GB2306009A - Coating thickness gauge - Google Patents
Coating thickness gauge Download PDFInfo
- Publication number
- GB2306009A GB2306009A GB9620878A GB9620878A GB2306009A GB 2306009 A GB2306009 A GB 2306009A GB 9620878 A GB9620878 A GB 9620878A GB 9620878 A GB9620878 A GB 9620878A GB 2306009 A GB2306009 A GB 2306009A
- Authority
- GB
- United Kingdom
- Prior art keywords
- coating thickness
- winding
- dual function
- measuring probe
- thickness measuring
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000000576 coating method Methods 0.000 title claims abstract description 48
- 239000011248 coating agent Substances 0.000 title claims abstract description 46
- 238000004804 winding Methods 0.000 claims abstract description 92
- 239000000523 sample Substances 0.000 claims abstract description 50
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 claims abstract description 35
- 230000009977 dual effect Effects 0.000 claims abstract description 25
- 230000000694 effects Effects 0.000 claims abstract description 11
- 230000006698 induction Effects 0.000 claims abstract description 11
- 239000000463 material Substances 0.000 claims abstract description 8
- 230000003750 conditioning effect Effects 0.000 claims abstract description 5
- 230000005672 electromagnetic field Effects 0.000 claims description 18
- 230000000712 assembly Effects 0.000 claims description 16
- 238000000429 assembly Methods 0.000 claims description 16
- 239000000758 substrate Substances 0.000 claims description 15
- 230000004907 flux Effects 0.000 claims description 11
- 230000001939 inductive effect Effects 0.000 claims description 4
- 230000005674 electromagnetic induction Effects 0.000 abstract description 2
- 230000006870 function Effects 0.000 description 7
- 230000008859 change Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000035515 penetration Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000036039 immunity Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 239000000696 magnetic material Substances 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
- G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
- G01B7/10—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance
- G01B7/105—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance for measuring thickness of coating
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
Abstract
A dual function coating thickness measuring probe comprises a first winding assembly for a ferrous probe function comprising an induction winding 6 and two search or pick-up windings 5 and 7. A second winding assembly for a non-ferrous eddy current based probe function comprises a search winding 2 disposed on a non-magnetic and non-conductive former 9. A magnetic cylindrical core 1 of a material with a high resistance to impact and abrasive wear passes through the windings. A conductive non-magnetic coaxial screen 3 through which the core extends separates induction windings 5, 6 and 7 from eddy current winding 2. The position of the screen is such that it has a minimal effect on the eddy current winding whilst shielding its field from the electromagnetic induction windings. The windings are connected to signal conditioning circuitry which produces outputs representing the coating thickness measured. The probe automatically switches between the induction windings and eddy current winding in response to the nature of the article under test.
Description
A COATING THICKNESS MEASURING PROBE
The present invention relates to a dual function coating thickness measuring probe which can measure the thickness of coatings on both magnetic (ferrous) and non-magnetic (non4errous) substrates.
Instruments of this general nature are known, for example, from US 3,986,105, but these prior instruments are either complex or have operating problems caused by interference between those parts of the probe operative to provide the two functions.
According to the present invention, there is provided a dual function coating thickness measuring probe comprising a first winding assembly operative to generate a varying magnetic flux depending upon coating thickness to be measured and a second winding assembly operative to generate an electromagnetic field and thereby eddy currents which are dependant upon the coating thickness to be measured, and a screen disposed between the first and second winding assemblies operative to reduce any mutual inductive loading between the two winding assemblies.
In a prefened embodiment of the invention, a signal processing circuit processes signals received from the winding assemblies to give an indication of coating thickness. The first winding assembly comprises induction and search windings. Preferably there is one induction winding and two search windings. The second winding assembly comprises a search winding. Both winding assemblies are wound around a former and a magnetic core. The front face of this core is used as the point of contact with the coating to be measured. The core is advantageously cylindrical, mounted on the axis of symmetry of the probe and made of material with a high resistance to impact and wear. The screen is advantageously coaxially arranged with the winding assemblies and surrounds the core.The screen may be a metal disc or other metallic windings and may be positioned such that its effect on the first or second winding assembly is small compared with the effect of the substrate. The screen should be positioned a fixed distance away from one or both of the winding assemblies so that its effect is the same for all probes. The material and thickness of the screen is advantageously chosen so that it has only a small effect on either winding assembly and the signals they produce. The winding assemblies may all be wound on a single former or on separate formers. Processing software can be devised to determine the cunent substrate of the coating being measured by analysing the values of the signals produced by the signal processing circuitry.
Automatic selection of the ferrous or non-ferrous mode can be determined by identifying the level of signal from the first (ferrous) winding assembly and associated signal conditioning and using this as an absolute reference of ferritic material.
In order that the invention may be more clearly understood, one embodiment thereof will now be described by way of example with reference to the accompanying drawing, in which:
Figure 1 diagrammatically shows a side elevational view in crosssection of one form of dual function coating thickness measuring probe according to the invention, adjacent a coating to be measured,
Figure 2 diagrammatically shows a side elevational view in crosssection of another form of probe to that shown in figure 1, and
Figure 3 shows a block circuit diagram of circuitry forming the signal conditioning and display system for the probe of figures I or 2.
Referring to the drawings, the ferrous probe, for use on magnetic (ferrous) substrates, comprises a set of three windings 5,6 and 7 disposed on a non-magnetic and non-conductive former 8. The three windings are configured in such a manner that they share a common axis of cylindrical symmetry XV. There is one induction winding 6 and two search or pick-up windings 5 and 7. The non-ferrous probe, for use on non-conductive coatings on conductive but non-magnetic (nonferrous) substrates, is comprised of only one search winding 2. This winding is situated on a nonmagnetic and non-conductive former 9 and is used as a high frequency eddy current detector.
A magnetic cylindrical pin I of a material with a high resistance to impact and abrasive wear, passes through windings 2,5,6 and 7. The pin is situated on the axis of cylindrical symmetry of the probe XV. The front face II of the pin I is used as the point of contact of the probe with the coated (or uncoated) substrate 13, 15. The probe is oriented in an outer sleeve (not shown) in such a way that it is always presented at a right angle to the plane of the substrate.
A conductive non-magnetic coaxial screen in the form of a metallic annulus 3, through which the pin I passes, separates the ferrous windings 5,6 and 7 from the non-ferrous winding 2. The conductive screen is positioned such that it has a minimal effect on the eddy current winding, whilst shielding its field from the electromagnetic induction windings. A cylindrical non-magnetic and non-conductive shroud 10 is used to cover and protect the non-fenous winding. A cylinder 4 of magnetic material encloses the ferrous windings 5,6 and 7. The probe winding wires 14 are terminated on a printed circuit board 12 which is situated on the rear face of the nonmagnetic and non-conductive former 8.The embodiment shown in Figure 2 is the same as that shown in Figure 1 except that the metallic annulus 3 is replaced by a metallic winding 33 which is wound on a single former 38 which replaces formers 8 and 9. In other respects the embodiments of
Figures 1 and 2 are the same.
In use a time varying fixed low frequency (up to several KiloHertz) sinusoidal electric current is supplied to the induction winding 6 which generates an electromagnetic time varying field. The magnetic flux which is associated with the electromagnetic field flows in a closed loop about the induction winding 6. The magnetic pin I provides a low reluctance (magnetic resistance) path for the flow of magnetic flux. This means that the magnetic flux is presented to the measuring surface through the front face II of the probe tip. The magnetic cylinder 4 which encompasses the ferrous windings 5,6 and 7 also offers a low reluctance path and therefore functions as a return path for the flow of magnetic flux. The cylinder 4 gives the probe a degree of immunity from electromagnetic interference, it also reduces the effect of complex substrate geometries on the distribution of magnetic flux.The coaxial screen 3 is positioned in such a way that the magnetic flux must pass through it at some point. This will result in some of the energy of the electromagnetic field being given up as heat to the coaxial screen 3. As the electromagnetic field from winding 6 passes through the screen, eddy currents are generated in the screen which oppose the applied electromagnetic field and modify it. As the thickness of the coaxial screen is very much less than the penetration depth of the electromagnetic field only a minimal amount of energy is lost to the screen.
This will take the form of a mutual inductive loading on the ferrous windings 5,6 and 7. The search windings 5,7 generate an EMF which is a measure of the rate at which magnetic flux is cutting each search winding 5,7. The amount of magnetic flux present is dependent upon the coating thickness 13 covering the substrate 15 and has been found to vary logarithmically with coating thickness. A differential signal (EMF) taken between the search windings 5,7 is presented to the electronic circuits for processing.
The non-ferrous search winding 2 generates a high frequency electromagnetic field. As in the case of the ferrous induction winding 6 the non-ferrous search winding has an associated magnetic flux which flows in a closed loop about the search winding 2. The electromagnetic field generated by the search winding 2 interacts with the substrate of the coated surface 15. This interaction dissipates energy from the electromagnetic field mainly as heat in the form of eddy currents which flow within the confines of the substrate 15. The eddy currents in turn generate an electromagnetic field which opposes the applied electromagnetic field of the search winding 2. The effect of this is to change the impedance of the search winding 2 which is then monitored and used as a measurement of coating thickness.An alternative approach could use the variation in inductance of the search winding and thereby a variation in frequency of the electromagnetic field to provide an indication of coating thickness 13. The change in search winding 2 impedance has been found to vary in a logarithmic manner with coating thickness. The electromagnetic field which interacts with the coaxial screen 3 responds in a similar fashion to the substrate of the coated surface 13. Since the penetration depth of the electromagnetic field at high frequencies (frequencies greater than one
MegaHertz) is much less than the thickness of the screen 3 none of the electromagnetic field is able to interact with the ferrous windings 5,6,7.All the energy of the applied electromagnetic field taken into the screen is used in the establishment of eddy currents which re-radiate the electromagnetic field in the manner already described. The coaxial screen 3 then vastly reduces any mutual inductive loading which would exist between the nonferrous winding 2 and the ferrous windings 5,6,7.
Referring to Figure 3 the ferrous and non-ferrous winding assemblies 2,5,6 and 7 are connected to two separate ferrous and non-ferrous electronic circuits 16 and 24 for signal conditioning. The ferrous circuit 16 derives a signal relating to coating thickness from the ferrous search windings 5,7. The non-ferrous circuit 24 excites the eddy current probe with a fixed amplitude signal 17 via a resistor 25. The signal from the probe then has a level of phase offset compensation applied 18. The sinusoidal signal produced by the ferrous and non-ferrous circuits 16 and 24 varies in both phase and amplitude with respect to the thickness of the applied coating 13, and is converted to a DC level by means of an AC to DC stage 19, 20.The output from either AC to DC converter may be selected by a switching device to determine their respective signal amplitude levels.
These levels may then be used by a processing device to determine the status of the ferrous 5,7 or non-ferrous windings 2. Initially the processing device 21 switches on the ferrous circuitry 16 and evaluates the returned signal. If this signal is within the measuring range of the instrument, then the signal is converted into a thickness measurement by the use of a look up table 22 which is resident in non-volatile memory. This would then be displayed on a display device 23. If this signal is not within its measuring range, then the non-ferrous signal amplitude level is evaluated. If this signal is within its measuring range, then the signal is converted into a thickness value by the use of another separate look up table 22 stored in non-volatile memory.Should neither signal be within their measuring range then the instrument carries out a full self calibration and repeats the process awaiting a valid reading.
In the above embodiment only one probe is needed for use on both types of substrate, which would not be possible for single function probes.
The processing system decides upon the appropriate probe function, which takes the decision out of the hands of the operator, who may well be nontechnically minded. For work done in the field there is no possibility of selecting and using the wrong type of probe for the required application, which would possibly result in loss of time, incorrect data and costly reworking. As the probe is manufactured from simple turned components and windings, assembly of the object is far simpler and more cost effective than other products which currently exist on the market.
It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention.
Claims (21)
1. A dual function coating thickness measuring probe comprising a first winding assembly operative to generate a varying magnetic flux depending upon coating thickness to be measured and a second winding assembly operative to generate an electromagnetic field and thereby eddy currents which are dependant upon the coating thickness to be measured, and a screen disposed between the first and second winding assemblies operative to reduce any mutual inductive loading between the two winding assemblies.
2. A dual function coating thickness measuring probe as claimed in claim 1, in which the first winding assembly comprises induction and search windings.
3. A dual function coating thickness measuring probe as claimed in claim 1 or 2, in which the first winding assembly comprises one induction winding and two search windings.
4. A dual function coating thickness measuring probe as claimed in claim 1, 2 or 3, in which the second winding assembly comprises a search winding.
5. A dual function coating thickness measuring probe as claimed in any preceding claim, in which both winding assemblies are wound around a former and a magnetic core.
6. A dual function coating thickness measuring probe as claimed in claim 5, in which the front face of this core is used as the point of contact with the coating to be measured.
7. A dual function coating thickness measuring probe as claimed in claim 5 or 6, in which the core is cylindrical.
8. A dual function coating thickness measuring probe as claimed in claim 5, 6 or 7, in which the core is mounted on the axis of symmetry of the probe.
9. A dual function coating thickness measuring probe as claimed in claim 5, 6, 7 or 8, in which the core is made of material with a high resistance to impact and wear.
10. A dual function coating thickness measuring probe as claimed in any preceding claim, in which the screen is advantageously coaxially arranged with the winding assemblies and surrounds the core.
11. A dual function coating thickness measuring probe as claimed in any preceding claim, in which the screen is an annulus.
12. A dual function coating thickness measuring probe as claimed in any of claims I to 10, in which the screen is a metallic winding.
13. A dual function coating thickness measuring probe as claimed in any preceding claim, in which the screen is positioned such that its effect on the first or second winding assembly is small compared with the effect of the substrate.
14. A dual function coating thickness measuring probe as claimed in claim 13, in which the screen is positioned a fixed distance away from one or both of the winding assemblies.
15. A dual function coating thickness measuring probe as claimed in any preceding claim, in which the material and thickness of the screen is chosen so that it has only a small effect on either winding assembly and the signals they produce in operation.
16. A dual function coating thickness measuring probe as claimed in any preceding claim, in which the winding assemblies may be wound on a single former.
17. A dual function coating thickness measuring probe as claimed in any of claims 1 to 15, in which the winding assemblies may be wound on separate formers.
18. A dual function coating thickness measuring probe as claimed in any preceding claim, in which a signal processing circuitry is provided for processing signals received from the winding assemblies to give an indication of coating thickness.
19. A dual function coating thickness measuring probe as claimed in claim 18, in which processing means are provided for determining the current substrate of the coating being measured and for analysing the values of the signals produced by the signal processing circuitry.
20. A dual function coating thickness measuring probe as claimed in claim 18 or 19, in which means are provided for automatically selecting a ferrous or non-ferrous mode by identifying the level of signal from the first (ferrous) winding assembly and associated signal conditioning and using this as an absolute reference of ferritic material.
21. A dual function coating thickness measuring probe substantially as hereinbefore described with reference to Figure 1, 2 or 3 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9620878A GB2306009B (en) | 1995-10-05 | 1996-10-07 | A coating thickness measuring probe |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GBGB9520515.9A GB9520515D0 (en) | 1995-10-05 | 1995-10-05 | A thickness coating measuring instrument |
| GB9620878A GB2306009B (en) | 1995-10-05 | 1996-10-07 | A coating thickness measuring probe |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9620878D0 GB9620878D0 (en) | 1996-11-27 |
| GB2306009A true GB2306009A (en) | 1997-04-23 |
| GB2306009B GB2306009B (en) | 1999-06-16 |
Family
ID=26307906
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9620878A Expired - Fee Related GB2306009B (en) | 1995-10-05 | 1996-10-07 | A coating thickness measuring probe |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2306009B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2806790A1 (en) * | 2000-03-24 | 2001-09-28 | Helmut Fischer Gmbh & Co | METHOD AND DEVICE FOR NON-DESTRUCTIVE MEASUREMENT OF THE THICKNESS OF THIN LAYERS |
| GB2367135A (en) * | 2000-07-06 | 2002-03-27 | Elcometer Instr Ltd | Dual sensitivity coating thickness measuring instrument |
| NL1027373C2 (en) * | 2004-10-29 | 2006-05-03 | Sonimex B V | Method and device for non-destructive examination of an object. |
| US20140039830A1 (en) * | 2012-08-06 | 2014-02-06 | Hon Hai Precision Industry Co., Ltd. | Test device to measure coating thickness and test system |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2257520A (en) * | 1991-06-25 | 1993-01-13 | Helmut Fischer Gmbh & Co | Method and device for measuring the thickness of thin layers |
| EP0576714A1 (en) * | 1992-07-03 | 1994-01-05 | Norbert Dr. Nix | Magnetic induction and Eddy current probe for measuring the thickness of a layer |
-
1996
- 1996-10-07 GB GB9620878A patent/GB2306009B/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2257520A (en) * | 1991-06-25 | 1993-01-13 | Helmut Fischer Gmbh & Co | Method and device for measuring the thickness of thin layers |
| EP0576714A1 (en) * | 1992-07-03 | 1994-01-05 | Norbert Dr. Nix | Magnetic induction and Eddy current probe for measuring the thickness of a layer |
| US5467014A (en) * | 1992-07-03 | 1995-11-14 | Nix; Norbert | Device for measuring the thickness of a layer or coating on a ferrous and/or non-ferrous substrate |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2806790A1 (en) * | 2000-03-24 | 2001-09-28 | Helmut Fischer Gmbh & Co | METHOD AND DEVICE FOR NON-DESTRUCTIVE MEASUREMENT OF THE THICKNESS OF THIN LAYERS |
| GB2361999A (en) * | 2000-03-24 | 2001-11-07 | Helmut Fischer Gmbh & Co | Layer thickness measurement |
| GB2361999B (en) * | 2000-03-24 | 2005-02-23 | Helmut Fischer Gmbh & Co | Method and apparatus for the nondestructive measurement of the thickness of thin layers |
| GB2367135A (en) * | 2000-07-06 | 2002-03-27 | Elcometer Instr Ltd | Dual sensitivity coating thickness measuring instrument |
| GB2367135B (en) * | 2000-07-06 | 2004-06-23 | Elcometer Instr Ltd | Dual mode coating thickness measuring instrument |
| NL1027373C2 (en) * | 2004-10-29 | 2006-05-03 | Sonimex B V | Method and device for non-destructive examination of an object. |
| WO2006046859A1 (en) * | 2004-10-29 | 2006-05-04 | Sonimex Bv | Device for non-destructively examining an object |
| US20140039830A1 (en) * | 2012-08-06 | 2014-02-06 | Hon Hai Precision Industry Co., Ltd. | Test device to measure coating thickness and test system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2306009B (en) | 1999-06-16 |
| GB9620878D0 (en) | 1996-11-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20111007 |