CA1230379A - Measuring the thickness of a non-metallic coating on an arcuate metal surface - Google Patents
Measuring the thickness of a non-metallic coating on an arcuate metal surfaceInfo
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- CA1230379A CA1230379A CA000485969A CA485969A CA1230379A CA 1230379 A CA1230379 A CA 1230379A CA 000485969 A CA000485969 A CA 000485969A CA 485969 A CA485969 A CA 485969A CA 1230379 A CA1230379 A CA 1230379A
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Abstract
MEASURING THE THICKNESS OF A NON-METALLIC
COATING ON AN ARCUATE METAL SURFACE
ABSTRACT OF THE DISCLOSURE
Measuring the thickness of a non-metallic coating on an arcuate metal surface of an article by engaging the coating with a measuring head which carries a sensing member of a reactance monitoring means, and creating an electromagnetic field in the region of the head and in adjacent regions of the coated surface. The reactance which is affected by the position and degree of curvature of the metal surface is then measured and produces a first signal indicative of the apparent thickness of the coating in the regions adjacent the head for a given degree of surface. The degree of curvature of the metal surface is also monitored for the regions adjacent the head to provide a second signal indicative of the actual degree of curvature. A correction factor which is dependent upon the second signal is then caused to influence the first signal and produce a modified signal which more accurately represents the true thickness of the part of the coating being measured.
- i -
COATING ON AN ARCUATE METAL SURFACE
ABSTRACT OF THE DISCLOSURE
Measuring the thickness of a non-metallic coating on an arcuate metal surface of an article by engaging the coating with a measuring head which carries a sensing member of a reactance monitoring means, and creating an electromagnetic field in the region of the head and in adjacent regions of the coated surface. The reactance which is affected by the position and degree of curvature of the metal surface is then measured and produces a first signal indicative of the apparent thickness of the coating in the regions adjacent the head for a given degree of surface. The degree of curvature of the metal surface is also monitored for the regions adjacent the head to provide a second signal indicative of the actual degree of curvature. A correction factor which is dependent upon the second signal is then caused to influence the first signal and produce a modified signal which more accurately represents the true thickness of the part of the coating being measured.
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Description
MEASURING THE THICKNESS Of A NON-METAL~IC
COATING ON AN ARCUATE METAL SURFACE
This inven-tion relates to the measuring of the thickness of a non-metallic coating, on an arcuate metal surface.
In the production of metal articles having a non-metallic coating such as a plastics material it is desirable to control the -thickness of the coating for certain reasons, including -that of economy. In the production of one such article, i.e. an electrical cable such as a telecommunications cable, then a non-metallic coating in the form of a jacket around the cable should have a desirable minimum thickness commensurate with meeting specification requirements for the cable. Such a jacket is provided by an extrusion process and it is well-known that the thickness of the extrusion can vary. Such a variation may be caused by either the cable core not being centrally located within the extrusion die, or by the core having an oval cross-sectional configura-tion as distinct from a desirable true circular configuration. For such a product, it is well-known to provide a quality control procedure which entails the measuring of the jacket thickness at various positions circumferentially around the cable to enable the extrusion process to be controlled so as to produce a jacket having a thickness at any position which lies between desirable limi-ts.
Capaci-tance type measuring devices are used widely for the purpose of measuring jacket thickness upon cable coreO Usually, a measuring head is rotated about the cable axis and the head is held stationary for a short predetermined time at predetermined angular positions around the cable.
There are certain disadvantages with capacitance type measuring devices. The presence of water affects the measurement as ~3~
such devices are extremely sensitive to water. Further to this, variations are of-ten made to the composition of an extrusion material for forming a jacket and this has an effect upon the capacitance.
Thus, variation in the composition of the material affects the measurements taken by the measuring head thus requiring recalibration.
These problems lead to inaccuracies in the measurements taken, thereby producing results which are unreliable for the purpose of controlling the thickness of the extruded jacket by adjustments to the extrusion apparatus or to the line speed of the cable core.
These problems inherent in the use of capacitance type measuring devices were overcome with the use of an inductance type measuring device as described in U.S. patent 4,053,827, granted Octsber 11, 1977, entitled "Apparatus for Measuring, and Indicating, the Thickness of a Non-Metallic Coating on an Arcuate Metal Surface", in the names of L.G. Millette, P. Murphy, G.M. Miller and W.J. Tyszewicz.
In addition to this, another U.S. patent concerns a measuring apparatus for the thickness of a non-metallic coating which involved a particular profiled surface shape for a support member for a measuring head. This support member is conveniently for use with an inductance type measuring head and for use in the apparatus described in U.S. patent 4,053,827 referred to aboveO The apparatus having the particular profiled surface on the support member is as described in U.S. patent 4,051,430, granted September 27, 1977, enti-tled "Apparatus for Measuring and Indicating the Thickness of a Non-Metallic Coating of an Arcuate Metal Surface" in the names oF L.G. Millette, P. Murphy and G.M. Miller. As described in the latter speciFication, the support member may be used upon a range of diameters of cable for measuring the thickness of a jacket, thereby reducing the number of support members required for a complete range of cable diameters.
The apparatus described in both of the aforementioned patents is commercially successful in helping to control the thickness of jacket material upon an electrical cable. Ho~ever, measurements ~hich are taken with the apparatus described in the above two patents and - 5 also upon previous capacitance type measuring devices, all relate to a theoretically desirable circular cable core shape. Inductance or capacitance measurements taken by a sensing means positioned in the measuring head adjacent to an arcuate metal surface depend not only on the distance of the sensing device from the metal surface but also upon the degree of curvature of that surface. Thus, if the degree of curvature is known, such as is the case for a predetermined completely circular object, then the inductance measurements may be used to substantially accurately determine the thickness of the non-metallic coating. However, should the degree of curvature of the arcuate metal surFace differ from the supposed degree of curvature, then this changes the inductance measurements to values which are interpreted to represent the thickness of non-metallic coatings upon arcuate metal surfaces having the supposed degree of curvature. It follows that if ; the arcuate metal surface has shapes other than substantially circular, i.e. oval, then the inductance measurements at any pos~tion around the circumference of such an oval surface will be affected by the degree of curvature at any particular position. ~ence, the inductance measurements on such an oval surface will produce values which while being interpreted as representing thicknesses of the coatings upon the metal surface of a particular diameter, will in fact be misinterpreted and give inaccurate results. If inaccurate results are given, then the coating thickness cannot be accurately controlled.
The particular problems discussed above in relation to both capacitance and inductance measuring devices are particularly relevant ,~
,., . ~
4 ~ ~3~37~
in the electrical cable field. For instance, in the manufacture of a telecommunications cable, a cross-sectional oval shape is commonp1aee.
The present invention provides a method and apparatus for measuring the thickness of a non-metallic coating on an arcuate metal - 5 surface in which the inaccuracies in measurement discussed above are reduced.
Accordingly, the present invention provides a method of measuring the thickness of a non-metallic coating on an arcuate metal surface of an article having an ovality, said method comprising:
engaging a part of the coating with a measuring head ~hich carries a sensing element having a reactance which is affected by the position and degree of curvature of the arcuate metal surface, monitoring hte reactance of the sensing element to produce a first signal indicative of the apparent thickness of the coating in a region adjacent to the measuring head for a given degree of surface curvature, monitoring the degree of curvature of the coated metal surface in said adjacent region to provide a second signal indicative of the actual degree of curvature of said adjacent region by measuring the diameter of the surface between two opposed positions around the circumference of the article with the part of the coating engaged by the measuring head disposed intermediate these positions, the measured diameter being representative of a particular degree of curvature and the second signal indicative of the measured diameter; and applying a correction factor dependent upon the second signal to influence the first signal and produce a modified signal which more accurately represents the true thickness of said part of the coating.
It follows that in the above method, apparatus may be calibrated for measuring non-metallic coating thicknesses upon articles having a truly cylindrical shape of a particular diameter and may be , ~ .
4 a ~0~
used to indicate the thickness upon an oval shaped metal surface whic'n is nominally of that diameter, by measuring the degree of curvature of the coated surface to apply the correction factor so as to adjust the first signal to~ards a more accurate signal relating to the thickness - of the coating.
3~
In the above method where the article has an arcuate metal surface which is continuous around the article and has an ovality, the degree of curvature is monitored by measuring the diameter of the surface between two opposed positions having the coating part disposed intermediate these positions such that the diameter is representative of a particular degree of curvature. The method includes providing the second signal based upon the diameter measurement.
The invention also includes an apparatus for measuring the thickness of a non-metallic coating on an arcuate annular metal surface of an article having an ovality, the apparatus comprising: a measuring head for positioning against a part of said coating, the measuring head including a sensing element having a reactance which is affected by the position and degree of curvature of said arcuate metal surface; at least one support member for supporting said measuring head relative to said coating; reactance monitoring means for monitoring the reactance of the sensing element to develope a first signal representative of the apparent distance between the sensing member and the metal surface and thus of the apparent thickness of the coating for a given degree of curvature of the metal surface; curvature monitoring means for providing a second signal indicative of the degree of survature of the coated metal surface in regions adjacent to said part of the coating, said curvature monitoring means comprising means for measuring hte diameter of the surface between two opposed positions disposed to opposite sides of the measuring head, the measured diameter being representative of a particular degree of curvature and the second signal being indicative of the measured diameter, and means responsive to the first and second signals for appying a correction factor, dependent upon the second signal, to influence the first signal and produce a corrected signal which more accurately represents the true "~ .
5a ~ ,3~
thickness of said part of the coating.
In the apparatus according to the invention, the curvature monitoring means comprises a diameter measuring means for measuring the diameter of the coated arcuate metal surface at a position such that said coating part is disposed intermediate to opposed positions across the article at which the diameter measurement is taken.
One embodiment of the invention will now be described by way of example, w~th reference to the accompanying drawings in which:-Figure 1 is part of a block schemat;c diagram of a circuit and accompanying thickness measuring apparatus for providing measurements of jacket thickness on a telecommunications cable - 5 structurej Figure 2 is a cross-section taken along a longitudinal axis of a measuring head of the thickness measuring apparatus and on a larger scale;
Figure 3 is a side view of one form of measuring head probe which is included in the measuring head of Figure 2 and on a larger scale than Figure 2;
Figure 4 is on a smaller scale than Figure 3 and is a perspective view of a plurality oF measuring heads in an assembly and shown in greater detail than is shown in Figure l;
Figure 5 is a diagrammatic cross-sectional view taken through a cable and in the axial direction to show the measuring head assembly ; and its relationship to a diameter measuring means also included in the apparatus; and Figure 6 is another part of the block schematic circuit of Figure l.
As shown in Figure 1, apparatus is provided for measuring the thickness of a polymeric jacket 8 of a telecommunications cable 10 and formed around an arcuate metal surface in the form of a metallic sheath 12 (see Figure 5) provided around a core 1~ of the cable. The cable is of a conventional construction for telecommunications cables and the : core is formed from any required number of twisted together pairs of insulated conductors.
: The apparatus comprises four measuring head and support assemblies 16 (shown in Figure 1) which are spaced apart at 90 6a ~3~
intervals around a centre which coincides with the feedpath for t'ne 7 ~3~33~
cable. For ease of description later in the specification, the four measuring head and support assemblies are designated 16A, 16B, 16C and 16D. The four assemblies are of the same common design, which is shown in Figure 2 for assembly 16A~ Assembly 16A comprises a housing 18 which encloses d support member 22 for a measuring head 24. Each measuring head 24 comprises an elongated housing 26. Two probes 28 (to be described) are mounted in the housing 26, a probe at each end of the housing~ Only one probe is active while the other probe is inactive.
The two probes are generally of cylindrical form, as shown with reference to Figures 2 and 3~ and the active probe has a sensing element 29 which is a coil wound around the active probe and forms part of an oscillator circuit (to be described) of a reactance monitoring means. The head 24 is attached to a support rod 30 by a flexible diaphragm 32 which is secured to the housing 26. The rod is attached at its other end to a slide member 34, which is slidable on a rod 36.
The rod 36 is mounted at one end directly to the housing 18 and, at the other end within support member 22. A damper 38 damps movement of the slide member 34~ To restrict khe movement of the head 24 beyond desirable limits, a short projecting member 40 on the rod 30 moves within an enclosure 42 mounted on the housing 26. A spring 44 provides a load on the slide member 34. In the particular example, the rod 30 is pivotally attached to the slide member 34 by a pin 46. A shear pin 48 prevents pivotting of the rod 30 except in emergencies.
The positioning and support structure assembly 49 comprises a support back plate 50 which carries each of the measuring head and support assemblies 16A, 16B, 16C and 16D. The mounting of the assemblies is provided by cantilever arms 52 which are secured to outer ends of the housings 18 and are attached to racks 54 which extend radially of the back plate 50 and are movable radially within brackets 8 ~3~37~
56 mounted upon the back plate. Extending axially from the back plate 50 are four pinions 58 fixed on shafts 60 and the pinions engage one with each of the racks 54. The positioning and support structure assembly and each measuring head and support assembly 16 is described in greater detail as in U.S. Patent Numbers 4,051,430 and 4,053,827.
Each shaft 60 has a chain gear (not shown) at the other side of the back plate 50 with a chain (not shown) passing over each chain gear, the chain being movable to rotate the pinions 58 synchronously so as to move the heads 16A to 16D radially in or out from the axis of the back plate. Such movement is required during initial setting up or disassembly of the apparatus so as to locate the measuring heads correctly upon the apparatus, as shown in Figure 4.
As shown particularly in Figure 3, each of the probes 26 has a stem portion 62 and a head portion 64. The stem portion 62 is mounted within the housing 26 and the coil 29 is positioned within a groove 66, as shown in Figure 3. The head portion 64 is circular in plan view and, when viewed in side elevation in a direction coincident with the axis of the cable, it has a contact surface 68 which is profiled in a predetermined manner. The profile of the surface 68 is obtained from calibration curves in such a way that9 for a given jacket thickness, the inductance of the coil 29, when the contact surface 68 is brought into contact with a cable jacket, remains substantially constant oYer a range of cable diameters. The profile of the surface is obtained in the manner described in U~S. patent ~,051,430, referred to above. A bore 70 extends axially through the probe. The bore may contain a tuning element (not shown) such as a slug or core of appropriate material, such as ferrite. ~y such tuning elements an individual head can be tuned and in an apparatus using a plurality of heads, as in this embodiment, tuning of the heads can be matched. The 11S, ~
~3~.3~9 tuning element can vary the sensitivity of the probe and change its resonant frequency.
As indicated above, the coils 29 form parts of oscillator circuits which are provided in the reactance monitoring means. The resonant frequencies of the circuits are varied by variations in the inductive effect of each probe, resulting from variations in the distance of the metallic surface of the sheath 12 from a probe datum.
Such variations of frequency are utilized in this apparatus to produce signals indicative of the variation in thickness of the jacket, such as on dial indicators and/or chart recorders. The circuits for providing this facility are shown in Figure lo Operation of part of this circuit and which provides an indication of jacket thickness is as described in U.S. Patent Number 4,053,827. The measurements obtained with this particular part of the circuit do not take into account any variation 15 in the inductive effect caused by ovality of the cable, but may be used as a general guide by a machine operator of the thickness of the jacket and the centralization of the cable core together and the sheath within in the jacket. This part of the circuit which operates in the manner described in UOS. patent 4,053,827 operates basically in the following
COATING ON AN ARCUATE METAL SURFACE
This inven-tion relates to the measuring of the thickness of a non-metallic coating, on an arcuate metal surface.
In the production of metal articles having a non-metallic coating such as a plastics material it is desirable to control the -thickness of the coating for certain reasons, including -that of economy. In the production of one such article, i.e. an electrical cable such as a telecommunications cable, then a non-metallic coating in the form of a jacket around the cable should have a desirable minimum thickness commensurate with meeting specification requirements for the cable. Such a jacket is provided by an extrusion process and it is well-known that the thickness of the extrusion can vary. Such a variation may be caused by either the cable core not being centrally located within the extrusion die, or by the core having an oval cross-sectional configura-tion as distinct from a desirable true circular configuration. For such a product, it is well-known to provide a quality control procedure which entails the measuring of the jacket thickness at various positions circumferentially around the cable to enable the extrusion process to be controlled so as to produce a jacket having a thickness at any position which lies between desirable limi-ts.
Capaci-tance type measuring devices are used widely for the purpose of measuring jacket thickness upon cable coreO Usually, a measuring head is rotated about the cable axis and the head is held stationary for a short predetermined time at predetermined angular positions around the cable.
There are certain disadvantages with capacitance type measuring devices. The presence of water affects the measurement as ~3~
such devices are extremely sensitive to water. Further to this, variations are of-ten made to the composition of an extrusion material for forming a jacket and this has an effect upon the capacitance.
Thus, variation in the composition of the material affects the measurements taken by the measuring head thus requiring recalibration.
These problems lead to inaccuracies in the measurements taken, thereby producing results which are unreliable for the purpose of controlling the thickness of the extruded jacket by adjustments to the extrusion apparatus or to the line speed of the cable core.
These problems inherent in the use of capacitance type measuring devices were overcome with the use of an inductance type measuring device as described in U.S. patent 4,053,827, granted Octsber 11, 1977, entitled "Apparatus for Measuring, and Indicating, the Thickness of a Non-Metallic Coating on an Arcuate Metal Surface", in the names of L.G. Millette, P. Murphy, G.M. Miller and W.J. Tyszewicz.
In addition to this, another U.S. patent concerns a measuring apparatus for the thickness of a non-metallic coating which involved a particular profiled surface shape for a support member for a measuring head. This support member is conveniently for use with an inductance type measuring head and for use in the apparatus described in U.S. patent 4,053,827 referred to aboveO The apparatus having the particular profiled surface on the support member is as described in U.S. patent 4,051,430, granted September 27, 1977, enti-tled "Apparatus for Measuring and Indicating the Thickness of a Non-Metallic Coating of an Arcuate Metal Surface" in the names oF L.G. Millette, P. Murphy and G.M. Miller. As described in the latter speciFication, the support member may be used upon a range of diameters of cable for measuring the thickness of a jacket, thereby reducing the number of support members required for a complete range of cable diameters.
The apparatus described in both of the aforementioned patents is commercially successful in helping to control the thickness of jacket material upon an electrical cable. Ho~ever, measurements ~hich are taken with the apparatus described in the above two patents and - 5 also upon previous capacitance type measuring devices, all relate to a theoretically desirable circular cable core shape. Inductance or capacitance measurements taken by a sensing means positioned in the measuring head adjacent to an arcuate metal surface depend not only on the distance of the sensing device from the metal surface but also upon the degree of curvature of that surface. Thus, if the degree of curvature is known, such as is the case for a predetermined completely circular object, then the inductance measurements may be used to substantially accurately determine the thickness of the non-metallic coating. However, should the degree of curvature of the arcuate metal surFace differ from the supposed degree of curvature, then this changes the inductance measurements to values which are interpreted to represent the thickness of non-metallic coatings upon arcuate metal surfaces having the supposed degree of curvature. It follows that if ; the arcuate metal surface has shapes other than substantially circular, i.e. oval, then the inductance measurements at any pos~tion around the circumference of such an oval surface will be affected by the degree of curvature at any particular position. ~ence, the inductance measurements on such an oval surface will produce values which while being interpreted as representing thicknesses of the coatings upon the metal surface of a particular diameter, will in fact be misinterpreted and give inaccurate results. If inaccurate results are given, then the coating thickness cannot be accurately controlled.
The particular problems discussed above in relation to both capacitance and inductance measuring devices are particularly relevant ,~
,., . ~
4 ~ ~3~37~
in the electrical cable field. For instance, in the manufacture of a telecommunications cable, a cross-sectional oval shape is commonp1aee.
The present invention provides a method and apparatus for measuring the thickness of a non-metallic coating on an arcuate metal - 5 surface in which the inaccuracies in measurement discussed above are reduced.
Accordingly, the present invention provides a method of measuring the thickness of a non-metallic coating on an arcuate metal surface of an article having an ovality, said method comprising:
engaging a part of the coating with a measuring head ~hich carries a sensing element having a reactance which is affected by the position and degree of curvature of the arcuate metal surface, monitoring hte reactance of the sensing element to produce a first signal indicative of the apparent thickness of the coating in a region adjacent to the measuring head for a given degree of surface curvature, monitoring the degree of curvature of the coated metal surface in said adjacent region to provide a second signal indicative of the actual degree of curvature of said adjacent region by measuring the diameter of the surface between two opposed positions around the circumference of the article with the part of the coating engaged by the measuring head disposed intermediate these positions, the measured diameter being representative of a particular degree of curvature and the second signal indicative of the measured diameter; and applying a correction factor dependent upon the second signal to influence the first signal and produce a modified signal which more accurately represents the true thickness of said part of the coating.
It follows that in the above method, apparatus may be calibrated for measuring non-metallic coating thicknesses upon articles having a truly cylindrical shape of a particular diameter and may be , ~ .
4 a ~0~
used to indicate the thickness upon an oval shaped metal surface whic'n is nominally of that diameter, by measuring the degree of curvature of the coated surface to apply the correction factor so as to adjust the first signal to~ards a more accurate signal relating to the thickness - of the coating.
3~
In the above method where the article has an arcuate metal surface which is continuous around the article and has an ovality, the degree of curvature is monitored by measuring the diameter of the surface between two opposed positions having the coating part disposed intermediate these positions such that the diameter is representative of a particular degree of curvature. The method includes providing the second signal based upon the diameter measurement.
The invention also includes an apparatus for measuring the thickness of a non-metallic coating on an arcuate annular metal surface of an article having an ovality, the apparatus comprising: a measuring head for positioning against a part of said coating, the measuring head including a sensing element having a reactance which is affected by the position and degree of curvature of said arcuate metal surface; at least one support member for supporting said measuring head relative to said coating; reactance monitoring means for monitoring the reactance of the sensing element to develope a first signal representative of the apparent distance between the sensing member and the metal surface and thus of the apparent thickness of the coating for a given degree of curvature of the metal surface; curvature monitoring means for providing a second signal indicative of the degree of survature of the coated metal surface in regions adjacent to said part of the coating, said curvature monitoring means comprising means for measuring hte diameter of the surface between two opposed positions disposed to opposite sides of the measuring head, the measured diameter being representative of a particular degree of curvature and the second signal being indicative of the measured diameter, and means responsive to the first and second signals for appying a correction factor, dependent upon the second signal, to influence the first signal and produce a corrected signal which more accurately represents the true "~ .
5a ~ ,3~
thickness of said part of the coating.
In the apparatus according to the invention, the curvature monitoring means comprises a diameter measuring means for measuring the diameter of the coated arcuate metal surface at a position such that said coating part is disposed intermediate to opposed positions across the article at which the diameter measurement is taken.
One embodiment of the invention will now be described by way of example, w~th reference to the accompanying drawings in which:-Figure 1 is part of a block schemat;c diagram of a circuit and accompanying thickness measuring apparatus for providing measurements of jacket thickness on a telecommunications cable - 5 structurej Figure 2 is a cross-section taken along a longitudinal axis of a measuring head of the thickness measuring apparatus and on a larger scale;
Figure 3 is a side view of one form of measuring head probe which is included in the measuring head of Figure 2 and on a larger scale than Figure 2;
Figure 4 is on a smaller scale than Figure 3 and is a perspective view of a plurality oF measuring heads in an assembly and shown in greater detail than is shown in Figure l;
Figure 5 is a diagrammatic cross-sectional view taken through a cable and in the axial direction to show the measuring head assembly ; and its relationship to a diameter measuring means also included in the apparatus; and Figure 6 is another part of the block schematic circuit of Figure l.
As shown in Figure 1, apparatus is provided for measuring the thickness of a polymeric jacket 8 of a telecommunications cable 10 and formed around an arcuate metal surface in the form of a metallic sheath 12 (see Figure 5) provided around a core 1~ of the cable. The cable is of a conventional construction for telecommunications cables and the : core is formed from any required number of twisted together pairs of insulated conductors.
: The apparatus comprises four measuring head and support assemblies 16 (shown in Figure 1) which are spaced apart at 90 6a ~3~
intervals around a centre which coincides with the feedpath for t'ne 7 ~3~33~
cable. For ease of description later in the specification, the four measuring head and support assemblies are designated 16A, 16B, 16C and 16D. The four assemblies are of the same common design, which is shown in Figure 2 for assembly 16A~ Assembly 16A comprises a housing 18 which encloses d support member 22 for a measuring head 24. Each measuring head 24 comprises an elongated housing 26. Two probes 28 (to be described) are mounted in the housing 26, a probe at each end of the housing~ Only one probe is active while the other probe is inactive.
The two probes are generally of cylindrical form, as shown with reference to Figures 2 and 3~ and the active probe has a sensing element 29 which is a coil wound around the active probe and forms part of an oscillator circuit (to be described) of a reactance monitoring means. The head 24 is attached to a support rod 30 by a flexible diaphragm 32 which is secured to the housing 26. The rod is attached at its other end to a slide member 34, which is slidable on a rod 36.
The rod 36 is mounted at one end directly to the housing 18 and, at the other end within support member 22. A damper 38 damps movement of the slide member 34~ To restrict khe movement of the head 24 beyond desirable limits, a short projecting member 40 on the rod 30 moves within an enclosure 42 mounted on the housing 26. A spring 44 provides a load on the slide member 34. In the particular example, the rod 30 is pivotally attached to the slide member 34 by a pin 46. A shear pin 48 prevents pivotting of the rod 30 except in emergencies.
The positioning and support structure assembly 49 comprises a support back plate 50 which carries each of the measuring head and support assemblies 16A, 16B, 16C and 16D. The mounting of the assemblies is provided by cantilever arms 52 which are secured to outer ends of the housings 18 and are attached to racks 54 which extend radially of the back plate 50 and are movable radially within brackets 8 ~3~37~
56 mounted upon the back plate. Extending axially from the back plate 50 are four pinions 58 fixed on shafts 60 and the pinions engage one with each of the racks 54. The positioning and support structure assembly and each measuring head and support assembly 16 is described in greater detail as in U.S. Patent Numbers 4,051,430 and 4,053,827.
Each shaft 60 has a chain gear (not shown) at the other side of the back plate 50 with a chain (not shown) passing over each chain gear, the chain being movable to rotate the pinions 58 synchronously so as to move the heads 16A to 16D radially in or out from the axis of the back plate. Such movement is required during initial setting up or disassembly of the apparatus so as to locate the measuring heads correctly upon the apparatus, as shown in Figure 4.
As shown particularly in Figure 3, each of the probes 26 has a stem portion 62 and a head portion 64. The stem portion 62 is mounted within the housing 26 and the coil 29 is positioned within a groove 66, as shown in Figure 3. The head portion 64 is circular in plan view and, when viewed in side elevation in a direction coincident with the axis of the cable, it has a contact surface 68 which is profiled in a predetermined manner. The profile of the surface 68 is obtained from calibration curves in such a way that9 for a given jacket thickness, the inductance of the coil 29, when the contact surface 68 is brought into contact with a cable jacket, remains substantially constant oYer a range of cable diameters. The profile of the surface is obtained in the manner described in U~S. patent ~,051,430, referred to above. A bore 70 extends axially through the probe. The bore may contain a tuning element (not shown) such as a slug or core of appropriate material, such as ferrite. ~y such tuning elements an individual head can be tuned and in an apparatus using a plurality of heads, as in this embodiment, tuning of the heads can be matched. The 11S, ~
~3~.3~9 tuning element can vary the sensitivity of the probe and change its resonant frequency.
As indicated above, the coils 29 form parts of oscillator circuits which are provided in the reactance monitoring means. The resonant frequencies of the circuits are varied by variations in the inductive effect of each probe, resulting from variations in the distance of the metallic surface of the sheath 12 from a probe datum.
Such variations of frequency are utilized in this apparatus to produce signals indicative of the variation in thickness of the jacket, such as on dial indicators and/or chart recorders. The circuits for providing this facility are shown in Figure lo Operation of part of this circuit and which provides an indication of jacket thickness is as described in U.S. Patent Number 4,053,827. The measurements obtained with this particular part of the circuit do not take into account any variation 15 in the inductive effect caused by ovality of the cable, but may be used as a general guide by a machine operator of the thickness of the jacket and the centralization of the cable core together and the sheath within in the jacket. This part of the circuit which operates in the manner described in UOS. patent 4,053,827 operates basically in the following
2 0 manner.
Four identical channels are utilized to derive four D.C.
control voltages. Identical elements in each of the channels are identified by similar reference numerals, followed by additional reference characters, which correspond to the reference characters A, 25 B, C and D for the measuring head and support assemblies 16A to 16D.
In the following description, the letter designations A to D will be generally omitted. Reference will be made to specific letter designations when it is warranted.
As shown in Figure 1, the circuit functions to display g a 3L~30 .379 visually the quasi-thickness of the jacket and the eccentricity of the .: i cable core within the jacket~ The circuit generally comprises four channels 72 for developing D,C. control voltages which are indicative of the thickness of the sheath at four circumferential points, i.e. at parts of the coating at 90 apart and at which the measuring heads 5 are applied. In addition, the circuit includes a quadrature oscillator 74, and a network 76, for multiplying and summing the D.C. voltages From the channels 72 with those of the quadrature oscillator to produce output voltages which are used to drive an oscilloscope 78.
The active inductive probes 26 form part of the frequency determining portion of frequency controlled oscillators 80 having a nominal frequency of 1.25 MHz. The thickness of the cable jacket adjacent the probes 26 produces varying eddy currents and/or reluctance therein which in turn independently alters the frequency of each of the oscillators 80. The output signals from each of the oscillators 80 are 15 fed to discriminators 82 which produce varying D.C. voltages that are centered about a nominal reference thickness of the cable sheath.
Thus, a variation of +20 mils in the thickness of the cable sheath develops a voltage of +5 volts at the output of the discriminator 82. In order to eliminate the instantaneous variations in the 20 thickness of the sheath, the varying D.C. output voltages from the discriminators 82 are fed to sample and hold networks 84 having selectable sample periods which vary from 2 to 80 seconds.
The varying D.C. output voltages from the sample and hold networks 84 are coupled to the inputs of gates 86, each of which is 25 controlled by a 60 cycle square wave oscillator having a 90~ duty ; cycle. The square wave signal from the oscillator 88 is utilized to open the gates 86, thereby coupling the output signals ~rom the sample and hold networks 84 to the inverting inputs of operational amplifiers 90. The non-inverting inputs of the amplifiers 90 are connected to a ~, ll nominal +10 volt reference 92 source. Also, the amplifiers 90 utilize heavy negative feedback (as indicated by the unnumbered resistors) to maintain unity gained therethroughO The input signals to the inverting inputs can vary between -10 and +10 volts; hence, the output signals from the amplifiers 90 can vary between zero and +20 volts respectively. These output signals are coupled to the input of gates 94, which in turn are controlled by the output of a nominal 4 KHz square wave oscillator 96 having a 50% duty cycle.
The outputs of the gates 94 are clamped to a minimum voltage of 5 volts by zener diodes 98 and series connected resistors 100 and 102 coupled to a nominal +10 volt source 104. Thus, when the gates 94 are opened, their outputs are either the output of the amplifiers 90 or the zener diode voltage, whichever is the greater.
The quadrature oscillator 74 comprises a 1 KHz sinusoidal oscillator 106, one output of which is fed through a 90 phase-shift network 108. Another output from the oscillator 106 and the output of the phase-shift network 108 are each half-wave rectified by diodes 110 to produce four half-wave signal voltages. The two positive-going half-wave signals from the diodes 110B and llOC are coupled to the inputs of multipliers 112B and 112C respectively, while the two negative-going half wave signals from the diodes 110D and llOA are coupled to the inputs of multipliers 112D and 112A respectively. These half-wave signals are multiplied by the varying D.C. output signals from the gates 94 in the multipliers 112 to produce four half-wave output signals (two positive-going and two negative-going) which are displaced 90 with respect to each other, and that are proportional to the magnitude of the signals from the gates 94. The half-wave signals from the multipliers 112D and 112B having l80~ phase and an opposite polarity relationship, are connected to the inputs of a summing ~ '~3~37~
amplifier 114. Similarly, the two half wave signals from the multipliers 112A and 112C are connected to the inputs of a summing amplifier 116. The ou-tputs of the summing amplifiers 114 and 116 provide the required Y and X drive signals respectively for the oscilloscope 78.
As disclosed in U.S. patent number 4,053,827, with -the use of the above circuitry, the oscilloscope shows four different wave forms which are, namely:
1. nominal reFerence thickness of cable sheath 2. minimum allowable thickness of cable sheath
Four identical channels are utilized to derive four D.C.
control voltages. Identical elements in each of the channels are identified by similar reference numerals, followed by additional reference characters, which correspond to the reference characters A, 25 B, C and D for the measuring head and support assemblies 16A to 16D.
In the following description, the letter designations A to D will be generally omitted. Reference will be made to specific letter designations when it is warranted.
As shown in Figure 1, the circuit functions to display g a 3L~30 .379 visually the quasi-thickness of the jacket and the eccentricity of the .: i cable core within the jacket~ The circuit generally comprises four channels 72 for developing D,C. control voltages which are indicative of the thickness of the sheath at four circumferential points, i.e. at parts of the coating at 90 apart and at which the measuring heads 5 are applied. In addition, the circuit includes a quadrature oscillator 74, and a network 76, for multiplying and summing the D.C. voltages From the channels 72 with those of the quadrature oscillator to produce output voltages which are used to drive an oscilloscope 78.
The active inductive probes 26 form part of the frequency determining portion of frequency controlled oscillators 80 having a nominal frequency of 1.25 MHz. The thickness of the cable jacket adjacent the probes 26 produces varying eddy currents and/or reluctance therein which in turn independently alters the frequency of each of the oscillators 80. The output signals from each of the oscillators 80 are 15 fed to discriminators 82 which produce varying D.C. voltages that are centered about a nominal reference thickness of the cable sheath.
Thus, a variation of +20 mils in the thickness of the cable sheath develops a voltage of +5 volts at the output of the discriminator 82. In order to eliminate the instantaneous variations in the 20 thickness of the sheath, the varying D.C. output voltages from the discriminators 82 are fed to sample and hold networks 84 having selectable sample periods which vary from 2 to 80 seconds.
The varying D.C. output voltages from the sample and hold networks 84 are coupled to the inputs of gates 86, each of which is 25 controlled by a 60 cycle square wave oscillator having a 90~ duty ; cycle. The square wave signal from the oscillator 88 is utilized to open the gates 86, thereby coupling the output signals ~rom the sample and hold networks 84 to the inverting inputs of operational amplifiers 90. The non-inverting inputs of the amplifiers 90 are connected to a ~, ll nominal +10 volt reference 92 source. Also, the amplifiers 90 utilize heavy negative feedback (as indicated by the unnumbered resistors) to maintain unity gained therethroughO The input signals to the inverting inputs can vary between -10 and +10 volts; hence, the output signals from the amplifiers 90 can vary between zero and +20 volts respectively. These output signals are coupled to the input of gates 94, which in turn are controlled by the output of a nominal 4 KHz square wave oscillator 96 having a 50% duty cycle.
The outputs of the gates 94 are clamped to a minimum voltage of 5 volts by zener diodes 98 and series connected resistors 100 and 102 coupled to a nominal +10 volt source 104. Thus, when the gates 94 are opened, their outputs are either the output of the amplifiers 90 or the zener diode voltage, whichever is the greater.
The quadrature oscillator 74 comprises a 1 KHz sinusoidal oscillator 106, one output of which is fed through a 90 phase-shift network 108. Another output from the oscillator 106 and the output of the phase-shift network 108 are each half-wave rectified by diodes 110 to produce four half-wave signal voltages. The two positive-going half-wave signals from the diodes 110B and llOC are coupled to the inputs of multipliers 112B and 112C respectively, while the two negative-going half wave signals from the diodes 110D and llOA are coupled to the inputs of multipliers 112D and 112A respectively. These half-wave signals are multiplied by the varying D.C. output signals from the gates 94 in the multipliers 112 to produce four half-wave output signals (two positive-going and two negative-going) which are displaced 90 with respect to each other, and that are proportional to the magnitude of the signals from the gates 94. The half-wave signals from the multipliers 112D and 112B having l80~ phase and an opposite polarity relationship, are connected to the inputs of a summing ~ '~3~37~
amplifier 114. Similarly, the two half wave signals from the multipliers 112A and 112C are connected to the inputs of a summing amplifier 116. The ou-tputs of the summing amplifiers 114 and 116 provide the required Y and X drive signals respectively for the oscilloscope 78.
As disclosed in U.S. patent number 4,053,827, with -the use of the above circuitry, the oscilloscope shows four different wave forms which are, namely:
1. nominal reFerence thickness of cable sheath 2. minimum allowable thickness of cable sheath
3. actual wall thickness of cable sheath
4. maximum allowable thickness of cable sheath.
In addition, the oscilloscope provides values relating to the apparent thickness of the jacket upon the cable core as provided by signals received from the measuring heads 16. The actual values given on the oscilloscope 78 for the thickness of the jacket material are based upon the assumption that the inductance measurements taken by the heads are obtained from a substantially circular cable. The inductance measurements obtained are, in fact, converted into thickness measurements by using criteria based upon the cable diameter for the jacket being measured. This is because the inductance measurements are affected not only by the distance of the coils 28 from the surface of the sheath, but also by the degree of curvature of that surface away from the coils~ Thus, for any given nominal cable diameter, the inductance measurements are theoretically affected in an invariable fashion by the degree of curvature of the sheath and hence any change in inductance is related solely to change in distance between each coil 28 and the sheath surface, this change being caused by change in thickness of the jacket which controls this distance. Hence, the - 13 ~ 3 thickness is theoretically calculable from the inductance measurement.
However, if the cable has a degree of ovality, as is normal, then the degree of curvature on the metal surface changes around the cable and at most positions is different from that for a truly circular cable of
In addition, the oscilloscope provides values relating to the apparent thickness of the jacket upon the cable core as provided by signals received from the measuring heads 16. The actual values given on the oscilloscope 78 for the thickness of the jacket material are based upon the assumption that the inductance measurements taken by the heads are obtained from a substantially circular cable. The inductance measurements obtained are, in fact, converted into thickness measurements by using criteria based upon the cable diameter for the jacket being measured. This is because the inductance measurements are affected not only by the distance of the coils 28 from the surface of the sheath, but also by the degree of curvature of that surface away from the coils~ Thus, for any given nominal cable diameter, the inductance measurements are theoretically affected in an invariable fashion by the degree of curvature of the sheath and hence any change in inductance is related solely to change in distance between each coil 28 and the sheath surface, this change being caused by change in thickness of the jacket which controls this distance. Hence, the - 13 ~ 3 thickness is theoretically calculable from the inductance measurement.
However, if the cable has a degree of ovality, as is normal, then the degree of curvature on the metal surface changes around the cable and at most positions is different from that for a truly circular cable of
5 the nominal diameter. As the induc-tance measurements are affected by degree of curvature, then these measurements cannot accurately represent the thickness of the jacket on an oval cable, but only represent an apparent thickness which is that shown by the oscilloscope 78.
The problem discussed above is minimized in the present invention by the use of a curvature monitoring means which provides a second signal indicative of the degree of curvature of the coated metal surface in regions adjacent to the parts of the coating upon which the measuring heads operate. As shown in Figure 1, the curvature monitoring means comprises a diameter measuring means 118 which is in line with the measuring heads and positioning and support structure, downstream along the feedpath for the cable. The diameter measuring means has an arcuate track arrangemen-t 120 which surrounds the cable.
This diameter measuring means is of conventional construction and is sold by Zumbach Electronic AG. with gauge head identification ODAC 150, and its indicator unit identification reference is 19M while the rotating mechanism is identified as DV1. It operates by using a laser measuring device 124 which moves around the track 120, i.e. around the circumference of the cable, to pass a laser beam diametrically across the track to be received by a sensing means 126 at the other side. The degree of light received by the sensing device is dependent upon the diameter of the cable, including its jacket, and the diameter measuring means can accurately determine the width or diameter of the cable at any particular position around it.
~L~3~
The diameter measuring means is linked to the measuring head arrangement in that it is intended for the diameter measuring means to provide measurements of the diameter of the cable at positions which will give some indication of the curvature at the regions of the jacket lying adjacent each measuring head 24 and which correspond to those diameter measurements. Hence, when considering the operational relationship of the measuring heads and the diameter measuring means, Figure 5 is illustrative of the operational arrangement. As shown by Figure 5, the measuring heads 16A and 16C are diametrically opposed across the axis of the cable as it is fed along the pass line. Also, the measuring heads 16B and 16D are diametrically opposed while lying at 90 to the other two heads. Thus, the heads could be said to lie along X and Y axes as shown by Figure 5, with measuring heads 16A and 16C on the Y axis and the other measuring heads on the X axis. It should be borne in mind that while the drawings, particularly Figure 5, show the measuring heads in vertical or horizontal positions, the X-Y
axis system could be rotated for the performance of the invention. The heads could lie at other angular positions away from the vertical and horizontal axes and the apparatus would still operate in a similar fashion to that now to be described. However, it is convenient for the operation of the diameter measuring means in conjunction with the measuring heads that the measuring heads are opposed in pairs, as shown by Figure 5.
As shown by Figure 6, the curvature monitoring means includes a monitoring circuit shown generally at 127 in Figure l. This monitoring circuit includes a diameter gauge 130 which receives signals, corresponding to diameter of cable, as received from the sensing means 126. Voltage signals are sent From the diameter gauge to two sample and holds 132 and 134. The sample and hold 132 is - 15 - ~3(~37~
controlled by a first switch which becomes closed when laser 124 is emitting light along the 'X' axis. Upon closure of the first switch, the diameter measurement voltage held in sample and hold 132 at that time, and corresponding -to diameter of cable along the 'Y' axis, is allowed -to travel to two operational amplifiers, i.e. a subtraction amplifier 136 and addition amplifier 138. On the other hand, a second swi-tch becomes closed when laser 124 is emitting light along the 'Y' axis whereby the diameter measurement voltage held in sample and hold 134 at that time, and corresponding to diameter of cable along the 'X' axis, is allo~ed to travel to the amplifiers 136 and 138.
Signals representing the sum and difference of the 'X' and 'Y' axis voltage signals then proceed to a divider 140 which emits a signal representing percentage or degree of ovality of the cable at the position measured and this ovality signal proceeds to four operational amplifiers 142, 144, 146 and 148.
As indicated above, the measurements which are transmitted through the circuit frorn the measuring heads to the oscilloscope 78 correspond to current thicknesses of the jacket upon the cable. The measurements given on the oscilloscope 78, while being useful as a general guide to the operator of the apparatus, are preferably not to be used for control of the thickness of the jacket by, for instance, controlling the extrusion output speed for forming the jacketO It is intended that the measurements oF thickness to be used for control of the extrusion and for controlling the concentricity of the core within the jacket, are to be provided upon a display 150 produced by signals received from the amplifiers 142, 144, 146, 148, these signals being corrections of the signals sent along lines 128. As may be seen from Figures 1 and 6 the lines 128A, B, C and D connect channels 72A, B, C
and D, at positions downstream from amplifiers 90, to the amplifiers - 16 - 3L~,;3~337~
142 to 148. The signals issuing from amplifiers 90 are influenced by the ovality signals from the divider 140 in the amplifiers 14Z to 148 to emit the corrected signals which mGre accurately represen-t the thickness of the layer 8 after compensation for any ovality of the cable. Thus the ovality signals are correction factors to the signals in channels 72 which have inaccuracies caused by the ovality, because, as has already been said, the induc-tance measurements are affected by degree of curvature. The degree of curvature at the positions of the measuring heads is, in turn, affected by the degree of ovality as judged by the diame-ter measurements taken along the 'X' and 'Y' axes by the diameter measuring means 118.
The apparatus of this embodiment operates on the theory that the degree of curvature at any one position of a measuring head is affected, in an oval cable, by the diameter or width across the cable between two opposed peripheral positions disposed so that the measuring head lies substantially intermediate these peripheral positions. Thus, when measuring in one direction across an oval cable of a given nominal diameter, if the diameter measurement is greater than the nominal, then the degree of curvature is expected to be less than the nominal diameter. Conversely, if the diameter measurement is less than the nominal, then the degree of curvature is expected to be greater than for the nominal diameter.
As may be seen from the above embodiment, the apparatus of the invention successfully takes into account any degree of ovality in a cable cross-sectional shape to minimize any error in jacket thickness measurement which is produced by the measuring heads for display or control purposes.
While the apparatus of the embodiment has been described with regard to control involving measurement of inductance as influenced by ~ '~3~33~
degree of curvature of the sheath surface within a cable, it is to be understood that the degree of curvature of the sheath may also affect other reactance values such as capacitance. The invention therefore also extends to apparatus and methods of measurement in which the capacitance values are measured by appropriate capacitive measuring heads which produce the apparent measurement signals. The diameter measuring means operates in a manner similar to that discussed in the first embodiment to produce correction factors so as to provide corrected signals which produce a thickness measurement display which is a more accurate representation of the thickness of the jacket at - each position at which it is being taken.
The problem discussed above is minimized in the present invention by the use of a curvature monitoring means which provides a second signal indicative of the degree of curvature of the coated metal surface in regions adjacent to the parts of the coating upon which the measuring heads operate. As shown in Figure 1, the curvature monitoring means comprises a diameter measuring means 118 which is in line with the measuring heads and positioning and support structure, downstream along the feedpath for the cable. The diameter measuring means has an arcuate track arrangemen-t 120 which surrounds the cable.
This diameter measuring means is of conventional construction and is sold by Zumbach Electronic AG. with gauge head identification ODAC 150, and its indicator unit identification reference is 19M while the rotating mechanism is identified as DV1. It operates by using a laser measuring device 124 which moves around the track 120, i.e. around the circumference of the cable, to pass a laser beam diametrically across the track to be received by a sensing means 126 at the other side. The degree of light received by the sensing device is dependent upon the diameter of the cable, including its jacket, and the diameter measuring means can accurately determine the width or diameter of the cable at any particular position around it.
~L~3~
The diameter measuring means is linked to the measuring head arrangement in that it is intended for the diameter measuring means to provide measurements of the diameter of the cable at positions which will give some indication of the curvature at the regions of the jacket lying adjacent each measuring head 24 and which correspond to those diameter measurements. Hence, when considering the operational relationship of the measuring heads and the diameter measuring means, Figure 5 is illustrative of the operational arrangement. As shown by Figure 5, the measuring heads 16A and 16C are diametrically opposed across the axis of the cable as it is fed along the pass line. Also, the measuring heads 16B and 16D are diametrically opposed while lying at 90 to the other two heads. Thus, the heads could be said to lie along X and Y axes as shown by Figure 5, with measuring heads 16A and 16C on the Y axis and the other measuring heads on the X axis. It should be borne in mind that while the drawings, particularly Figure 5, show the measuring heads in vertical or horizontal positions, the X-Y
axis system could be rotated for the performance of the invention. The heads could lie at other angular positions away from the vertical and horizontal axes and the apparatus would still operate in a similar fashion to that now to be described. However, it is convenient for the operation of the diameter measuring means in conjunction with the measuring heads that the measuring heads are opposed in pairs, as shown by Figure 5.
As shown by Figure 6, the curvature monitoring means includes a monitoring circuit shown generally at 127 in Figure l. This monitoring circuit includes a diameter gauge 130 which receives signals, corresponding to diameter of cable, as received from the sensing means 126. Voltage signals are sent From the diameter gauge to two sample and holds 132 and 134. The sample and hold 132 is - 15 - ~3(~37~
controlled by a first switch which becomes closed when laser 124 is emitting light along the 'X' axis. Upon closure of the first switch, the diameter measurement voltage held in sample and hold 132 at that time, and corresponding -to diameter of cable along the 'Y' axis, is allowed -to travel to two operational amplifiers, i.e. a subtraction amplifier 136 and addition amplifier 138. On the other hand, a second swi-tch becomes closed when laser 124 is emitting light along the 'Y' axis whereby the diameter measurement voltage held in sample and hold 134 at that time, and corresponding to diameter of cable along the 'X' axis, is allo~ed to travel to the amplifiers 136 and 138.
Signals representing the sum and difference of the 'X' and 'Y' axis voltage signals then proceed to a divider 140 which emits a signal representing percentage or degree of ovality of the cable at the position measured and this ovality signal proceeds to four operational amplifiers 142, 144, 146 and 148.
As indicated above, the measurements which are transmitted through the circuit frorn the measuring heads to the oscilloscope 78 correspond to current thicknesses of the jacket upon the cable. The measurements given on the oscilloscope 78, while being useful as a general guide to the operator of the apparatus, are preferably not to be used for control of the thickness of the jacket by, for instance, controlling the extrusion output speed for forming the jacketO It is intended that the measurements oF thickness to be used for control of the extrusion and for controlling the concentricity of the core within the jacket, are to be provided upon a display 150 produced by signals received from the amplifiers 142, 144, 146, 148, these signals being corrections of the signals sent along lines 128. As may be seen from Figures 1 and 6 the lines 128A, B, C and D connect channels 72A, B, C
and D, at positions downstream from amplifiers 90, to the amplifiers - 16 - 3L~,;3~337~
142 to 148. The signals issuing from amplifiers 90 are influenced by the ovality signals from the divider 140 in the amplifiers 14Z to 148 to emit the corrected signals which mGre accurately represen-t the thickness of the layer 8 after compensation for any ovality of the cable. Thus the ovality signals are correction factors to the signals in channels 72 which have inaccuracies caused by the ovality, because, as has already been said, the induc-tance measurements are affected by degree of curvature. The degree of curvature at the positions of the measuring heads is, in turn, affected by the degree of ovality as judged by the diame-ter measurements taken along the 'X' and 'Y' axes by the diameter measuring means 118.
The apparatus of this embodiment operates on the theory that the degree of curvature at any one position of a measuring head is affected, in an oval cable, by the diameter or width across the cable between two opposed peripheral positions disposed so that the measuring head lies substantially intermediate these peripheral positions. Thus, when measuring in one direction across an oval cable of a given nominal diameter, if the diameter measurement is greater than the nominal, then the degree of curvature is expected to be less than the nominal diameter. Conversely, if the diameter measurement is less than the nominal, then the degree of curvature is expected to be greater than for the nominal diameter.
As may be seen from the above embodiment, the apparatus of the invention successfully takes into account any degree of ovality in a cable cross-sectional shape to minimize any error in jacket thickness measurement which is produced by the measuring heads for display or control purposes.
While the apparatus of the embodiment has been described with regard to control involving measurement of inductance as influenced by ~ '~3~33~
degree of curvature of the sheath surface within a cable, it is to be understood that the degree of curvature of the sheath may also affect other reactance values such as capacitance. The invention therefore also extends to apparatus and methods of measurement in which the capacitance values are measured by appropriate capacitive measuring heads which produce the apparent measurement signals. The diameter measuring means operates in a manner similar to that discussed in the first embodiment to produce correction factors so as to provide corrected signals which produce a thickness measurement display which is a more accurate representation of the thickness of the jacket at - each position at which it is being taken.
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:-
1. A method of measuring the thickness of a non-metallic coating on an arcuate annular metal surface of an article having an ovality comprising:-engaging a part of the coating with a measuring head which carries a sensing element having a reactance which is affected by the position and degree of curvature of the arcuate metal surface;
monitoring the reactance of the sensing element to produce a first signal indicative of the apparent thickness of the coating in a region adjacent to the measuring head for a given degree of surface curvature;
monitoring the degree of curvature of the coated metal surface in said adjacent region to provide a second signal indicative of the actual degree of curvature of said adjacent region by measuring the diameter of the surface between two opposed positions around the circumference of the article with the part of the coating engaged by the measuring head disposed intermediate these positions, the measured diameter being representative of a particular degree of curvature and the second signal indicative of the measured diameter; and applying a correction factor dependent upon the second signal, to influence the first signal and produce a modified signal which more accurately represents the true thickness of said part of the coating.
monitoring the reactance of the sensing element to produce a first signal indicative of the apparent thickness of the coating in a region adjacent to the measuring head for a given degree of surface curvature;
monitoring the degree of curvature of the coated metal surface in said adjacent region to provide a second signal indicative of the actual degree of curvature of said adjacent region by measuring the diameter of the surface between two opposed positions around the circumference of the article with the part of the coating engaged by the measuring head disposed intermediate these positions, the measured diameter being representative of a particular degree of curvature and the second signal indicative of the measured diameter; and applying a correction factor dependent upon the second signal, to influence the first signal and produce a modified signal which more accurately represents the true thickness of said part of the coating.
2. A method according to claim 1 comprising:-engaging circumferentially spaced parts of the coating with a plurality of measuring heads, one at each coating part for providing first signals indicative of the apparent thickness of the coating parts;
moving a diameter measuring means around the article to provide second signals indicative of measured diameter at different locations around the article; and coordinating the locations at which the diameter is being measured with said coating parts to ensure that a correction factor applied to each first signal is dependent upon a second signal of diameter measured between two spaced positions having the appropriate coating part intermediate these positions.
moving a diameter measuring means around the article to provide second signals indicative of measured diameter at different locations around the article; and coordinating the locations at which the diameter is being measured with said coating parts to ensure that a correction factor applied to each first signal is dependent upon a second signal of diameter measured between two spaced positions having the appropriate coating part intermediate these positions.
3. A method according to claim 2 comprising coordinating the locations by providing a voltage in a circuit, said voltage changing as the angular position of the measuring means around the article changes with certain voltages relating to certain angular positions, and upon providing specific voltages thus indicating certain specific locations around the cable which are to be coordinated with said coating parts, triggering a switch means to provide said second signals.
4. Apparatus for measuring the thickness of a non-metallic coating on an arcuate metal surface of an article having an ovality, the apparatus comprising:-a measuring head for positioning against a part of said coating, the measuring head including a sensing element having a reactance which is affected by the position and degree of curvature of said arcuate metal surface;
at least one support member for supporting said measuring head relative to said coating;
reactance monitoring means for monitoring the reactance of the sensing element to develop a first signal representative of the apparent distance between the sensing member and the metal surface and thus of the apparent thickness of the coating for a given degree of curvature of the metal surface;
curvature monitoring means for providing a second signal indicative of the degree of curvature of the coated metal surface in regions adjacent to said part of the coating, said curvature monitoring means comprising means for measuring the diameter of the surface between two opposed positions disposed to opposite sides of the measuring head, the measured diameter being representative of a particular degree of curvature and the second signal being indicative of the measured diameter; and means responsive to the first and second signals for applying a correction factor, dependent upon the second signal, to influence the first signal and produce a corrected signal which more accurately represents the true thickness of said part of the coating.
at least one support member for supporting said measuring head relative to said coating;
reactance monitoring means for monitoring the reactance of the sensing element to develop a first signal representative of the apparent distance between the sensing member and the metal surface and thus of the apparent thickness of the coating for a given degree of curvature of the metal surface;
curvature monitoring means for providing a second signal indicative of the degree of curvature of the coated metal surface in regions adjacent to said part of the coating, said curvature monitoring means comprising means for measuring the diameter of the surface between two opposed positions disposed to opposite sides of the measuring head, the measured diameter being representative of a particular degree of curvature and the second signal being indicative of the measured diameter; and means responsive to the first and second signals for applying a correction factor, dependent upon the second signal, to influence the first signal and produce a corrected signal which more accurately represents the true thickness of said part of the coating.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000485969A CA1230379A (en) | 1985-06-28 | 1985-06-28 | Measuring the thickness of a non-metallic coating on an arcuate metal surface |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000485969A CA1230379A (en) | 1985-06-28 | 1985-06-28 | Measuring the thickness of a non-metallic coating on an arcuate metal surface |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1230379A true CA1230379A (en) | 1987-12-15 |
Family
ID=4130884
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000485969A Expired CA1230379A (en) | 1985-06-28 | 1985-06-28 | Measuring the thickness of a non-metallic coating on an arcuate metal surface |
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| Country | Link |
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| CA (1) | CA1230379A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114353656A (en) * | 2022-01-11 | 2022-04-15 | 中北大学 | Eddy current measurement curved surface correction method for thickness of coating of workpiece with gradually-changing curvature |
-
1985
- 1985-06-28 CA CA000485969A patent/CA1230379A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114353656A (en) * | 2022-01-11 | 2022-04-15 | 中北大学 | Eddy current measurement curved surface correction method for thickness of coating of workpiece with gradually-changing curvature |
| CN114353656B (en) * | 2022-01-11 | 2024-01-30 | 中北大学 | Vortex measurement curved surface correction method for gradually-changed curvature workpiece coating thickness |
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