Combination coating thickness gauge using a magnetic flux density sensor and an eddy current search coil

Abstract

A gauge probe for a handheld combination coating thickness gauge allows the combination coating thickness gauge to measure both nonferrous coatings on ferrous substrate and nonconductive coatings on conductive nonferrous substrate. The gauge probe enables the combination coating thickness gauge to determine automatically, with a single probe, the substrate characteristics, and to effect a measurement of the coating thickness on that substrate. The technique used to measure coatings on a ferrous substrate utilizes a permanent magnet to provide a constant magnetic flux and a Hall sensor and thermistor arranged to measure the temperature-compensated magnetic flux density at one of the poles of the permanent magnet. The flux density at the magnet pole can be related to a nonferrous coating thickness on a ferrous substrate. The technique used to measure nonconductive coatings on a conductive nonferrous substrate utilizes eddy current effects. A coil near the gauge probe tip is excited by an alternating current oscillating between about 6 MHz and about 12 MHz. The coil sets up eddy currents on the surface of the conducting substrate. The resulting eddy currents set up an opposing magnetic field which in turn have an effect on the excited coil. The eddy current effects on the coil are quantified, and the degree of the eddy current effects on the coil are related to the nonconductive coating thickness on a conductive substrate. The gauge probe detects the substrate type and automatically determines the coating thickness on the detected substrate.

What is claimed is: 
     
       1. A coating thickness gauge for measuring both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, comprising: a permanent magnet having a pole face;   a magnetic flux density sensor disposed near the pole face of said permanent magnet so as to sense a magnetic field in a neighborhood of said pole face;   an eddy current search coil disposed around the neighborhood of said pole face; and   control means for receiving inputs from said magnetic flux density sensor and said eddy current search coil, selecting one of said inputs for calculating a coating thickness, and calculating a coating thickness based on the selected input.   
     
     
       2. The gauge of claim 1, wherein said magnet, sensor, and eddy current search coil are located in a single gauge probe. 
     
     
       3. The gauge of claim 2, further comprising: a temperature sensor connected to said magnetic flux density sensor so as to sense temperature in a neighborhood of said magnetic flux density sensor.   
     
     
       4. A coating thickness gauge for measuring both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, comprising: a permanent magnet having a pole face;   magnetic flux density sensor means disposed near the pole face of said permanent magnet for sensing a magnetic field in a neighborhood of said pole face;   an eddy current search coil disposed around the neighborhood of said pole face;   temperature sensor means connected to said magnetic flux density sensor means for sensing temperature in a neighborhood of said magnetic flux density sensor means, wherein said sensed temperature can be used to compensate a magnetic field measurement of said magnetic flux density sensor; and   control means for receiving inputs from said magnetic flux density sensor means and said eddy current search coil, selecting one of said inputs for calculating a coating thickness, and calculating a coating thickness based on said selected input.   
     
     
       5. The gauge of claim 1, wherein the magnetic flux density sensor is a Hall effect magnetic sensor. 
     
     
       6. The gauge of claim . .1.!. .Iadd.3.Iaddend., wherein the temperature sensor is a thermistor. 
     
     
       7. The gauge of claim 4, wherein the magnetic flux density sensor means is a Hail effect magnetic sensor. 
     
     
       8. The gauge of claim 4, wherein the temperature sensor means is a thermistor. 
     
     
       9. A gauge probe for a combination coating thickness gauge that allows the combination coating thickness gauge to measure both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, the gauge probe enabling the combination coating thickness gauge to determine automatically, with a single probe, substrate characteristics, and to effect a measurement of coating thickness on said characterized substrate, the gauge probe comprising: a permanent magnet having a pole face;   a Hall effect magnetic sensor disposed near the pole face of said permanent magnet so as to sense a magnetic field in a neighborhood of said pole face;   an eddy current search coil disposed around the neighborhood of said pole face;   a thermistor connected to said Hall effect magnetic sensor so as to sense temperature in a neighborhood of said Hall effect magnetic sensor, wherein said sensed temperature can be used to compensate a magnetic flux density measurement; and   control means for receiving inputs from said Hall effect magnetic sensor, said eddy current search coil and said thermistor and for determining the substrate characteristics and the coating thickness based on one or more of said inputs.   
     
     
       10. A gauge probe for a combination coating thickness gauge that allows the combination coating thickness gauge to measure both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, the gauge probe enabling the combination coating thickness gauge to determine automatically, with a single probe, substrate characteristics, and to effect a measurement of coating thickness on said characterized substrate, the gauge probe comprising: a permanent magnet having a pole face;   Hall effect magnetic sensor means disposed near the pole face of said permanent magnet for sensing a magnetic field in a neighborhood of said pole face;   an eddy current search coil disposed around the neighborhood of said pole face;   thermistor means connected to said Hall effect magnetic sensor means for sensing temperature in a neighborhood of said Hall effect magnetic sensor means, wherein said sensed temperature can be used to compensate a magnetic flux density measurement; and   control means for receiving inputs from said Hall effect magnetic sensor, said eddy current search coil and said thermistor and for determining the substrate characteristics and the coating thickness based on one or more of said inputs.   
     
     
       11. A method for gauging thickness of both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, using a coating thickness gauge, the gauge probe enabling the combination coating thickness gauge to determine automatically, with a single probe, substrate characteristics, and to effect a measurement of coating thickness on said characterized substrate, the method comprising the steps of: placing the probe on a coating that is on a substrate;   determining if the substrate is ferrous by measuring a magnetic flux density at a pole of a permanent magnet disposed in said gauge probe;   if it is determined that the substrate is ferrous, using said magnetic flux density to determine the coating thickness;   if it is determined that the substrate is not ferrous, then measuring effects of eddy currents generated in the substrate to determine the coating thickness.   
     
     
       12. The method of claim 11, further comprising the steps of: effecting temperature compensation of the magnetic flux density using a temperature sensor.   
     
     
       13. The gauge of claim 1, wherein the eddy current search coil comprises about 60 turns of 39 AWG wire wound in a pancake configuration with an inside diameter of about 3 mm, an outside diameter of about 5.25 mm, a thickness of about 0.5 mm. 
     
     
       14. The gauge of claim 1, wherein the eddy current search coil is excited by an alternating current oscillating with a frequency between about 6 MHz and about 12 MHz. 
     
     
       15. A gauge probe for a combination coating thickness gauge that allows the combination coating thickness gauge to measure both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, the gauge probe enabling the combination coating thickness gauge to determine automatically, with a single probe, substrate characteristics, and to effect a measurement of coating thickness on said characterized substrate, the gauge probe comprising: a controller;   a permanent magnet connected to said controller;   a Hall effect magnetic sensor connected to said controller, wherein said Hall effect magnetic sensor is disposed near a pole face of said permanent magnet so as to sense a magnetic field in a neighborhood of said pole face;   an eddy current search coil connected to said controller, wherein said eddy current search is disposed around the neighborhood of said pole face; and   a thermistor connected to said controller, wherein said thermistor is connected to said Hall effect magnetic sensor so as to sense temperature in a neighborhood of said Hall effect magnetic sensor, wherein said sensed temperature can be used to compensate a magnetic flux density measurement.   
     
     
       16. A gauge probe for a combination coating thickness gauge that allows the combination coating thickness gauge to measure both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, the gauge probe enabling the combination coating thickness gauge to determine automatically, with a single probe, substrate characteristics, and to effect a measurement of coating thickness on said characterized substrate, the gauge probe comprising: controller means;   a permanent magnet connected to said controller;   Hall effect magnetic sensor means connected to said controller means, wherein said Hall effect magnetic sensor means is disposed near a pole face of said permanent magnet for sensing a magnetic field in a neighborhood of said pole face;   an eddy current search coil connected to said controller means, wherein said eddy current search coil is disposed around the neighborhood of said pole face; and   thermistor means connected to said controller means, wherein said thermistor means is connected to said Hall effect magnetic sensor means for sensing temperature in a neighborhood of said Hall effect magnetic sensor means, wherein said sensed temperature can be used to compensate a magnetic flux density measurement.   
     
     
       17. The gauge probe for a combination coating thickness gauge of claim 15, the gauge probe further comprising: an indicator connected to said controller, wherein said indicator indicates said measurement of coating thickness on said characterized substrate.   
     
     
       18. The gauge probe for a combination coating thickness gauge of claim 16, the gauge probe further comprising: indicator means connected to said controller means, wherein said indicator means indicates said measurement of coating thickness on said characterized substrate.   
     
     
       19. The gauge probe for a combination coating thickness gauge of claim 15, the gauge probe further comprising: a user interface connected to said controller, wherein said user interface facilitates an interface between an operator and said controller.   
     
     
       20. The gauge probe for a combination coating thickness gauge of claim 16, the gauge probe further comprising: user interface means connected to said controller means, wherein said user interface means facilitates an interface between an operator and said controller means. .Iadd.   
     
     
       21.  A coating thickness gauge for measuring both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, comprising: a magnet having a pole face;   a magnetic flux density sensor disposed near the pole face of said magnet so as to sense a magnetic field in a neighborhood of said pole face;   an eddy current search coil disposed around the neighborhood of said pole face; and   control means for receiving inputs from said magnetic flux density sensor and said eddy current search coil, selecting one of said inputs for calculating a coating thickness, and calculating a coating thickness based on the selected input..Iaddend..Iadd.22. The gauge of claim 21, wherein said magnet, sensor, and eddy current search coil are located in a single gauge probe..Iaddend..Iadd.23. The gauge of claim 22, further comprising:   a temperature sensor connected to said magnetic flux density sensor so as to sense temperature in a neighborhood of said magnetic flux density sensor..Iaddend..Iadd.24. A coating thickness gauge for measuring both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, comprising:   a magnet having a pole face;   magnetic flux density sensor means disposed near the pole face of said magnet for sensing a magnetic field in a neighborhood of said pole face;   an eddy current search coil disposed around the neighborhood of said pole face;   temperature sensor means connected to said magnetic flux density sensor means for sensing temperature in a neighborhood of said magnetic flux density sensor means, wherein said sensed temperature can be used to compensate a magnetic field measurement of said magnetic flux density sensor means; and   control means for receiving inputs from said magnetic flux density sensor means and said eddy current search coil, selecting one of said inputs for calculating a coating thickness, and calculating a coating thickness based   
     
     
        on said selected input..Iaddend..Iadd.25.  A method for gauging thickness of both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, using a gauge probe for a combination coating thickness gauge, the gauge probe enabling the combination coating thickness gauge to determine automatically, with a single probe, substrate characteristics, and to effect a measurement of coating thickness on said characterized substrate, the method comprising the steps of: placing the gauge probe on a coating that is on a substrate;   determining if the substrate is ferrous by measuring a magnetic flux density at a pole of a magnet disposed in said gauge probe;   if it is determined that the substrate is ferrous, using said magnetic flux density to determine the coating thickness;   if it is determined that the substrate is not ferrous, then measuring effects of eddy currents generated in the substrate to determine the   
     
     
        coating thickness..Iaddend..Iadd.26.  The method of claim 25, further comprising the step of: effecting temperature compensation of the magnetic flux density using a temperature sensor..Iaddend..Iadd.27. An automatic combination coating thickness gauge for measuring both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, comprising:   a magnet having a pole face;   a magnetic flux density sensor disposed near the pole face of said magnet so as to sense a magnetic field in a neighborhood of said pole face;   an eddy current search coil disposed around the neighborhood of said pole face; and   control means for receiving inputs from said magnetic flux density sensor and said eddy current search coil, automatically selecting one of said inputs for calculating a coating thickness, and calculating a coating thickness based on the selected input..Iaddend..Iadd.28. The gauge of claim 27, wherein said magnet, sensor, and eddy current search coil are located in a single gauge probe..Iaddend..Iadd.29. The gauge of claim 28, further comprising:   a temperature sensor connected to said magnetic flux density sensor so as to sense temperature in a neighborhood of said magnetic flux density sensor..Iaddend..Iadd.30. A method for gauging thickness of both a nonferrous coating on a ferrous substrate and a nonconductive coating on a conductive nonferrous substrate, using a gauge probe for an automatic combination coating thickness gauge, the gauge probe enabling the combination coating thickness gauge to determine automatically, with a single probe, substrate characteristics, and to effect a measurement of coating thickness on said characterized substrate, the method comprising the steps of:   placing the gauge probe on a coating that is on a substrate;   determining if the substrate is ferrous by measuring a magnetic flux density at a pole of a magnet disposed in said gauge probe;   if it is determined that the substrate is ferrous, using said magnetic flux density to determine the coating thickness;   if it is determined that the substrate is not ferrous, then automatically switching the gauge probe over to test for a conductive nonferrous substrate; and   if it is determined that the substrate is a conductive nonferrous substrate, then measuring effects of eddy currents generated in the   
     
     
        substrate to determine the coating thickness..Iaddend..Iadd.31.  The method of claim 30, further comprising the step of: effecting temperature compensation of the magnetic flux density using a temperature sensor..Iaddend.