JP3305445B2 - Current detector for line current detection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detector for detecting a line current of a telephone, a facsimile, or the like. The present invention relates to a current detector in which is improved.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional line current detecting current detector. A gap 31 is provided in a part of the magnetic path of the magnetic core 11, and a Hall element 41 is provided in the gap 31.
Is provided, the output voltage of the Hall element 41 is amplified through a differential amplifier 44,
Is input to, by comparing the output voltage from the reference voltage 43 and the differential amplifier 44 to correspond to the detected current set in advance to detect a line current I _1. FIG. 5 shows the principle of the detection. In the hysteresis curve shown in FIG. 5, the magnetic core 11 is initialized to almost the origin of the BH hysteresis curve. When a detected direct current flows through the line, a magnetomotive force is generated in the magnetic core 11, and the applied magnetic field generates a magnetic field in the gap 31 of the magnetic core 11. The operating point of the magnetic core 11 moves on the BH hysteresis curve.
Reference voltage 43 of the comparator 42 the output voltage from the Hall element 31 by a magnetic field H ₁ generated by ₁ as a threshold
Is set, it is detected that the line current has reached the current value I ₁ at the point A of the hysteresis curve in FIG. In general,
The line current flows up to about ± 100 mA at maximum, and within this range, the magnetization state of the ferromagnetic core, that is, the BH hysteresis curve characteristic is in a substantially linear range. If the line current is cut off after a large line current flows and the operating point reaches the saturation magnetization state, the operation point reaches the residual magnetization state along the hysteresis curve and is held. This state is clearly different from the earlier initial state. Therefore, when the line current flows in the same direction again, the operation starts in the residual magnetization state, and the magnetic flux B increases along the hysteresis curve. Thus, the output of the current detected by the set point B point of the comparator 42 is obtained, a line current value I ₂ actual current values corresponding to the applied magnetic field H _2. Therefore, as shown in the figure, a current value ΔI corresponding to a difference between applied magnetic fields of ΔH = H ₁ −H ₂ is generated as an error. The present invention is to eliminate this error.

[0003]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is that the residual magnetization state of the BH hysteresis curve characteristic of the magnetic core, which is a main component of the current detector, causes the current detector to fail. An error occurs in the measured value. An object of the present invention is to provide a current detector in which an error in the measured value is eliminated.

[0004]

According to the present invention, in order to solve the above-mentioned problems, in order to initialize a magnetization state inside a magnetic core, (1) a Hall element is provided in a gap provided in the magnetic core. The magnetic flux generated in the magnetic core is detected by the Hall element by the line current flowing through the coil winding wound on the magnetic core, and the output voltage is detected by the circuit unit in the circuit unit. In a current detector to be measured as a value, a switch circuit is connected to a terminal portion of a coil winding, and the switch circuit is used to supply a current for initialization for initializing a coil to be measured or a magnetic core to initialize the coil winding. And (2) a current flowing for initializing the magnetic core is DC, and the magnetic core is connected to at least B- H hysteresis After passing a current value necessary for transitioning to the saturation magnetization state of the curve, the current value is set to zero and the magnetization state of the magnetic core is initialized to always have the same magnetization and residual magnetization. The line current detection current detector of (1) and the Hall element (3) are installed in a gap provided in the magnetic core, and the line current flows through a coil wound around the magnetic core. A first coil portion wound around the magnetic core in a current detector for detecting a magnetic flux generated in the magnetic core by the Hall element and measuring an output voltage thereof as a line current value in a circuit portion; Is for line current detection, is connected to the line through which the current to be measured flows, and the second coil portion wound around the magnetic core is a DC coil for initializing the magnetization state inside the magnetic core. An electric current can be passed through the magnetic body The current flowing to initialize the magnetic core is a direct current, and a current value necessary for causing the magnetic material core to at least transition to the saturation magnetization state of the BH hysteresis curve is applied. A current detector for line current detection, wherein the magnetization state of the body core is always initialized to have the same polarity and residual magnetization, and (4) the magnetization state of the magnetic core described in (1) above is initialized. The current that flows is an alternating current,
After the magnetomotive force increases the magnetization state of the magnetic core to the saturation state of the BH hysteresis curve, the AC current value is gradually reduced, and then the AC current value is gradually reduced to almost zero. Wherein the magnetization state of the magnetic core is initialized to substantially the origin where the residual magnetization is close to zero.

[0005]

As a first method for solving the problems, a first coil portion (detected winding) and a second coil portion (current supply for initializing the magnetic core) are applied to the ferromagnetic core. Coil, and direct current or alternating current can be applied to the second coil, so that the magnetic core can be initialized. Alternatively, as a second method,
A switch circuit is provided in the first coil portion, and the circuit is switched to an output terminal of the line through which the current to be measured flows or a circuit for supplying a current for initialization, and a specific coil for initializing the magnetic core is provided in the first coil portion. This is a method of applying a direct current or an alternating current, and only one coil portion needs to be wound around the magnetic core, so that a downsized and inexpensive current detector can be provided. By such a method, the magnetization state in the magnetic core is always kept in the initialized state, and the magnetization state in the magnetic core due to the measured current is always calculated from the initialized state, so that the measured value is always stable. And it is possible to minimize measurement errors.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A shows an embodiment of the current detector of the present invention. A first coil portion (detection coil) 2 is provided on a magnetic core 1 in which a gap 3 is provided in a part of a magnetic path of the magnetic core 1.
1. A second coil portion 22 for initialization is wound. A Hall element 4 is provided in the air gap 3, and its output voltage is amplified by the differential amplifier 44 of the circuit section 5 a, and the comparator 42 compares the reference voltage 43 with the output voltage. First coil part 2 for detection
1 is connected to the line to be measured. On the other hand, the second coil portion 22 for initialization is a current-carrying coil for initializing the magnetization state of the magnetic core 1, and the output current of the waveform generator 48 and the amplifier 45 in the circuit portion 5a is reduced. Power is supplied to the second coil portion 22 for initialization. Examples of the initializing current supplied to the second coil portion 22 for initialization include, as a first example, a DC current waveform in which a unidirectional DC current is applied only once (described in FIG. 1B), As a second example, there is an alternating current waveform that decreases with time [described in FIG. 1C]. FIG. 2 shows another embodiment of the current detector according to the present invention. In FIG. 2A, a magnetic core 1 has the same configuration as that of the above-described embodiment, and a gap 3 is provided in a part. A hole element 3 is mounted in the gap 3, and a coil winding 23 is wound around the magnetic core 1. The changeover switch 6 is capable of switching the terminals 211 and 212 of the coil winding 23 with the line side to be measured and the output of the amplifier 45 of the initialization current setting circuit. Switching of the changeover switch 6
It is driven by a switch drive circuit 47 by a signal from the timing circuit 46. The initialization current has the same waveform as that of the first embodiment, and the DC initialization method shown in FIG. 2B or the AC initialization method shown in FIG. 2C is used. The changeover switch 6 may be either a contact switch or an electronic changeover switch. According to the present embodiment, the two functions of the initialization of the magnetic core 1 and the detection of the current to be measured can be processed by one coil winding, and the winding of the sensor portion and the terminal formation step are performed in the first step. It can be shorter than the embodiment. Figure 1 above
FIGS. 3A and 3B show BH hysteresis curves showing the state of the magnetic characteristics of the magnetic core 1 at the initialization currents shown in FIGS. 3B and 1C, respectively. In FIG. 3A,
A case where a magnetomotive force generated by a DC initialization current is used on the X axis is shown. After the application of the initialization current, all operating points of the magnetic core 1 are held as residual magnetic fields at all points. Thereafter, when the line current to be measured flows as the detection state, B in FIG.
Moving on the curve line from the point to the −H hysteresis curve →, for example, the magnetic field H ₁ corresponding to the magnetic flux density B ₁ can be detected with high accuracy, and the line current I ₁ corresponding to this can be stably detected. FIG. 3B shows a case in which an AC initialization current is supplied. After the specific initialization current is supplied, the operating point becomes B-
Origin of the coordinates of the H hysteresis curve [point in FIG. 3 (B)]
Calm down. After that, when a line current for measurement flows as a detection state, the operation line of the magnetic core 1 becomes B
Move point → curve line above the -H hysteresis curve, magnetic field H ₂ corresponding to the magnetic flux density B ₂ is detected stably with high precision. In the conventional method, since the initial operating point (starting point) varies, the operation loop of the BH hysteresis curve when the line current flows varies, and therefore, the detected current value after passing through the comparator 42 at the subsequent stage varies. There is a problem that an error occurs. The present invention solves this point.

[0007]

As described above, according to the present invention, conventionally, the magnetization state in the magnetic core is initially in a random state,
A large error occurred in the line current detection value. According to the present invention, by supplying a specific initialization current to the magnetic core, the magnetization state in the magnetic core can always be set to a constant value. The movement of the operating point is performed via a certain value, and the accuracy of the line current detection value is remarkably improved as compared with the related art.

[Brief description of the drawings]

FIG. 1A is a circuit block diagram showing a first embodiment of a current detector for detecting a line current according to the present invention, and FIGS. 1B and 1C are magnetic circuits in the embodiment. A current waveform for initializing the body core 1.

FIG. 2A is a circuit block diagram showing a second embodiment of a line current detection current detector according to the present invention, and FIGS. 2B and 2C are magnetic circuit diagrams of the embodiment. A current waveform for initializing the body core 1.

FIG. 3 is a diagram of a BH hysteresis curve showing the initialization of the operating point of the magnetic core in the embodiment of FIG. 1 or FIG. 2, and FIG. 3 (A) is a diagram of the BH hysteresis curve initialized by DC. FIG. 3B is a diagram of a BH hysteresis curve initialized by alternating current.

FIG. 4 is a circuit block diagram showing an example of a conventional line current detection current detector.

FIG. 5 is a BH hysteresis curve showing a magnetization state in a magnetic core in a conventional line current detection current detector.

[Explanation of symbols]

 1,11 Magnetic core 2,21 First coil part (for detection) 3,31 Air gap 4,41 Hall element 5a, 5b, 51 Circuit part 6 Changeover switch 22 Second coil part (for initialization) Reference Signs List 23 Coil winding 42 Comparator 43 Reference voltage 44 Differential amplifier 45 Amplifier 46 Timing circuit 47 Switch driving circuit 48 Waveform generator 211, 212 Terminal of coil winding 23

Claims (4)

(57) [Claims] 1. A magnetic sensor according to claim 1, wherein a Hall element is provided in a gap provided in the magnetic core, and a magnetic flux generated in the magnetic core is generated by a line current flowing through a coil winding wound on the magnetic core. In a current detector which detects the output voltage with a Hall element and measures the output voltage as a line current value in a circuit section, a switch circuit is connected to a terminal portion of the coil winding, and the coil winding is connected to the circuit to be measured by the switch circuit. Or a line current detecting current detector capable of switching to an amplifier for supplying an initializing current for initializing a magnetic core. 2. A current flowing to initialize the magnetic core is a direct current, and the magnetic core is supplied with at least B-
After passing a current value necessary for shifting to the saturation magnetization state of the H hysteresis curve, the current value is set to zero and the magnetization state of the magnetic core is initialized to always have the same magnetization and residual magnetization. 2. The current detector for detecting line current according to claim 1, wherein 3. A Hall element is provided in a gap provided in a magnetic core, and a magnetic flux generated in the magnetic core by a line current flowing through a coil wound on the magnetic core. In a current detector for detecting the output voltage as a line current value in a circuit section, a first coil portion wound around the magnetic core is used for detecting a line current, and And a second coil portion wound around the magnetic core is capable of passing a DC current for initializing a magnetization state inside the magnetic core. The current flowing to initialize the magnetic core is a direct current, and after passing a current value necessary to cause the magnetic core to at least transition to the saturation magnetization state of the BH hysteresis curve, the current value is set to zero, and The magnetization state of the core is always the same pole A current detector for detecting a line current, wherein the current detector is initialized so as to have residual magnetization. 4. A current for initializing the magnetization state of the magnetic core is an alternating current. In the initial stage of energization, the magnetomotive force changes the magnetization state of the magnetic core to a saturation state of a BH hysteresis curve. After applying the current, the AC current value is gradually reduced, and the AC current value is reduced to almost zero, thereby initializing the magnetization state of the magnetic core to the origin where the residual magnetization is close to zero. 2. The current detector for detecting line current according to claim 1, wherein: