JPS6138418B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic measuring device for measuring the strength of a magnetic field.

A Hall element can be used as a magnetic sensing element, but the magnetic sensing part is easily influenced by the temperature of the measurement point, and tends to cause errors in measurement. In addition, since the output voltage is small, about several hundred mV, if the measurement point and the place where the output voltage is read are far apart, noise may occur in the cable that connects the Hall element and the measuring device that measures the Hall element output voltage. etc., which tends to cause errors in measurement and makes handling inconvenient.

The present invention solves the above-mentioned drawbacks of the prior art, and provides a magnetic measuring device that is less susceptible to induced interference caused by external noise and that can easily perform measurements even when the measuring point and reading position are far apart. It provides:

The present invention will be described in detail with reference to the drawings.

First, the principle of the present invention will be explained.

When the magnetic field H applied to the magnetic material is gradually increased,
The magnetic flux density B in the cross section of the magnetic material increases and draws a hysteresis curve as shown in FIG. When the magnetic field H reaches the saturation magnetic field +H _S , the magnetic flux density B becomes the saturation magnetic flux density +B _S , and even if the magnetic field H is increased beyond this point, the magnetic flux density B only increases slightly.

Next, when this magnetic body is magnetized in the opposite direction from the state where the magnetic field +H _S is applied, the magnetic flux density B becomes 0 due to the magnetic field with the saturation coercive force -H _C of the magnetic body, and further decreases - At H _S , the magnetic flux density is −B _S
There is a property that

Here, as shown in FIG. 2, an applied magnetic field of −H is applied to the magnetic body M around which the detection coil L _P is wound for a time Δt.
Let's examine the detection output when changing from _S to + _HS at a constant speed. Detection coil L _P by +H _S
If the magnetic flux passing through the sensing coil L P is -Φ _S and the magnetic flux penetrating the sensing coil L _P by -H _S is -Φ _S , then the applied magnetic field H changes from -H _S to + during time Δt as shown in Figure 3a.
It is well known that when the voltage changes to H _S , a voltage of e _Lp =2Φ _S /Δt is generated in the detection coil L _P .
Figure 3b shows the change in e _Lp over time. In the above, the time during which the external magnetic field H applied to the magnetic material changes from _-HS to + _HS was Δt, but the time during which the external magnetic field H changes from _-HS to + _HS is Δt ₂ (Δ
t ₂ >Δt), it is clear that the detection output e _Lp decreases.

Next, in order to detect magnetic field changes, the detection output e _Lp
When a threshold circuit as shown in Fig. 4 is connected to the detection coil L _P to determine _the presence or absence of
It is impossible to detect that the magnetic body M has saturated from saturated to reverse polarity.

In the present invention, the predetermined changing magnetic field H _X is configured to be applied to the magnetic body M constituting the sensing element, and a sensing output e _Lp always equal to or higher than a certain value is generated regardless of how fast or slow the change in the external magnetic field H is. In order to have such a configuration, a magnetic field applying coil and a reference power source are provided for generating a changing magnetic field _H.sub.X.

Next, after explaining the relationship with the applied magnetic field _Hx , the principle by which the external magnetic field H can be measured will be explained.

For ease of explanation, it is assumed that the external magnetic field H changes with time according to the following approximate formula: H=at...(1) (a is the amount of change in the magnetic field per unit time, t is time). Also, when the detection range of the external magnetic field H is +H _n ~ -H _n ,
If _a magnetic material exhibiting magnetization characteristics as shown in FIG. 1 is used as the magnetic material _{M of} the sensing element, _the applied _{magnetic field H} ).

Next, the change in H _X from -H _SS to +H _SS is expressed as H _X = bt - H _SS ...(2) (b is the amount of change per unit time of the applied magnetic field _H Approximate by However, b is at least several times as large as a.

Now, at the same time that the external magnetic field H starts to change from t=0 _{, the} applied magnetic field _H
When the magnetic field is changed as shown in FIG. 5b, the resultant magnetic field is as shown in FIG. _5b , and as shown in FIG. _5a , _the applied magnetic field H The magnetic body M of is brought to reverse saturation, and t
= t ₁ , the detection coil L _P as shown in Fig. 5C
An output voltage e _Lp1 is generated. Here, t ₁
Since the absolute values of equation (1) and equation (2) are equal and the signs are opposite, the right-hand side of equation (1) and the right-hand side of equation (2) are changed to a negative sign and connected by a sign, and t=t Substituting ₁ to find a, we get a=-(bt ₁ - H _SS )/t ₁ , and this value is expressed in equation (1).
By substituting , H=-(bt ₁ - H _SS ), and the strength and polarity of the external magnetic field H can be determined.

Next, let us assume that the shape of the magnetic field applying coil L _f that generates the applied magnetic field H _x is as shown in FIG. 6, with the number of turns being N and the coil length being radius r _. The strength of the applied magnetic field H _x at the central point P on the concentric axis of By measuring I from the proportional relationship in equation (3), the applied magnetic field H _x can be changed.

An embodiment of the present invention is shown in FIG. 7, and the configuration and operation of each circuit will be described in detail below.

FIG. 8 is an external view of the sensing element 10 in which a sensing coil L _P is wound around a magnetic body M, and a magnetic field applying coil L _f is further wound thereon.

As shown in FIG. 4, the threshold circuit 2 connected to the detection coil L _P in order to detect the output of the detection coil L _P has a differential amplifier 2-1 equipped with a positive input terminal and a negative input terminal. One end of the detection coil L _P is connected to the input terminal, and the threshold power supply V _TH is connected to the negative input terminal.
The configuration is such that the two are connected. Here, the detection output e
If _Lp is equal to or greater than _VTH , it is possible to obtain the desired threshold circuit output _Vp .

Various types of reference current source 1 can be considered, but as an example, when using a reference current source whose output voltage changes in the form of a triangular wave, a reference current source that can extract the desired output waveform by integrating and amplifying a rectangular wave signal is used. It is possible to obtain the source.

As an example of extracting the reference current, if a reference resistor 5 is inserted in series with the magnetic field applying coil L _f and connected to the reference current source 1 as shown in FIG. 9, when the reference current I _r is applied, the resistor R At both ends of the reference resistor 5,
A voltage drop E _r =I _r ×R is generated, from which the reference current value can be easily determined.

Next, in order to read the voltage E _r across the reference resistor 5 when the external magnetic field H and the applied magnetic field H _x are in equilibrium,
This device includes a level extraction and holding circuit 3 as shown in FIG. This level extraction and holding circuit 3 operates only while extracting the input voltage E _r , and the switch control circuit 3 -
After applying V _p as a switch control signal from the output obtained from the threshold circuit 2 to 2 and closing the switch 3-1, the capacitor 3-4 whose input side is connected in parallel to the high-impedance amplifier 3-3 is charged. , the switch 3-1 is opened to output the value held in the capacitor 3-4.

The magnetic material M used in the sensing element 10 has a coercive force H
If a magnetic material with a small _C is used, measurement accuracy can be improved, but since it is still biased by the coercive force H _C , in order to perform even more accurate measurements, the component of the coercive force H _C is need to be corrected. The specific method is (1) applying a bias of -H _C with a permanent magnet, (2) applying a bias of H C during level extraction and holding.
Any means such as applying a bias voltage corresponding to _C as shown in FIG. 11 may be selected.

Next, the operating waveforms of each part when measuring the external magnetic field H with this device will be explained using FIG. 12.
The output e _Lp of the detection coil L _P is output in the form of a pulse of positive or negative polarity in the direction that brings the magnetic material M from saturation to reverse saturation, but in order to simplify the configuration of the device, the detection output is of positive polarity. e _Lp shall be used. The detected output e _Lp is shown in FIG. 12a. Next, in FIG. 12b, the external magnetic field applied to the magnetic body M of the sensing element 10 is indicated by H, and the applied magnetic field is indicated by _H.sub.X. In the same figure, the applied magnetic field H _X has a polarity opposite to that of the external magnetic field H, and the intensity changes from |H _X |>|H| to |H _X |
When <|H|, a detection output e _Lp can be obtained. As described above, the applied magnetic field H _x is proportional to the current flowing through the magnetic field applying coil L _f and proportional to the voltage E _r generated across the reference resistor 5 . Therefore, the first
The thin line in FIG. 2c is the waveform of the voltage E _r obtained by extracting and holding the reference current I _r when the detection output e _Lp is generated, and the thick line is the extracted waveform E _p having the same polarity as the external magnetic field H. In order to obtain the output waveform E _p shown by the bold line, it is sufficient to connect an amplifier with a gain of -1 after the level extraction and holding circuit 3. or H _C connected to reference resistor 5
If the input terminals of the amplifier 4-1 of the component correction circuit 4 are reversely connected, the aforementioned amplifier with a gain of -1 becomes unnecessary.

The magnetic measurement device of the present invention has a simple structure in principle and is small in size. Additionally, it is less susceptible to external noise. Since the magnetic sensing element 10 has good temperature characteristics, it is possible to change the external magnetic field with high reliability.

As an example of the use of this device, as shown in FIG. 13, _the magnetic field _H Since _B can be measured without contact, a current transformer can be considered, which makes it easy to insulate from the power transmission line, especially when measuring the current of a high-voltage power transmission line. Furthermore, since the magnetic sensing element used in the present invention is small and lightweight, it has the advantage that mechanical strength is not required during installation compared to conventional current transformers. Furthermore, as is clear from the principle of the present invention, when the measured magnetic field is large, it is possible to increase the number of turns of the magnetic field application coil L _f or increase the voltage of the reference current source 1 applied to the magnetic field application coil L _f . It has the advantage of being easier to deal with.

As described in detail above, according to the present invention, the measurement value can be read simply by reading the output value of the reference power source when the pulse-like voltage generated from the magnetic sensing element is detected. Even if the location is far away, it is unlikely to be affected by external noise, and the voltage of the reference power supply can be adjusted by changing the number of turns of the reference magnetic field generating coil of the magnetic sensing element, so there is a lot of external noise. In such cases, it is possible to increase the voltage of the reference power supply to minimize measurement errors. Furthermore, if the magnetic sensing element is constructed using a magnetic material with a high Curie temperature and a heat-resistant insulated copper wire for the winding, magnetic sensing can be performed in an environment of about 200°C. Furthermore, a great feature of this magnetic measurement device is that it can be configured extremely simply.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram showing an example of the magnetization curve of the magnetic material used in the present invention, Fig. 2 is a perspective view showing the magnetic material used in the present invention and a detection coil wound around it, and Fig. 3 a and b are Fig. 2 is a diagram showing an example of changes in magnetic flux and detection output in the detection coil configured as shown in Fig. 4. Fig. 4 is a circuit diagram showing an example of a threshold circuit used in the present invention. A waveform diagram showing an example of changes in the external magnetic field and applied magnetic field in the device of the invention, FIG. 6 is a cross-sectional schematic diagram showing an example of the shape of the magnetic field applying coil used in the invention, and FIG. 7 is a connection diagram showing an embodiment of the invention. 8th
Figure 9 is an external view of the magnetic sensing element used in the present invention.
Fig. 10 is a circuit diagram showing an example of the reference current extraction in the device of the present invention, Fig. 10 is a circuit diagram showing an example of the level extraction/holding circuit used in the present invention, and Fig. 11 is a circuit diagram showing an example of the level extraction _/ holding circuit used in the present invention. A circuit diagram showing an example, FIGS. 12a, b, and c are operation waveform diagrams of each part of the device of the present invention, and FIG. 13 is a device diagram showing a specific example of use of the device of the present invention.

Claims (1)

[Claims] 1. A magnetically sensitive sensing element having at least a first coil and a second coil arranged around the outer periphery of a magnetic material, and a reference current source for applying a known current to the first coil that is greater than or equal to magnetically saturating the magnetic material. and a threshold circuit that outputs a detection output when the output level of the second coil connected to the second coil exceeds a predetermined value; a level extraction and holding circuit for extracting an instantaneous value of the known current, the magnetic body of the magnetically sensitive sensing element to which a magnetic field to be detected is applied, converts the known current from the reference current source into the first When the magnetic body of the magnetic sensing element is reversely saturated by applying a magnetic field to the magnetic sensing element by changing the output of the reference current source and applying a magnetic field in the opposite direction to the magnetic sensing element. The detection output is generated from the second coil, and the instantaneous value of the known current when this detection output is detected is sequentially extracted and held by the level extraction and holding circuit, thereby making a measurement proportional to the instantaneous value of the magnetic field to be measured. A magnetic measuring device configured to obtain an output.