WO2005121708A1 - Transformateur differentiel variable - Google Patents

Transformateur differentiel variable Download PDF

Info

Publication number
WO2005121708A1
WO2005121708A1 PCT/GB2005/002282 GB2005002282W WO2005121708A1 WO 2005121708 A1 WO2005121708 A1 WO 2005121708A1 GB 2005002282 W GB2005002282 W GB 2005002282W WO 2005121708 A1 WO2005121708 A1 WO 2005121708A1
Authority
WO
WIPO (PCT)
Prior art keywords
coil
current
voltage
differential transformer
variable differential
Prior art date
Application number
PCT/GB2005/002282
Other languages
English (en)
Inventor
Andrew Paul Bridges
William Peter Stuart-Bruges
Original Assignee
Sondex Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sondex Limited filed Critical Sondex Limited
Publication of WO2005121708A1 publication Critical patent/WO2005121708A1/fr

Links

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
    • G01D5/22—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
    • G01D5/2208—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 self-induction of the coils
    • G01D5/2216—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 self-induction of the coils by a movable ferromagnetic element, e.g. a core
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F21/00—Variable inductances or transformers of the signal type
    • H01F21/02—Variable inductances or transformers of the signal type continuously variable, e.g. variometers
    • H01F21/06—Variable inductances or transformers of the signal type continuously variable, e.g. variometers by movement of core or part of core relative to the windings as a whole

Definitions

  • This invention relates to a variable differential transformer (VDT), and in particular to a linear variable differential transformer (LVDT) in which measurement errors arise as a result of the resistance in the windings of the coil.
  • VDT variable differential transformer
  • LVDT linear variable differential transformer
  • a known LVDT 2 shown in Figure 1 consists of a primary winding 4, an electrically isolated centre tapped secondary winding 6, and a magnetic slug 8 mounted on a linear actuator 10.
  • the secondary winding is grounded at its mid-point.
  • the magnetic slug varies the magnetic coupling between the primary winding and each half of the secondary winding according to its position.
  • the primary winding is driven with an excitation waveform, usually a sinusoidal voltage, by an alternating current voltage source 12.
  • the ratio of the voltages developed in the two halves of the secondary winding is then measured by ratio detecting circuit 14 to give an accurate indication of the linear position of the actuator.
  • the secondary winding is terminated into a high impedance to minimise the current in the winding. If significant current is allowed to flow, an additional voltage is developed in each half of the secondary winding due to the effect of the current flowing through the winding's own resistance, and the reading of the measurement is degraded as a result.
  • the current in the primary winding has a similar effect on the total voltage developed across the secondary winding, but this has no effect on the reading if the ratio of the voltages developed across the two halves of the secondary is used to establish the position of the actuator.
  • This error can be reduced, but not completely eliminated, by reducing the resistance of the winding.
  • One way to achieve this is to wind the coil of the LVDT using a larger diameter and hence lower resistance wire. In some applications however, again due to space constraints, the windings must be made with small diameter wire and the resulting winding resistance will be high.
  • variable differential transformer addresses measurement errors arising out of the resistance in the transformer coil windings.
  • the variable differential transformer comprises current sensing means for sensing when the current flowing in the coil is ⁇ ero. At the zero-current point, the voltage on the mid-point of the coil is measured to give an indication of the position of the moveable core in the coil. At the time when zero-current is flowing, the voltage induced across the resistive part of the winding is zero, and the voltage measurement taken is therefore free of resistive errors.
  • Figure 1 illustrates a known LVDT comprising a primary and a secondary coil
  • Figure 2 illustrates a known LVDT comprising only a single coil
  • FIG. 3 illustrates a preferred embodiment of the invention
  • Figure 4 illustrates the voltages and currents across the LVDT coil of the preferred embodiment over time.
  • the preferred embodiment 20 of the LVDT apparatus comprises a centre tapped sensor coil 22 connected at its mid-point M to an Analogue to Digital Converter (ADC) circuit 24.
  • the coil is driven by four transistors Q1 to Q4 arranged in a full bridge configuration.
  • the gates of Q1 and Q4, are connected to a first drive signal generator 26, and the gates of Q2 and Q3 are connected to a second drive signal generator 28.
  • the coil 22 is connected between the transistors Q1 to Q4 such that one end of the coil A is connected to the source of Q1 and the drain of Q3, while the other end of the coil B is connected to the source of Q2 and the drain of Q4.
  • the coil 22 can therefore be alternately electrically connected between transistors pairs Q1 and Q4, and Q2 and Q3 respectively.
  • the bridge is driven from a stable reference voltage provided by a power supply unit 30 connected to the drains of Q1 and Q2, as well as to the reference voltage terminal of the ADC 24.
  • the sources of Q3 and Q4 on the other hand are connected to ground.
  • the source of Q3 is connected via a resistor 32.
  • a comparator circuit 34 is connected with its inputs terminals arranged in parallel across the resistor, and its output terminal connected to the ADC.
  • ADC 24 has an output 36 for providing an indication of the measured voltage at the mid-point of the coil.
  • the measurement error introduced by the effects of drive current in known LVDT windings is caused by the voltage induced across the resistive part of the winding impedance. This error voltage is proportional to the current flowing in the winding. If the driving voltage is an AC voltage, the current in the windings of the coil will periodically fall to zero, regardless of the actual excitation waveform used.
  • the preferred embodiment of the LVDT sensor Rather than using the usual continuous wave voltage measuring techniques, the preferred embodiment of the LVDT sensor therefore measures the current flowing in the coil and samples the voltage across the two halves of the coil only at the instant that the current in the winding passes through zero. A number of samples taken on consecutive cycles of the excitation is preferably then averaged to offer improved noise immunity.
  • the first and second drive signal generators produce gate drive signals that are antiphase so that the current path through the bridge is alternately through Q1 and Q4, and Q2 and Q3.
  • the drive signals are illustrated in the top two graphs a) and b) of Figure 4.
  • the current flow across the coil is illustrated in graph e).
  • the zero current point through the coil lags the transition of the gate drive signal and corresponds to the zero voltage position at terminal A.
  • the comparator circuit 34 measures the voltage across the resistor 32 to determine the zero current position. Once this position is sensed by the comparator, it provides an output to the ADC, causing the ADC to sample the voltage on the centre tap M of the LVDT. At this instant there is no current flowing anywhere in the system, so the left hand end of the LVDT will be at ground potential and the right hand end will be at the bridge reference voltage. The voltage on the centre tap is thus measured with respect to ground, and ratiometric to the bridge reference voltage. This technique thereby avoids errors associated with the resistance of the coil windings.
  • the resistor 32 adds to the error voltage when a current is flowing, its contribution at the zero-current point is zero.
  • the ADC stores the values of the voltage on the mid-point of the coil measured across several cycles, and takes the average of the these values to output a final voltage reading to output 36.
  • the preferred embodiment of the invention uses current sensing to ensure that the sample point of the voltage on the coil occurs when zero current is flowing, regardless of the drive technique and the way in which the LVDT is sampled.
  • the voltage measurement is only sampled once every cycle.
  • the circuit could be modified so that Q4 is also connected to ground through a resistor, and an additional comparator is provided to measure the voltage across this resistor. This would allow a measurement to be taken on each half cycle of the excitation waveform, instead of once per complete cycle.
  • the excitation waveform may be a conventional sinusoidal voltage, but any waveform that causes the current in the winding to periodically reverse may be used.
  • a square wave drive is preferred as it is simpler to generate and is less lossy.
  • the zero-current measurement technique described above in connection with the preferred embodiment may be implemented in a variety of alternative ways.
  • the full bridge implementation described above is preferred however as it has the added advantage that the energy stored in the inductance of the LVDT winding at the end of one half cycle is returned to the power supply in the first portion of the next half cycle. This charge recycling can significantly reduce the LVDT drive power requirement.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Transmission And Conversion Of Sensor Element Output (AREA)

Abstract

La présente invention concerne un Transformateur Différentiel Variable Linéaire qui fait supporter aux enroulements de bobine du Transformateur Différentiel Variable les erreurs de mesure survenant en sortie de résistance. Le Transformateur Différentiel Variable Linéaire comprend des organes de détection de courant permettant de savoir quand le courant dans le bobinage du Transformateur Différentiel Variable Linéaire est nul. A cet instant, on mesure la tension au point médian du bobinage, ce qui permet de connaître la position du noyau mobile dans le bobinage. A l'instant du courant nul, la tension induite aux bornes de la résistance de l'enroulement est nulle, ce qui fait que la mesure de tension est exempte d'erreur de résistivité. Cette logique peut également s'appliquer à un Transformateur Différentiel Variable Rotatif.
PCT/GB2005/002282 2004-06-08 2005-06-08 Transformateur differentiel variable WO2005121708A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0412770A GB2415046A (en) 2004-06-08 2004-06-08 A variable differential transformer in which the coil voltage is measured at the zero current point
GB0412770.0 2004-06-08

Publications (1)

Publication Number Publication Date
WO2005121708A1 true WO2005121708A1 (fr) 2005-12-22

Family

ID=32696855

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2005/002282 WO2005121708A1 (fr) 2004-06-08 2005-06-08 Transformateur differentiel variable

Country Status (2)

Country Link
GB (1) GB2415046A (fr)
WO (1) WO2005121708A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10756531B2 (en) 2018-03-29 2020-08-25 Hamilton Sunstrand Corporation Voltage differential transducer (VDT) fault detection

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0438103A2 (fr) * 1990-01-15 1991-07-24 Dieter Dr. Weiss Procédé et dispositif pour mesurer de grandeurs physiques
US5521496A (en) * 1992-10-02 1996-05-28 Positek Limited Detection circuits for position sensors
DE19538575A1 (de) * 1995-10-17 1997-06-12 Becker Wolf Juergen Univ Prof Induktiver Näherungssensor mit hoher Schaltgeschwindigkeit

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4140998A (en) * 1976-03-15 1979-02-20 Sangamo Weston, Inc. High accuracy position indicator
JP3248832B2 (ja) * 1995-08-31 2002-01-21 三菱電機株式会社 センサ回路
ITBO20010269A1 (it) * 2001-05-07 2002-11-07 Marposs Spa Dispositivo di condizionamento per un trasduttore analogico
US6753686B2 (en) * 2001-05-21 2004-06-22 Mitutoyo Corporation Method and apparatus for detecting failure of differential transformer, and method and apparatus for signal processing of differential transformer

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0438103A2 (fr) * 1990-01-15 1991-07-24 Dieter Dr. Weiss Procédé et dispositif pour mesurer de grandeurs physiques
US5521496A (en) * 1992-10-02 1996-05-28 Positek Limited Detection circuits for position sensors
DE19538575A1 (de) * 1995-10-17 1997-06-12 Becker Wolf Juergen Univ Prof Induktiver Näherungssensor mit hoher Schaltgeschwindigkeit

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10756531B2 (en) 2018-03-29 2020-08-25 Hamilton Sunstrand Corporation Voltage differential transducer (VDT) fault detection

Also Published As

Publication number Publication date
GB2415046A (en) 2005-12-14
GB0412770D0 (en) 2004-07-07

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