JP2000131343A - Clamp tester for leakage-current measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a clamp tester which prevents the effects of an external current without using an amplitude adjusting circuit, a phase-adjusting circuit, an addition circuit or the like and which reduces a residual current by a method, wherein a preset resistance is connected to a plurality of arbitrary coils in every circuit, so as to add their outputs and the outputs of every circuit are added, subtracted or converted into a current or a voltage. SOLUTION: When a current to be measured exists inside a core 1a and a core 1b, currents whose phases are all identical flow to a coil 2a, a coil 2b and a coil 2c and a coil 2d. Their added output appears at an output terminal 10. A preset resistance 9 is adjusted, in such a way that the output becomes a prescribed value with reference to the prescribed current to be measured. When there is a current at the outside, in-phase currents is identical flow ideally to the coils 2a, 2b, and 2c, 2d, and currents whose phase is opposite flow to the coil 2a, 2b and 2c, 2d. Although their added output ought to be zero, in general, the amplitudes of their respective outputs become different. Then, the imbalance of the outputs is adjusted, by using a preset resistance 3a and a preset resistance 3b, and the outputs are adjusted so as to become zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leak clamp tester for measuring a leakage current of a circuit in a live state without interrupting the circuit, and in particular, to reduce the influence of a residual current and the influence of a magnetic field due to an external current. And improvement of the current detection circuit.

[0002]

2. Description of the Related Art First, the principle of a clamp tester will be described with reference to FIG. When an electric wire through which the current I to be measured flows is arranged in an annular core in which the coil 2 is wound N ₂ times,
It is assumed that the magnetic flux of φ is linked to the coil 2 by the current I.

The mutual inductance M between the current I and the coil 2 is defined by M = N ₂ (φ / I). The electromotive force e induced in the coil 2 is e = −MdI / dt. The current i is as follows. i = e / Z =-(M / Z) dI / dt where Z is the impedance of the coil 2.

Here, it is assumed that the DC resistance of the coil 2 is R, the inductance is L, and the current I is I = Asinωt. Although Z = R + jωL, if ωL≫R, R can be neglected, and the current i becomes as follows. i ≒ − (M / jωL) dI / dt = − (M / jωL) Aωcosωt = − (M / jL) Acosωt

Since M and L are both proportional to μ _{0 μs} ,
i is an amount proportional to I irrespective of μ _{0 μs} of the core 1, and
As a result, the measured current I can be measured. This is the principle that a clamp tester can detect current.

FIG. 5 is a principle diagram of a leak clamp tester. A pair of wires through which current flows in the opposite direction
There the the connected) L _1, L ₂ and simultaneously clamped by the clamp tester, to measure the core 1 and the chain interlinked that the current amount in the above principle. If the amount of current (I ₁ , I ₂ ) flowing in the pair of electric wires L ₁ and L ₂ is the same, the current interlinking with the core 1 becomes 0, but when there is a leakage current somewhere in the line Can detect the leakage current amount ir.

[0007] Such a clamp tester is required to have the following characteristics. (1) When a wire is clamped by a clamp tester, the pair of wires is not always at the same position with respect to the clamp. If the position of the current in the core of the clamp is different,
In some cases, a current that would otherwise be canceled and not detected is detected. This is called a residual current, and it is important that such a residual current is small in a leak crumb tester.

(2) Influence of external magnetic field In a high-performance leak clamp tester, the amount of current that must be detected is very small, about 1 mA, so a large current (for example, a large current of about 100 A) flows outside. In some cases, under the influence of the current, the current value may be detected even though the current interlinking with the core of the clamp is zero. Therefore, it is important to eliminate the influence of the external current in the leak clamp for detecting the small current.

Since both (1) and (2) relate to the asymmetry of the magnetic circuit of the clamp, it is necessary to correct the asymmetry in some way. For example, Japanese Patent Application Laid-Open No. 9-2693
No. 37, "Divided Leakage Current Measuring Apparatus" discloses a technique for improving the residual current error by focusing on the above (1).

In this current measuring device, as shown in FIG. 6, a pair of cores 20A and 20B are formed in an annular shape with their end faces facing each other, and coils (A, B, C and D) are respectively provided near the end faces.
And amplifiers 21 and 23 amplify the series connection output of each coil pair near the end face, respectively.
The two phase adjustment outputs are added by the adder 25. The output of the adder 25 is displayed on a meter 26.

Each of the phase adjusting means and the amplifier can adjust the phase and the gain, respectively. By this adjustment, a state similar to a state where the magnetic coupling of the core division surface is balanced can be obtained. The current can be reduced.

[0012]

However, such a current measuring device has the following problems.

A current is detected from two sets of coils, and a pair of gain adjusting means, a pair of phase adjusting means and an adding circuit are required for the current. In addition, a leak clamp tester often has a range for measuring not only a very small current but also a large current in order to detect a current actually flowing in a line. In addition to each circuit, another circuit for a large current is required, and there is a problem that the circuit scale becomes large. Such a large circuit scale has been an obstacle to downsizing and cost reduction of the leak clamp tester.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to reduce the residual current by preventing the influence of an external current without using a conventional amplitude adjustment circuit, phase adjustment circuit, and addition circuit. It is an object of the present invention to realize a leak current measuring clamp tester capable of measuring a leakage current.

[0015]

In order to achieve the above object, according to the first aspect of the present invention, an annular core which can be separated, at least two or more coils wound around each of the cores, Two or more independent circuits with semi-fixed resistors connected in series or in parallel such that the output is added to any two or more of these coils, and the output of each circuit is added or subtracted or the current Means for converting the voltage to obtain a voltage corresponding to the current to be measured;
By adjusting the semi-fixed resistor, an error in a measured value due to a residual current or an external current can be adjusted.

By adjusting the semi-fixed resistor, the unbalance of the output of each coil is adjusted, and the error of the measured value due to the residual current or the external current can be adjusted.

Further, the amplitude of the signal input to the means for performing addition or subtraction is limited by switching the resistance according to the magnitude of the current to be measured. This enables a large current measurement in the same circuit. In this case, it is desirable to switch the value of the resistor according to the current range.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of a clamp tester according to the present invention. Each of the cores 1a and lb has 2
A pair of windings (hereinafter, windings are referred to as coils) 2a, 2b and 2
c and 2d are given. The terminals of the coils 2a and 2b are connected in series with a semi-fixed resistor 3a interposed therebetween so that currents detected by the two coils are added.

The coils 2c and 2d in the other core 1b and the semi-fixed resistor 3b are similarly connected. The terminals of the coils 2b and 2d that are not connected to the semi-fixed resistors are connected to the inverting input of the operational amplifier 8a, which is a component of the adder 8, via the semi-fixed resistors 7b and 7a, respectively.

The output of the coil is a semi-fixed resistor 4b,
4a, the fixed resistors 5b and 5a and the switch 6
a and 6b are connected to zero potential as shown in the figure. The semi-fixed resistor 9 is a feedback resistor for determining the overall gain of the adder 8. The output of the adder 8 is guided to an output terminal 10.

The operation in such a configuration will now be described. When measuring minute current such as leakage current, switch 6
a, 6b are opened so that the input of the adder 8 is not short-circuited.

Hereinafter, a method for reducing the influence of the external current will be described. If the current to be measured is inside the cores 1a and 1b (space portion), the coils 2a, 2b, 2c and 2d
, All the in-phase currents flow, and their summed output appears at the output terminal 10. The semi-fixed resistor 9 is adjusted so that the output becomes a specified value for a specified measured current.

When there is a current outside, ideally, current outputs of the same amplitude appear in the four coils, the coils 2a and 2d are in phase, the coils 2d and 2c are also in phase, and the coils 2a and 2c are in phase.
Since b is a negative-phase current and a negative-phase current also flows through the coils 2c and 2d, the output of the adder should be zero.

However, generally, the fitting portions 11a, 11b
The amplitude of each output differs due to the asymmetry of the output. Therefore, the imbalance of the respective outputs is adjusted using the semi-fixed resistors 3a and 3b, so that the outputs become zero. Further, the unbalance that cannot be adjusted here is adjusted by the semi-fixed resistors 4a and 4b and the input resistor 7b of the adder. Generally, when the influence of the external current is reduced as described above, the residual current error is reduced.

When measuring a large current, the switches 6a and 6b connected to the short-circuit resistors 5a and 5b are closed to limit the amplitude of the signal input to the adder 8 and to measure the large current in the same circuit. Is also possible. Although only one circuit is shown for each of the short-circuit resistors 5a and 5b and 6a and 6b, a plurality of combinations may be provided according to a required current range. It is convenient if the resistance value can be switched in conjunction with the switching of the current measurement range.

FIG. 2 is a block diagram showing another embodiment of the present invention. The difference from FIG. 1 lies in the coil connection method. In this embodiment, the coils 2a and 2b are connected in series via the resistor 3, so that current is output from the other ends of the coils 2a and 2b. The sliding contact of the semi-fixed resistor 3 is grounded so that the unbalance of the coil output can be adjusted. With such a configuration, the effect of the external current can be prevented and the residual current can be removed as in the case of FIG.

FIG. 3 is an embodiment diagram of another connection method. The coils 2a and 2d are connected via a semi-fixed resistor 3a, and the other coils 2b and 2c are similarly connected via a semi-fixed resistor 3b. The sliding contacts of the semi-fixed resistors 3a and 3b are connected via a semi-fixed resistor 3c. The sliding contact of the semi-fixed resistor 3c is grounded. And coil 2
Output currents from the common connection point of a and 2d and the common connection point of coils 2b and 2c are input to the adder side.

With such a configuration, the effect of the external current can be prevented and the residual current can be removed as in the case of FIG.

The foregoing description has been directed to specific preferred embodiments for the purpose of describing and illustrating the invention. Therefore, the present invention is not limited to the above-described embodiment, and includes many more modifications without departing from the spirit thereof.
This includes deformation.

[0030]

As described above, according to the present invention, the following effects can be obtained. (1) The amplitude adjustment circuit, the phase adjustment circuit, and the addition circuit as provided in the conventional example are unnecessary, and the influence of the external current and the residual current can be removed only by one addition circuit, a small resistor and a semi-fixed resistor. (2) Further, according to the configuration of claim 2, even in a range where a large current is measured, detection can be performed by the same circuit, so that the circuit scale can be significantly reduced. (3) The high-performance leakage current clamp tester can be reduced in size and cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a clamp tester according to the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a configuration diagram showing still another embodiment of the present invention.

FIG. 4 is a diagram illustrating the principle of a clamp tester.

FIG. 5 is a principle configuration diagram of a leak clamp tester.

FIG. 6 is a configuration diagram showing an example of a conventional clamp tester.

[Explanation of symbols]

 1, 1a, 1b core 2, 2a, 2b, 2c, 2d coil 3, 3a, 3b, 3c semi-fixed resistor 4a, 4b semi-fixed resistor 5a, 5b, 7a fixed resistor 6a, 6b switch 8 adder 8a operational amplifier 9 Semi-fixed resistor 10 Output terminal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naomichi Senda 1-19-18 Nakamachi, Musashino-shi, Tokyo Yokogawa M & C Co., Ltd. F-term (reference) 2G014 AA16 AB33 AC19 2G025 AA03 AA14 AB14 2G035 AA01 AB07 AC13 AD10 AD12 AD18 AD19 AD22

Claims (3)

[Claims] 1. A separable annular core, at least two or more coils wound around each of said cores, and a serial or parallel coil such that the output is added to any two or more of these coils. And two or more independent circuits each having a semi-fixed resistor connected thereto, and means for adding or subtracting the output of each circuit or performing current / voltage conversion to obtain a voltage corresponding to the current to be measured. A clamp tester for measuring a leakage current, wherein an error in a measured value due to a residual current or an external current can be adjusted by adjusting the semi-fixed resistance. 2. A separable ring-shaped core, at least two or more coils wound around each of said cores, respectively connected between output terminals of these coils and zero potential via switching means. And a means for adding or subtracting a voltage generated in the resistor to obtain a voltage corresponding to the current to be measured, and controlling the switching means according to the magnitude of the current to be measured. A clamp tester for measuring a leakage current, wherein switching of connection / disconnection of a resistor or switching of a resistance value is performed. 3. The leak current measuring clamp tester according to claim 2, wherein the switching of the resistance is linked with the switching of the range of the current to be measured.