument. • As cultural resources age and decay, valuable information can be lost. • This research allow for affordable eddy current instruments to be applied to cultural materials. Cultural Material - Los Adaes - Photographs courtesy of Curtis Desselles
  70. 70. Acknowledgements • Northwestern State University of Louisiana (NSU) • National Center for Preservation Technology and Training (NCPTT) • Dr. Mary Striegel • Dr. Hiram Gregory • Dr. ElizaBeth Guin • Jason Church • Houren Zhu
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