Saturable core magnetometer with a parallel resonant circuit in which the W3 DC level changes with a change in an external magnetic field

• US 5,287,059 A
• Filed: 01/14/1992
• Issued: 02/15/1994
• Est. Priority Date: 05/19/1990
• Status: Expired due to Fees

• Current Assignee: NKK Corporation (JFE Holdings Incorporated)
• Original Assignee: NKK Corporation (JFE Holdings Incorporated)
• Inventors: Murakami, Yoshihiro, Ando, Seigo
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US07/807,863
• Time in Patent Office: 763 Days
• Field of Search: 322/244, 322/253, 322/254, 322/255, 324/256, 324/258, 324/260, 33/361
• US Class Current: 324/253
• CPC Class Codes: G01N 27/82 for investigating the presence of flaws
• CPC Class Codes: G01N 27/9046 by analysing electrical signals
• CPC Class Codes: G01R 33/04 using the flux-gate principle

Abstract

A magnetism detecting apparatus of this invention includes a magnetic sensor (11) constituted by a ferromagnetic core (12) and a detection coil (13) wound around the core (12), a parallel resonance circuit (15) constituted by the detection coil (13) of the magnetic sensor (11) and a capacitance element (14) connected in parallel with the detection coil (13), an oscillation circuit (18), which is constituted by an amplifier (16) to which the parallel resonance circuit (15) and a resistor (17) are connected as a feedback circuit, and the parallel resonance circuit (15), and excites the core (12) to a saturation region by using an oscillation current, and a waveform change detecting circuit (22, 24) for detecting a change in waveform of an output signal from the oscillation circuit (18). That is, the core (12) is excited to the saturation region by the oscillation circuit (18) using the detection coil (13) of the magnetic sensor (11) as part of the parallel resonance circuit (15), and an external magnetic field (H) applied to the magnetic sensor (11) is detected on the basis of the amount of change in waveform of an output signal (a) from the oscillation circuit (18). As a result, the circuit arrangement can be simplified, and a reduction in size and manufacturing cost of the overall apparatus can be realized while maintaining high measurement precision.

Claims

1. A device for sensing magnetism, comprising:

a magnetic sensor having a ferromagnetic core and a detection coil wound around said core;

a parallel resonance circuit comprising said detection coil of said magnetic sensor, and a capacitance element connected in parallel with said detection coil, said parallel resonance circuit providing an output signal;

a DC level of said output signal of said parallel resonance circuit changing in accordance with a change in an external magnetic field without changing a waveform of said output signal of said parallel resonance circuit;

an oscillation circuit including;

an amplifier having an output and an input; and

a feedback circuit comprising said parallel resonance circuit and a resistor coupled between said output and said input of said amplifier; and

a waveform change detecting circuit for detecting a change in a waveform of an output signal from said oscillation circuit, said waveform change detecting circuit comprising;

a signal separator for separating said output signal of said oscillation circuit into a first positive waveform component and a second negative waveform component;

a positive pulse width measuring circuit for measuring a width of said first positive waveform component separated by said signal separator;

a negative pulse width measuring circuit for measuring a width of said second negative wavefrom component separated by said signal separator; and

subtracting circuit means for subtracting a first pulse width measured by one of said positive and negative pulse width measuring circuits from a second pulse width measured by the other one of said positive and negative pulse width measuring circuits.

3. The device for sensing magnetism according to claim 1, wherein said positive pulse width measuring circuits respectively comprise pulse width counters.

2. A device for sensing magnetism, comprising:

a magnetic sensor having a ferromagnetic core and a detection coil wound around said core;

a parallel resonance circuit comprising said detection coil of said magnetic sensor, and a capacitance element connected in parallel with said detection coil, said parallel resonance circuit providing an output signal;

a DC level of said output signal of said parallel resonance circuit changing in accordance with a change in an external magnetic field without changing a waveform of said output signal of said parallel resonance circuit;

an oscillation circuit including;

a differential amplifier having an output terminal and first and second input terminals, said first input terminal being connected to a ground potential, and said second input terminal being connected to receive said output signal from said parallel resonance circuit so that said differential amplifier amplifies said output signal from said parallel resonance circuit into positive and negative portions when measured with respect to said ground potential;

a feedback circuit, comprising said parallel resonance circuit and a resistor, said resistor being coupled between said output terminal and said second input terminal of said differential amplifier;

said parallel resonance circuit being connected between an input terminal of said resistor and said ground potential; and

a waveform change detecting circuit for detecting a change in a waveform of an output signal from said oscillation circuit,

said waveform change detecting circuit comprising;

a signal separator for separating said output signal of said oscillation circuit into a first positive waveform component and a second negative waveform component;

a positive pulse width measuring circuit for measuring a width of said first positive waveform component separated by said signal separator;

a negative pulse width measuring circuit for measuring a width of said second negative wavefrom component separated by said signal separator; and

subtracting circuit means for subtracting a first pulse width measured by one of said positive and negative pulse width measuring circuits from a second pulse width measured by the other one of said positive and negative pulse width measuring circuits.

4. The device for sensing magnetism according to claim 2, wherein said positive and negative pulse width measuring circuit respectively comprise pulse width counters.