Abstract:
Die Erfindung betrifft einen Wirbelstromsensor (100) mit einer Sensorspule (102), einer Sensorfläche (104) und einem Federelement (106). Die Sensorspule (102) ist elektrisch leitfähig und dazu ausgebildet, ein elektromagnetisches Wechselfeld (108) bereitzustellen. Die Sensorfläche (104) ist dazu ausgebildet, das elektromagnetische Wechselfeld (108) zu beeinflussen. Die Sensorspule (102) und die Sensorfläche (104) sind beweglich zueinander angeordnet. Das Federelement (106) ist mit der Sensorspule (102) und der Sensorfläche (104) gekoppelt oder wird durch die Sensorfläche (104) gebildet, und ist dazu ausgebildet, einer Relativbewegung zwischen der Sensorfläche (104) und der Sensorspule (106) mit einer Federkraft (1 14) entgegenzuwirken.
Abstract:
Le capteur proposé est un capteur électromagnétique de forces. Son principe de fonctionnement repose sur le phénomène d'influence par induction magnétique entre deux bobines plates, de même diamètre et comportant le même nombre de spires, situées à une certaine distance, x, l'une de l'autre, sur un même axe passant par leurs centres. L'une des bobines est fixée sur un support horizontal, et alimentée par un oscillateur de Wien, avec des conditions de phase et d'amplification précises. Cette bobine engendre une tension sinusoïdale de 84Hz et d'amplitude 2.5V. La deuxième bobine plate est enroulée sur un cylindre isolent, relié à l'extrémité d'un ressort. L'autre extrémité de ce même ressort est accrochée à un support fixe. La deuxième bobine est donc solidaire au cylindre suspendu verticalement au ressort. Les deux bobines, le ressort et le cylindre sont alignés sur un même axe vertical. Le cylindre joue le rôle de guidage, puisqu'il peut se déplacer verticalement et traverse un orifice sur le contour duquel est placée la bobine fixe. A l'extrémité inférieure du cylindre, nous avons fixé un crochet permettant de suspendre des masses ou accrocher une tare pour poser des masses. L'induction magnétique créée par la bobine fixe, donne naissance à une force électromotrice aux bornes de la bobine mobile, qui dépend de la distance x entre les bobines. Lorsqu'on pose une masse sur la tare, le ressort s'allonge, le cylindre se déplace vers le bas, et la distance x entre les bobines diminue. Cela se traduit par une augmentation de la tension aux bornes de la bobine mobile. Le ressort joue donc le rôle d'un convertisseur force - déplacement. Le dispositif conçu est un capteur électromagnétique de forces, et peut être considéré aussi comme un capteur de déplacements : - Capteur de forces : de 0 à 10g, avec une précision de 8mg ≤ Δm ≤ 20mg; - Capteur de déplacements : de 0 à 5mm, avec une précision de 4μm ≤ Δx ≤ 10 μm. Dans les meilleures conditions de fonctionnement, les précisions de ces capteurs deviennent : 4mg ≤ Δm≤ 10mg et 2μm ≤ Δx ≤ 5 μm. Enfin, des améliorations pourraient être apportées à ce capteur, pour le rendre plus performant et prometteur à de nombreuses applications industrielles.
Abstract:
The invention relates to a system for calibrating and measuring the magnetizability of at least a part of a rail, for instance a rail for guiding means of transport. The system includes a magnetic field generator (MFP) for generating a changing magnetic field transverse to a longitudinal direction of the rail. The magnetic field generator comprises a substantially saddle - shaped transmitter coil (Wl) arranged to be placed partly around the rail. The system further includes an induction detector (M5) for measuring a transverse induction. The system may further include a magnetic field generator for generating a changing magnetic field in the longitudinal direction, an induction detector arranged for measuring a longitudinal induction, and a processing unit arranged for determining a reference induction, on the basis of the transverse induction, and determining a longitudinal mechanical stress in rail on the basis of the longitudinal induction and the reference induction.
Abstract:
An apparatus for the nondestructive measurement of materials that includes at least two layers of electrical conductors. Within each layer, a meandering primary winding is used to create a magnetic field for interrogating a test material while sense elements or conducting loops within each meander provide a directional measurement of the test material condition. In successive layers extended portions of the meanders are rotated so that the sense elements provide material condition in different orientations without requiring movement of the test circuit or apparatus. In a bidirectional implementation the angle is 90° while in a quadridirectional implementation the relative angles are -45, 0, 45, and 90°. Multidirectional permeability measurements are used to assess the stress or torque on a component. These measurements are combined in a manner that removes temperature effects and hysteresis on the property measurements. This can be accomplished through a correction factor that accounts for the temperature dependence. After the corrections, the permeability measurement is then used to assess the local stresses and strains in the material of interest.
Abstract:
Stress in the wall of a pipe (12) is measured using a pig (10) carrying at least one linear array of probes, so that the probes (30) in the array pass in succession over a location on the pipe wall. Each probe (30) comprises an electromagnetic core (32) with two spaced apart electromagnetic poles (34), and a magnetic sensor (36) arranged to sense the reluctance of that part of the magnetic circuit between the poles (34), and an alternating magnetic field is generated in the electromagnet means and consequently in the pipe wall. Successive probes (30) in the array are oriented differently so that the corresponding orientations of the magnetic field in the pipe wall are different. Preferably the probes (30) also include sensors (38) between the two poles (34) to sense magnetic flux perpendicular to the direction of the free space magnetic field between the poles. The signal from the sensor (36) and (38) enable the stress to be determined. Such an array may be used with any long object of ferromagnetic material. (figure 2)
Abstract:
A load cell comprises a magnetostrictive core (83), a coil (85) arranged near the core, and a load detection circuit (10) connected with the coil (85) for detecting the load acting on the core (83). The load detection circuit (10) includes an excitation circuit (102) for supplying AC detection current to the coil (85); a pulse current generator (103) for supplying the coil with reset current greater than the maximum value of the detection current; a switch circuit (104) for switching the excitation circuit (102) and pulse current generation circuit (103) to supply the coil with the detection current following the reset current; and a microcomputer (100) for determining the magnitude of the load acting on a magnetostrictive element based on the change in impedance of the coil in the presence of the detection current flowing in the coil.
Abstract:
An instrument (17) for determining one or more stress characteristics within a surface layer of magnetisable material. Instrument (17) includes probe (7) having a carrier (8) rotatable about a rotation axis (Y) extending perpendicularly outwardly from a magnetisable material surface (M). An electromagnet (1) is mounted on t he carrier (8) and provides a pair of poles (3) spaced apart, one on either side of the rotation axis, on a pole axis (X) so that on carrier rotation the poles (3) circulate about the rotation axis (Y). The electromagnet (1) is energisable to produce a magnetic field (H) between the poles (3). A search coil (5) is fixed relative to the electromagnet (1) between the poles (3), on an axis (x) so as to lie in the magnetic field (H). Drive means (12) is operable to rotate the carrier (8) to selected angular positions. The probe (7) is positioned with the poles (3) adjacent the material surface (M) so that the magnetic field (H) extends into the surface, shifts in the magnetic field (H) caused by stress in the material surface (M) inducing representative voltages in the search coil (5) at the angular positions. Instrument (17) also includes control apparatus (18) for controlling operation of the drive means (12) and, at each selected angular position of the carrier (8) for receiving parameters from the probe (7) for determining the stress characteristics.
Abstract:
A method is described for measuring a change in the mechanical state aiming at detecting the disturbance the change in state has on a magnetic flux (o). This flux is brought to flow through at least a part of the body (1) under the influence of a driving magnetizing force (H0). In order to achieve an unambiguous measuring result the average length ((Alpha)) of the magnetic circuit is kept constant and independent of the change in the mechanical state. The flux (o) consists partly of a main flux (o0) having a definite direction and being of such a magnitude that the magnetic properties of the body depart from the region of irreversibility and partly of an alternating, gradually vanishing flux (oy) superimposed upon the main flux. The alternating flux must have such an initial magnitude that saturation is obtained in both directions of the alternating flux (ov). After the vanishing of the alternating flux (ov the disturbance generated through the change in the mechanical state is indicated or registered as a voltage which is induced by the change in flux corresponding to the disturbance. A device which works as explained above comprises means for generating the flux (o) through the body (1) which is arranged to form a magnetic circuit with at least a part of the body (1). This circuit should be essentially free from air gaps and have an average length ((Alpha)) for the driving magnetic force (H0) which is independent of the change in the mechanical state. The device is arranged to force partly the main flux (o0) and partly the superimposed alternating flux (ov) through the magnetic circuit. By means of a coil system (5) connected to a measuring or indicating device (8) the change in flux corresponding to the disturbance caused by the change in state is detected.