JPH07280847A - Current sensor - Google Patents

Abstract

PURPOSE:To enhance the current detection accuracy by eliminating the variation of insertion loss over a frequency band. CONSTITUTION:The magnetic current sensor comprises a coil 2 having an input terminal to be connected with a line for detecting a loop current at one side of a core 1, and a magnetic sensor 3 for detecting a magnetic field generated by the coil 2 in order to detect a loop current, wherein the core 1 is further provided with a short coil 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor used for detecting a line current in a network control unit (NCU) of a communication line used for a facsimile, a modem or the like, and particularly inserted in the line. The present invention relates to a current sensor in which the magnetic field generated in the coil is detected by a magnetic sensor such as a Hall element and the frequency characteristics of insertion loss and sensor sensitivity can be significantly improved.

[0002]

2. Description of the Related Art Generally, in a network control unit unit (NCU) of a communication line used in a facsimile (FAX) or a modulator / demodulator (modem) or the like, a normal current sensor circuit is used to detect the presence / absence of a loop current in the line. It is detected, and line control processing and the like are performed based on the detection result.

Further, the loop current is not limited to such a FAX and a modem, but may be applied to other devices using a telephone line adopting an LP (Loop Signaling) system for transmitting and receiving a signal by opening and closing a DC loop circuit, for example. A current sensor circuit is provided in order to perform call processing and disconnection processing from the terminal equipment by turning on and off, and to perform response end call processing from the exchange depending on the polarity of the loop current.

As a conventional current sensor circuit, a magnetic type current sensor circuit is known which detects a loop current by passing a loop current to a coil and detecting a magnetic field generated by the coil with a Hall element or a magnetic resistance element. Has been.

That is, as shown in FIG. 4, in the conventional current sensor circuit, a coil 2 having an input terminal to which a line for detecting a loop current is connected is wound around an annular magnetic core 1 with a part cut away. The magnetic sensor 3 using a Hall element or the like is inserted and arranged in the notch of the core 1. The magnetic sensor 3 detects the value of the input current (current flowing in the coil winding) as the value of the output voltage (output terminal voltage of the Hall element).

However, in the conventional current sensor circuit described above, the insertion loss fluctuates due to the influence of the inductance of the coil 2, and the insertion loss increases in the high frequency band, and the current detection accuracy deteriorates. there were.

That is, assuming that the inductance value of the coil 2 is L (H), the impedance Z of the electric signal to the coil is Z = ωL (ω = 2πf),
The impedance Z increases as f (frequency) increases, and the insertion loss increases (see the dotted line in FIG. 5).

Therefore, in the past, in order to make up for the above-mentioned drawbacks,
As shown by the dotted line in FIG. 4, a capacitor 4 is provided in parallel with the coil 2 so that the impedance Z is lowered as the frequency f increases (the impedance Zc for the capacitor c is Zc = 1 / ωc). Will be).

However, even the conventional method of providing the capacitor 4 has a drawback that the insertion loss fluctuates as shown by the alternate long and short dash line in FIG. 5 and the current detection accuracy decreases, that is, the sensor becomes non-linear. It was

[0010]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a current sensor circuit that can significantly improve the current detection accuracy by eliminating the insertion loss or the variation in sensitivity with respect to the frequency band. And

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a current sensor in which a coil is provided on one of the cores and a magnetic field generated by a current flowing through the coil is detected by a magnetic sensor to detect the current. A short coil is further provided on the core, and a resistance or impedance element having a small value is inserted into the short coil to detect a current flowing through the short coil, and the detected value is added to the output value of the magnetic sensor. It is characterized by having means.

[0012]

The present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 is a schematic configuration diagram showing an embodiment of a current sensor according to the present invention.

In FIG. 1, this current sensor has a coil 2 wound around one side of a ring-shaped core 1 with a part cut out, and a magnetic sensor 3 such as a Hall element is provided in the cut-out part of the core 1 and is additionally provided. The short coil 5 is wound around the core 1.

As the operation of the current sensor, when a line or the like is connected to the input terminal of the coil 2 and a current flows through the line, a magnetic field is generated by the coil 2 and the magnetic sensor 3 detects the magnetic field. However, by adding the short coil 5 to the core 1, the following operational effects are produced.

First, when an alternating current is passed through the coil 2,
An impedance of Z = ωL (Ω) is generated, but the change of the magnetic flux generated in the core 1 at the same time is proportional to the change of the current.

On the other hand, when the magnetic flux changes, a counter electromotive force due to mutual induction is generated in the short coil 5 added to the core 1, and a voltage causes a current to flow in the short coil 5.

As described above, the primary coil 2 for the current sensor
When a current flows through the short coil 5, which can be regarded as a secondary coil when viewed from the viewpoint, this acts to reduce the magnetic flux generated in the core 1 and reduces the self-inductance of the coil 2 of the current sensor. That is, it is equivalent to the reduction of the inductance of the current sensor coil 2.

When considering the impedance Z = ωL, Z increases as ω increases as described above. At the same time, however, the inductance L decreases as described above, and as a result, impedance increases even if ω increases. Z
The impedance Z can be made substantially flat irrespective of ω by increasing the value of ω becomes small or canceling the change.

Therefore, according to the first embodiment, as shown by the solid line in FIG. 5, the insertion loss with respect to the frequency is substantially flat without changing, and the current detection accuracy is improved.

The structure of the short coil 5 and the coil 2 in the first embodiment is not only that shown in FIG. 1 but also a copper flat plate as the short coil 5 as shown in FIG. You may wind the coil 2 for current detection,
Alternatively, conversely, a short coil may be superposed on the winding detection coil 2. .

Next, a second embodiment of the current sensor according to the present invention will be described.

The second embodiment is made to compensate for a slight decrease in the sensing sensitivity of the current sensor due to the consumption of energy by the short coil 5 in the first embodiment, and FIG. As shown in
For example, a load resistor 6 having a small value such as a low input impedance circuit is inserted in the short coil 5, the current flowing in the short coil 5 is converted into a voltage and detected, and the detected value is converted into a current value. The output value of the magnetic sensor 3 is added.

That is, as shown in FIG. 3, in the second embodiment, the load resistor 6 inserted in the short coil 5 is inserted.
And a short-circuit current detection circuit 7 that detects the voltage across the load resistor 6 and converts it into a current value and outputs the current value. The output from the magnetic sensor 3 is amplified by an amplifier 8 to the short-circuited value. An addition circuit 9 for adding and outputting the output values from the current detection circuit 7 is provided,
The other structure is similar to that of the first embodiment.

Therefore, according to the second embodiment, in addition to the effect of the first embodiment, a slight decrease in the sensing sensitivity due to the insertion of the short coil 5 can be compensated. Although the short coil is used in order to suppress the fluctuation of the insertion loss in the above-mentioned embodiment, the same effect can be expected by using a metal of solid muku (mass) having good conductivity as a coil.

[0025]

As described above, according to the present invention, since the short coil is also provided in the core provided with the coil connected to the line for detecting the current, the variation of the insertion loss with respect to the frequency band is eliminated. The current detection accuracy can be significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a current sensor according to the present invention.

FIG. 2 is a diagram showing a specific structure of a short coil and a coil shown in FIG.

FIG. 3 is a schematic configuration diagram of a second embodiment of the current sensor according to the present invention.

FIG. 4 is a schematic configuration diagram of a conventional current sensor.

FIG. 5 is a graph of insertion loss with respect to frequency in the conventional and inventive current sensors.

[Explanation of symbols]

1 ... Core, 2 ... Coil, 3 ... Magnetic sensor, 4 ... Capacitor, 5 ... Short coil,
6 ... Load resistance, 7 ... Short current detection circuit,
8 ... Amplifier, 9 ... Adding circuit,

Claims (2)

[Claims] 1. A current sensor in which a coil is provided on one side of a core, and a magnetic field generated by a current flowing through the coil is detected by a magnetic sensor to detect the current, a short coil is further provided on the core. Characteristic current sensor. 2. A means for detecting a current flowing through the short coil by inserting a resistance or impedance element having a small value into the short coil and adding the detected value to an output value of the magnetic sensor. The current sensor according to claim 1.