Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
  • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
  • G01D5/20—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature
  • G01D5/2006—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils
  • G01D5/2013—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature by influencing the self-induction of one or more coils by a movable ferromagnetic element, e.g. a core
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
  • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
  • G01D5/20—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature
  • G01D5/22—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature differentially influencing two coils
  • G01D5/225—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature differentially influencing two coils by influencing the mutual induction between the two coils
  • G01D5/2258—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature differentially influencing two coils by influencing the mutual induction between the two coils by a movable ferromagnetic element, e.g. core
  • G01D5/2266—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying inductance, e.g. by a movable armature differentially influencing two coils by influencing the mutual induction between the two coils by a movable ferromagnetic element, e.g. core specially adapted circuits therefor

Definitions

• the present invention relates to a device for detecting a displacement of an object, comprising a ferromagnetic material and which can move along a path, which device comprises a magnetic circuit generator, provided with a first and '' a second ferromagnetic material core as well as an excitation coil and a measurement coil, which magnetic circuit generator is connected to a detection unit arranged to detect a change in reluctance caused in the circuit by the displacement of the object and deduce a position from the object.
• the magnetic circuit generator comprises two U-shaped cores and ferromagnetic material arranged back to back in the same plane.
• the measuring coil is formed by a single coil winding in phase opposition around the central part of each core.
• the excitation coil is itself wound in series around the two cores.
• the detection device is mounted in such a way that the object moves perpendicular to the plane in which the two cores are located.
• the object whose displacement is to be detected is itself formed by a series of ferromagnetic material elements which are each arranged at a predetermined distance from each other.
• the magnetic circuit formed by this core surrounded by the excitation coil will form. Since an alternating current is injected into the excitation coil, the latter will create a magnetic field in the ferromagnetic cores. The elements which move along the path will modify the flux induced in the magnetic circuit, thus modifying the reluctance of the latter. Measuring this change in reluctance using the detector then makes it possible to determine the rate of displacement of the object.
• a disadvantage of the known device is that the magnetic circuit generator is of complex construction. Indeed, the way in which the excitation coil and the measurement coil are arranged requires covering the cores in ferromagnetic material on each side with a shielding plate in non-magnetic material. Thus, the excitation coil is separated from the measurement one. This complexity therefore requires having to build the entire device without being able to use components generally used to detect a variation in the magnetic field.
• a device is characterized in that the magnetic circuit generator comprises a first and a second transformer with open magnetic circuit, said first transformer having the first core and the second transformer having the second core, said transformers being juxtaposed and each comprising an axis which extends through their respective core, said axes extending substantially perpendicular to said path, said excitation coil comprising a series connection of two coils which form the primaries of the first and second transformer and said measuring coil comprising a series connection of two coils which form the secondaries of the first and second transformer, said secondaries being connected in phase opposition.
• the choice of the first and second transformer allows the use of generally used components. Since the transformers are open circuit and their axes extend substantially perpendicular to the path along which the object is moves, the movement of the object along the path will cause the magnetic circuit to close when the object, which contains ferromagnetic material, crosses one of the axes. It being understood that the excitation coil forms the primaries of the two transformers, the voltage applied to the excitation coil will induce a voltage in the secondary when the magnetic circuit closes due to the movement of the object. This secondary induced voltage will change as the object moves along the path. Since the secondaries form the measuring coil, the change in voltage measured in the secondaries will make it possible to deduce the displacement and therefore the position of the object. Thus, the use of transformers allows a reliable measurement of the position of the object.
• a first embodiment of a detection device is characterized in that the transformers are separated from the object by a metal wall which is weakly conductive of electric current. Displacement detection can thus also be carried out through a wall. Such an application is particularly useful when the object moves in an environment which must remain isolated such as for example a chemical or nuclear reactor.
• a second embodiment of a detection device is characterized in that each transformer comprises a ferrite screw placed in each of said axes and arranged to compensate for a difference in magnetic characteristic in the magnetic circuit of each transformer.
• the use of ferrite screws offers a simple and reliable solution to compensate for the difference in magnetic characteristic.
• a third embodiment of a detection device is characterized in that said primaries are connected to a first input of the detector and the secondary in opposition to a second input of the detector, which detector comprises an operational amplifier connected to the second input and one output of which is connected via a phase shift circuit to a first input of a multiplier, which multiplier comprises a second input connected to the first of the detector, an output of the multiplier being connected to a low-pass filter.
• the detector comprises linearization means connected to the output of the low-pass filter and arranged to linearize the output signal of the filter.
• linearization means are intended in particular to compensate for the effects of variations in ambient temperature which can influence the value of the filter output signal.
• the coils of the transformers used in the device according to the invention being made up of metallic wires, generally copper or steel, the effects of temperature on the physical properties of these wires are felt on the signal measured at the secondary coils of the transformers and therefore on said filter output signal.
• These linearization means may consist in applying to this filter output signal, directly or after subsequent processing of the signal, an interpolation polynomial, preferably of the 6 th order.
• FIG. 1 shows an overall view of an embodiment of a device according to the invention
• Figure 2 schematically illustrates an embodiment of a device according to the invention and Figures 2b and 2c illustrate the voltage measured in the secondary before and after linearization
• Figure 3 schematically illustrates the device with its detector
• Figures 4 and 5 illustrate with a graph the displacement and rotation of the object
• FIG. 6 schematically illustrates another embodiment of a device according to the invention.
• the device 1 for detecting a displacement of an object 4 comprises, as illustrated in FIG. 1, a first 2 and a second 3 transformer which are juxtaposed in parallel with one another.
• Each transformer has a ferromagnetic core and is part of a magnetic circuit generator.
• a first axis ai and a second axis a2 extend respectively through the first core and the second core of the first and second transformers, as illustrated in FIG. 2.
• the two transformers are with open magnetic circuit and their axes extend substantially perpendicular to the path 7 that the object 4 travels when it moves on the support 5.
• the axes ai and a2 intersect the path of the object.
• object 4 includes ferromagnetic material.
• the support 5 for its part is made of non-magnetic material so as not to disturb the generator of the magnetic circuit as will be described below.
• a metal wall 6, which is weakly conductive of electric current, separates the object 4 from the transformers 2 and 3. Thus, the displacement of the object 4 can even be detected through this wall.
• the presence of this wall is not essential for the operation of the detection device.
• the primaries 2-1 and 3-1 of the first and second transformer are connected in series.
• the secondary 2-2 and 3-2 of the two transformers are also connected in series.
• the primary forms an excitation coil and the secondary forms a measurement coil.
• a source 8 of alternating voltage, controlled by an oscillator, is connected to the primaries as well as to a first input 9-1 of a detection unit 9.
• the oscillator preferably provides a wave having a frequency situated between 3KHz and 6KHz .
• a second input 9-2 of the detector 9 is connected to the secondary ones, which are connected in phase opposition with respect to the primary ones.
• the two transformers 2 and 3 each have a ferrite screw (indicated by the arrow in the secondary) placed in the axis of the primary and secondary and arranged to compensate for a difference in magnetic characteristic in the magnetic circuit of each transformer.
• a sinusoidal voltage is applied using the source 8 to the primary 2-1 and 3-1 transformers. Since the transformers are at open magnetic circuit and their axes ai and a2 intersect the trajectory of the object, which contains a ferromagnetic material, the crossing of one of the axes ai or a2 by the object will cause the closing of the magnetic circuit whose axis is cross. This closing of the magnetic circuit will in turn cause that the voltage Vi injected into the primaries, which form an excitation circuit, will induce a voltage Vs in the secondary which form a measurement circuit.
• the movement of the object will cause a variation of reluctance in the magnetic circuit of the transformers. It is the measurement of this change in reluctance which will make it possible to determine, using the detection unit 9, the relative or absolute position of the object on its trajectory.
• the presence of the two transformers and the winding connected in series allows detection of the direction of movement.
• the voltage Vs induced in the secondary 2-2 and 3-2 is collected at the second input 9-2 of the detection unit. This latter voltage is slightly out of phase with respect to the excitation voltage (Vi) which is applied to the input 9-1 of the detection unit 9.
• Vi excitation voltage
• a preferred embodiment of this detection unit is illustrated in the Figure 3.
• the secondary are connected to an operational amplifier 11 whose output is connected to a phase shift circuit 12.
• the primary are connected to a trapezoid-shaped voltage generator, which generator is controlled by an oscillator 13 whose signal is also supplied to a second input of a multiplier 14.
• a first input of the multiplier 14 is connected to the output of the phase shift circuit 12.
• An output of the multiplier 14 is connected to an input of a low-pass filter 15 whose output is connected via a digital analog converter 16 to a display unit 17 arranged to display the position of the object. Since the secondaries are connected to the operational amplifier 11 in phase opposition, the operational amplifier performs an operation on a subtraction result.
• the multiplier 14 carries out the multiplication between the voltages Vi and Vs and thus functions as a synchronous detector.
• FIG. 2b In order to obtain a displacement value, it is necessary to linearize the signal V1 obtained at the output of the low-pass filter and illustrated in FIG. 2b.
• an interpolation polynomial preferably of the 6th order, is applied to the digital signal supplied at the output of the analog digital converter 16.
• the result (V2) of this linearization applied to the signal V1 is illustrated in FIG. 2c.
• the voltage V2 is then equal to a constant (k) multiplied by the position x of the object. From this value the position x can then be determined.
• FIG. 4 illustrates the position x of the object as a function of the value V2 determined.
• FIG. 5 illustrates the rotation of the object which can also be determined from the voltage V2, in a similar manner to the linear displacement of the object.
• FIG. 6 illustrates another embodiment of a device according to the invention. This is distinguished from that illustrated in Figure 2 by the application of a capacitor 10 connected in parallel to the secondary. The value of this capacitor is chosen so as to produce a parallel resonant circuit with the coils 2-2 and 3-2 secondary. The addition of this capacitor makes it possible to raise the level of the useful signal before synchronous detection and to increase higher in frequency for reasons of response time.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
• Transmission And Conversion Of Sensor Element Output (AREA)

Priority Applications (1)

Applications Claiming Priority (4)

Publications (1)

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ID=8180771

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Family Applications Before (1)

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• 2001
  • 2001-08-08 EP EP01203020A patent/EP1283409A1/de not_active Withdrawn
• 2002
  • 2002-08-06 AU AU2002333357A patent/AU2002333357A1/en not_active Abandoned
  • 2002-08-06 US US10/486,269 patent/US7132825B2/en not_active Expired - Fee Related
  • 2002-08-06 EP EP02794567A patent/EP1417457A2/de not_active Withdrawn
  • 2002-08-06 JP JP2003519359A patent/JP2004537735A/ja active Pending
  • 2002-08-06 WO PCT/EP2002/008814 patent/WO2003014675A2/fr active Application Filing

Non-Patent Citations (1)

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