GB2031157A - Displacement transducer - Google Patents

Displacement transducer Download PDF

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Publication number
GB2031157A
GB2031157A GB7930953A GB7930953A GB2031157A GB 2031157 A GB2031157 A GB 2031157A GB 7930953 A GB7930953 A GB 7930953A GB 7930953 A GB7930953 A GB 7930953A GB 2031157 A GB2031157 A GB 2031157A
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GB
United Kingdom
Prior art keywords
former
winding
displacement
windings
transducer
Prior art date
Legal status (The legal status 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 status listed.)
Granted
Application number
GB7930953A
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GB2031157B (en
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ZF International UK Ltd
Original Assignee
Lucas Industries Ltd
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Filing date
Publication date
Application filed by Lucas Industries Ltd filed Critical Lucas Industries Ltd
Priority to GB7930953A priority Critical patent/GB2031157B/en
Publication of GB2031157A publication Critical patent/GB2031157A/en
Application granted granted Critical
Publication of GB2031157B publication Critical patent/GB2031157B/en
Expired legal-status Critical Current

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    • 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
    • G01D5/202—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 movable a non-ferromagnetic conductive element

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Transmission And Conversion Of Sensor Element Output (AREA)

Abstract

A displacement transducer includes a non-magnetic non-conductive former 10 mounting interengaged helical windings 15, 16. Slidable within the former is a conductive non-magnetic member 13 the position of which is varied for the purpose of measuring displacement. The windings in use form the frequency determining component of an oscillator the frequency of which is a measure of the setting of the member, since the self-inductance of the windings, which is very small when the member 13 is withdrawn, increases as the member is inserted. <IMAGE>

Description

SPECIFICATION Displacement transducers This invention relates to displacement transducers of the inductive type.
Known forms of such transducer comprise a coil of wire in which the direction of current flow at any instant is the same in each turn of the coil and a core member formed from magnetisable material and which can be moved axially into the coil so as to vary the inductance of the coil.
The inductance measurement provides an indication of the position of the core within the coil and hence an indication of the displacement. A disadvantage of such an arrangement derives from the hysterisis effect of the material from which the core member is constructed. This reduces the accuracy of the measurement of the inductance value and also limits the frequency of the alternating current supply to which the coil is connected for the purpose of the measurement.
The object of the invention is to provide a displacement transducer in a simple and convenient form.
According to the invention, a displacement transducer comprises a former of non-magnetic and non-conductive material, winding means carried on said former, a core member slidable within said former, said core member in use being connected to or forming part of a member the displacement of which is to be measured, said core member being formed from electrically conductive non-magnetisable material and said winding means comprising first and second interengaged helical windings having the same number of turns and interconnected such that the current flow in one winding is opposite to that in the other winding, said windings in use being supplied with alternating current such that eddy currents are induced in the portion of the core member which lies within the former, the inductance of the winding means being dependent due to the eddy currents, on the position of the core member within the former.
One example of a displacement transducer in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side elevation of the transducer and Figure 2 is a block diagram of an oscillator and amplifier for use with the transducer.
The transducer comprises a former 10 formed from plastics or like non-conductive and non-magnetizable material and on which is formed or mounted a pair of helical ribs 11, 1 2 which can be regarded as forming the equivalent of a two start screw thread.
The former 10 is provided with a bore in which is slidable a member 1 3 having a cylindrical outer surface. The member 1 3 may be solid or of hollow form but is formed from an electrically conductive non-magnetic material such for example as copper or aluminium.
The member 1 3 is provided with a head 1 4 whereby in use, the member can be secured to another member, the displacement of which is to be measured.
Located between the ribs 11 and 1 2 are a pair of windings 15, 1 6 each winding in the particular example shown, having three turns.
Conveniently the windings are formed from a continuous length of wire wound along one of the grooves defined between adjacent ribs 11 and 1 2 and returning to the same end of the former along the other groove.
With the member 1 3 removed from the former the self-inductance of the windings is very small because they are wound in bifilar fashion. However, when the member 1 3 is inserted into the former and a high frequency alternating current passed through the windings, eddy currents flow in the surface of the member 1 3 and the eddy currents oppose the change in current in the windings 1 5 and 1 6 so that the latter do exhibit inductance. The inductance value depends upon the amount by which the member 1 3 extends within the former and as the penetration increases so also does the inductance value.
The transducer as described can be operated at frequencies in the order of 2MHz and the response is extremely fast. Moreover, the hysterisis effect is negligible and the linearity is extremely high being less than one per cent over the full travel.
In a practical example the wall thickness of the former was 0.5mm with the diameter of the member 1 3 being 4.0mm and the length of the winding 25.0mm. In this example moreover, each winding had five turns.
A transducer can be made of any desired length to accommodate the travel of the member to which the member 1 3 is connected.
As shown in Fig. 2 the combined winding 1 7 of the transducer forms the frequency control component of an LC oscillator 1 8 and the frequency of operation of the oscillator will vary as the member is moved within the former. The output of the oscillator is connected to an amplifier 1 9 and the output of the amplifier is utilised to supply a frequency counter 20 which may be calibrated to give a direct indication of the displacement.
If temperature variation proves to vary the inductance to the extent that the calibration is upset, a standard inductor 21 subject to the same temperature variation can be switched into the oscillator circuit for the purpose of recalibration, by means of an electronic switch 22.
1. A displacement transducer comprising a former of non-magnetic and non-conductive material, winding means carried on said for
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Displacement transducers This invention relates to displacement transducers of the inductive type. Known forms of such transducer comprise a coil of wire in which the direction of current flow at any instant is the same in each turn of the coil and a core member formed from magnetisable material and which can be moved axially into the coil so as to vary the inductance of the coil. The inductance measurement provides an indication of the position of the core within the coil and hence an indication of the displacement. A disadvantage of such an arrangement derives from the hysterisis effect of the material from which the core member is constructed. This reduces the accuracy of the measurement of the inductance value and also limits the frequency of the alternating current supply to which the coil is connected for the purpose of the measurement. The object of the invention is to provide a displacement transducer in a simple and convenient form. According to the invention, a displacement transducer comprises a former of non-magnetic and non-conductive material, winding means carried on said former, a core member slidable within said former, said core member in use being connected to or forming part of a member the displacement of which is to be measured, said core member being formed from electrically conductive non-magnetisable material and said winding means comprising first and second interengaged helical windings having the same number of turns and interconnected such that the current flow in one winding is opposite to that in the other winding, said windings in use being supplied with alternating current such that eddy currents are induced in the portion of the core member which lies within the former, the inductance of the winding means being dependent due to the eddy currents, on the position of the core member within the former. One example of a displacement transducer in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side elevation of the transducer and Figure 2 is a block diagram of an oscillator and amplifier for use with the transducer. The transducer comprises a former 10 formed from plastics or like non-conductive and non-magnetizable material and on which is formed or mounted a pair of helical ribs 11, 1 2 which can be regarded as forming the equivalent of a two start screw thread. The former 10 is provided with a bore in which is slidable a member 1 3 having a cylindrical outer surface. The member 1 3 may be solid or of hollow form but is formed from an electrically conductive non-magnetic material such for example as copper or aluminium. The member 1 3 is provided with a head 1 4 whereby in use, the member can be secured to another member, the displacement of which is to be measured. Located between the ribs 11 and 1 2 are a pair of windings 15, 1 6 each winding in the particular example shown, having three turns. Conveniently the windings are formed from a continuous length of wire wound along one of the grooves defined between adjacent ribs 11 and 1 2 and returning to the same end of the former along the other groove. With the member 1 3 removed from the former the self-inductance of the windings is very small because they are wound in bifilar fashion. However, when the member 1 3 is inserted into the former and a high frequency alternating current passed through the windings, eddy currents flow in the surface of the member 1 3 and the eddy currents oppose the change in current in the windings 1 5 and 1 6 so that the latter do exhibit inductance. The inductance value depends upon the amount by which the member 1 3 extends within the former and as the penetration increases so also does the inductance value. The transducer as described can be operated at frequencies in the order of 2MHz and the response is extremely fast. Moreover, the hysterisis effect is negligible and the linearity is extremely high being less than one per cent over the full travel. In a practical example the wall thickness of the former was 0.5mm with the diameter of the member 1 3 being 4.0mm and the length of the winding 25.0mm. In this example moreover, each winding had five turns. A transducer can be made of any desired length to accommodate the travel of the member to which the member 1 3 is connected. As shown in Fig. 2 the combined winding 1 7 of the transducer forms the frequency control component of an LC oscillator 1 8 and the frequency of operation of the oscillator will vary as the member is moved within the former. The output of the oscillator is connected to an amplifier 1 9 and the output of the amplifier is utilised to supply a frequency counter 20 which may be calibrated to give a direct indication of the displacement. If temperature variation proves to vary the inductance to the extent that the calibration is upset, a standard inductor 21 subject to the same temperature variation can be switched into the oscillator circuit for the purpose of recalibration, by means of an electronic switch 22. CLAIMS
1. A displacement transducer comprising a former of non-magnetic and non-conductive material, winding means carried on said for mer, a core member slidable within said former, said core member in use being connected to or forming part of a member the displacement of which is to be measured, said core member being formed from electrically conductive non-magnetisable material and said winding means comprising first and second interengaged helical windings having the same number of turns and interconnected such that the current flow in one winding is opposite to that in the other winding, said windings in use being supplied with alternating current such that eddy currents are induced in the portion of the core member which lies within the former, the inductance of the winding means being dependent due to the eddy currents, on the position of the core member within the former.
2. A displacement transducer according to claim 1 in which the winding means forms the frequency control component of an oscillator, the frequency of oscillation of the oscillator being representative of the setting of said member.
3. A displacement transducer according to claim 2 including a standard inductor and switch means operable to connect the standard inductor to the oscillator for the purpose of calibration.
4. A displacement transducer according to claim 1 in which said core member is formed from copper or aluminium.
5. A displacement transducer comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.
GB7930953A 1978-09-28 1979-09-06 Displacement transducer Expired GB2031157B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB7930953A GB2031157B (en) 1978-09-28 1979-09-06 Displacement transducer

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB7838586 1978-09-28
GB7930953A GB2031157B (en) 1978-09-28 1979-09-06 Displacement transducer

Publications (2)

Publication Number Publication Date
GB2031157A true GB2031157A (en) 1980-04-16
GB2031157B GB2031157B (en) 1982-11-17

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB7930953A Expired GB2031157B (en) 1978-09-28 1979-09-06 Displacement transducer

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2502324A1 (en) * 1981-03-21 1982-09-24 Lucas Industries Ltd Linear displacement transducer - has winding formed on strip of insulating material and direction of current flow in one winding is opposite other
EP0339983A2 (en) * 1988-04-29 1989-11-02 LUCAS INDUSTRIES public limited company Movement transducer
GB2219664A (en) * 1988-06-09 1989-12-13 Technical Software Consultants Position transducer
US4887465A (en) * 1986-05-16 1989-12-19 Kollmorgen Corporation Transducers for hostile environments
WO1994019206A1 (en) * 1993-02-17 1994-09-01 V.O.F. Hedon Electronic Developments Inductive system for measuring the length of a shock absorber

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2502324A1 (en) * 1981-03-21 1982-09-24 Lucas Industries Ltd Linear displacement transducer - has winding formed on strip of insulating material and direction of current flow in one winding is opposite other
US4887465A (en) * 1986-05-16 1989-12-19 Kollmorgen Corporation Transducers for hostile environments
EP0339983A2 (en) * 1988-04-29 1989-11-02 LUCAS INDUSTRIES public limited company Movement transducer
EP0339983A3 (en) * 1988-04-29 1990-09-26 LUCAS INDUSTRIES public limited company Movement transducer
GB2219664A (en) * 1988-06-09 1989-12-13 Technical Software Consultants Position transducer
GB2219664B (en) * 1988-06-09 1992-11-18 Technical Software Consultants Position transducer
WO1994019206A1 (en) * 1993-02-17 1994-09-01 V.O.F. Hedon Electronic Developments Inductive system for measuring the length of a shock absorber
US5610514A (en) * 1993-02-17 1997-03-11 V.O.F. Hedon Electronic Developments Inductive system for measuring the length of a shock absorber

Also Published As

Publication number Publication date
GB2031157B (en) 1982-11-17

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PCNP Patent ceased through non-payment of renewal fee