JPS59126961A - Measuring device of large current - Google Patents

Abstract

PURPOSE:To make the observation of a waveform in a high speed possible and to simplify the handling, by connecting a buffer amplifier to the output terminal of an RC integrating circuit which is connected in parallel to a coil which detects the variance of the magnetic field generated by a current to be measured. CONSTITUTION:When a pulse large current (i) is flowed, an electromotive force is induced in a coil 1 by the magnetic field generated by the large pulse current, and a voltage is generated between both ends of a load resistance 2. This voltage is integrated by an integrating circuit 5 consisting of a resistance 3 and a capacitor 4 to generate a voltage waveform corresponding to the current (i) to be measured. This voltage waveform is inputted to an oscilloscope through a high-input impedance buffer amplifier 9, load resistance 10, and a coaxial cable 7. Thus, the operation of the integrating circuit 5 is not affected at all even if the coaxial cable 7 is terminated by a terminal resistance 8, and the load resistance 2, the integrating circuit 5, the amplifier 9, an the resistance 10 can be stored in a shield case which is made into one body together with a case incorporating the coil 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a current measuring device that measures current values and current waveforms by detecting changes in magnetic fields created by current.

(b) Technical Background Methods for measuring large currents of tens to hundreds of kiloamps include indirect methods such as the magnetic probe method that detects changes in the magnetic field created by the current, the current transformer method, and methods that utilize the magneto-optical effect. There is a direct method in which the current to be measured is passed through a resistor and the voltage drop across the resistor is measured.

Among these, the magnetic probe method is widely used because it allows easy measurement and provides high accuracy.

In the magnetic probe method, the electromotive force induced in the coil by the magnetic field created by the current to be measured is proportional to the time derivative of the current, so by integrating the voltage across a load resistor connected in parallel to the coil, The current value and current waveform are observed, and an RC integration circuit is usually used as an integrator for this purpose.

(C) Prior Art and Problems Measurement of large currents is easily affected by noise, and particularly in the case of pulsed large currents, sufficient noise countermeasures are required. For this reason, it is necessary to place the oscilloscope used to observe the current waveform far away from the current measurement location (eg, 5 m or more).

In this case, the current measurement point and the onoscilloscope are connected by a coaxial cable, and the characteristic impedance of the coaxial cable is approximately 50Ω, and in order to prevent signal reflection within the coaxial cable. , it is necessary to terminate the coaxial cable with a terminating resistor having a resistance value equal to the characteristic impedance of the coaxial cable.

However, the RC integrating circuit has a load resistance of 50Ω.
If this happens, the integrator will no longer function properly. For this reason, in the past, it was necessary to connect the RC integration circuit directly to the input end of the oscilloscope and to use an oscilloscope with a high input impedance.

As a result, it is not possible to integrate the magnetic probe and the RC integration circuit, making it inconvenient to handle the measurement system.Also, since it is not possible to use a wide-band onoscilloscope with an input impedance of 50Ω, the current waveform has a fast rise. There were drawbacks such as the inability to observe

(d) Object of the Invention The object of the present invention is to solve the above-mentioned conventional drawbacks, and to provide a large current measuring device that is capable of high-speed waveform observation and is convenient to handle.

(e) Structure of the Invention The present invention consists of a coil for detecting changes in the magnetic field created by a current to be measured, a load resistor connected in parallel to the coil, and a resistor and a capacitor connected in parallel to the load resistor. A high current measuring device comprising an RC integrator circuit, in which a buffer amplifier with high input impedance is connected to the output terminal of the RC integrator circuit, and a load resistance of the coil, the RC integrator circuit, the buffer amplifier, and the buffer The load resistance of the amplifier is housed in a shield case that is integrated with the metal case that houses the coil.

(f) Examples of the invention Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 (A) shows the principle of large current measurement using the magnetic probe method. For example, when a pulsed large current i flows, an electromotive force is induced in the coil l by the magnetic field created by the pulsed large current, and the load resistor 2 A voltage is generated at both ends. The voltage is integrated by an integrating circuit 5 consisting of a resistor 3 and a capacitor 4, producing a voltage waveform across the resistor 6 corresponding to the current i to be measured.

When the resistance value of resistor 6 is high impedance, the same figure (
As shown in Figure B), the voltage waveform is equal to the waveform of the current to be measured i, but in the case of low impedance,
), the result is a distorted waveform with an extremely fast rise.

Conventionally, as mentioned above, it was necessary to use a high-impedance resistor 6, so it was not possible to connect a coaxial cable and a terminating resistor of the coaxial cable after the integrating circuit 5. A circuit configuration was adopted.

That is, the coil 1 of the magnetic probe and the integrating circuit 5 are connected by a coaxial cable 7, and both ends of the coaxial cable 7 are terminated by the load resistor 2 and the terminating resistor 8 of the coaxial cable 7. It is connected just before an oscilloscope (not shown) that has a high impedance input resistance (for example, IMΩ).

In the present invention, a buffer amplifier 9 is provided after the integrating circuit 5, as shown in FIG.

The buffer amplifier 9 is used to prevent the circuits in the preceding stage and the circuit in the succeeding stage from influencing each other, and a buffer amplifier 9 having a high input impedance is suitable. If you use an IC operational amplifier for this purpose, you can easily
An input impedance of about MΩ can be achieved.

According to the configuration shown in FIG. 3, the output of the buffer amplifier 9 is connected to the onoscilloscope (not shown) via the coaxial cable 7 via the load resistor 10, and the coaxial cable 7 is connected to the terminating resistor 8 of the coaxial cable 7. Even if the terminal is terminated, the integral circuit 5
It has no effect on the operation.

Therefore, it is possible to construct a device in which the load resistor 2, the integrating circuit 5, the buffer amplifier 9, and the resistor 10 are housed in a shielded case that is integrated with a case containing the magnetic 7-tube coil 1.

Figure 4 shows the circuit configuration when using an oscilloscope with an input impedance of 50Ω, in which the coaxial cable 7 is directly connected to the oscilloscope (not shown) without providing a terminating resistor for the coaxial cable 7. ing.

Even in this case, since the buffer amplifier 9 is provided, the operation of the integrating circuit 5 is performed in a sealed manner.

(g) Effects of the Invention According to the present invention, there is an effect that it is possible to observe waveforms with higher precision in large current measurements. In addition, on the oscilloscope side, you only need to terminate the coaxial cable with its characteristic impedance, and if you are using an oscilloscope with low input impedance, you only need to connect the coaxial cable directly. This has the effect of simplifying the process.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the principle of a current measurement method using a magnetic probe, Fig. 2 is a diagram showing a conventional current measurement circuit configuration using a magnetic probe, and Figs. 3 and 4 are diagrams according to the present invention. FIG. 2 is a circuit configuration diagram of a current measuring device according to the present invention. In the figure, 1 is a coil, 2, 3, 6, 8, and 10 are resistors, 4 is a capacitor, 5 is an integrating circuit, 7 is a coaxial cable, and 9 is a buffer amplifier. 321-J

Claims (2)

[Claims] (1) An RC integrating circuit consisting of a coil that detects changes in the magnetic field created by the current to be measured, a load resistor connected in parallel to the coil, and a resistor and capacitor connected in parallel to the load resistor. A large current measuring device comprising: a high input impedance Hasofer amplifier connected to the output end of the RC integrating circuit. (2) The load resistance of the coil, the RC integration circuit, the HaSofa amplifier, and the load resistance of the HaSofa amplifier are housed in a shield case that is integrated with the metal case that houses the coil. A large current measuring device according to claim 1.