Contactless, transformer-based measurement of the resistivity of materials

• US 6,639,401 B2
• Filed: 07/19/2001
• Issued: 10/28/2003
• Est. Priority Date: 07/19/2001
• Status: Active Grant

• Current Assignee: Hong Kong University of Science and Technology
• Original Assignee: Hong Kong University of Science and Technology
• Inventors: Li, Zongjin, Li, Wenlai
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US09/907,817
• Publication Number:
  US 20030016009A1
• Time in Patent Office: 831 Days
• Field of Search: 324/201, 324/211, 324/227, 324/228, 324/239-243, 324/445, 324/545, 324/117.R, 324/691, 324/693, 324/696, 324/704, 324/705, 324/713, 324/724, 324/654, 324/656
• US Class Current: 324/239
• CPC Class Codes: G01N 27/023 where the material is placed in the field of a coil
• CPC Class Codes: G01N 33/383 Concrete or cement

Abstract

The present invention provides an apparatus and method for measuring the resistivity of a sample of cement-based material. A transformer is formed with a primary coil, a secondary formed by means of a sample of said cement-based material, means for supplying a voltage to said primary, means for measuring the voltage induced in said sample, and means for measuring the current induced in said sample. The resistance of the sample can be measured and thus the resistivity of the concrete sample can be calculated.

Claims

1. Apparatus for measuring the resistivity of a sample of material, comprising:

a transformer formed with a primary coil, a secondary formed by a sample of said material that is inductively coupled to said primary coil, means for supplying a voltage to said primary, means for measuring the voltage induced in said sample, and means for measuring the current induced in said sample.

2. Apparatus as claimed in claim 1 wherein said transformer includes a core having a leg about which said primary and said secondary are both formed.

3. Apparatus as claimed in claim 1 wherein said transformer includes a core having a first leg about which said primary is wound and a second leg around which said secondary is formed.

4. Apparatus as claimed in claim 1 wherein said sample is formed as a ring of cement-based material.

5. Apparatus as claimed in claim 4 wherein said ring is annular.

6. Apparatus as claimed in claim 4 wherein said ring is rectangular.

7. Apparatus as claimed in claim 4 wherein said voltage measuring means comprises a coil formed adjacent a surface of said ring and extending circumferentially around said sample.

8. Apparatus as claimed in claim 4 wherein said current measuring means surrounds a radial section of said sample.

9. Apparatus as claimed in claim 8 wherein said current sensing means is a leakage current meter.

10. Apparatus as claimed in claim 8 wherein said current sensing means is a Rogowski coil.

11. A method for measuring the resistivity of a sample of material, comprising:

(a) forming a sample of said material as a secondary of a transformer,

(b) applying a voltage to a primary of said transformer,

(c) measuring the voltage induced in said sample,

(d) measuring the current induced in said sample, and

(e) determining the resistivity of said sample from the results of steps (c) and (d).