JPS61155983A - Magnetic body detector - Google Patents

Abstract

PURPOSE:To always obtain max. detection sensitivity regardless of temp., by making the temp. change in the oscillation frequency of a magnetic field exciting LC oscillation circuit due to temp. same to that in the resonance frequency of a detection LC circuit due to temp. CONSTITUTION:The oscillation frequency of an oscillation circuit containing an exciting coil 1, a resonance condenser 3 and a positive feedback circuit 4 is determined by the product of L and C mounted to the oscillation circuit and the change in said frequency due to temp. is prescribed by the change in the temps. of L and C. A resonance condenser is properly selected to be mounted to a voltage detection circuit containing a detection coil 2 so as to make the resonance frequency and change therein due to temp. of said detection circuit equal to the oscillation frequency and change therein due to temp. of the oscillation circuit containing the coil 1.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a magnetic material detector that magnetically detects a magnetic material.

<Prior art and its problems> Magnetic material detector (sensor technology VO1, 1, Nct 12
) are as follows. FIG. 5 shows an example of a conventional detector. An oscillator 6 is connected to the excitation coil 1, and an alternating current is passed through the excitation coil IK. The magnetic field emitted from the excitation coil 1 penetrates the detection coil 2 placed near the excitation coil 1.
As a result, an induced voltage in the sensing coil 2iC is generated. When a magnetic body approaches the detector, the distribution of the magnetic field changes, thereby changing the induced voltage generated in the sensing coil. By detecting this voltage change with the voltage detection section 5, it is possible to know the presence or absence of the magnetic material, the distance between the magnetic material and the detector, etc.

Here, the pure induced voltage of the sensing coil when there is no magnetic material is called the base voltage, and the change in the induced voltage of the sensing coil when the magnetic material approaches the detector is called the detection sensitivity. To increase detection sensitivity, capacitors of appropriate capacitance are attached to the excitation coil and detection coil to align the electrical resonance points and cause oscillation at that resonance frequency.

Conventionally, an oscillator that is stable against temperature, such as a crystal resonator, was used, so the oscillation frequency was extremely stable against ambient temperature. However, the resonant frequencies of the excitation coil and detection coil change depending on the temperature.

For this reason, the oscillation frequency deviates from the resonance point of the excitation coil and the detection coil, causing sensitivity fluctuations.

In contrast, in the past, the detection sensitivity was increased by attaching a temperature compensation capacitor to the LC resonator of the detection coil and excitation coil so that the resonant frequency did not fluctuate due to temperature changes and causing the LC resonator to oscillate at a fixed frequency. has been kept to a maximum. However, this adjustment places significant restrictions on element selection, making coil design difficult.

<Objective of the Invention> An object of the present invention is to provide a sensor having a circuit configuration that automatically compensates for temperature so that maximum detection sensitivity can always be maintained even if the temperature of the detector changes.

<Structure of the Invention> In a magnetic material detector equipped with a magnetic field excitation coil and a magnetic field detection coil, a coil (L) and a capacitor (C) are used in each of the magnetic field excitation oscillation circuit and the detection circuit, and the LC
The temperature change in the resonant frequency of the circuit is not zero, and the temperature change in the oscillation frequency of the LC oscillation circuit for magnetic field excitation and the detection L
The C circuit is characterized in that the resonant frequency changes with temperature in the C circuit are the same.

<Operation/Principle of the Present Invention> The present invention is designed to efficiently flow an excitation current with minimum electric power by incorporating an excitation coil that generates an alternating magnetic field into an LC oscillator. Additionally, the sensing coil is configured to generate the maximum voltage using a capacitor in parallel.

In the case of the above configuration, the resonant frequency of the oscillation circuit including the excitation coil is determined by the product of L and C applied to one oscillation circuit, and its temperature change is defined by the temperature change of L and C, respectively. On the other hand, the voltage detection circuit including the detection coil has
An appropriate resonant capacitor is selected so that its resonant frequency and its temperature change are equal to the resonant frequency and its temperature change of the oscillation circuit including the excitation coil. Therefore, even if the temperature of the detector changes, both the oscillation circuit and the detection circuit continue to operate at the resonant frequency, providing maximum detection sensitivity.

In this case, there is no need for the resonant frequency to shift at all due to the presence change as in the conventional case, and it is sufficient that the temperature change at the same resonant wave number is the same in the excitation LC circuit and the detection & detection LC circuit.

<Embodiment> A block diagram showing an embodiment of the present invention is shown in FIG. For the excitation coil 1 and the detection coil 2, a case is shown in which an LC resonator having the same number of turns wound around the core and an appropriate resonance capacitor 3 attached is used. 4 is a positive feedback circuit, and 5 is a voltage detection section.

FIG. 2 shows an example of an oscillation circuit in which an excitation coil is incorporated into a Colpitts oscillator. The excitation coil 1 is
Since it is used as L of the LC oscillator in combination with a positive feedback circuit, the oscillation frequency always matches the resonant frequency.

Note that 2 is a detection coil and a 3-piece resonance capacitor.

The capacitances CI and C2 are the capacitances of two capacitors connected to the transistors.

In Fig. 2, feedback is applied by transistor 7, but I
It can also be replaced with a suitable power element such as C.

As an example is shown in FIG. 3, the oscillation frequency of the magnetic field excitation oscillation circuit (solid line) and the resonance frequency of the detection circuit (broken line) decrease as the temperature rises. By using the same new core quality and using capacitors with appropriate temperature coefficients, the rates of change are approximately equal.

An example of a comparison of the detection level of magnetic substances with conventional methods is shown in Part 4.
As shown in the figure. . . , mu indicate the pace voltage of the conventional type and the present invention, respectively, and 101Δ indicates the output voltage when the magnetic body approaches a certain distance of the same conventional type and the present invention, respectively. Therefore, the detected voltage is the voltage difference between the broken line and the solid line. In the conventional type, the detection voltage changes as the pace voltage changes, but in the present invention, the pace voltage, the detection voltage, and the temperature each take a substantially constant value.

As described above, the detector of the present invention is temperature compensated so that it exhibits a nearly constant detection voltage against temperature changes.

Furthermore, compared to conventional circuit configurations that have an oscillator outside the excitation LC resonator, the troublesome initial adjustment of matching the LC resonance point of the excitation coil to the oscillation frequency is eliminated, and the circuit configuration is simple. However, the number of elements is reduced and reliability is increased, while there are secondary benefits such as cost reduction.

<Effects of the Invention> By employing the configuration of the present invention, it is possible to always operate at a frequency that has the maximum detection sensitivity against temperature changes, and accordingly, the base voltage and the detection voltage are adjusted to f! J
? ! can be kept constant.

In addition, compared to conventional detectors, the single circuit configuration is simpler, the number of adjustment points is reduced, and the product can be manufactured at a lower cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a diagram showing an example of the circuit configuration of the present invention. FIG. 3 and FIG. 4 are diagrams showing an example of the effects of the present invention. FIG. 5 is a block diagram showing a conventional embodiment. In the figure: 1. . . . Excitation coil, 2 . . . Detection coil, 31. Resonance capacitor, 4. ...Positive feedback circuit, 5.・Voltage detection section, 6. ...oscillator, 7. ...Transistor. Leap 11, Valve T knee, 31 Bow (Mist 1st Figure Tsuchiya (1: Nυhiko 4le 2; & Arrow Locoil 3; Container for only #) 7: Transistor Star 3rd figure Temperature (0C)

Claims (1)

[Claims] In a magnetic detector equipped with a magnetic field excitation coil and a magnetic field detection coil, a coil (L) and a capacitor (C) are used in the magnetic field excitation oscillation circuit and the detection circuit, respectively, and the temperature change in the resonance frequency of the LC circuit is zero. What is claimed is: 1. A magnetic substance detector characterized in that a temperature change in the oscillation frequency of the magnetic field excitation LC oscillation circuit and a temperature change in the resonant frequency of the detection LC circuit are the same.