Abstract: Apparatus for 360.degree. azimuthal imaging of steel casing employs a transducer that is rotated around the inside wall of the casing for inducing and measuring variations in induced flux density within the casing as an indication of changes in casing thickness.

Abstract: Both a system and a method are provided which allows an eddy current probe to accurately determine both the proximity and dimensions of non-conductive structures which are normally invisible to such probes. The system comprises a portable target medium that is movable into a known position with respect to the non-conductive structure, and that includes a conductive material that couples strongly with a fluctuating magnetic field, and a movable eddy current probe that emanates a fluctuating magnetic field and which generates a signal indicative of the magnitude of the interaction between the field and the portable target medium from which the distance between the two may be computed. The system may be used to determine the proximity of non-conductive structures such as plastic pipes that have been buried under ground, as well as the dimensions of such non-conductive structures.

Abstract: A non-contact thickness measuring sensor is disclosed which determines the thickness of an overlying material on a substrate. The sensor includes two non-contact separation distance measuring devices which may be utilized to measure the distance from the first device to a portion of the interface between the substrate and the overlying material, while the second device determines the distance from the second device to a portion of the surface of the overlying layer. The difference in the measured distances is related to the thickness of the overlying material. In one embodiment, two lasers are used to measure the separation distances. In another embodiment, the two measured distances are coincident. Because of the coincident geometry of these two measurements, the thickness measuring sensor of this embodiment is substantially insensitive to misalignment of the sensor from the normal to the surface of the overlying layer being measured.

Abstract: A measuring apparatus which accurately locates reinforcing bars in underwater concrete structures such as piers, retaining walls, easements and the like and measures the amount of concrete covering each reinforcing bar. The measuring apparus comprises a probe which generates a magnetic field and which is moved over the surface of the underwater concrete structure under test. When the poles of the magnetic field are in parallel alignment with and directly over a reinforcing bar within the structure a disturbance occurs in the magnetic field with the magnitude of the disturbance being indicative of the depth of concrete covering the reinforcing bar. An electronics module electrically coupled to the probe provides an analog output signal which is indicative of the distance between a reinforcing bar within the concrete structure under test and the probe.

Abstract: A sensor, system and method for determining the various Z-directional properties of a sheet by measuring the caliper of a moving sheet of material at a plurality of pressures. The invention employs a caliper gauge and a set of pressure transducers that can measure and send signals indicative of the caliper as well as pressures exerted on the sheet. The signals are then digitized by an analog-to-digital converter and sent to a computer. The computer uses the compressibility data to construct a compression stress-strain diagram where the slope of the curve in the linear region of the curve is defined as the compression modulus of elasticity which can be empirically correlated to the tensile modulus of elasticity for various grades of paper. The tensile modulus of elasticity can be then used in various formulas to determine other Z-directional physical properties of the sheet, such as tensile strength, extensional stiffness and Scott bonding.

Abstract: An arrangement for measuring a thickness of a sheet article during a sheet article transportation, especially for measuring the thickness of an X-ray sheet film in an X-ray cassette loading and unloading device, has a magnet carrier arranged in a spring-biased manner on a sheet article transportation path perpendicularly to one side of the transportation path, a permanent magnet arranged on the magnet carrier near the first side of the magnet transportation path, at least one roller body arranged on the magnet carrier rotatably in a transportation direction of the sheet aarticle, a probe carrier fixedly arranged parallel to a second side of the transportation path opposite to the matnet carrier, a Hall probe arranged on the probe carrier opposite to the permanent magnet, at least one roller body arranged on the probe carrier. The probe carrier has a number of the roller bodies which corresponds to a number of the roller bodies on the magnet carrier.

Abstract: A method for determining the thickness of a pipe by inserting a coil into the pipe and applying a voltage to the coil and measuring the time it takes for current in the coil to magnetically saturate the pipe and determining the thickness of the pipe from the measure time.

Abstract: There is provided a transient electromagnetic method and apparatus for inspecting objects using moving sensors. The apparatus includes a sensing portion, which has a transmitting antenna and at least one receiving antenna thereon. The sensing portion is located adjacent to the object which is to be inspected such that the antennas are adjacent to the object. The sensing portion is moved along the object at the same time the transmitting antenna is inducing current in the wall and the receiving antenna is producing a received signal of the induced current diffusion in the wall. Because the antennas are moving during data acquisition, the speed of inspection is increased. The data is then interpreted to determine the thickness of the object.

Abstract: The duplex tube (1) comprises a tubular core (2) and a cladding or covering layer (3) made from an alloy, the base metal of which is identical to the base metal of the alloy constituting the tubular core (2).

Abstract: Both a system and a method are provided which allows an eddy current probe to accurately determine both the proximity and dimensions of non-conductive structures which are normally invisible to such probes. The system includes a portable target medium that is movable into a known position with respect to the non-conductive structure, and that includes a conductive material that couples strongly with a fluctuating magnetic field, and a movable eddy current probe that emanates a fluctuating magnetic field and which generates a signal indicative of the magnitude of the interaction between the field and the portable target medium from which the distance between the two may be computed. The system may be used to determine the proximity of non-conductive structures such as plastic pipes that have been buried under ground, as well as the dimensions of such non conductive structures.

Abstract: Method for measuring the thickness of a lubricant film between two surfaces which are in motion with regard to one another, characterized by the fact that a lubricant with high relative permeability is used, whereby the polar pieces of an electromagnetic sensor are brought into contact with the lubricant film to be measured in such manner that they are bridged by the lubricant film.

Abstract: The present invention relates to a method and apparatus for remotely detecting impedance. It is specifically adapted for use on a polishing machine wherein the end point of polishing for removing a surface layer during the processing of semiconductor substrates is detected. A first, or stationary coil having a high permeability core is wound having an air gap and an AC voltage is applied to the stationary coil to provide a magnetic flux in the air gap. A second coil is mounted for rotation on the polishing table, in a position to periodically pass through the air gap of the stationary coil as the table rotates. The second coil is connected at its opposite ends to contacts which are embedded in the surface of the polishing wheel. The contacts are positioned to engage the surface of the substrate which is being polished and provide a load on the second or rotating coil.

Abstract: A metallic material measuring method and apparatus. The material is positioned within a coil and a high frequency alternating current is applied to the coil. The change in inductive resistance in the coil from a reference state to a state where the material to be measured is positioned within the coil allows a determination of the properties of the metallic materials to be made.

Abstract: A contacting thickness gauge comprising a unique surface follower (46). The bottom surface (56) of the surface follower (46) has both contacting areas (64,66) and non-contacting areas (62). The surface follower (46) is in substantially continuous contact with a moving sheet (2) and embodies an electrically conductive target having a target surface that intersects a magnetic field but is substantially free from contact with the sheet during normal operation. The surface follower (46) is designed to minimize damage to the sheet (2) that would otherwise occur from contact between the surface follower and a protruberance of the sheet, and to preserve the characteristics of the target surface.

Abstract: A sheet thickness measuring apparatus comprises a metallic back-up surface for supporting the sheet, a magnetic field utilizing sensor disposed above the metallic back-up surface and the sheet for outputting a measured value representative of a distance up to the metallic back-up surface, an optical sensor and a computing unit.

Abstract: A device for measuring the thickness of a wet or dry paint film applied on a substrate without contacting the film is disclosed. The device uses an ultrasonic sensor positioned adjacent to an inductive eddy-current proximity sensor where the ultrasonic sensor measures the distance between the device and the upper surface of the paint film and the proximity sensor measures the distance between the device and the upper surface of the substrate. The two distances measured, when compared, produce the film thickness value. The device is capable of accurately measuring thickness of various paint films, such as flat, glossy and metal-flake containing paint films.

Abstract: A method for contactless measuring the values of magnitudes which relate to an electrically conductive material in solid or liquid form, for instance such magnitudes as the distance of the conductive material from a given point, linear dimension(s) of a body that incorporates such material, the electrical conductivity value of the material, and the temperature of the material. In accordance with the method, an electromagnetic field, generated with the aid of a constant current which flows through at least one field generating coil, is caused to penetrate at least partially into the material. The supply of current to the at least one coil is discontinued subsequent to the magnetic field having penetrated the electrically conductive material to an extent sufficient for the intended magnitude to be measured.

Abstract: A carding machine comprises a main carding cylinder and parts which are adjustable relative thereto, such as a licker-in, a stationary flat, a revolving flat and a doffing cylinder, such parts preferably having a nominal spacing relative to the main carding cylinder. For checking a spacing, namely an existing spacing or an already adjusted spacing between the main carding cylinder and the aforesaid parts arranged opposite thereto, there is provided a sensor at at least one end or end portion of the main carding cylinder, but preferably at each one of the two ends or end portions thereof, such sensor or respective sensors being connected to an electronic evaluation unit by means of a coupling device.

Abstract: For use with automatic machinery for packaging a food product in foil pouches and then inserting a desired number of pouches in a box, a method and apparatus for scanning the boxes to check for missing pouches. The scan is accomplished by applying like alternating magnetic fields through each box and through the foil used to make the pouches at a point upstream from where the pouches are formed. Detected field absorption associated with the upstream foil is used as a reference, and the difference between it and detected field absorption associated with a box is proportional to the number of pouches in the box. The apparatus can detect if one out of two, one out of three, or one out of four is missing, and compensates the differential signal for variations in foil thickness by multiplying the reference signal by N-1, where N is desired pouch count per box. If a pouch is missing from a box, a signal is generated which can be used to trigger a rejection mechanism to remove the short-count box.

Abstract: An apparatus for the detection of body filler components utilized in damage repair of automotive sheet metal is set forth. The device utilizes an elongate housing including a reciprocatable shaft mounted coaxially within the housing, wherein the reciprocatable shaft includes a forward terminal end mounting a magnet member thereon. Upon the magnet being retracted relative to a non-metallic or filled body surfaces utilizing various polymeric or even lead fillers, the shaft remains retracted in the housing biased therewithin. Intermediate levels of body filler effects various degrees of extension of the shaft relative to the housing, wherein a stepped plate is provided to lock the shaft in its extension relative to the housing.

Abstract: A transient electromagnetic method for detecting irregularities on container walls by measuring wall thickness. The method utilizes a transmitting antenna and a separate receiving antenna arranged in a loop-loop configuration. The transmitting antenna induces current into the container wall and the receiving antenna and the receiver detect the decay of the induced current, which is then analyzed to detect wall thickness. A receiving antenna array of many receiving antennas is used to increase the spatial resolution. Simultaneous measurement of the induced current by the receiving antennas reduces noise that is coherent across the array. Use of a noise antenna located so as to be unaffected by the transmitting antenna further reduces noise. The received signal from the receiving antenna array is displayed on a two-dimensional display in a spatial arrangement that corresponds to the spatial arrangement of the receiving antennas.

Abstract: A transient electromagnetic method for detecting irregularities on container walls by measuring wall thickness. The method utilizes a transmitting antenna and separate receiving antennas so as to form a loop-loop configuration. The transmitting antenna induces current into the container wall and the receiving antennas detect the induced current and produce received signals. The distance between the antennas and the container wall can vary, particularly where insulation is interposed therebetween. The variations in antenna distance affects the received signals. The affects are corrected by determining the maximum of the respective received signal and determining the arrival time of the maximum. The maximum and the arrival time are used to determine the thickness of the wall.

Abstract: A portable, battery powered, electronic wheel wear gauge is described for use in train wheel wear measurements. The gauge consists of a portable computer controller electrically connected to a portable gauge head. The gauge automatically determines proper positioning of the gauge head with respect to a wheel and then automatically measures rim thickness, flange thickness, flange height and, optionally, rim diameter of a train wheel using suitable contact and non-contact sensors. The measurement readings are displayed and can be stored in a non-volative memory of the controller for subsequent transfer to another computer or a printer.

Abstract: Various devices are constructed with gap-modified magnetic bridge circuits. In a magnetic bridge device for evaluation of samples, a magnetic bridge circuit has at least four arms, a driving leg and a sensing leg, one of the arms being utilized for evaluating a sample, pole pieces of a sample-evaluating arm having end faces defining between them a sample-evaluating gap. An electrically conductive gap insert produces an enhanced fringing flux exteriorly of it. The sample is placed in juxtaposition to the sample-evaluating gap for affecting the fringing flux. A driving circuit for the driving leg provides a time-varying flux path within the four arms of the bridge. A sensing device associated with the sensing leg senses changes in the sensing leg caused by changes in the fringing flux resulting from characteristics or movement of the sample. A specific single-side modification provides an accelerometer.

Abstract: A monitoring system monitoring electrical components of an apparatus for electrodynamic wall-thickness and defect testing includes a transmitter generating brief signals. An electrodynamic converter has a transmitter coil connected to the transmitter for receiving the brief signals and feeding the brief signals into a workpiece to be tested in which the brief signals are reflected. The electrodynamic converter has a receiver coil receiving the reflected signals. An amplifier is connected to the receiver coil for receiving the reflected signals and an evaluation unit is connected to the amplifier for receiving the reflected signals. At least one damping element and a delay line are connected to the transmitter for delaying and damping the brief signals. The delay line is coupled through the electrodynamic converter to the evaluation unit for feeding the delayed and damped signals to the transmitter coil.

Abstract: A thickness measurement of non-metallic material molded bodies, particularly, walls of tubular ceramics or plastics, can be simply performed with a high precision, by interposing such a molded body between a metal and a measuring probe, such as a solenoid coil, generating an alternating magnetic field, and measuring an energy loss of the magnetic field which depends on the thickness of the molded body. The energy loss can be measured by detecting a variation of voltage of an A.C. bridge circuit including said coil as a component.

Abstract: Apparatus is disclosed for locating and measuring wear in nuclear reactor control rods. Circumferential and radial eddy current test probes produce outputs corresponding respectively to volume and thickness of the control rod. A method is disclosed to determine cladding wear when the volume and thickness varies beyond preselected limits.

Abstract: A method and apparatus for measuring casing wall thickness using an axial main coil for generating a flux field enveloping the casing wall, and sensing actual field distribution by means of plural radial sensing coils each disposed at a radial position within the casing thereby to derive data sufficient to model a reference calibration for good casing wall structure; and, sensing flux leakage from the casing wall to detect anomalies of wall structure relative to the established reference calibration for output indication versus position along the casing.

Abstract: There is disclosed a method for detecting corrosion on the walls of conductive containers wherein a transmitting antenna induces a current into a portion of the container wall and the decay of the induced current is detected by a receiving antenna, with a record of the decay of the induced current being created. The record is interpreted to determine the thickness of the container wall portion and the presence or absence of corrosion is inferred. The effects of variations in distance between the transmitting antenna and the receiving antenna and the pipe wall at one location on the pipe and between the transmitting antenna and the receiving antenna and the pipe wall at another location on the record of the decay are corrected for by examining the rate of decay of the induced current.

Abstract: There is disclosed a method for detecting corrosion on the walls of conductive containers wherein a transmitting antenna induces a current into a portion of the container wall and the decay of the induced current is detected by a receiving antenna, with a record of the decay of the induced current being created. The record is interpreted to determine the thickness of the container wall portion and the presence or absence of corrosion is inferred. One method of interpretation uses reference records from container walls having known parameters for comparison. Another method of interpretation examines the times that the induced current reaches the container wall portion surface that is farthest from the antennas.

Abstract: An apparatus and method for measuring the gap, tram, deflection, and wear of rotating grinding plates wherein inductive sensors are mounted in a recessed manner inset from the surface of a first grinding plate and located opposite recessed non-wear surfaces of a second grinding plate, thereby providing data by which plate gap and plate wear may be derived. A plurality of such sensors provide data by which plate tram and/or deflection may be deduced.

Abstract: A sensor including an eddy current loop and an ultrasonic transducer transmitting along a common axis is placed against a second surface of a graphite/epoxy composite structure whose first surface has been formed over the surface of a steel model. The eddy current coil can produce a signal measuring the separation between the sensor and the surface of the steel model, and the ultrasonic transduer can produce a signal representing the thickness of the graphite/epoxy composite panel. The distance and thickness signals are passed to electrical circuitry that computes their difference and displays the calibrated result as a measure of the gap between the steel model and the graphite/epoxy tool.

Abstract: A contacting thickness gauge for measuring the caliper of paper includes a U-shaped pole piece on one side of the paper with a return path being provided by a simple ferrite slab on the other side where the magnetic reluctance of the gaps provides a measure of the caliper. The pole piece has one leg of relatively small diameter contacting the paper; the other larger leg of the U-shaped pole piece being spaced from the paper by either jewel or air bearings to minimize the contact with the sensitive surface of the moving sheet material. The area ratio provides for an insensitivity of the gap of the large leg. In addition, the stray self inductance of the windings is eliminated due to the use only of a mutual inductance measurement to determine the final resonant frequency which is a measurement of the caliper.

Abstract: A method and an apparatus are provided for testing final coating layer thicknesses on motor vehicle bodies by means of measuring probes moved along a body by way of automatic manipulators. A measuring probe (20), disposed in a guide member suspended on gimbals, is attached to the surface of the body by means of a suction cup (15), an inner stop ring (16) and a spring (21) which cooperate to ensure that the measuring probe is applied with a specific pressure.

Abstract: The sensor is constituted by a magnetic core with pole pieces and by an electric coil wound on the body of said core. With said coil there are associated a sinusoidal current generator and impedance measurement means. A processor determines the thickness from the measured value of said impedance.

Abstract: A probe (10) inductively couples radio-frequency electromagnetic energy into a test piece that is made of a multi-ply graphite-epoxy composite material whose fiber volume, ply count and/or thickness are to be measured. The probe (10) and the test piece form a system characterized by an electrical impedance vector, whose magnitude and phase are determined by the composition of the test piece. A frequency synthesizer (16) drives a compensating circuit (15), which applies the output of the frequency synthesizer (16) to the probe (10). The waveform and frequency of the frequency synthesizer (16) are selected to optimize the amount of energy coupled from the probe (10) into the test piece.

Abstract: A non-contacting, eddy current, measuring method for determining the thickness and temperature of a moving metal sheet as in a metal rolling operation. Two separate magnetic fields are generated by applying two voltages of differing frequencies to a primary winding on one side of the sheet to induce two voltages in an opposed secondary winding on the other side of the sheet. The generated voltages are used to determine the calibration constants required to calculate the thickness and temperature of the moving sheet.

Abstract: A method of measuring a characteristic, such as thickness, of a test part makes use of the variation in impedance of a coil in a senor caused by eddy currents generated as a result of the proximity of the test part. The sensor measures two orthogonal components of the complex impedance. In use the sensor is moved towards the test part until one component of the impedance reaches a predetermined value and the characteristic measured as the value of the other component. The first component is selected during calibration as that component which is most sensitive to variation in the distance between the sensor and the test part.

Abstract: A tubing trip tool for use in determining the extent of defects in tubular sections of a continuous tubing string used in subterranean oil and gas wells is disclosed. The tubing trip tool is mounted on a surface rig surrounding the tubing string and defects are magnetically detected during tubing removal from the well bore. The tool comprises a segmented expandable detector head containing elements for measuring average wall thickness and local and axially extending defects. The expandable head is spring loaded and pneumatically actuated. Coupling detectors are located on the ends of the head to count tubing sections and to detect the presence of obstructions on the tubing to prevent damage to the detector head.

Abstract: A probe for the continuous measurement of the thickness of strips of electrically conducting, magnetic or nonmagnetic strips of material, comprises a the measuring pole (7) arranged in a roller (4) with a narrow running surface. The roller (4) has a ring-shaped crowned middle part (9) in alignment with the measuring pole (7) and is pivoted on a fixed axis of rotation (10) on both sides of the measuring pole (7). The axis of rotation (10) forms part of a housing (12) which screens the measuring pole (7) against external magnetic fields. The roller (4) can consist of a suitable nonmagnetic material, such as nonmagnetic steel, bronze, titanium, ceramic, etc., and the probe can operate according to the magnetic inductive process, according to the eddy current process or according to a combination of these two processes.

Abstract: A sewing machine with a sensing device positioned ahead of a stitch-forming point, senses changes in the thickness of a material being fed by the sewing machine. In order to determine the difference in thickness, the sensing device has a pickup foot capable of vertical movement with a sensing surface that lies on the material adjacent the point the stitch is formed. A sensing lever is movably mounted on the pick-up foot with a sensing arm that lies on the material ahead of the sensing surface, a measuring member detects the relative movement between the pickup foot and the sensing lever.

Abstract: Apparatus for measuring thickness, two light measuring heads (2, 3) being mounted by air bearings in housings on either side of the web (1). The measuring heads are provided with specially implemented nozzles blowing against the surface and maintaining a constant distance of 60-100 m to the respective paper surfaces. The thickness is measured by the distance between the nozzles being measured via an electrical measuring probe (13) in one, and a means (13') sensed by the measuring probe. By the special implementation of the nozzles (12, 12') and by their being pneumatically pressing (via 11) against the surfaces, great accuracy (better than 0.5 m) is achieved even if the position of the paper is altered, rapidity also being considerable. The time to indication for a thickness alternation of about 100.mu. is about 0.5 msec.

Abstract: A procedure for nondestructively determining a physical characteristic of a test object (10) involves introducing an electromagnetic energy pulse into the test object, and measuring elapsed time before the signature of a time-dependent function of the energy thereby propagated through the test object (10) reaches a value larger than a pre-set threshold value. For example, the volume density of graphite fibers in a graphite-epoxy composite material can be determined by introducing a pulse of radio-frequency electromagnetic energy into the composite material, and by measuring the elapsed time before the voltage signature of the energy propagated through the composite material reaches a value larger than the threshold value.

Abstract: A method and apparatus are provided for effecting the inspection of a ferromagnetic element, or piping, and particularly piping that is already installed. The invention incorporates a device for indicating wall thickness of a length of the ferromagnetic element, including means for producing a value of magnetic flux extending longitudinally through a portion of the element. A voltage generating device is disposed in surrounding relationship to the element and is movable axially relative to the length of the element containing the value of the magnetic flux. Means for indicating the voltage generated in the voltage generating means by the value of the magnetic flux also are provided. Preferably, an axially split spool is provided which may be closed in surrounding relationship to an installed pipe. A saturation level of magnetic flux is induced in the pipe by a flexible cable which is wrapped around the spool in a multi-turn configuration and supplied with electrical current sufficient to produce saturation.

Abstract: A method and apparatus are provided for effecting the inspection of a ferromagnetic element, or piping, and particularly piping that is already installed. The invention incorporates a device for indicating wall thickness of a length of the ferromagnetic element, including means for producing a value of magnetic flux extending longitudinally through a portion of the element. A voltage generating device is disposed in surrounding relationship to the element and is movable axially relative to the length of the element containing the value of the magnetic flux. Means for indicating the voltage generated in the voltage generating means by the value of the magnetic flux also are provided. A saturation level of magnetic flux is induced by a multi-turn supplied with electrical current sufficient to produce saturation. The voltage induced in a central pickup coil is amplified, integrated and correlated to average thickness of the pipe.

Abstract: For measuring a property such as caliper of a traveling sheet, a sensor body and a target body are located on opposite sides of the sheet and constrained (e.g., by gas bearings) along a sensor path intersecting the path of the sheet. Gas bearings maintain these bodies at, substantially constant distances from the opposite surfaces of the sheet while permitting them to move in response to the position and thickness of the sheet. An active sensor element aboard the sensor body and a passive sensor element aboard the target body interact through the sheet to produce aboard the sensor body a response dependent on the sheet property. Manifestations of this response, such as light beam modulations, are produced, without solid bodily connections, at a location spaced from the sensor body where the manifestations are detected to produce a sheet property-indicative signal.

Abstract: A method and apparatus for determining the extent of defects in ferromagnetic tubular elements comprising a continuous string for use in an oil or gas well is disclosed. The tubing trip tool measures tubing average wall thickness, local defects, such as corrosion pitting, and axial defects, such as sucker rod wear during removal of the tubing from the well. Tubing velocity is also measured, and couplings between tubing sections are detected and counted, in order to specify the axial location of defects on each tube, and also provide a profile of the condition of the overall string. A saturating magnetic field and a fluctuating magnetic field are applied to the tubing and the magnitude of the induced fields and the changes are measured to quantify defects in the tubing.

Abstract: A gauging apparatus for sheet materials and the like comprises a surface follower body (14,20,30) adapted to be constrained without substantial solid bodily contact and guided (e.g., by gas bearings between 32 and 36 and 38) for movement along a surface follower path that intersects the path of a traveling sheet (10) to be gauged. The body has a passage (46) adapted to carry a flow of pressurized gas to be discharged against one surface of the sheet. The discharge of the gas is effective when the body is at a predetermined distance from the surface to generate a levitating force (on 20) urging the body away from the sheet surface. Means (70,64,62) responsive to the pressure of the gas in the passage exerts on the body (at 64) a counteracting force that tends to move the body closer to the surface.

Abstract: An apparatus such as a caliper gauge can be utilized in performing a measurement, such as a thickness measurement, of a traveling sheet or the like. The apparatus comprises a surface follower body (18, 72, 74) adapted to be constrained during the measurement for movement along a surface follower path intersecting the path of the sheet (10, 80) and urged by a force toward one surface of the sheet. The body has a gas confining wall (32a, 90, 104) bounded by a uniformly distributed pressurized gas supply aperture or apertures (46, 92, 106) for pressurizing a gas bearing region (48, 108, 110) contiguous to the sheet surface with sufficient pressure against the sheet and the wall to levitate the body against the urging force. The pressurization is effected without producing substantial amounts of high velocity gas flow over the surface of the sheet within the gas bearing region.

Abstract: A pulsed magnetic procedure and apparatus for measuring wall thickness. It is especially applicable to pipelines. It includes pulsing a magnetic reluctance coil that is located close to the wall, and measuring the inductance of the pulsed coil. Also the distance of the coil from the wall is accurately determined so that the inductance is a measure of the wall thickness.Apparatus may include the combination of an ultrasonic transducer mounted fixed relative to the magnetic pulse coil and arranged so that ultrasonic energy pulses are directed toward the wall. In this manner reflected ultrasonic pulses will provide a measure of the distance. In addition, by proper angle thereof, ultrasonic pulses may also determine the presence of any anomaly.