Abstract: A method and apparatus for testing steel components for temper embrittlement uses magneto-acoustic emission to nondestructively evaluate the component. Acoustic emission signals occur more frequently at higher levels in embrittled components. A pair of electromagnets are used to create magnetic induction in the test component. Magneto-acoustic emission signals may be generated by applying an AC current to the electromagnets. The acoustic emission signals are analyzed to provide a comparison between a component known to be unembrittled and a test component. Magnetic remanence is determined by applying a DC current to the electromagnets, then turning the magnets off and observing the residual magnetic induction.

Abstract: The invention provides an arrangement for determining the speed and rotor position of an electric machine, which arrangement consists of a tachometer generator having a permanent-magnet-excited rotor and a coaxially arranged rotor position transmitter which has a rotor body equipped with permanent magnets. Around the circumference of the rotor body magnetic-field sensitive sensor elements are arranged. A compact assembly of the tachometer generator and rotor position transmitter without detrimental mutual interference is possible by the provision that first permanent magnets magnetized in the tangential direction are arranged centered to the pole gaps of the tachometer generator rotor at the rotor body in such a manner that the sides of two adjacent permanent magnets facing each other have the same polarity as the magnet pole extending between the respective pole gaps of the tachometer generator rotor.

Abstract: A method and apparatus for ascertaining internal stresses in a hardened region to be tested for a component made of a predetermined material includes measuring coercive field strength and amplitude of magnetic Barkhausen noise as a function of mechanical stress and hardness in calibration samples of a predetermined material of known hardness and known internal stress. Calibration functions are ascertained from the measured values indicating the dependency of the hardness and the amplitude of the magnetic Barkhausen noise as functions of the hardness and mechanical stress. The coercive field strength and the amplitude of the magnetic Barkhausen noise is measured in a location-dependent manner over the region of the component to be tested. The measured values of the coercive field strength and the amplitude of the magnetic Barkhausen noise are converted in the region to be tested into location-dependent hardness and into location-dependent mechanical stress using the ascertained calibration functions.

Abstract: A proximity detection system having two eddy current probes, one a measurement and the other a reference probe. In one embodiment, one probe is energized by a high frequency AC signal and the other by a DC signal. The energizing signals are periodically switched between the two probes and the difference between responses of the probes when AC energized is detected. The difference eliminates drift and variations in the probe outputs from environmental effects like temperature, one of the probes measures the proximity of a selected material, and the other probe is set-up with a target of the same material at a constant distance, as a reference. The DC constant current signal which alternately energizes each probe when not energized by the AC signal, prevents each probe from being dead when not energized by the AC signal. The probes are operated in a resonant mode to increase both the system linearity and sensitivity to target position.

Abstract: There is disclosed herein a method and apparatus wherein conveyor belt cords are first de-gaussed to remove any stray magnetic fields, and then longitudinal unidirectionally magnetized. The belt is then magnetically scanned and the electrical output signal is passed through a low pass filter in order to produce a break signal indicative of breaks in the magnetically permeable cords of the conveyor belt.

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 proximity detector includes a magnet having steel or iron pole piece plates mounted at front and rear pole ends of the magnet, and a silicon integrated circuit mounted to the outer surface of the front pole piece centered about at the magnet pole axis. The integrated circuit includes two essentially identical Hall elements having outputs connected series opposing, i.e. differentially rather than aiding, so that distortion of the magnet field ambient to the integrated circuit caused by a ferromagnetic article passing by results in a gradient field between the Hall elements producing a differential output signal. The dual Hall element integrated circuit leads to a low differential composite offset voltage while the front pole piece renders the magnetic flux density much more uniform further reducing this dual-Hall-element composite offset voltage.

Abstract: In a pipeline through which a vehicle such as a pig is travelling, a magnetically activated detector detects the presence of the approaching pig and sends a signal to switch on a transmitter unit which supplies an alternating current to an AC coil. This generates a magnetic field for a preselected period, the flux signal being then sensed by a pair of crossed coil sensors on board the pig after which the signal is processed in a unit on-board the pig. A reference pulse is then output for recording on a tape recorder also on-board the pig. This technique enables a geographical reference of the vehicle to be fixed.

Abstract: An apparatus by which a sensor holder of a surface testing apparatus can be moved along a preselected path of movement over the surface to be examined. The apparatus has a guide rail establishing the path of movement, which can emulate the contour of the surface and on which the sensor holder is supported.

Abstract: An electrical defect testing device for a non-magnetic test object, for example crack detection on hot continuously cast billets, is provided with means for detecting and suppressing the influence of disturbing magnetic regions of the object (e.g. regions of cold oxide scale). The device comprises at least one sensing transducer for harmful faults which is adapted to move relative to the test object. At least one detector is associated with the transducer for identifying the presence of magnetic material, and a blocking circuit is provided which, directly or indirectly, is controlled by the magnetic detector and is used for suppressing signals originating from a fault vector, for example a signal indicating a harmful fault. The presence of magnetic material can be detected using an eddy current technique.

Abstract: A system for measuring the hardness of cartridge cases employs an eddy current probe for inducing and sensing eddy currents in each cartridge case. A first component of the sensed signal is utilized in a closed loop system for accurately positioning the probe relative to the cartridge case both in the lift off direction and in the tangential direction, and a second component of the sensed signal is employed as a measure of the hardness. The positioning and measurement are carried out under closed loop microprocessor control facilitating hardness testing on a production line basis.

Abstract: A system is disclosed for nondestructive object testing comprising a magnetic probe responsive to an excitation signal for generating a magnetic field and thereby inducing eddy-currents in the object. The probe further provides an output signal indicative of the presence of a flaw in the object. A distance sensor generates an output signal indicative of the spacing of the probe from the object. Circuitry is provided for receiving the distance sensor output signal and is responsive thereto to supply such excitation signal to the probe. The circuitry employs the distance indication in the distance sensor output signal as an exponent in generating the excitation signal.

Abstract: A detector for producing an electrical signal proportional to the concentration of ferromagnetic particulate material in a fluid stream includes a sensing coil arranged to form the inductance coil of a radio frequency oscillator arranged to produce an electrical signal at a base frequency, a magnetic trap for producing a magnetic field and a support for supporting the sensing coil and the magnetic trap in juxtaposition to one another such that, when the coil is disposed within or proximate the fluid stream and electrically connected to the oscillator, energization of the magnetic trap causes ferromagnetic particulate material proximate the coil to be attracted toward the coil resulting in a deviation of the frequency of the signal from the base frequency proportional to the concentration of ferromagnetic particulate material in the fluid stream.

Abstract: A system for verified detection of flaws in an object, comprises a synchronizing sensor for generating an output signal once per mutual rotational revolution as between itself and the object, a flaw sensor for generating output signals responsive to detection of flaws in the object and extraneous influences, a switch unit responsive to operator input for providing output signals respectively indicative of a preselected number of flaws for such flaw verification and of a preselected number of object revolutions for such flaw verification, and a processor responsible to the output signals of the sync sensor, the flaw sensor and the switch unit for providing verified flaw output indication.

Abstract: A method and apparatus for measuring the overlayer of a nonmagnetic mater such as concrete and the diameter of steel reinforcement bars embedded therein. A steady state magnetic flux field is generated in the area of the concrete which is to be tested. A reinforcement bar embedded within the concrete generates a scatter field which is superimposed on the excitation field. By scanning the concrete surface, an amplitude locus is determined which is subtracted from an amplitude locus determined in the absence of ferromagnetic objects, whereby a difference locus is obtained. The concrete overlayer and the diameter of the steel reinforcement bar are determined from the location and magnitude of the maximum values of the difference locus with the aid of an evaluation computer.

Abstract: A wire rope tester which can detect broken wires, area reductions, or wire contact irregularities. The tester includes two permanent magnetic stacks which produce axial adjacent and opposed DC magnetic fields which magnetize the rope. Broken wires are indicated by flux variations when the flux density is at saturation; area reductions are related to flux variations; also at saturation flux density; and wire contact pattern changes produce detachable eddy current flux variations when the flux density gradient is constant.

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 method and apparatus for the determination of thickness of plastic materials, as well as of bonding and coating materials, by high frequency electric and magnetic alternating fields. The method enables a simple test of components, as well as of coatings and bondings, even if the plastic parts to be tested or the coatings or bondings to be tested are not yet completely cured and the surfaces to be tested are located, so as to be concealed or are accessible only with difficulty. The method and apparatus consists in that electrically conductive or ferromagnetic particles are added to the materials to be measured and subsequently the electrical conductivity or magnetic permeability is measured at the completed or coated test specimen by high-frequency electrical and magnetic alternating fields, whose progression in space and time is adapted to the measuring task.

Abstract: A method and apparatus for determining the extent of axially extending defects in ferromagnetic elements, such as tubing comprising a continuous string for use in an oil or gas well is disclosed. The tubing trip tool detects axial defects, such as sucker rod wear during removal of the tubing from the well. 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 magnetic detector for detecting the magnetic field of a magnetic field generating substance including an even number of saturable coils aligned in a straight line with the distance between adjacent ones larger than the width of the magnetic field generating substance. The saturable coils are separated into at least two pairs, and a high frequency oscillator is provided to supply a high frequency voltage through a resistor circuit to each pair of the saturable coils. A rectifying voltages circuit is arranged across the resistors in a differential manner as an output. When the magnetic field generating substance is displaced over an interval wider than the width thereof relative to the saturable coils, the magnetic detector generates a linear output voltage.

Abstract: Apparatus for electromagnetically testing pipeline walls of steel or the like ferromagnetic material which is equipped, for example with a magnetizing coil for leakage-flux measurements, can be extended for ultrasonic measurement which is inductively excited and inductively measured with regard to the travel time as far as a reflecting surface and back, in the disposed in one or more of the pole regions there is a high-frequency current coil for the transmission and/or reception of steep-edged waves which are inductively coupled at the wall of the pipeline. The associated method starts from a stationary magnetic field in which high-frequency current pulses are produced in order to initiate vibrations in the pipe wall through induced currents. The travel time of these vibrations to a reflecting point and back can be measured in order to obtain an indication regarding the intact thickness of the pipe wall.

Abstract: A device for measuring or testing of an object, for example rolled wire, a tube, or a billet, to detect surface discontinuities employs a sensing transducer which is oscillated backwards and forwards over the surface of the test object by means of a motor, the oscillations taking place in the form of a curved path extending transversely of the longitudinal extent of the object.

Abstract: An improved method and apparatus for monitoring the thickness of a film includes a sensor roll which cooperates with a compliant roll to form a nip through which the film passes. As the two rolls rotate relative to each other, magnets disposed in the sensor roll are sequentially moved to and from the nip. As a magnet moves by the nip, the field emanating from the magnet is concentrated by a body of material having a relatively high magnetic permeability and disposed in the compliant roll. This results in an induced voltage being generated in a sensor coil. The output from the sensor coil is transmitted to control circuitry which effects operation of a suitable apparatus to control the thickness of the film.

Abstract: The specification describes a method and an apparatus for detecting and quantitatively assessing wear of a machine having ferromagnetic components subjected to wear during operation resulting in the production of ferromagnetic particulate wear debris, and a lubrication system utilizing a lubricating fluid, in which the wear debris becomes entrained, for lubricating the components. The method comprises the steps of passing a sample stream of the lubricating fluid at a predetermined rate of flow axially through the core of an inductance coil of a sample oscillator for producing a time varying signal which deviates from a predetermined value in proportion to the mass of ferromagnetic material contained in the fluid passing through the core, monitoring the rate of change of signal and activating an indicator when the rate of change of the signal exceeds a predetermined level.

Abstract: Apparatus for determining the location of surface defects on a test piece of electrically conductive material by scanning the surface with at least one sensor arrangement comprising proximity sensors based on eddy current induction. The test piece may be moveable, e.g. advanced, in relation to the holder arrangement which is arranged to move the sensor arrangement in a sweeping or scanning movement from one side of the test piece to the other. The position of the edge of the test piece, is determined successively, e.g. for each scan cycle and the location of detected cracks is calculated with a starting point from the detected edge position.

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 and apparatus for measuring the thickness of thin metallic layers deposited on a conductive support, wherein the thickness is determined from the measurement of the losses corresponding to the Joule effect, due to the eddy currents which appear when a magnetic circuit excited by an alternating voltage is brought close to the metallic surface.

Abstract: Equipment to measure flaws in an object using an eddy current. According to this equipment, attention is given to a relation between the amplitude of signal detected when the eddy current probe is scanning and the position of the eddy current probe, and the size of flaw is measured based upon the fact that scan distance of probe in which flaw detection signals of greater than a predetermined threshold value are obtained, is subject to change depending upon the depth of penetration of eddy current.

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 method and apparatus for determining the extent of defects in ferrogmagnetic elements, such as tubing comprising a continuous string for use in an oil or gas well is disclosed. The tubing trip tool measures the depth of local defects, such as corrosion pitting, 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 is applied to the tubing and a comparison of two derivatives of flux leakage is made to quantify defects in the tubing.

Abstract: A torque sensor for electrically detecting torque, such as the torque of an automobile engine, wherein a strain disk is provided in the path of torque transmission and the torque is magnetically detected in terms of the magnetostriction generated in the strain disk. The torque sensor comprises a magnetic rotating disk and a magnetic sensor disposed in the vicinity of and opposed to the strain disk. The magnetic sensor comprises a detection coil and an excitation coil oriented perpendicularly to each other with the excitation coil ordinarily being disposed outside of the detection coil. Supplying alternating current to the excitation coil causes an alternating field to be produced within the strain disk and the configuration of this alternating magnetic field is varied by the anisotropy of the strain caused within the strain disk by the transmitted torque.

Abstract: Defect detection in testing pipes, particularly in heat exchangers of nuclear reactors by means of eddy current in which interference influences due to the design are suppressed by measurements with different frequencies and the frequencies interlinked to give a signal only if there is a defect indication.

Abstract: A system for online-detection of a transformation value and/or a flatness of a steel or a magnetic material includes: an exciting coil disposed at either side of the plate-shaped steel or magnetic material and capable of generating alternating magnetic fluxes by alternating current excitations; two or more detecting coils arranged on the same side as the exciting coil and at positions different in distance from the exciting coil, and mutually induced with the exciting coil; and an arithmetic unit for obtaining the transformation value and the flatness of the steel or the magnetic material or either one of those from a difference between detection signals generated from a difference in values of interlock magnetic fluxes in the respective detecting coils. The transformation value and the flatness of the steel or the flatness of the magnetic material can be detected with high accuracy.

Abstract: Methods and apparatus for sensing, switching and modulating relying upon apparent resonant properties of thin conductive materials are provided in accordance with the teachings of the present invention. According to the present invention, an output of an oscillating circuit is selectively varied as a function of the relationship between a coil within the oscillating circuit, a thin conductive member and the apparent resonant condition of the thin conductive member to achieve appropriate sensing, switching and modulating conditions.

Abstract: A device for detecting defects in the bore of a tubular member. The device includes an inspection head including an electromagnet for magnetizing the internal surface of a tubular member. The device also includes a sensor or sensors to detect magnetic flux leakage indicative of a defect. The magnetic flux sensor output is sent to a control-data acquisition system concurrently with signals as to the axial and circumferential position of the defect, which are obtained by their respective encoders. The control-data acquisition system is capable of processing and displaying the data in analog and digital form.

Abstract: An apparatus for determining the position of an object has an outer fixed field winding extending along an axis, a source for energizing the field winding with alternating current and thereby creating a magnetic field, and an inner coreless detecting winding displaceable coaxially in the field winding. Thus the field induces a voltage in the inner winding. A link displaces the detecting winding axially in the field winding with the object and thereby changes the voltage induced by the field in the detecting winding. An equalizing winding coaxial between the field winding and the detecting winding is fixed in the field winding. The field also induces a voltage in the equalizing winding. An electronic unit divides the voltages induced in the detecting and equalizing windings into each other and derives a detection signal corresponding to the position of the object and inner winding relative to the outer winding.

Abstract: An improved method and apparatus for monitoring the thickness of a film includes a sensor roll which cooperates with a compliant roll to form a nip through which the film passes. As the two rolls rotate relative to each other, magnets disposed in the sensor roll are sequentially moved to and from the nip. As a magnet moves by the nip, the field emanating from the magnet is concentrated by a body of material having a relatively high magnetic permeability and disposed in the compliant roll. This results in an induced voltage being generated in a sensor coil. The output from the sensor coil is transmitted to control circuitry which effects operation of a suitable apparatus to control the thickness of the film.

Abstract: The specification describes a method and an apparatus for detecting and quantitatively assessing wear of a machine having ferromagnetic components subjected to wear during operation resulting in the production of ferromagnetic particulate wear debris, and a lubrication system utilizing a lubricating fluid, in which the wear debris becomes entrained, for lubricating the components. The method comprises the steps of passing a sample stream of the lubricating fluid at a predetermined rate of flow axially through the core of an inductance coil of a sample oscillator for producing a time varying signal which deviates from a predetermined value in proportion to the mass of ferromagnetic material contained in the fluid passing through the core, monitoring the rate of change of signal and activating an indicator when the rate of change of the signal exceeds a predetermined level.

Abstract: An eddy current magnetic field effects measurement apparatus employs, a reference sensor located so that it measures an applied field and any environmental fields but does not measure eddy current effects. Then an estimate(s) of the applied field at the locus of a plurality of measurement sensors is constructed and stored. Next, a conductive object or material to be measured is placed in the applied field in the vicinity of the plurality of measurement sensors away from the reference sensor and measurements are made of the applied field, any environmental fields and any fields due to the effects of eddy currents induced into the conductive object or material. Finally, the aforementioned stored estimate(s) are used to compensate the applied field at the locus of the plurality of measurement sensors so that the eddy current magnetic field effects due to the placement of the conductive object or material can be observed on a keyboard/display or printed via a printer/plotter.

Abstract: A flaw detection apparatus for detecting flaws at the outer surface of a product, such as a steel bar, wire or steel pipe, which is round in section and produced by the hot rolling, by use of a probe of non-contact type and rotating around the product to be inspected, the apparatus providing a means for suppressing vibrations of an object to be inspected, a means for measuring a distance (lift-off) between the object to be inspected and the probe, and a means for carrying out positional control on the basis of the detection result of the lift-off measurement so that the axis of rotation of probe is allowed to be coincident with the axis of object to be inspected.

Abstract: A tubing trip tool for use in determining the extent of defects in tubular elements comprising a continuous string used in a subterranean oil or gas well during removal of the string from the well is disclosed. Local defects and axially extending defects, as well as the average wall thickness of the tubular elements, are measured. The position of the defects is determined by measuring the variable velocity of the tubular elements as they are removed from the well and by detecting end couplings having a larger cross-sectional area and the direction in which the end couplings are moving. A string profile of the position of the defects in the continuous string can also be established.

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, and axial defects, such as sucker rod wear during removal of the tubing from the well. Tubing velocity is also measured. A saturating magnetic field and a fluctuating magnetic field are applied to the tubing. Signals corresponding to changes in the induced fields are divided into channels for complete circumferential coverage. Phase shift is then determined by a zero crossing technique to quantify axial defects, such as sucker rod wear.

Abstract: A method and an apparatus for testing materials using the eddy current principle enables a better exploitation of the sensitivity of measurement. Initially, the complex values appearing during a test cycle are examined as to whether only disturbance signals, disturbance signals in connection with flaw signals, or only flaw signals are present. The complex values are selectively further processed directly if there are flaw signals only, or are further processed for disturbance signal elimination. The direct further processing as well as the further processing made after elimination of the disturbance signal comprises the determination of the type of flaw and the depth of the flaw.

Abstract: The invention relates to a portable device for the non-destructive examination of a surface along a line, by means of at least one detection probe displaced along said line and guided by a guide removably fixed on said surface, wherein said guide has a length such that any portion of said line of comparable length presents a negligible variation in curvature, said probe is mounted in a probe-holder adapted to be displaced by hand and connected to said guide in rigid manner parallel thereto and in loose manner transversely to said guide, and means are provided for indicating, at each instant of a displacement of said probe-holder along said guide, the position of the probe-holder on the latter. The invention is particularly applicable to the verification of the riveted joints of aircraft fuselages.

Abstract: A technique for detecting flaws in a metal product which uses a combined eddy current and magnetic flaw detection technique. A first magnetic field having flux lines parallel to the surface of the test object and a second field having flux lines perpendicular to the surface of the test object are generated. The resultant magnetic field is affected by faults in the metal test object. A magnetic field detector adjacent the test object detects the resultant magnetic field and produces an output signal which is processed by a circuit to provide a pair of component signals representing the portion of the output signal corresponding to the individual components of the resultant magnetic field, thus providing an indication of the type of faults that are present in the test object.

Abstract: Apparatus for detecting flaws on the circumference of a rounded bar of metal. A circular rotator means held by a support is rotated around the material to be inspected for flaws. The rotator means has a number of probes which are revolved around the circumference of the material to detect flaws when the rotator means is rotated. If and when the material deviates from its axis predetermined through the apparatus while passing therethrough, the deviation is detected and the support is displaced in the same direction and distance as the material so that the probes remain spaced apart from the circumference of the material at a predetermined distance while inspecting the material for flaws.

Abstract: Technical functional components variable relatively to a starting position are examined by comparing an image of the component, produced by relative motion with respect to sensor means, with a corresponding earlier, stored image, and by triggering a warning signal in accordance with the congruence and/or the differences of the two images.

Abstract: A liftoff suppression apparatus utilizing a liftoff sensing coil to sense the amount a ferromagnetic resonance probe lifts off the test surface during flaw detection and utilizing the liftoff signal to modulate the probe's field modulating coil to suppress the liftoff effects.

Abstract: Measurement apparatus receives a signal from an eddy current transducer (20) excited by a generator (24). A signal generator (21) generates a signal at a predeterminable reference level which is combined with the transducer signal to produce a measurable signal at output (23). The output of the signal generator (12 ) is determined by a set balance control (15) which may be set by amplitude controls (29,30) in accordance with control coefficients applied via data bus 43. The output of the signal generator (21) may be predetermined iteratively in a calibration phase preceeding measurement. The present invention overcomes the problem of providing an inactive matched eddy current transducer to balance the signal provided by the measurement transducer (20). A second transducer (49) may be switched (50) to replace the signal generator (21) to enable positioning of the measurement transducer (20) with respect to a workpiece.