JPH06201731A - Magnetic balance type current measuring device - Google Patents

Abstract

PURPOSE:To demagnetize a magnetic core without providing a special AC damped oscillation circuit by changing over the direction of an electric current, applied to a bias coil for switching a current measuring range to large and small, to positive or negative in accordance with lead-in of a change-over signal. CONSTITUTION:The device is set within a small current measuring range according to a current applied to a bias coil 45. When an overcurrent flows in an electric wire to be measured at the time of measurement in the small current measuring range, a voltage in accordance with the overcurrent is generated in a Hall element 2, amplified by an amplifier 31 and an excessive output current based on the overcurrent flows in a feedback coil 4 and outputted from an output terminal Iout. A magnetic core is magnetized by the overcurrent. A comparison circuit 33 generates a detection signal when the overcurrent exceeds an upper limit value in a measuring current range. According to this detection signal, a change-over signal is generated from an AND circuit 37 via a flip-flop circuit 34 to instantaneously change over the measuring range to a large current measuring range, and therefore the magnetic core is demagnetized and an offset error of the current measuring device is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic balance type current measuring device.

[0002]

2. Description of the Related Art When measuring a minute current with a magnetic balance type current measuring device, a hysteresis characteristic of the magnetic core of the current measuring device causes a measurement error due to the influence of nonlinearity or magnetization, which causes a magnetic balance circuit. A so-called magnetic balance type current measuring device is conventionally known in which the magnetic flux of the magnetic core is always zero by performing feedback including the magnetic core.

As shown in FIG. 7, a magnetic balance type current measuring device is schematically shown. A magnetic core 1 forming a closed magnetic circuit, a Hall element 2 inserted in the core, and a magnetic balance circuit 3 composed of an amplifier.
And the feedback winding 4 form a negative feedback loop.
I ₁ The wire flowing in, and the number of turns the feedback winding 4 is n, the wire i ₂ flowing through the feedback winding 4
When the feedback amount is sufficiently large, the following equation (1)
It is a well-known fact that the magnetic core 1 is not affected by the non-linearity and magnetism. i ₂ = i ₁ / n (1)

In the magnetic balance type current measuring device, since the core magnetic flux is basically zero and the magnetic balance is in the magnetic balance state, the core 1 is not magnetized. However, if there is an excessively large measured current that exceeds the magnetic balance range or a sudden change in measured current that prevents the magnetic balance circuit 3 from responding, the operation of the magnetic balance method is deviated, and due to the magnetization of the core. After the operating point changes significantly, a measurement error will occur.

As a conventional technique, a core material having a small coercive force is generally selected to take measures to reduce the maximum magnetizing amount, but there is a problem that the material cost and the processing cost are increased. Further, although a measure to widen the gap of the magnetic core to weaken the magnetic susceptibility is taken, there is a problem that the sensitivity of the current measuring device is lowered.

[0006] Further, as a countermeasure by demagnetizing the magnetized core,
As shown in Japanese Utility Model Publication No. 63-13496, FIG.
Sample hold circuit 7, comparator circuit 8, monostable multivibrator circuit 9, and AC attenuation oscillation circuit 1
0 is added to the magnetic balance type current measuring device. 6 is a current amplifier circuit. The structure is shown in FIG.
In the above configuration, in the normal measurement, the sample hold circuit 7 is in the sample state and the electric wire i flowing through the measured electric wire 5 is measured.
The voltage e proportional to is output. Now, as shown in FIG. 9, when the measured current i has a sudden change and the circuit cannot respond and deviates from the magnetic equilibrium operation, the output of the magnetic equilibrium circuit 3 is practically zero in the case of normal measurement. The output waveform outputs an error voltage as shown in a. In the invention, the error voltage is input to the comparison circuit 8 and the "threshold" V of the comparison circuit 8 is inputted.
_{When S} is exceeded, the comparator circuit 8 generates an output having a waveform b, drives the monostable multivibrator circuit 9, and generates a smoothed output voltage having a waveform c. This output voltage puts the sample-hold circuit 7 in the hold state, and at the same time, drives the AC attenuation oscillation circuit 10 to eliminate the method of attenuating the AC magnetic flux with the AC attenuation signal as shown in d. However, there is a problem to be solved that a special AC attenuation oscillation circuit is newly required.

[0007]

DISCLOSURE OF THE INVENTION The present invention focuses on the magnetic balance range of a magnetic balance type current measuring device having a function of switching the measurement range, and obtains a predetermined reverse magnetic force for demagnetizing the magnetic core. By changing the measurement range and forming a magnetic force unbalanced state, the magnetic core is demagnetized without providing a special AC damping oscillation circuit.

[0008]

In order to solve the above-mentioned problems, the present invention provides a magnetic core which forms a closed magnetic circuit and produces a magnetic flux according to the current flowing through an electric wire to be measured, and a Hall element inserted in the magnetic core. A feedback winding wound around the magnetic core; a magnetic balancing circuit connected to the output side of the Hall element to flow an output current according to the measured current in the feedback winding to perform magnetic balancing; A bias winding that is wound around the core to switch the current measurement range between large and small by generating positive and negative bias magnetic flux in the magnetic core, and the direction of the current flowing in the bias winding is changed to positive or negative depending on the introduction of the switching signal. A switchable measuring range switching circuit is provided, and a magnetizing detection for generating a detection signal by detecting that the magnetic core is magnetized by flowing a measuring current that deviates from a predetermined measuring range into the measured electric wire. Step, and after the detection signal of the magnetizing detection means is generated, the reverse magnetic force necessary for degaussing is detected by the measurement of the small current measurement range as the specific measurement current generated in the magnetic unbalanced range of the large current measurement range. And a switching signal generating means for applying the switching signal to the measuring range switching circuit when the magnetic balance type current measuring device is operated.

[0009]

FUNCTION FIG. 3 shows the demagnetization characteristics of the magnetic core material. The horizontal axis represents the magnetic force H (Oe), the vertical axis represents the magnetic flux density B (G), and the solid line represents the DC magnetization characteristic. The broken line shows the demagnetization characteristic when the inverse magnetic force −x (Oe) is applied once from the state where the core material is magnetized at 1.2 Hc (Oe) or more. As shown in FIG. 3, the demagnetizing force H _A that is demagnetized through the locus of a substantially straight broken line A passing through the origin is determined.

Demagnetization of the magnetic core can be performed by a single reverse magnetic force as shown in FIG. The inverse magnetic force is a value determined by the magnetic core material. For example, a reverse magnetic force H _A that is demagnetized according to the locus of A in FIG. 3 is applied to the magnetic core that is magnetized by applying a magnetic force to the positive side. The inverse magnetic force H _A can be generated by the degaussing means using the measurement range switching function shown in FIG. At a measured current (50 A or less) outside the large current measurement range, the magnetic equilibrium state inside the current measuring device is broken and an inverse magnetic force is generated in the magnetic core. When the measurement current being measured in the small current measurement range switches to the large current measurement range and the specific measurement current αH _A (30A) that causes the demagnetizing force H _A to be demagnetized, by switching the measurement range to the large current measurement range for a moment, Since the reverse magnetic force H _A is generated in the magnetic core, the core can be easily demagnetized. Here, α is a constant determined by the magnetic core of the current measuring device.

In the present invention, the magnetizing detection means generates a detection signal when a measurement current deviating from the predetermined measurement range flows through the wire to be measured, and after the detection signal is generated, the switching signal generation means changes the specific measurement current. When α H _A is detected, a switching signal is generated and the switching signal is applied to the measurement range switching circuit. Therefore, the measurement range switches to the large current measurement range, and the reverse current flowing in the bias winding causes a reverse magnetic force H _A in the magnetic core. Demagnetization is performed.

[0012]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a current measuring device showing an embodiment.
The current measuring device includes a magnetic balance circuit 3 and a measurement range switching circuit 40.
And is configured to operate with a single power supply. The magnetic balance circuit 3 uses the current generated in the Hall element 2 as an amplifier 3
Amplify by 1 and send the current to the feedback winding 4,
The current is output to the output terminal I _out . The magnetism detecting means 32 is connected to the output terminal I _out . The magnetization detection means 32 is composed of, for example, a comparison circuit 33 and a flip-flop circuit 34, and generates a detection signal when a measurement current that deviates from a predetermined measurement range flows to the output terminal I _out . The switching signal generating means 35 is composed of, for example, a comparison circuit 36 and a logical product circuit 37, and the comparison circuit 36 detects that the current is a measurement current that generates a reverse magnetic force necessary for degaussing, and the magnetism detecting means 32.
When the detection signal is applied to the AND circuit 37, a switching signal is generated and the switching signal is applied to the switching signal terminal SW.

The measurement range switching circuit 40 has an H-shaped bridge circuit composed of transistors 41 and 42 and field effect transistors 43 and 44 as shown in FIG. The H-shaped bridge circuit has a bias winding 45 connected between one of the diagonal points, and when a switching signal is applied to the switching signal terminal SW, the transistors 41 and 44 and the transistors 42 and 43 are switched on and off. As a result, the direction of the current flowing through the bias winding 45 can be switched.

FIG. 2 is a perspective view showing the magnetic core 1.
The magnetic core 1 has a feedback winding 4 and a bias winding 4
5 is wound, and the Hall element 2 is inserted in the gap provided in the magnetic core 1. Hall element 2
A current is passed through electrodes (not shown), and a voltage is generated in a direction perpendicular to the direction of the current and the magnetic field of the core 1. C
The electric wire 5 to be measured penetrates through the magnetic core 1 of the mold. The magnetic flux generated in the feedback winding 4 is the measured electric wire 5
And the magnetic flux generated in the core 1 by measuring the current i ₁ flowing through, as canceled by the magnetic flux generated by the bias winding 45, current in the feedback winding 4 in the magnetic balance circuit 3 i ₂
Current is controlled to flow into the magnetic equilibrium state, and the output terminal I
_The current i ₂ is output to out and the measured current i ₁ is obtained by an equation.

In the above structure, when an excessively large measured current i _1m flows through the measured current 5, the magnetic balance circuit 3 cannot cope with it, and the magnetic core 1 is magnetized based on the magnetic flux generated by the excessively large measured current i _1m. It Then, when the magnetic core 1 is magnetized, an offset error voltage corresponding to the magnetized magnetic flux φ may occur in the Hall element 2. The present invention automatically demagnetizes the magnetic flux to eliminate the offset error.

FIG. 4 is a characteristic diagram showing the output characteristics of the magnetic balance type current measuring device. The conditions for demagnetizing the magnetic flux of the magnetic core 1 will be described based on this characteristic diagram. Small current measurement range (-50A to + 50A) and large current measurement range (+ 50A
A to +150 A) is the magnetic equilibrium range, and the magnetic core 1 is kept at zero magnetic flux, but outside the measurement range, the magnetic flux corresponding to the current outside the measurement range is generated as the inverse magnetic force of the magnetic core 1. Current I outside the measurement range and inverse magnetic force F of magnetic core 1
The relationship with _n is determined by the magnetic core 1 and can be expressed by the following equation. F _n = αI α: constant

The operation of the first embodiment will be described. In FIG. 1, the small current measurement range is set by the current flowing through the bias winding 45. When an excessive current i _1m flows through the measured electric wire 5 during measurement in the small current measurement range, a voltage corresponding to the excessive current is generated in the hall element 2 and is amplified by the amplifier 31 to be fed back to the feedback winding 4 An excessive output current i _2m based on the excessive current is flown to the output terminal I _out .
At the same time, the magnetic core 1 is magnetized by the excessive current i _1m . The comparator circuit 33 generates a detection signal when the excessive output current i _2m exceeds the measured current range upper limit value (150 A).
The flip-flop circuit 34 generates an output signal from the time when the detection signal is generated in the comparison circuit 33 and adds the output signal to the logic circuit 37, so that the comparison circuit 36 causes the measurement current αH.
_{When A} (A) is detected and an output signal is generated, a switching signal is generated from the AND circuit 37 and is input to the switching signal terminal SW. Therefore, the H-shaped bridge circuit formed by the transistors 41 to 44 is switched by the switching signal, and the measurement range is instantaneously switched to the large current measurement range. Therefore, the direction of the current flowing through the bias winding 45 is the H-bridge circuit. By switching, the inverse magnetic force H _A (Oe) for demagnetizing the magnetic core 1 is applied to the core 1, the demagnetization is completed, and the offset error of the current measuring device disappears.

FIG. 5 is a system diagram of a charging system in a vehicle for explaining the second embodiment. The control computer 19 is configured to measure the charge / discharge current of the battery 17 by the current measuring device A having the magnetic core 1 and control the power generation amount of the vehicle-mounted generator 18. Engine 14
A starter 20 is provided for starting the engine, and the ignition switch 15 and the starting switch 16 are connected to the battery 17. A general load 21 is connected to the battery 17 via a switch, and an idle speed control device 22 is connected to the computer 19.

The operation of the second embodiment will be described. Figure 5
At the start of operation of the vehicle, the ignition switch 1
When the switch 5 is turned on, the switch of the regular electric load 21 is closed and current is supplied from the battery 17, and the control computer (ECU) 19 and the current measuring device A start operating. Next, in order to start the engine 14, the start switch 16 of the starter 20 is turned on and the starter 20 is rotated. Since the lock current of the starter 20 at the initial stage of rotation greatly exceeds the large current measurement range, the magnetic core 1 of the current measuring device A is magnetized to the positive side sufficiently large at 1.2 H _C or more. The magnetization on the positive side may not depend on the lock current at the initial stage of starting the starter 20, but may depend on other currents. Alternatively, the operation of the magnetic balance circuit 3 of the current measuring device A may be stopped and no current may flow through the feedback winding 4.

After the engine 14 is started and the starter 20 is stopped, the vehicle enters a normal traveling operation state, and the current measuring device A measures the charging / discharging current of the battery 17 during traveling in a small current range. There is a measurement error due to the magnetization of the magnetic core 1. As shown in FIG. 6, when the lock current exceeds the high current measurement range in step 100 (I ₂ >).
150 (A)) The magnetic core 1 is magnetized. The ECU 19 manages the battery 17 current in a small current range during traveling and controls the vehicle-mounted generator 18 to adjust the battery 17 current to the battery current αH _A that is the demagnetizing condition of the magnetic core 1 (step 101). The ECU 19 outputs a switching signal to the switching signal terminal SW of the measuring range switching circuit 40 to switch to a large current / current measuring range for a moment (step 102), thereby causing the magnetic core 1 to generate a reverse magnetic force H _A necessary for degaussing. After completing the demagnetization by adding (Step 10
3) The predetermined charging system control can be performed by the accurate measured value of the charge / discharge current of the battery 17.

In order to obtain a measured current measurement (offset error) of ± 0.05 A or less due to the magnetization of the magnetic core 1, the measured current αH _A (A) under degaussing conditions should be adjusted with an accuracy of ± 5 A from the characteristics shown in FIG. good. Since the measurement current error due to the magnetization on the positive side of the magnetic core 1 is actually about ± 0.3 _A , there is no problem in adjusting the conditions of the measurement current αH _A. These control values are determined by the material characteristics of the magnetic core 1, the magnetic circuit, and the target demagnetization amount.

Another embodiment will be described below. In the second embodiment, when the ignition switch 15 is turned on during driving of the vehicle, the magnetic balance circuit 3 of the current measuring device A is prevented from starting up.
It is also possible to provide a circuit for delaying the rising in 9 to perform the negative side magnetization on the magnetic core 1 and apply the negative side reverse magnetic force. In the second embodiment, even if the current measuring device A with the measuring range switching function is not used, the ECU 19 is used for the magnetic balance circuit 3.
If it is possible to turn on and off, by setting the magnetic imbalance amount when the magnetic balance circuit 3 is off to the inverse magnetic force H _A of the degaussing condition,
Can be degaussed. The second embodiment may be implemented for the purpose of demagnetization by providing a range for the measured current αH _A (A) according to the accuracy of the intended current measuring device.

[0023]

As described above, the current measuring device of the present invention is
The magnetic balance type current measuring device is provided with a measuring range switching means, and the measuring range switching means can form a magnetic imbalance range outside the measuring current range so that a predetermined reverse magnetic force for demagnetizing the magnetic core can be obtained. Therefore, it is possible to use the reverse magnetic force in the magnetic unbalanced range, and by providing the magnetizing detection means and the switching signal generating means, according to the demagnetizing characteristic of the magnetic core,
Since the magnetic core is demagnetized by a single reverse magnetic force, there is an excellent effect that the magnetic core can be demagnetized without providing a special AC attenuation oscillation circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a current measuring device showing an embodiment.

FIG. 2 is a perspective view showing a magnetic core.

FIG. 3 is a characteristic diagram showing demagnetization characteristics of a magnetic core material.

FIG. 4 is a characteristic diagram showing output characteristics of a magnetic balance type current measuring device.

FIG. 5 is a system diagram of a charging system in a vehicle for explaining a second embodiment.

FIG. 6 is a flow chart for explaining the operation of the second embodiment.

FIG. 7 is a circuit diagram showing an outline of a conventional magnetic balance type current measurement range.

FIG. 8 is a circuit diagram showing a countermeasure by demagnetizing a magnetized magnetic core in a conventional magnetic balance type current measuring device.

FIG. 9 is a timing chart showing a degaussing operation of a conventional magnetic balance type current measuring device.

[Explanation of symbols]

1 ... Magnetic core, 2 ... Hall element, 3 ... Magnetic balance circuit, 4 ... Feedback winding, 5 ... Wire to be measured, 32 ... Magnetic field detecting means, 35 ... Switching signal generating means, 40 ... Measuring range switching circuit, 45 ... Bias winding, 19 ... Control computer, 100-10
3 ... step.

Claims (1)

[Claims] 1. A magnetic core that forms a closed magnetic circuit and generates a magnetic flux according to a current flowing through a measured electric wire, a Hall element inserted in the magnetic core, and a feedback winding wound around the magnetic core. , A magnetic balance circuit connected to the output side of the Hall element for performing magnetic balance by flowing an output current according to a measured current in the feedback winding, and a positive and negative bias magnetic flux wound around the magnetic core to the magnetic core. A bias winding that switches the current measurement range between large and small by generating the bias, and a measurement range switching circuit that can switch the direction of the current flowing through the bias winding between positive and negative depending on the introduction of the switching signal are provided. A measuring current flowing out of a predetermined measuring range on the measuring wire flows, a magnetizing detection means for detecting that the magnetic core is magnetized and generating a detection signal, and a detection signal for the magnetizing detection means being generated. , When the reverse magnetic force required for degaussing is detected by the measurement in the small current measurement range as a specific measurement current generated in the magnetic unbalanced range in the large current measurement range, a switching signal is generated and the switching signal is switched to the measurement range. A magnetic balance type current measuring device comprising a switching signal generating means to be added to a circuit.