GB1601572A - Linear displacement transducer - Google Patents

Linear displacement transducer Download PDF

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Publication number
GB1601572A
GB1601572A GB19154/77A GB1915477A GB1601572A GB 1601572 A GB1601572 A GB 1601572A GB 19154/77 A GB19154/77 A GB 19154/77A GB 1915477 A GB1915477 A GB 1915477A GB 1601572 A GB1601572 A GB 1601572A
Authority
GB
United Kingdom
Prior art keywords
tube
tubes
pair
conductor
fixed
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.)
Expired
Application number
GB19154/77A
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.)
Davy Loewy Ltd
Original Assignee
Davy Loewy 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 Davy Loewy Ltd filed Critical Davy Loewy Ltd
Priority to GB19154/77A priority Critical patent/GB1601572A/en
Priority to DE19782820040 priority patent/DE2820040A1/en
Publication of GB1601572A publication Critical patent/GB1601572A/en
Expired 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
    • G01D5/24—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 capacitance
    • G01D5/241—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 capacitance by relative movement of capacitor electrodes
    • G01D5/2412—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 capacitance by relative movement of capacitor electrodes by varying overlap

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
  • Measuring Fluid Pressure (AREA)

Description

(54) LINEAR DISPLACEMENT TRANSDUCER (71) We, DAVY-LOEWY LIMITED, a British company of Prince of Wales Road, Sheffield S9 4EX, Yorkshire, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to transducers capable of indicating the linear displacement of a member. Such transducers are known but heretofore the transducers have a limited stroke over which the output of the transducer is an accurate representation of the displacement when compared to the overall transducer length.
It is an object of the present invention to provide a linear displacement transducer which provides an accurate output of its displaceable member over a substantial stroke.
According to the present invention, a variable capacitance linear displacement transducer comprises a pair of conductive tubes mounted in parallel spaced apart relation one within the other, the outer tube of the pair being fixed at one end and the other tube being displaceable in the direction of its length relative to the fixed tube, a further conductive tube positioned around and spaced from the outer one of said pair of tubes, said further tube being mounted such as to provide an electrostatic screen around any part of the inner one of the pair of tubes which projects outwardly from one end of the outer tube of the pair and the end of the inner tube of the pair which is closest to the fixed end of the outer tube of the pair having an electrostatic guard conductor connected thereto.
The variable transducer operates on the principle that the electrical capacitance between the two tubes is proportional to the area of axial overlap of the two tubes. Thus, by moving one tube axially with respect to the other, the capacitance between the two tubes is proportional to the area of overlap between the two tubes.
In use, the transducer is connected in an electrical circuit including an oscillator and a current measuring device. This device is.
conveniently an operational amplifier.
Because the transducer is designed for use with an alternating source, a feature of the invention is that the inner of the pair of tubes is protected by an electrostatic screen which is in the form of a further tube positioned outside of and spaced from the outer of said pair of tubes and the tube protects any part of the inner of the pair of tubes which projects outwardly from one end of the outer tube of the pair.
To allow for end or fringe electrostatic effects, the inner of said pair of tubes has a conductive electrostatic guard insulatingly mounted at that end which is closest to the fixed end of the outer of the pair of tubes.
In order that the invention may be more readily understood it will now be described, by way of example only, with reference to the drawing filed with the provisional specification, which is a longitudinal sectional view of a linear transducer according to the invention.
The linear displacement transducer depends for its operation on the capacitance between a pair of conductive tubes positioned in spaced relation one within the other. One of the tubes is displaceable in the direction of its length relative to the other thereby varying the capacitance between the two tubes.
The two tubes comprise an inner tube 1 axially within and spaced from an outer tube 3. The outer tube 3 abuts at one end against a sleeve 5 positioned in an opening 7 in a metal block 9. The outer tube is mounted within and in engagement with the inner surface of a tube 11 of insulating material. The tube 11 also extends at one end into the opening 7 in the block 9. The tube is thus fixed at its left-hand end as viewed in the figure.
The inner tube 1 is slidable axially of the tube 3 and is mounted on a pair of insulating bearings 13, 15. One end of the tube 1 projects out of the end of the tube 3 which is away from the fixed end thereof and is supported in a spring guide 17 and a spring 19 acts between this guide and a cover member 21 which is bolted to a housing 22 forming part of and insulated from a structure 25 by a spacer 23. The end of the tube 1 which is nearest to the fixed end of the tube 3 has an electrostatic guard conductor 27 connected thereto. A body of insulation 28 projecting from the end of the tube 1 supports the conductor 27 and a ring of insulation 29 separates the tube and the conductor. A conductor in the form of a wire 31 extends from the guard through the bore of the tube 1 and is connected to tensioning means 33 mounted on the cover 21.By adjusting the tensioning means, the tension in the conductor 31 is adjusted and the spring 19 is compressed.
Movement of the structure 25 towards and away from the block 9 causes the tube 1 to be displaced axially within the fixed tube 3. A bellows 35 of cylindrical form surrounds the tubes and is secured at its opposite ends to the block 9 and the structure 25. The space within the bellows is formed into a sealed container and is filled with a dry, non-corrosive gas at constant pressure. inner tube As the inner tube 1 is withdrawn from the right-hand end of the tube 3, the tube could be electrostatically affected from the structure 25 and to prevent this from occurring the housing 22 carries a further conductive tube 37 which is of substantially the same length as the tube 1. This tube 37 is secured at one end to the housing and extends around and coaxial with the tubes 1 and 3. At the left-hand end of the further tube a slide 39 contacts the outside of the insulating tube 11.The further tube 37 is connected electrically to the housing 22 and forms an electrostatic screen around any part of the inner tube which projects from the right-hand end of the fixed tube 3.
A further electrostatic shield 41 is mounted at the right-hand end of the insulating tube 11.
In order to obtain an electrical output from the transducer, a voltage from a high accuracy oscillator, having voltage amplitude compensation, stable frequency and waveform is supplied through an opening in the block 9 to a terminal member 45 mounted in the block. From this terminal a flexible lead 47 supplies the voltage to the fixed tube 3. A short flexible conductor 49 permanently connected to the right-hand end of the tube I passes through the housing 22 into a cavity 50 formed in the structure 25 and is connected to an operational amplifier located in the cavity whose output voltage amplitude is proportional to the capacitance of the two inner tubes. The length of the flexible conductor between the tube 1 and operational amplifier is thus very limited.The common zero voltage line of the oscillator is also connected to a terminal in the block 9 and is connected via a flexible conductor 51 which extends along a groove 53 provided in the outer surface of the insulating tube 11. The conductor is connected to the electrostatic guard element 41. The tube 37 is connected by a flexible conductor 55 to the insulated casing 22 and a flexible conductor 57 from the casing extends into the cavity 50 and is connected via the operational amplifier to the common zero voltage line.
The advantages of the transducer are its high accuracy and fast response over a relatively long stroke, the protection provided for the active tubes from electrical interference makes it suitable for use in electrically noisy environments. It is unnecessary to provide a bridge-balance system as is usually required with such transducers. The short connection wire from the tubes to the amplifier contained in the cavity 50 is an advantage as it reduces the chance of electrical interference. The construction of the structure 25 and the block 9 is rugged and in use a force is applied to the structure 25 to displace the tube 1 within the tube 3. An electrical signal which is accurately responsive to this displacement is produced and the output of the operational amplifier is an accurate indication of the displacement.The accuracy of the displacement is sustained for displacement of the inner tube over a stroke of up to about 200 mm.
WHAT WE CLAIM IS: 1. A variable capacitance linear displacement transducer comprising a pair of conductive tubes mounted in parallel spaced apart relation one within the other, the outer tube of the pair being fixed at one end and the other tube being displaceable in the direction of its length relative to the fixed tube, a further conductive tube positioned around and spaced from the outer one of said pair of tubes, said further tube being mounted such as to provide an electrostatic screen around any part of the inner one of the pair of tubes which projects outwardly from one end of the outer tube of the pair and the end of the inner tube of the pair which is closest to the fixed end of the outer tube of the pair having an electrostatic guard conductor connected thereto.
2. A variable displacement transducer as claimed in claim 1, in which the three tubes are coaxial and the inner tube of the pair and the further tube are fixed to a movable member at their ends which are opposite to the fixed end of the outer tube.
3. A variable displacement transducer as
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. away from the fixed end thereof and is supported in a spring guide 17 and a spring 19 acts between this guide and a cover member 21 which is bolted to a housing 22 forming part of and insulated from a structure 25 by a spacer 23. The end of the tube 1 which is nearest to the fixed end of the tube 3 has an electrostatic guard conductor 27 connected thereto. A body of insulation 28 projecting from the end of the tube 1 supports the conductor 27 and a ring of insulation 29 separates the tube and the conductor. A conductor in the form of a wire 31 extends from the guard through the bore of the tube 1 and is connected to tensioning means 33 mounted on the cover 21. By adjusting the tensioning means, the tension in the conductor 31 is adjusted and the spring 19 is compressed. Movement of the structure 25 towards and away from the block 9 causes the tube 1 to be displaced axially within the fixed tube 3. A bellows 35 of cylindrical form surrounds the tubes and is secured at its opposite ends to the block 9 and the structure 25. The space within the bellows is formed into a sealed container and is filled with a dry, non-corrosive gas at constant pressure. inner tube As the inner tube 1 is withdrawn from the right-hand end of the tube 3, the tube could be electrostatically affected from the structure 25 and to prevent this from occurring the housing 22 carries a further conductive tube 37 which is of substantially the same length as the tube 1. This tube 37 is secured at one end to the housing and extends around and coaxial with the tubes 1 and 3. At the left-hand end of the further tube a slide 39 contacts the outside of the insulating tube 11.The further tube 37 is connected electrically to the housing 22 and forms an electrostatic screen around any part of the inner tube which projects from the right-hand end of the fixed tube 3. A further electrostatic shield 41 is mounted at the right-hand end of the insulating tube 11. In order to obtain an electrical output from the transducer, a voltage from a high accuracy oscillator, having voltage amplitude compensation, stable frequency and waveform is supplied through an opening in the block 9 to a terminal member 45 mounted in the block. From this terminal a flexible lead 47 supplies the voltage to the fixed tube 3. A short flexible conductor 49 permanently connected to the right-hand end of the tube I passes through the housing 22 into a cavity 50 formed in the structure 25 and is connected to an operational amplifier located in the cavity whose output voltage amplitude is proportional to the capacitance of the two inner tubes. The length of the flexible conductor between the tube 1 and operational amplifier is thus very limited.The common zero voltage line of the oscillator is also connected to a terminal in the block 9 and is connected via a flexible conductor 51 which extends along a groove 53 provided in the outer surface of the insulating tube 11. The conductor is connected to the electrostatic guard element 41. The tube 37 is connected by a flexible conductor 55 to the insulated casing 22 and a flexible conductor 57 from the casing extends into the cavity 50 and is connected via the operational amplifier to the common zero voltage line. The advantages of the transducer are its high accuracy and fast response over a relatively long stroke, the protection provided for the active tubes from electrical interference makes it suitable for use in electrically noisy environments. It is unnecessary to provide a bridge-balance system as is usually required with such transducers. The short connection wire from the tubes to the amplifier contained in the cavity 50 is an advantage as it reduces the chance of electrical interference. The construction of the structure 25 and the block 9 is rugged and in use a force is applied to the structure 25 to displace the tube 1 within the tube 3. An electrical signal which is accurately responsive to this displacement is produced and the output of the operational amplifier is an accurate indication of the displacement.The accuracy of the displacement is sustained for displacement of the inner tube over a stroke of up to about 200 mm. WHAT WE CLAIM IS:
1. A variable capacitance linear displacement transducer comprising a pair of conductive tubes mounted in parallel spaced apart relation one within the other, the outer tube of the pair being fixed at one end and the other tube being displaceable in the direction of its length relative to the fixed tube, a further conductive tube positioned around and spaced from the outer one of said pair of tubes, said further tube being mounted such as to provide an electrostatic screen around any part of the inner one of the pair of tubes which projects outwardly from one end of the outer tube of the pair and the end of the inner tube of the pair which is closest to the fixed end of the outer tube of the pair having an electrostatic guard conductor connected thereto.
2. A variable displacement transducer as claimed in claim 1, in which the three tubes are coaxial and the inner tube of the pair and the further tube are fixed to a movable member at their ends which are opposite to the fixed end of the outer tube.
3. A variable displacement transducer as
claimed in claim 2, in which the inner tube and the further tube are slidable relative to the outer tube of the pair.
4. A variable displacement transducer as claimed in claim 2 or claim 3, in which the outer tube of the pair is secured to a fixed metal block and a flexible bellows surrounding said tubes is connected to the fixed block and to the movable member.
5. A variable displacement transducer as claimed in claim 4, in which the space within the bellows is filled with a dry, noncorrosive gas at constant pressure.
6. A variable displacement transducer substantially as hereinbefore described with reference to the drawing filed with the provisional specification.
GB19154/77A 1977-05-06 1977-05-06 Linear displacement transducer Expired GB1601572A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB19154/77A GB1601572A (en) 1977-05-06 1977-05-06 Linear displacement transducer
DE19782820040 DE2820040A1 (en) 1977-05-06 1978-05-08 LINEAR SHIFT CONVERTER

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB19154/77A GB1601572A (en) 1977-05-06 1977-05-06 Linear displacement transducer

Publications (1)

Publication Number Publication Date
GB1601572A true GB1601572A (en) 1981-10-28

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ID=10124648

Family Applications (1)

Application Number Title Priority Date Filing Date
GB19154/77A Expired GB1601572A (en) 1977-05-06 1977-05-06 Linear displacement transducer

Country Status (2)

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DE (1) DE2820040A1 (en)
GB (1) GB1601572A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005003688A1 (en) * 2003-07-01 2005-01-13 Tiax Llc Capacitive position sensor and sensing methodology
WO2005038270A1 (en) * 2003-10-17 2005-04-28 Clark Equipment Company Method and apparatus for stroke-position sensor for hydraulic cylinder

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH642432A5 (en) * 1978-05-11 1984-04-13 Rotovolumetric Ag DEVICE WITH A CYLINDER, A SLIDING PISTON AND A CAPACITIVE TRANSDUCER.

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005003688A1 (en) * 2003-07-01 2005-01-13 Tiax Llc Capacitive position sensor and sensing methodology
US7141988B2 (en) 2003-07-01 2006-11-28 Tiax Llc Capacitive position sensor and sensing methodology
US7420377B2 (en) 2003-07-01 2008-09-02 Tiax Llc Capacitive position sensor and sensing methodology
WO2005038270A1 (en) * 2003-10-17 2005-04-28 Clark Equipment Company Method and apparatus for stroke-position sensor for hydraulic cylinder
US7059238B2 (en) 2003-10-17 2006-06-13 Clark Equipment Company Method and apparatus for stroke position sensor for hydraulic cylinder

Also Published As

Publication number Publication date
DE2820040A1 (en) 1978-11-09

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Legal Events

Date Code Title Description
PS Patent sealed [section 19, patents act 1949]
PCNP Patent ceased through non-payment of renewal fee