Magnetoelastic force transducer

• US 4,802,368 A
• Filed: 12/09/1987
• Issued: 02/07/1989
• Est. Priority Date: 12/15/1986
• Status: Expired due to Fees

• Current Assignee: Asea Aktiebolag (ABB Limited)
• Original Assignee: Asea Aktiebolag (ABB Limited)
• Inventors: Nordvall, Jan O.
• Primary Examiner(s): NOT, DEFINED
• Application Number:
  US07/130,545
• Time in Patent Office: 426 Days
• Field of Search: 73/862.69, 73/779, 73/DIG. 2, 324/209, 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 is made of two identical, cylindrical bodies of magnetic material which are held together by means of a stud bolt. In an axially extending and concentrically located inner space there is placed a bobbin with two measuring windings connected in opposition and an excitation winding supplied with alternating current. The interior of the transducer is shaped such that a thin cylindrical tubular wall is formed immediately opposite to the respective measuring winding in each one of the bodies. When the transducer is force-loaded via the stud bolt, a compressive stress arises in one of these tubular walls and a tensile stress arises in the other tubular wall. This influences the magnetic conditions such that a signal is obtained from the measuring windings which is proportional to the applied force.

Claims

1. A magnetoelastic force transducer comprising a core of solid magnetoelastic material defining a closed magnetic circuit, an excitation winding surrounding part of said core and adapted to be fed with alternating current for generating a magnetic flux in the core and two measuring windings each surrounding parts of the core and adapted together to sense changes in the magnetic flux in the core when the latter is loaded with a force to be measured,

characterized in that:

the closed core includes two hollow cylindrical bodies each having outer and inner end faces which are connected together centrally and axially over their inner faces to provide an inner tubular space, a bobbin, on which the measuring windings and the excitation winding are wound located in said tubular space, first holes extending axially from the outer end faces of the cylindrical bodies, the axial length of each said first hole being shorter than the axial length of the respective body, second holes extending from the inner end faces of the cylindrical bodies and communicating with the respective first hole, a stud bolt inserted in one of said first holes and both of said second holes for securing together said two bodies, the diameter of said first hole in which the stud bolt is located being greater than the diameter of the stud bolt to provide clearance around the stud bolt in said first hole, and said second holes are provided in a central part of the bodies where said inner faces of the two bodies are in contact.

2. Magnetoelastic force transducer according to claim 1, in which said two bodies are identical and are screwed together by said stud bolt.

3. Magnetoelastic force transducer according to claim 2, in which each measuring winding is located within a respective one of the two bodies and the measuring windings, in the axial direction, are placed outside of a cylindrical tubular wall which is formed between the first holes and the inner concentric, tubular space.

4. Magnetoelastic force transducer according to claim 2, in which the excitation winding extends axially over the entire length of the bobbin.

5. Magnetoelastic force transducer according to claim 2, in which the stud bolt is made of a non-magnetic material and is longer than the length of the first hole in which it is located.

6. Magnetoelastic force transducer according to claim 1, in which each measuring winding is located within a respective one of the two bodies and the measuring windings, in the axial direction, are placed outside of a cylindrical tubular wall which is formed between the first holes and the inner concentric, tubular space.

7. A magnetoelastic force transducer having a magnetic core formed from two identical, cylindrical bodies which are held together and define an axially extending and concentrically located inner space, a bobbin located in said inner space and supporting two measuring windings connected in opposition, and an excitation winding supplied with alternating current, the interior of the transducer core being shaped such that a thin cylindrical tubular wall is formed immediately opposite to the respective measuring winding in each one of said two cylindrical bodies, a stud bolt extending axially of said two cylindrical bodies and holding said two cylindrical bodies together in the vicinity of said tubular walls, whereby when the transducer is influenced, via the stud bolt, by an externally applied force, a compressive stress arises in one of said tubular walls and a tensile stress arises in the other of said tubular walls to influence the magnetic conditions in the core such that a signal is obtained from the measuring windings which is proportional to the applied force.