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Contactless, Transformer-Based Measurement of the Resistivity of Materials

Traditional methods for resistivity measurements of concrete have to use two plate electrodes at opposite sides of a prism specimen. The major drawback of such a method is that the electrodes can be easily detached from the specimen due to shrinkage of concrete. Thus the measurement of resistivity is not accurate and sometimes easily has an unacceptable error. To get accurate measurement of resistivity of cement-based materials, a new device is invented. The new device utilizes a toroidal current principle. The concrete to be measured is case into a ring shape specimen and acts as the secondary of a transformer.

A formulae to provide accurate resistivity of concrete has been developed according to the relationship between the toroidal current, the toroidal voltage and the phase difference between them.
Technology Benefits
This new method is strict and sound in both theory and practice. It can provide the accurate measurement of electrical properties for materials, especially cement-based ones. The non-contact measurement without electrodes for electrical properties and the new formula to obtain resistivity are also new in this field.

The introduction of this invention solves the problem of inaccuracy measurement of electrical properties due to insecure electrode contacting and resistivity calculation in a toroidal current situation.
Technology Application
- Electrical property measurement of cement-based and/or concrete-like materials
- Material properties monitoring during construction
Supplementary Information
Patent Number: US6639401B2
Application Number: US2001907817A
Inventor: Li, Zongjin | Li, Wenlai
Priority Date: 19 Jul 2001
Priority Number: US6639401B2
Application Date: 19 Jul 2001
Publication Date: 28 Oct 2003
IPC Current: G01N002702 | G01N003338
US Class: 324239 | 324228 | 324693 | 324713
Assignee Applicant: The Hong Kong University of Science & Technology
Title: Contactless, transformer-based measurement of the resistivity of materials
Usefulness: Contactless, transformer-based measurement of the resistivity of materials
Summary: For measuring electrical resistivity of concrete and other cement-based building material's used in construction.
Novelty: Resistivity measurement method for cement-based material, uses double arm transformer whose secondary is made of sample and measures current induced in secondary on application of voltage to primary
Sub Category
Construction Engineering
Application Date
19 Jul 2001
Application No.
US 09/907817
Patent Information
US 6639401
ID No.
Hong Kong

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