JPH0462482A - Current detector - Google Patents

Abstract

PURPOSE:To improve the current detection accuracy by covering the surface of the whole core entirely and annularly without exposing it and providing a shield member which is grounded. CONSTITUTION:The four-directional flanks of the center space part 11 of the shield member 10 are covered with a shield member 10a which is joined electrically and mechanically with the upper and lower end surfaces of the shield member 10. Stray electrostatic capacity is present between a line 12 where a current to be detected flows and the shield member 10, but an induced current which flows through the stray capacity flows to the ground 7. The shield members 10 and 10a are, therefore, held at the ground potential, so the induced current flows to none of a core 2, a Hall element 3, and electric conductors 13, 14, 15, and 16 which are provided inside. Consequently, the accuracy of the current detection is improved.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a current detector with improved accuracy of current detection.

[Prior art]

A current detector using a current transformer has a structure that detects current by guiding the magnetic flux generated by the current to be detected flowing through an electric wire through a core, and detecting the magnetic flux with a Hall element placed in the gap between the core. It is. This current detector is used to detect current in a servo motor. In this case, when the servo motor is driven by a voltage inverter, the detected current has a low frequency sine wave as a fundamental wave, but the line voltage has a high frequency pulse waveform due to the switching action. Therefore, the differential value of the potential increases, and an induced current flows through various stray capacitances between the line through which the current to be detected flows and the current detector. This induced current has caused a problem in that current detection accuracy is reduced. In order to solve this problem, Japanese Patent Application Laid-Open No. 63-302371
A current detector described in the above publication has been proposed. This current detector prevents induced current from flowing from the core to the Hall element by connecting the core to a reference potential electrode (positive electrode) of a power source that supplies power to the Hall element using a conductive wire. Furthermore, by shielding the Hall element and its signal processing circuit section, other stray capacitances are reduced and detection accuracy is improved.

[Problem to be solved by the invention]

However, if the core is simply connected to the reference electrode of the power source with a conducting wire, an induced current will flow between the conducting wire through which the current to be detected flows, the core, the reference electrode of the power source, and the earth. This induced current flows non-uniformly through the core, resulting in potential distribution within the core. As a result, the core, Hall element and its signal output line,
There is a problem in that the stray capacitance between the control current supply lines causes an induced current to flow into the Hall element or the signal output line, and the accuracy of the detected current value is not improved. Further, the control current circuit is an unbalanced circuit with a resistor inserted therein, and a potential difference is likely to occur between the control current supply lines, and an induced current flows within the Hall element as a control current. As a result, a detection error occurs due to the induced current from the core. Furthermore, in the current detector described above, since the entire core is not shielded, an induced current flows into the core due to stray capacitance between the core and the line through which the current to be detected flows, resulting in the above-mentioned problem. Furthermore, since the Hall element and the shield plate of the circuit section are connected to the reference electrode of the power source, an induced current flows through the path of the conducting wire through which the current to be detected flows, the shield plate, and the earth. As a result, due to the stray capacitance between the shield plate, the Hall element, the signal output line for the Hall element, and the control current supply line, induced current flows into the Hall element due to the same cause as described above, and the current detection accuracy is not improved. There is.

[Means to solve the problem]

The structure of the invention for solving the above problem is that an electric wire through which a current to be detected passes through an inner space, a core formed in a substantially annular shape to guide magnetic flux generated by the current, and a magnetic field formed by the core. A magneto-electric transducer is disposed in the gap formed by the circuit, a detection circuit outputs a signal according to the detected current value from the output of the magneto-electric transducer, and the magneto-electric transducer and the detection circuit are internally connected. The core is covered in an annular shape so that the surface is not exposed, and a shield member is provided, which is made of a good conductor and is grounded, through which an electric wire passes through the annular central space.

[Action and effect of the invention]

The current detector of the present invention includes a shield member that covers the entire core in an annular manner so that the entire surface of the core is not exposed except for the portion through which the electric wire through which the current to be detected flows passes, and is grounded (earthed) to the earth. . Therefore, even if a stray capacitance exists between the conducting wire through which the current to be detected flows and the shield member, the induced current flows through the path of the line through which the current to be detected flows, the shield member, and the earth. As a result, even if a non-uniform potential distribution occurs in the shield member due to the induced current flowing within the shield member, the potential is the same as the potential with respect to the ground. Therefore, if there is a current induced in the Hall element or its wiring, the non-uniform potential will cause stray capacitance between the shield member and the Hall element or its wiring, and between the Hall element or its wiring and the ground. This is the current flowing in series connection with the stray capacitance of . Therefore, the stray capacitance is equivalently reduced, and the induced current flowing through the Hall element and the like is also reduced. As a result, current detection accuracy is improved.

【Example】

The present invention will be described below based on a specific example. FIG. 1 is a diagram showing the overall configuration of a current detector I according to a specific example. The box-shaped shield member 10 shown in horizontal cross section has a central space 11 that penetrates in the vertical direction of the paper, and the four side surfaces of the central space 11 are electrically connected to the upper and lower end surfaces of the shield member 10. Shield member 10 which is also mechanically joined
covered with a. A line 12 through which a current to be detected flows passes through this central space 11 . Also, is the shield member 10 the ground? is grounded (earth ground). Further, a ring-shaped core 2 is provided around the shield member 10a.
The core 2 constitutes a magnetic circuit that guides the magnetic flux generated by the current flowing through the wire 12. A gap 12 is formed in a part of the core 2, and a Hall element 3, which is a magnetoelectric conversion element, is disposed in the gap 12. A control current supply line 13.14 for passing a control current is connected to a pair of end faces perpendicular to the magnetic flux of the Hall element 3, and a detection voltage output line 15.16 is connected to the other pair of end faces perpendicular to the magnetic flux.
is installed. A control current is supplied to the Hall element 3 from a DC power supply 5 via a resistor 6. The detection voltage is amplified by the differential amplifier 4, and the amplified signal is outputted to the outside as a detection signal. FIG. 2 is a vertical cross-sectional view of the current detector 1 described above. A resin case 22.22a having the same shape is disposed outside the shield members 10 and 10a. A ring-shaped core 2 is disposed inside the shield member 10, and a Hall element 3 is disposed in the gap 12. The core 2 and the Hall element 3 are fixed to a printed circuit board 20, and the printed circuit board 20 is provided with an amplifier 4, a resistor 6, and a power source 5. Further, the printed circuit board 20 is held by the shield member 10 and is connected to a connector 21 fixed to the resin case 22. This connector 21 has a detection signal output terminal and a power supply terminal. FIG. 3 is a circuit diagram showing the electrical configuration. Between the wire 12 through which the current to be detected flows and the shield member 10,
There is a stray capacitance, but is the induced current flowing through that stray capacitance grounded? flows to Therefore, since the shield member 10.10a is at ground potential, the core 2, the Hall element 3, and the wiring 13.14.15.16 present inside the shield member 10.10a are at ground potential.
No induced current flows in. As a result, the accuracy of current detection improves. However, depending on how the shield members 10, 10a are grounded, the potential distribution of the shield members 10, 108 may become non-uniform due to the induced current flowing in the shield members 10, 108 to the ground. Due to this non-uniform potential, the shielding members 10 and 10a cause damage to the Hall element 3. An induced current can flow to the ground 7 via the wires 13, 14, 15° 16. However, Hall element 3
．． Considering that the stray capacitance between the wiring 13, 14, 15, 16 and the ground is small, the above-mentioned induced current is extremely small, and its influence on the current detection value is also extremely small. In this way, the current detector of the above embodiment can improve its current detection accuracy. The shield member 10.10a described above may be made of a metal body, or may be formed by applying a conductive paint to the inside of the resin case 22.22a. When the core 2 is completely surrounded by the shield member 10.10a,
If the resistance of the closed loop around the magnetic flux is small, the induced current due to time fluctuations in the magnetic flux will
a, and the magnetic flux caused by the induced current causes the Hall element 3
The phase of the magnetic flux detected is delayed. Therefore, in order to prevent such a situation, it is sufficient to provide a slit 25 in the shield member 10.10a.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the structure of a current detector according to a specific embodiment of the present invention, FIG. 2 is a vertical sectional view of the current detector, and FIG. 3 is an illustration of the structure of the current detector. FIG. 2 is a circuit diagram showing a typical configuration.

Claims (1)

[Scope of Claims] A core formed in a substantially annular shape through which an electric wire through which a current to be detected flows passes through an inner space and guides a magnetic flux generated by the current, and a magnetic circuit formed in a magnetic circuit formed by the core. a magnetoelectric conversion element disposed within the gap; a detection circuit that outputs a signal according to a detected current value from the output of the magnetoelectric conversion element; A current detector comprising: a grounded shield member which is made of a good conductor and which covers the core in an annular manner so that the core is not exposed, and through which the electric wire passes through the annular center space.