GB2215467A - Inductive linear displacement transducer - Google Patents

Inductive linear displacement transducer Download PDF

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Publication number
GB2215467A
GB2215467A GB8804301A GB8804301A GB2215467A GB 2215467 A GB2215467 A GB 2215467A GB 8804301 A GB8804301 A GB 8804301A GB 8804301 A GB8804301 A GB 8804301A GB 2215467 A GB2215467 A GB 2215467A
Authority
GB
United Kingdom
Prior art keywords
measuring device
spindle
winding
clalmed
materlal
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.)
Withdrawn
Application number
GB8804301A
Other versions
GB8804301D0 (en
Inventor
Richard Ward
Christopher Mcbride
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Joy Global Industries Ltd
Original Assignee
Dobson Park Industries Ltd
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 Dobson Park Industries Ltd filed Critical Dobson Park Industries Ltd
Priority to GB8804301A priority Critical patent/GB2215467A/en
Publication of GB8804301D0 publication Critical patent/GB8804301D0/en
Publication of GB2215467A publication Critical patent/GB2215467A/en
Withdrawn legal-status Critical Current

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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
    • G01D5/2291—Linear or rotary variable differential transformers (LVDTs/RVDTs) having a single primary coil and two secondary coils
    • 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

Abstract

A measuring device is provided which comprises electrical coil means (11, 12, 13,) and an armature, the armature comprising a length of wound material 18. The coil means comprises a central, primary coil with two secondary coils located axially one on each side of the primary coil. The degree of winding of the material is alterable, for example, by winding the material between two spindles 16 and 17, symmetrically spaced with respect to the coils and the altering of the winding of the material enables an electrical signal to be received from the coil means 11, 12, 13, in dependence upon the extent as to which the winding of the material is altered. Winding may be altered by pulling a nylon cord 23 from drum 22 which is geared to spindle 17, and the wound material 18 preferably comprises a constant tension spring which returns cord 23 when it is released. The invention enables the principle of the linear variable differential transformer to be used to measure relatively large displacements, for example of the order of one metre, but with relatively compact and inexpensive apparatus. The invention is particularly suitable for use in measuring the displacement of part of a hydraulic jack of a mine roof support. <IMAGE>

Description

MEASURING DEVICES The Invention relates to measuring devices, for example devices for measuring distance.
One known device for measuring distance comprlses a linear variable differential transformer. It comprlses three colls on a tubular former and an armature of Ferro magnetlc material such as iron Is arranged so that It can slide axially in the former. One of the three colls which may be wound around the middle of the former is the transformer primary coil and the other two, which are arranged at each side of the primary are secondary coils.
The armature is longer than the middle coil but shorter than the three coils overall and normal ly 1 les in the middle of the tubular former. When alternating current Is appi led to the primary coil, equal voltages are induced In the two secondary coils. These two secondary coils are connected in series, In phase opposition, so that no voltage appears across the ends. When however the armature Is moved so that It no longer lies In the middle of the former, the voltage Induced in one secondary coil Is reduced and that in the other secondary coil Is Increased. The change In net voltage at the terminals of the differentially connected secondary coils gives a signal which Is an analogue of the degree of movement of the armature.
Such linear variable differential transformers, generally referred to as LVDT's, are very commonly used as linear displacement transducers. However for any given application, one must use an LVDT which Is longer than the maximum armature displacement which is to be measured, so that if say, a distance of the order of one metre Is to be measured, a very long and expensive LVDT would be necessary.
The object of the invent ion Is to provide a measuring device which uses the principle of the LVDT to measure relatively large displacements, for example of the order of one metre, but with relatively compact and Inexpensive apparatus.
The invention provides a measuring device comprlsing electric coll means and an armature, the armature comprlsing a length of wound material , the degree of winding of the materlal being alterable, and altering of the winding of the material enabling an electric signal to be received from the coil means Independence upon the extent to which the winding of the material Is altered.
The degree of winding may be altered by unwinding the material.
Preferably, the electric coil means comprises a primary coil and two secondary coils.
There may be means for applying an alternating current to the primary coil and means for receiving a signal from the secondary colls.
The device may be arranged to measure length, for example, by measuring the length of material which Is unwound.
The device may be arranged to provide a signal which varies linearly with the unwinding of the material.
Preferably there are fIrst and second spindles, the material being unwound from the first spindle and rewound onto the second spindle.
The spindles and material may be such that the material unwinds from one of the spindles In a clockwise direction and rewinds onto the other spindle In an anticlockwlse direction.
The material may comprise spring material such that when the material is released, after having been unwound from the first spindle, It rewinds Itself from the second spindle back on to the first spindle.
The materlal may be arranged In the form of a constant force spring, such as that known as a Tensator spring.
Means may be provided to rotate the second spindle, thus unwinding the material from the first spindle and rewinding It on to the second spindle.
The means may comprise a cord or other flexible tensile member wound around the second spindle, or wound around a part connected to a second spindle, for example connected by gearing.
The measuring device is particularly suitable for measurIng the displacement of part of a hydraulic mine roof support, for example one of the hydraulic Jacks of a hydraulic mine roof support. Accordingly, the invention Includes a hydraulic mine roof support fitted with a measuring device according to the invention.
By way of example, a specific embodiment of the Invention will now be descrIbed, with reference to the accompanying drawings, In which : Figure 1 is a dlagrammatic view of the electrical arrangement of an embodiment of measuring device according to the Invention; Flgure 2 Is a diagrammatic side view of the armature, In cross-sectlon; and Figure 3 Is a diagrammatic plan view of the armature In cross-section.
The device comprises a tube 10 of non conductive material having a rectangular cross section. Wound onto to this tube Is a primary coll 11 and two secondary colls 12 and 13. The secondary coils 12 and 13 are connected together In series, In phase opposition. If an alternating signal Is applied across the ends 14 of the primary coll 11, a voltmeter 15 connected to the secondary col Is as shown will normally record zero voltage.
Within the tube 10 there are two spindles 16 and 17 mounted In bearlngs so that they extend transversely of the longitudinal axis of the tube. A steel spring 18, similar to a clock sprlng Is normally tightly wound around the spindle 16, with Its exposed end attached to the spindle 17.
Mounted on the spindle 17 is a first gear 19, which meshes with a second gear 20 arranged on a third spindle 21. Also mounted on the spindle 21 is a drum 22 and wound around this drum 22 Is a long length of nonmagnetic cord, for example nylon cord 23.
If the cord 23 Is pulled In the directlon of arrow A the drum 22 and gear 20 are rotated clockwise as vlewed In Figure 2. This causes the gear 19 and spindle 17 to be rotated antl-clockwlse. Thus the spring 18 Is unwound from the spindle 16 In a clockwise direction, and at the same tlme Is rewound onto the spindle 17 in an anti-clockwise direction.
The positioning of the spindles 16 and 17 is such that the spring material 18 extends from within the secondary coil 12, through a primary coil 11, and then Into the secondary coil 13. The two spindles are In fact positioned symmetrically about the primary coll, near to the ends of the primary coll.
As the spring material transfers from one spindle to the other, the bulk of the armature made up by the sprIng material effectively shifts along the length of the tube 10, thus producing a signal at the voltmeter 15, which signal Is linearly proportional to the length of the cord 23 which Is unwound from the drum 22.
The spring materlal 18 In this embodiment, comprises a constant force sprlng, of the kind known as a Tensator sprlng. Thus as the cord 23 Is drawn out, the sprlng exerts a constant tension on the cord, and winds the cord back when It Is released. Thus the spring acts both as a differential armature and a rewind motor.
The device descrlbed above enables relatively long displacements to be measured but with a compact device. The spring 18 and cord 23 can be of any convenlent length and may be many times the overall length of the colls 11, 12 and 13, I.e., many times longer than the length of the tube 10. The device may be particularly effective In measuring the extent to which a hydraulic ram of a mine roof support has extended or retracted.
The contents of all papers and documents filed concurrently with this specificatIon are Incorporated hereln by reference.
All of the features disclosed In this specificatIon (Including any accompanying Claims, Abstract and drawings), and/or all of the steps of any method or proceed so disclosed, may be combined in any combination, except combinations where at least some such features and/or steps are mutually exclusive.
The invention Is not restricted to the details of the foregoing embodiment(s). The Invention extends to any novel one, or any novel combination, of the features disclosed In this specification (Including any accompanying claims, abstract and drawings), or to any novel one, or novel combination, of the steps of any method or process so disclosed.

Claims (19)

1. A measuring device comprising electrical coil means and an armature, the armature comprising a length of wound materlal, the degree of winding of the material being alterable, and altering of the winding of the material enabling an electric signal to be received from the coil means In dependence upon the extent to which the winding of the materlal Is altered.
2. A measuring device as claimed in Claim 1, in which the degree of winding is altered by unwinding the material.
3. A measuring device as clalmed In Claim 1 or Claim 2, In which the electric coil means comprises a primary coil and two secondary coils.
4. A measuring device as claimed in Claim 3, In which there are means for applying an alternating current to the primary coil and means for receiving a signal from the secondary coils.
5. A measuring device as claimed in any one of the preceding Clalms, arranged to measure length.
6. A measuring device as claimed In Claim 5, in which the device measures length by measuring the length of material which Is wound or unwound.
7. A measuring device as claimed In any one of the preceding Claims arranged to provide a signal which varies linearly with the winding or unwinding of the material.
8. A measuring device as claimed In any one of the preceding Claims in which there are first and second spindles, the materlal belng unwound from the first spindle and rewound onto the second spindle.
9. A measuring device as clalmed In Claim 8, In which the spindles and material are such that the material unwinds from one of the spindles In a clockwlse direction and rewinds onto the other spindle In an antl clockwise dlrectlon.
10. A measuring device as clalmed in Claim 8 or Claim 9, In which the material comprises sprlng materlal such that when the material is released, after having been unwound from the first spindle, It rewinds Itself from the second spindle back on to the first spindle.
11. A measuring device as clalmed In Claim 10, in which the materlal Is arranged In the form of a constant force spring.
12. A measuring device as claimed in any one of Claims 8 to 11, in which means are provided to rotate the second spindle, thus unwinding the material from the first spindle and rewinding it on to the second spindle.
13. A measuring device as claimed In Claim 12, In which the means to rotate the second spindle comprises a cord or other flexible tensile member wound around the second spindle, or wound around a part connected to a second spindle.
14. A measuring device as clalmed in Claim 13, in which the said part Is connected to the second spindle by gearing.
15. A measuring device constructed and arranged substantially as hereln described with reference to the accompanying drawings.
16. A hydraulic Jack for a hydraulic mine roof support, the Jack being fitted with a measuring device as clalmed In any one of the preceding Claims.
17. A hydraulic Jack as claimed In Claim 16, in which the measuring device has a cord or other flexible tensile member, the device and the said member being fitted between a static member and a moving member of the hydraulic Jack.
18. A hydraulic mine roof support fitted with a measuring device as claimed in any one of the preceding Claims.
19. A hydraulic mine roof support as clalmed In Claim 18, In which the measuring device is arranged to measure the displacement of part of a hydraulic Jack of the mine roof support.
GB8804301A 1988-02-24 1988-02-24 Inductive linear displacement transducer Withdrawn GB2215467A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8804301A GB2215467A (en) 1988-02-24 1988-02-24 Inductive linear displacement transducer

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8804301A GB2215467A (en) 1988-02-24 1988-02-24 Inductive linear displacement transducer

Publications (2)

Publication Number Publication Date
GB8804301D0 GB8804301D0 (en) 1988-03-23
GB2215467A true GB2215467A (en) 1989-09-20

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Family Applications (1)

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GB8804301A Withdrawn GB2215467A (en) 1988-02-24 1988-02-24 Inductive linear displacement transducer

Country Status (1)

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GB (1) GB2215467A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11068840B2 (en) * 2017-03-10 2021-07-20 Scott A. Stensland Device to calculate and display remaining length of a coiled product

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1207955A (en) * 1966-11-16 1970-10-07 Honeywell Ltd Improvements in or relating to electrical recording and/or indicating apparatus
US4631478A (en) * 1982-05-19 1986-12-23 Robert Bosch Gmbh Method and apparatus for using spring-type resistive elements in a measurement bridge circuit

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1207955A (en) * 1966-11-16 1970-10-07 Honeywell Ltd Improvements in or relating to electrical recording and/or indicating apparatus
US4631478A (en) * 1982-05-19 1986-12-23 Robert Bosch Gmbh Method and apparatus for using spring-type resistive elements in a measurement bridge circuit

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11068840B2 (en) * 2017-03-10 2021-07-20 Scott A. Stensland Device to calculate and display remaining length of a coiled product

Also Published As

Publication number Publication date
GB8804301D0 (en) 1988-03-23

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WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)