Electromagnetic inductive probe

• US 5,793,214 A
• Filed: 05/06/1997
• Issued: 08/11/1998
• Est. Priority Date: 06/30/1994
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Wakamatsu, Hideki
• Primary Examiner(s): Karlsen, Ernest F.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US08/851,815
• Time in Patent Office: 462 Days
• Field of Search: 324/601, 324/202, 324/445, 324/74, 324/127, 324/204, 324/225
• US Class Current: 324/601
• CPC Class Codes: G01N 27/023 where the material is placed in the field of a coil
• CPC Class Codes: G01R 27/267 Coils or antennae arrangements, e.g. coils surrounding the sample or transmitter/receiver antennae
• CPC Class Codes: G01R 27/2676 Probes
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

Abstract

A highly accurate electromagnetic-induction-type conductivity and dielectric constant meter is obtained by using a calibration box (instrument) and a structure as below. The conductivity and dielectric constant meter employs an electromagnetic inductive probe which includes a primary transformer composed of a toroidal core with a wound primary coil, a secondary transformer composed of a toroidal core with a wound secondary coil, an electrostatic shield shielding the transformers, and cables that connect the probe to a meter. To eliminate the electrostatic capacity produced by causes other than electromagnetic induction, the structure of the probe is symmetrical. In a first embodiment, the secondary transformer is placed between two parts of the primary transformer, which has two cores of the same shape that are placed symmetrically. The structure, including the primary and secondary transformers, gaps in the electrostatic shields, and cables, are symmetrical with respect to a plane perpendicular to the central axis of the ring shapes and passes through the center of the annular core of the secondary transformer.

Claims

1. A method for calibrating an impedance meter employing an annular electromagnetic inductive probe, said method comprising the steps of:

providing a calibration instrument for said impedance meter, said impedance meter comprising;

a conductive box surrounding an outer surface of said probe;

a projection that passes through an inner circle of said probe;

a coaxial connector, an inner conductor of said coaxial connector connected to said projection, and an outer conductor of said coaxial connector connected to said conductive box;

a hole in said conductive box enabling passage of cables of said probe; and

means for opening and closing said box, so that said probe can be placed into and removed from the conductive box;

placing said probe into said calibration instrument so that said projection passes through the inner circle of said probe; and

calibrating said impedance meter by using three standard impedances to be successively connected to said coaxial connector.

2. A method for calibrating an impedance meter employing an, annular electromagnetic inductive probe as recited in claim 1, wherein said three standard impedances are OPEN, SHORT and LOAD.

3. A calibration instrument for an impedance meter employing an electromagnetic inductive probe having plural cables, one of said cables for applying a signal to an inductor included in said probe and another of said cables for connecting a measuring device to another inductor included in said probe, said calibration instrument comprising:

a conductive box surrounding an outer surface of said probe;

a conductive projection that passes through an inner circle of said probe and connects to one wall of said conductive box;

a coaxial connector mounted in a second wall that is opposite said one wall, an inner conductor of said coaxial connector connected to said conductive projection, and an outer conductor of said coaxial connector connected to said second wall of said conductive box;

a hole in said conductive box enabling passage of said cables of said probe; and

means for opening and closing said box, so that said probe can be placed into and removed from the conductive box.