Variable inductance displacement measuring device with slidable metal sleeve and ferrite bead core

• US 5,010,298 A
• Filed: 06/26/1989
• Issued: 04/23/1991
• Est. Priority Date: 10/27/1988
• Status: Expired due to Term

• Current Assignee: Macome Corporation Kawano BLDG
• Original Assignee: Macome Corporation
• Inventors: Uemura, Saburo
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US07/371,742
• Time in Patent Office: 666 Days
• Field of Search: 324/207, 324/208, 324/234, 324/207.18, 324/207.19, 324/207.24, 340/870.31-870.36, 336/175, 336/212, 336/233, 336/45
• US Class Current: 324/207.19
• CPC Class Codes: G01B 7/001 Constructional details of gauge heads G01B7/012 takes precedence
• CPC Class Codes: G01D 5/202 by movable a non-ferromagnetic conductive element G01D5/2033 takes precedence

Abstract

A displacement measuring apparatus including a variable inductance coil formed of a pair of coils, on a core of predetermined length made of a material having high magnetic permeability. The pair of coils are disposed on a core adjacent to each other in their axial directions and are covered by a metal sleeve of substantially the same length of one of the coils. A detecting circuit is provided including a high frequency oscillator and a rectifier and is connected to the variable inductance coil, wherein when the metal sleeve is slidably moved, the detecting circuit generates a direct current voltage in correspondence with the displacement of the metal sleeve.

Claims

1. A displacement measuring apparatus comprising:

a variable inductance coil formed of a pair of coils, each being wound at a predetermined length and disposed adjacent to each other in their axial directions about a core made of a material having high magnetic permeability and being covered by a protective tube and a slidable metal sleeve disposed over said inductance coil, said sleeve being of substantially the same length of one of said coils and being coupled to an object to be measured for movement in response thereto, said core being made of a metal wire and a plurality of ferrite beads connected in series and covering said metal wire; and

a detecting circuit comprising a high frequency pulse oscillator, the said pair of coils of said variable inductance coil, a pair of resistors, and a pair of rectifiers, said pair of coils being connected together at their one ends to one output terminal of said oscillator, said pair of resistors being connected at their one ends to the other ends of said pair of coils, respectively, while being connected together at their other ends to the other output terminal of said oscillator, said pair of rectifier rectifying voltages produced across said pair of resistors and delivering a difference voltage therebetween, wherein when said metal sleeve is slidably moved, said detecting circuit generating a direct current voltage in correspondence with the displacement of said metal sleeve.

2. The displacement measuring apparatus according to claim 1 in which the lengths of each of said pair of coils are selected equal to each other.

3. A displacement measuring apparatus comprising:

a variable inductance coil having a first coil of a predetermined length wound around a first core, said first coil being covered with a slidable first metal sleeve of substantially the same length as that of said first coil which is coupled to an object to be measured;

a fixed conductance coil having a second coil of a predetermined length wound around a second core, said second coil being fixedly covered with a second metal sleeve of substantially the same or shorter length as that of said second coil, each of said first and second cores being made of a metal wire and a plurality of ferrite beads connected in series and covering said metal wire, said first and second coils being directly wound around said first and second cores, respectively, and each covered with a protective tube, said metal sleeve covering said protective tube with a clearance; and

a detecting circuit comprising a high frequency pulse oscillator, said first and second coils, a pair of resistors, and a pair of rectifiers, said first and second coils being connected together at their one ends to one output terminal of said oscillator, said pair of resistors being connected at their one ends to one other ends of said first and second coils, respectively, while being connected together at their other ends to the other output terminal of said oscillator, said pair of rectifier rectifying voltages produced across said pair of resistors and delivering a difference voltage therebetween, wherein said fixed inductance coil is located distance from variable inductance coil so that when said first metal sleeve is moved, said detecting circuit generates a direct current voltage corresponding to a displaced amount of said first metal sleeve.

4. A displacement measuring apparatus comprising:

a variable inductance coil having a first coil of a predetermined length wound around a core, said first coil being covered with a slidable metal sleeve of substantially the same length as that of said coil, said core being made of a metal wire and a plurality of ferrite beads connected in series and covering said metal wire, said first coil being directly wound around said core and covered with a protective tube, said slidable metal sleeve covering said protective tube with a clearance;

a fixed conductance element having the same temperature characteristic as that of said variable inductance coil; and

a detecting circuit including a high frequency pulse oscillator, said first coil, said fixed inductance element, a pair of resistors, and a pair of rectifiers, said first coil and said fixed inductance element being connected together at their one ends to one output terminal of said oscillator, said pair of resistors being connected at their one ends to the other ends of said first coil and said fixed inductance element, respectively, while being connected together at their other ends to the other output terminal of said oscillator, said pair of rectifier rectifying voltages produced across said pair of resistors and delivering a difference voltage therebetween, wherein said fixed inductance element is located distance from said variable inductance coil and an inductance value of said fixed inductance element is selected to be equal to an inductance value of said variable inductance coil when said metal sleeve is fully inserted into said coil so that when said metal sleeve is slidably moved, said detecting circuit generating at its output side a direct current output corresponding to a displaced amount of said metal sleeve.

5. The displacement measuring apparatus as claimed in claim 4 in which said fixed inductance element is made of a second coil with a predetermined length wound around a second core, said second core being formed of a metal wire and a plurality of ferrite beads connected in series and covering said metal wire, said second coil being directly wound around said core and covered with a protective tube and fixedly covered with a second metal sleeve.