Magnetoelastic force transducer

• US 5,007,295 A
• Filed: 01/03/1990
• Issued: 04/16/1991
• Est. Priority Date: 01/03/1990
• Status: Expired due to Fees

• Current Assignee: Asea Brown Boveri AB (ABB Limited)
• Original Assignee: Asea Brown Boveri AB (ABB Limited)
• Inventors: Ornholmer, Lars, Sobel, Jarl, Gustafsson, Par
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US07/460,515
• Time in Patent Office: 468 Days
• Field of Search: 73/862.69, 73/779, 73/DIG. 2, 336/20
• US Class Current: 73/862.69
• CPC Class Codes: G01L 1/125 by using magnetostrictive means magnetostrictive sensors H10N35/101
• CPC Class Codes: G01L 1/127 by using inductive means G01L1/122, G01L1/125 take precedence

Abstract

A magnetoelastic force transducer according to the invention comprises two closed magnetic circuits. The transducer is constructed in such a way that the reluctance in one of the magnetic circuits will be changed when the transducer is subjected to a force as a result of changes in the magnetic permeability caused by magnetostriction. The second magnetic circuit is formed so as to have an essentially unchanged reluctance when the transducer is loaded and is used to compensate for those changes in the permeability of the material arising for reasons other than magnetostriction.

Claims

1. A magnetoelastic force transducer comprising a force-absorbing rotationally symmetrical core of magnetoelastic material provided with two excitation windings supplied with alternating current, two measuring windings, flux closure yokes in the form of a first, a second, and a third flange, and a surrounding sleeve, said core comprising:

a thin-walled tubular section and a thick-walled tubular or solid section with an intermediate first transition zone and a second transition zone located at the other end of the tick-walled tubular or solid section, said second zone changing into a short zone with the same outer diameter as the outer diameter of the thin-walled tubular section;

a first force-dependent magnetic circuit consisting of the thin-walled tubular section of the core, the first transition zone, the first and second flanges and that part of the sleeve which lies between these flanges and an excitation winding and a measuring winding;

a second force-independent magnetic circuit consisting of the thick-walled tubular or solid section of the core, the first and second transition zones, the second and the third flanges and the remaining part of the sleeve, and an excitation winding and a measuring winding;

the frequency of the supply voltage being chosen such that the penetration depth into the magnetoelastic material is much smaller than the wall thickness of the thick-walled tubular section and much smaller than the radius of the thick-walled section when this thick-walled section is formed as a solid part;

the numbers of turns of the excitation windings being adapted such that the magnetic conditions are the same in the two magnetic circuits;

the measuring windings being connected in opposition; and

the numbers of turns of the measuring windings being adapted such that the output voltage of the transducer amounts to the desired level in the case of an unloaded transducer.

2. A magnetoelastic force transducer according to claim 1, wherein the flanges are manufactured from the same piece as the core.

3. A magnetoelastic force transducer according to claim 1, wherein the flanges are welded or glued to the core.

4. A magnetoelastic force transducer according to claim 1, wherein the sleeve is welded or glued to the flanges.

5. A magnetoelastic force transducer according to claim 1, wherein the sleeve is arranged as a bellows which is compressible to a certain extent in the axial direction.

6. A magnetoelastic force transducer according to claim 1, wherein the core is separated from flanges, sleeve and windings to make possible contactless axial force measurement of freestanding shafts.

7. A magnetoelastic force transducer comprising a force-absorbing rotationally symmetrical core of magnetoelastic material provided with two excitation windings supplied with alternating current, two measuring windings, flux closure yokes in the form of a first, a second, and a third flange, and a surrounding sleeve, said core comprising:

a thin-walled tubular section and a first tubular section having the same outer diameter as the thin-walled tubular section, said first tubular section including an external, narrow, radial slot at the transition between said thin-walled tubular section and said first tubular section;

a first force-dependent magnetic circuit including the thin-walled tubular section of the core, the first and second flanges and that part of the sleeve lying between the flanges and an excitation winding and a measuring winding;

a second force-independent magnetic circuit including the first tubular section, the second and third flanges and the remaining part of the sleeve, and an excitation winding and a measuring winding;

the frequency of the supply voltage being selected such that the penetration depth into the magnetoelastic material is much smaller than the wall thickness of the first tubular section;

the number of turns of the excitation windings being adapted such that the magnetic conditions are the same in the two magnetic circuits;

the measuring windings being connected in opposition; and

the number of turns of the measuring windings being adapted such that the output voltage of the transducer amounts to the desired level in the case of an unloaded transducer.

8. A magnetoelastic force transducer comprising a force-absorbing rotationally symmetrical core of magnetoelastic material provided with two excitation windings supplied with alternating current, two measuring windings, flux closure yokes in the form of a first, a second and a third flange, and a surrounding sleeve, said core comprising:

a thin-walled tubular section and a second tubular section having the same outer diameter as said thin-walled tubular section, said second tubular section including a narrow axial slot extending from the free end of the second tubular section, said slot having an outer diameter equal to the inner diameter of said thin-walled tubular section and an axial length corresponding to the axial length of a lower zone;

a first force-dependent magnetic circuit including the thin-walled tubular section of the core, the first and second flanges and that part of the sleeve lying between the flanges and an excitation winding and a measuring winding;

a second force-independent magnetic circuit including the second tubular section, the second and third flanges and the remaining part of the sleeve, and an excitation winding and a measuring winding;

the frequency of the supply voltage being selected such that the penetration depth into the magnetoelastic material is much smaller than the wall thickness of the second tubular section;

the number of turns of the excitation windings being adapted such that the magnetic conditions are the same in the two;

the measuring windings being connected in opposition; and

the number of turns of the measuring windings being adapted such that the output voltage of the transducer amounts to the desired level in the case of an unloaded transducer.