JPH0194280A - Magnetic sensor for detecting magnetic material - Google Patents

Abstract

PURPOSE:To dispense with the adjustment of a coil interval, to facilitate preparation and to stabilize a detection sensitivity temp. characteristic, by providing a resonance circuit, an oscillator and an voltage detection part. CONSTITUTION:A resonance circuit wherein a coil 1 of a single winding empty core and a resonance frequency adjusting condenser 3 are connected in parallel is connected to the wiring of an oscillator 5 containing a current control resistor 2 and a voltage detector 6 detects the voltage between the terminal of the coil 1 and that of the condenser 3. A curve A shows the frequency characteristic of a magnetic sensor when a magnetic material 4 is absent within a detection distance range and the resonance frequency thereof is f0. A curve B shows a characteristic when the magnetic material 4 enters the detection distance range of the sensor and the resonance frequency f0' at that time becomes lower than f0. A curve C shows a frequency characteristic when iron being a soft magnetic material similar to the magnetic material 4 enters the detection distance range and the resonance f0'' at that time becomes higher than f0. Further, the voltage level of the whole of the curve C is lowered. By utilizing the frequency characteristic changing as mentioned above, the magnetic material and the soft magnetic material can be discriminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic material detection magnetic sensor, and particularly to a magnetic material detection magnetic sensor that uses a single-turn coil and performs excitation and detection on the same coil.

[Conventional technology]

Various methods have been announced for magnetic sensors that detect magnetic materials, but all magnetic sensors are equipped with separate excitation coils and detection coils, and the disturbances in the alternating current magnetic field transmitted from the excitation coil are sent to the detection coil. What they have in common is that they detect the signal and convert it into an electrical signal.

[Problem that the invention seeks to solve]

By the way, since this type of magnetic sensor is equipped with two separate coils, an excitation coil and a detection coil,
When a magnetic material approaches a magnetic sensor, there is a problem in that the interaction between the excitation coil and the detection coil causes disturbance of the magnetic field.

Therefore, in order to eliminate this effect, it is necessary to supply a large amount of power to the excitation coil. In addition, when manufacturing such magnetic sensors, variations in sensitivity and temperature characteristics occur due to changes in the spacing between the excitation coil and the detection coil, so it is necessary to delicately adjust the spacing between the excitation coil and the detection coil. There is a need.

However, no matter how delicately the adjustment is made, it is impossible to eliminate variations in detection characteristics within the same lot.

The purpose of the present invention is to solve the above-mentioned problems.
It is an object of the present invention to provide a magnetic substance detection magnetic sensor having the same characteristics.

[Means for solving problems]

The present invention uses frequency f. a resonant circuit including a single-turn air-core coil having a resonant frequency of , an oscillator that applies an excitation frequency f□ (fl<f,) to the resonant circuit, and a voltage detection unit that measures the voltage level between terminals of the resonant circuit. A magnetic material detection magnetic sensor is characterized by having the following features.

[Principle/effect]

The present invention basically utilizes the fact that when a magnetic material approaches the leakage magnetic field of one coil used in a magnetic sensor, the inductance L of the coil changes.

The inductance L of the coil is given by the following equation.

μ: Magnetic permeability N: Number of coil turns A: Coil cross-sectional area Q: Magnetic path length μ of the coil changes as the magnetic material approaches the coil. Further, L of the coil is also proportional to its cross-sectional area.

Utilizing this point, it is also possible to adjust the detection sensitivity of the sensor by adjusting the cross-sectional area of the coil.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of the sensor of the present invention. In the figure, a resonant circuit in which a single-turn air-core coil 1 and a resonant frequency adjustment capacitor 3 are connected in parallel is connected to the wiring of an oscillator 5 including a current control resistor 2. A voltage detector 6 detects the voltage between the terminals of the coil 1 and the capacitor 3.

In the present invention, the coil 1 serves both as an excitation coil and as a detection coil made of magnetic material.

When the magnetic material 4 approaches the leakage magnetic field of the coil 1, its inductance changes.

In FIG. 2, curve A shows the frequency characteristic of the magnetic sensor when the magnetic material 4 is not within the detection distance range. As is clear from the figure, its resonant frequency is fo. Curve B is the characteristic when the magnetic material 4 is within the detection distance range of the sensor.

=3- As is clear, the resonance frequency f at that time. ' is lower than fo. As the magnetic material 4 moves closer to the sensor, the resonant frequency drops further, but the level at each resonant frequency does not change much, as can be seen from curves A and B. On the other hand, a curve C shows the frequency characteristic when iron, which is a soft magnetic material similar to the magnetic material 4, comes within the detection distance range. In the case of soft magnetic materials, the resonance frequency f at that time is different from that when detecting magnetic materials. ' increases from fo. Moreover, the voltage level of the entire curve C is decreasing. This is thought to be due to eddy current loss caused by iron.

Magnetic materials and soft magnetic materials can be distinguished by using frequency characteristics that change depending on the type of magnetic material.

That is, the resonance frequency f defined by the original coil 1 and the circuit components 2 and 3. The excitation frequency of the oscillator 5 is fixed at a lower frequency, for example, fl, and identification is made from changes in the voltage level. The voltage corresponds to point P when no magnetic material is close.

When the magnetic material 4 approaches, the voltage increases to point Q, and when the soft magnetic material approaches, the voltage decreases to point R.

In this way, the excitation frequency is set to f. It can be seen that magnetic materials and soft magnetic materials can be distinguished by setting the value lower.

On the other hand, the excitation frequency is f. If it is set higher, for example f2, its identification becomes difficult.

In other words, the voltage when no magnetic material approaches corresponds to point P', but even if either magnetic material or soft magnetic material approaches, the voltage drops as shown at point 07. .

Further, since the state of the voltage drop differs depending on the degree of proximity of the magnetic materials, it is difficult to distinguish between magnetic materials and soft magnetic materials based on the degree of voltage drop.

Although the embodiments of the present invention have been described above using the differences in characteristics between magnetic materials and soft magnetic materials, the present invention is not limited thereto. Even if a magnetic material is used, it is possible to distinguish it from a soft magnetic material.

Further, the present invention sets the excitation frequency to f. I mentioned that it should be used at a lower level. Although there is no lower limit in principle, lowering it below the necessary level is undesirable because it lowers the effective detection sensitivity. In the present invention, the lower limit is (1-2/Q) fo (however, Q
is the sharpness at resonance).

〔Effect of the invention〕

As described in detail above, according to the present invention, there is no need to adjust the coil spacing, the manufacturing is easy, and a sensor with stable detection sensitivity and temperature characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram of a sensor, and FIG. 2 is a characteristic diagram showing an embodiment of the present invention. 1...Coil 2...Current control resistor 3
... Resonance frequency adjustment capacitor 4 ... Magnetic material 5
...Oscillator 6...Between voltage detectors Upper Oui Petrochemical Industry Co., Ltd. Figure 1

Claims (1)

[Claims] (1) A resonant circuit including a single-turn air-core coil with a resonant frequency f_0 and an excitation frequency f_1 (f_1<f_0
) to the resonant circuit; and a voltage detection section that measures the voltage level between terminals of the resonant circuit.