JPH0224475B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to, for example, signal detection in a traffic signal system, magnetic field measurement in a CRT test adjustment line,
This invention relates to a self-excited bridge type magnetic detection method using a magnetic thin wire as a magnetic core for measuring magnetic shielding effects in the medical field.

The conventional bridge method magnetic detection method is
At least one of the four elements that make up the AC bridge is an inductance element with a magnetic core placed in the center of the coil.The impedance of the inductance element is changed by the magnetic field to be measured applied to this magnetic core, Information is extracted as changes in the unbalanced voltage amplitude of the bridge.

In this type of bridge circuit, a constant voltage source or constant current source with a constant frequency is used as an AC power source as a driving power source. Therefore, the duty ratio of the drive power source does not change due to a change in the impedance of the inductance element, so the strength of the magnetic field to be measured is measured from the amplitude value of the unbalanced voltage at the bridge midpoint. Furthermore, in order to determine the direction of application of the magnetic field to be measured, a signal with the frequency of the AC power source doubled is used as a reference signal, and the frequency component 2 of the double frequency component 2 is determined from the unbalanced voltage at the bridge midpoint.
A phase detection circuit section is required to extract _e2 .

That is, the unbalanced voltage is input to a frequency doubler tuned amplification circuit to amplify the double frequency component, and the output thereof is input to a synchronous rectifier for phase detection, and a standard reference signal for synchronous rectification is input. The unbalanced voltage is detected for the first time by using the doubled frequency output signal _{e r obtained by inputting the AC applied voltage e f to} a multiplier.

By identifying the sign of this phase detection output voltage, the direction of application can be determined.

However, this kind of circuit configuration was
6856, it is exactly the same as the signal processing circuit in a fluxgate magnetometer, and it is impossible to completely measure the magnetic field to be measured using a simple bridge circuit, so this method simplifies the measurement circuit. is impossible. In addition, in such a bridge circuit, the transmission between the AC power supply section applied to the bridge circuit and the inductance element that senses magnetism, and the transmission between the entire bridge circuit and the signal processing circuit section are AC-AC transmission (AC (transmission), the longer the transmission line, the more attenuation will occur, and if the distance is several hundred meters, magnetic measurement will become impossible.

The present invention provides a magnetic detection method that solves the above-mentioned drawbacks by using a bridge circuit of a magnetic thin wire core that can be self-excited.

That is, in the present invention, a magnetic sensing part, which is constructed by winding a primary winding and a secondary winding around a magnetic thin wire core so that they have the same polarity, is inserted into one side of an AC bridge circuit, and an electric current is applied to the magnetic thin wire core. An unbalanced voltage generated at the intermediate point of the bridge circuit due to the magnetic field to be measured is detected by an operational amplifier in the previous stage, and a positive or negative saturated DC voltage, which is the output voltage of the operational amplifier, is fed back to the primary winding. In addition to making the magnetic thin wire core self-excitable, the positive excitation time from this reference level to the magnetic flux density level determined by the applied magnetic field to be measured until the magnetic sensitive part reaches the maximum positive and negative magnetic flux density levels, and A square wave voltage having both positive and negative polarities corresponding to the negative excitation time is generated on the output side of the operational amplifier, and the positive and negative square wave voltages are sent to the next stage operational amplifier to determine the strength and polarity of the magnetic field to be measured from the difference in excitation time between the two. A self-excited bridge type magnetic detection method that detects the saturated DC voltage, which is the output voltage of the operational amplifier in the previous stage, to the primary winding, and returns the output voltage of the operational amplifier in the next stage to the secondary winding. It is.

The first feature of the present invention is that a self-excited bridge circuit is configured by a magnetic thin wire core that can be self-excited and an operational amplifier, and that the positive and negative saturation DC voltages of the operational amplifier in the bridge are directly applied to the bridge circuit to adjust the strength of the magnetic field. This makes it possible to know the polarity.

The second feature is that by using an amorphous magnetic wire with high permeability and low coercive force as the magnetic core, high-sensitivity magnetic field measurement is possible with low power consumption.

The third feature is that while the AC-AC transmission method was used to transmit and receive power and signals such as AC excitation voltage and double frequency signals found in the fluxgate method and the bridge method, the present invention uses a DC-AC transmission method with less attenuation. By improving the DC method (direct current transmission method), it is now possible to perform highly sensitive magnetic field measurements even with cord lengths of several hundred meters.

The fourth feature is that the main basic component circuits such as AC excitation power supply, multiplier, tuned amplifier, and synchronous rectifier in the bridge circuit and fluxgate magnetometer circuit configurations are not required at all, and are simplified. The strength and polarity of the magnetic field can be measured using a coupling circuit consisting of a magnetic thin wire core and an operational amplifier.

A detailed explanation will be given below with reference to the drawings.

FIG. 1 shows the basic configuration of a magnetic detection element in the present invention. Figure 1a shows the case of magnetic field measurement.
is a glass tube, and a primary winding 2 of terminals 2a, 2b and a secondary winding 3 of terminals 3a, 3b are wound on the outside thereof. The capacitor 5 absorbs noise components generated from the magnetic core, and is connected to the winding terminals of the terminals 2a and 2b, and the terminals 2b and 3b are connected to ground G. The winding polarities of the windings 2 and 3 are the same as shown in the figure. A thin magnetic wire core 4 (hereinafter referred to as a magnetic core) is inserted into the central space of the glass tube 1 . As the magnetic core material, an amorphous magnetic material having high magnetic permeability and low coercive force is most suitable, but other materials such as permalloy are not limited thereto.

FIG. 1b shows the basic configuration when the magnetic detection element is configured for DC CT in the case of current measurement.
The magnetic core 4 is formed by winding a thin wire into an annular shape,
Windings 2 and 3 are wound around this annular magnetic core. The current Iex passing through this magnetic core is converted from the magnetic field H generated by Iex, and can be measured with high sensitivity.

FIG. 2 shows the operating principle of the present invention at B-H of the magnetic core 4.
FIG. 2 is a diagram for explaining using characteristics. Figure 2a
shows the B-H characteristic of the magnetic core 4 when the magnetic field to be measured Hex is zero (Hex=0). Since hysteresis exists in the magnetic core 4, in one cycle of excitation, →→→
You will follow the route →. Here, Hex
= 0, when a positive DC voltage is applied to the primary winding 2 and the magnetic core 4 is excited to the maximum magnetic flux density B _n by a positive excitation field, the range of change in magnetic flux density is △ as shown in the figure. B becomes ₁₂ . If the DC voltage is made zero at the same time that the magnetic flux density of the magnetic core 4 reaches B _n , the magnetic field applied to the magnetic core 4 disappears, and the magnetic flux density level quickly returns from the point to the level of the point. Next, when a negative DC voltage is applied and the magnetic core 4 is excited by a negative excitation field to the negative maximum magnetic flux density -B _n , the range of change in magnetic flux density becomes △B ₃₄ , and |△B ₁₂ |=|△B ₃₄ | holds true. However, as shown in FIG. 2b, if we consider the case where the above-mentioned excitation cycle is repeated from a state in which a positive measured magnetic field H'ex (>0) is applied to the magnetic core 4, The range of change in magnetic flux density when an excitation field is applied is △B′ ₁₂ and when a negative excitation field is applied, it becomes △B′ ₃₄ , and clearly between △B′ ₁₂ and △B ₃₄ , |△B′ ₁₂ | <|△B′ ₃₄ | holds true. In other words, during the positive excitation period t' ₊ and negative excitation period t' _- required for the excitation DC voltage to excite the magnetic core 4 from the zero state to the positive or negative maximum magnetic flux density level,
The relational expression t′ ₊ <t′ _- holds true.

Next, as shown in Figure 2c, the negative magnetic field to be measured is
When H″ex (<0) is applied to the magnetic core 4 and the above excitation cycle is repeated, the magnetic flux density changes by △B″ ₁₂ during positive excitation and △B″ ₃₄ during negative excitation. and between the positive excitation period t″ ₊ and the negative excitation period t″ _- ,
t″ ₊ >t″ _- holds true. Therefore, magnetic core 4
In order to prevent the excitation DC voltage value applied during the aforementioned excitation cycle from decreasing or fluctuating even at the maximum magnetic flux density level of the magnetic core 4, a variable resistor 6 is connected in series with the primary winding 2 as shown in the magnetic detection circuit of FIG. and adjust the impedance using this variable resistor. Therefore, considering the case where the polarity of the DC voltages Vc and -Vc is automatically switched at the same time as the magnetic flux level of the magnetic core 4 reaches the maximum magnetic flux density level or the maximum magnetic flux density level, the voltage waveform e at the terminal 7 (or terminal 8) is , it will be observed as a square wave voltage waveform with both positive and negative polarities. Figure 4 shows
Under these assumptions, Hex=0, H′ex>0,
2 illustrates the voltage waveform e at terminal 7 for each case of H″ex<0. As can be seen, the positive half-cycle duration of the bipolar square wave t ₊ ,
t′ ₊ , t″ ₊ and the negative half-cycle duration t ₋ , t′ ₋ , t″ ₋
It can be seen that is controlled by the magnetic fields to be measured Hex, H′ex, H″ex.Therefore, integrate e and find the signs and voltage values of the voltage integral values Eo, E′o, E″o. It can be seen that magnetic field measurement can be made possible by converting and displaying the polarity and strength of the magnetic field to be measured Hex.

FIG. 5 is an overall circuit diagram for automatically implementing the operating principle of the present invention. Functionally, it consists of a magnetic sensing section 100, a display circuit section 200, and a DC stabilized power supply section 300.

First, as elements constituting the bridge circuit of the magnetic sensing section 100, there are a variable resistor 6, a primary winding 2, and a capacitor 5 on one side, and a variable resistor 1 on the other side.
1 and a variable resistor 10 are present. Also, one end of each side of the bridge is the output terminal 7 of the operational amplifier _OP1 .
The other end is connected to ground G. The secondary winding generates an excitation field large enough to cancel Hex when the measured magnetic field Hex applied to the magnetic core 4 is strong. This is because the excitation current output from the display circuit section 200 is input to the terminal 3a It is executed by As can be seen from FIG. 5, this feedback system, which is connected for positive feedback, has the effect of stabilizing the self-excitation operation of the magnetically sensitive section while a strong magnetic field is being applied. It also contributes to improving the linearity of the input/output characteristics representing the relationship between the output voltage and the magnetic field to be measured and to expanding the measurement range, making it very useful in practice. The inputs to each input terminal of the operational amplifier OP ₁ are as follows: Terminal 2a of the primary winding 2 is input to the non-inverting terminal P via node A, and node B of variable resistors 10 and 11 is input to the inverting terminal N. It is entered through. The operation of operational amplifier OP ₁ is P,
It does not operate as an amplifier that amplifies the input voltage difference e _A - e _B between the N terminals, but the input voltage difference
It functions as a sign discriminator that distinguishes whether e _A - e _B is positive or negative and outputs a positive or negative saturated DC voltage corresponding to each. The capacitor 5 absorbs noise components generated in the magnetic core 4, and also suppresses the effects of magnetic flux flyback phenomenon caused by rapid changes in magnetic velocity, such as switching between positive and negative voltages applied to the bridge, thereby achieving self-excitation operation. It has the effect of stabilizing and, as a result, improving the linearity of input/output characteristics.

Next, the self-excitation operation will be explained.

Here, for ease of understanding, the resistance values of variable resistors 6, 10, and 11 are assumed to be R ₆ , R ₁₀ , R ₁₁ ,
The impedance of the primary winding 2 is Z ₂ , the impedance just before the magnetic core 4 reaches the maximum magnetic flux density ±B _n is Z ₂ m ^- , and the impedance when it reaches ±B _n is Z ₂ m, and between these For R ₆ > Z ₂ and R ₁₁
＞R ₁₀ and R ₆ =R ₁₁ and Z ₂ m ^- >R ₁₀ >Z ₂ m will be considered. Suppose, at this moment, the operational amplifier
If the output voltage at the output terminal 7 of OP ₁ were to switch to the positive saturated DC voltage +V _s , the magnetic flux density level in the magnetic core 4 would rapidly return to the magnetic flux density level defined by the magnetic field to be measured. (state of).
The positive voltage e _B (>0) divided by resistors 11 and 10 is input to the inverting terminal N, and the primary winding including the resistor 6 and capacitor 5 is input to the non-inverting terminal P. A positive voltage e _A (>0) determined by the voltage division with the impedance of 2 is input. Here, the impedance Z ₂ of the primary winding is very large because the magnetic core 4 is in a magnetic flux unsaturated state, and Z ₂ > R ₁₀ holds between it and the resistor 10, so the difference in operational amplifier input voltage The sign becomes positive (e _A −e _B >0), and the output voltage of the operational amplifier OP ₁ maintains the positive saturated DC voltage +V _s . However, magnetic core 4
As the magnetic flux density level at gradually increases and gradually approaches the maximum positive magnetic flux density B _n , the impedance of the primary winding 2 Z ₂ decreases as the magnetic permeability decreases.
decreases, and just before the magnetic core 4 reaches the maximum positive magnetic flux density B _n , Z ₂ = Z ₂ m ^- , and at this point Z ₂ m ^- >
R ₁₀ is established, but at the next moment the magnetic core 4 reaches the maximum magnetic flux density B _n (state), and now Z ₂
＝Z ₂ m＜R ₁₀ . As a result, the relationship e _A < e _B is established, and the sign of the input voltage difference between the input terminals of operational amplifier OP ₁ changes from positive (e _A − e _B > 0) to negative (e _A − _{e B} <
0), a negative saturated DC voltage _-Vs is generated at the output terminal 7 of the operational amplifier _OP1 .
And this voltage is connected to terminal 7 of the bridge and ground G.
At the same time, the magnetic flux density level of the magnetic core 4 quickly returns to the level defined by the magnetic field to be measured. When entering this negative excitation cycle, Z ₂ > R ₁₀ ; e _A <0; e _B <0; e _A −e _B
The relationship <0 is established, and the magnetic flux change in the magnetic core 4 progresses in the opposite direction. Then, as time passes, when the magnetic flux density level of the magnetic core 4 reaches the negative maximum magnetic flux density -B _n (state), Z ₂ = Z ₂ m <
R ₁₀ , e _A > e _B is established, the sign of the input voltage difference of operational amplifier OP ₁ is positive (e _A −e _B > 0), and the output terminal 7 of OP ₁ has a positive saturated DC voltage +V. _s will appear.

From the above circuit operation explanation, each time the magnetic core 4 reaches the maximum magnetic flux density +B _n or -B _n , the operational amplifier
It has become clear that the saturation DC voltage ±V _s of OP ₁ is automatically switched alternately.

In addition, the magnetic field to be measured Hex, H′ex (>0),
It is also easy to understand that if the above operation is performed with H″ex (<0) applied, a square wave voltage waveform as shown in Figure 4 will be observed at the output terminal of operational amplifier OP ₁ . However, if you want to be accurate, it is sufficient to replace ±V _c in Figure 4 with ±V _s and read it.

200 is a display circuit section, which includes an operational amplifier OP ₂ that integrates and amplifies the output voltage of the magnetically sensitive section 100, an integrating capacitor 12 connected to this, and a resistor 1.
3, 14, 16, 18 and chiyoke coil 1
7. Consists of an indicator needle 19.

At the output terminal 15 of the operational amplifier OP ₂ , a positive or negative DC voltage value corresponding to the N pole or S pole of the magnetic field to be measured and its strength is observed.

The chiyoke coil 17 is inserted to suppress noise components from the magnetically sensitive section 100 so that they do not affect the display circuit section. It is also possible to use a resistor instead of the choke coil 17. 300 is a DC stabilized power supply unit for driving operational amplifiers OP ₁ and OP ₂ . In the present invention, in which the purpose of transmission between the magnetically sensitive section 100 and the display circuit section is achieved with only a DC component, the transmission between the magnetically sensitive section 100 and the DC stabilized power supply section 300 is also a DC component, so that power transmission and reception is not possible. , signal transmission and reception is a complete DC-DC system. Therefore, for example, a DC stabilized power supply unit 300 is installed in the measurement room.
By installing the display circuit section 200, it becomes possible to monitor in the measurement room any magnetic changes or abnormal geomagnetic fluctuations that are detected by the magnetically sensitive section 100 installed several hundred meters away.

FIG. 6 shows a modified circuit of the magnetically sensitive section 100, in which a secondary winding 3 is used instead of the resistor 11 shown in FIG.
An example is shown in which .

Note that the self-excited operation can be easily inferred from the explanation of FIG. 5, so a description thereof will be omitted.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the basic configuration of the magnetic detection element in the present invention, FIG. 2 is an explanatory diagram explaining the operating principle of the present invention using the B-H characteristics of the magnetic core, and FIG. 3 is an explanatory diagram showing the basic configuration of the magnetic detection element in the present invention. FIG. 4 is a drawing showing an example of a magnetic detection circuit in which Hex=0, H'ex>0,
A diagram of the voltage waveform e at the terminal in each case of H″ex < 0, Figure 5 shows the output of the magnetically sensitive section, DC stabilized power supply section, and magnetically sensitive section that automatically switches the DC voltage that excites the magnetic core. FIG. 6 is a diagram showing an example of a modified circuit of the magnetically sensitive section shown in FIG. 5. 1...Glass tube, 2...Primary Winding wire, 3...Secondary winding, 4...Magnetic thin wire core, 5...Capacitor,
2a, 2b, 3a, 3b...terminal, G...earth, 100...magnetic sensing section, 200...display circuit section, 300...DC stabilized power supply section, A, B...junction, OP ₁ , OP ₂ ...Operational amplifier, P...Non-inverting terminal, 17...Chi York coil, N...Inverting terminal,
19... Indicator.

Claims (1)

[Scope of Claims] 1. A magnetic thin wire core is produced by inserting a magnetically sensitive part formed by winding a primary winding and a secondary winding around a magnetic thin wire core so that they have the same polarity into one side of an AC bridge circuit. The unbalanced voltage generated at the midpoint of the bridge circuit by the magnetic field to be measured applied to the bridge circuit is detected by the operational amplifier in the previous stage, and the positive or negative saturated DC voltage, which is the output voltage of the operational amplifier, is fed back to the primary winding. to enable self-excitation of the magnetic thin wire core, and positive excitation from this reference level to the magnetic flux density level determined by the applied measured magnetic field until the magnetic sensitive part reaches the maximum positive and negative magnetic flux density levels. A square wave voltage having positive and negative polarities corresponding to time and negative excitation time is generated on the output side of the operational amplifier, and the positive and negative square wave voltages are transmitted to the next stage operational amplifier, and the strength of the magnetic field to be measured is determined from the excitation time difference between the two. and a self-excited bridge type magnetic detection method characterized by detecting polarity. 2. Self-excitation according to claim 1, in which the positive or negative saturated DC voltage, which is the output voltage of the operational amplifier in the previous stage, is fed back to the primary winding, and the output voltage of the operational amplifier in the next stage is fed back to the secondary winding. Bridge type magnetic detection method.