JPH0921832A - Current measuring instrument - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To increase the upper limit of measurable current value. SOLUTION: A part of a conductor 13 is divided into two current paths, and a Hall element 1 is installed close to one current path.
The element 1 detects the difference in magnetic flux density generated by the two current paths, and the gain adjusting circuit 2 amplifies the output of the element 1 to a value corresponding to the current. The full-wave rectifier circuit 3 rectifies the output of the circuit 2, and the sample hold circuit 4 samples the output of the circuit 3. The A / D conversion circuit 5 converts the sampled value into a digital value, and the CPU 6 obtains the value of the current flowing through the conductor 13 from the obtained digital value. In this way, the magnetic flux density applied to the element 1 becomes smaller than in the conventional case, so that the upper limit of the measurable current value can be increased.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a current measuring device,
In particular, it relates to a current measuring device using a Hall element.

[0002]

2. Description of the Related Art Conventionally, for example, a method using a toroidal coil has been used as a method for measuring a large current such as a welding current flowing from a resistance welding machine to a workpiece. This is to measure the current by utilizing the electromotive force generated by the magnetic flux generated by the current interlinking with the toroidal coil. This method can measure the current in a non-contact manner, but since the electromotive force is a differential signal of the measured current, it must be integrated on the processing device side. At this time, since the noise component may be integrated at the same time, it is difficult to obtain an accurate current value. Therefore, as another measuring method, a method using a Hall element is used. Since the output of the Hall element is a signal (voltage value) proportional to the current value, there is no need to integrate it, and the circuit of the processing device is simple, but the measurable current value is usually up to about 2000A.

[0003]

As described above, in the conventional current measurement using the Hall element, there is a problem that the current can be measured only up to about 2000 A due to the characteristics of the Hall element. The present invention has been made to solve the above problems, and an object of the present invention is to provide a current measuring device capable of increasing the upper limit of the measurable current value as compared with the related art.

[0004]

The current measuring device of the present invention comprises:
A conductor part of which is divided into two parallel current paths and 2
A Hall element installed on one side between two current paths, a gain adjustment circuit for amplifying the output of the Hall element, a sample hold circuit for sampling the output of the gain adjustment circuit, and an A / D conversion circuit. , A CPU that obtains a current value from the output of the A / D conversion circuit. In such a configuration, the difference between the magnetic fields generated by the currents flowing through the first and second current paths is detected by the Hall element, and the detected output is amplified by the gain adjustment circuit to have a value corresponding to the current. It Then, the output of the gain adjustment circuit is sampled by the sample hold circuit, converted into a digital value by the A / D conversion circuit, and then the current value is obtained by the CPU.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a current measuring device showing one embodiment of the present invention, and FIG. 2 is an enlarged view of a portion of a Hall element shown in FIG. 1 is a Hall element that outputs a signal proportional to the applied magnetic field (magnetic flux density), 2 is a Hall element 1
A gain adjusting circuit for amplifying the output signal of 1 to a value corresponding to the current, 3 is a full-wave rectifying circuit for full-wave rectifying the output of the gain adjusting circuit 2, and 4 is a sample of the output of the full-wave rectifying circuit 3. A sample and hold circuit that holds the sampled value for a certain period of time,
5 is an A / D conversion circuit for converting the sample value obtained by the sample hold circuit 4 into a digital value, 6 is a CPU for obtaining the value of the current flowing through the conductor from the digital value obtained by the A / D conversion circuit 5, 7 Is a memory for storing the digital value, and 8 is a display for displaying a current value as a measurement result.

Further, 10 is a welding power source for supplying a welding current, 11 is a transformer for converting the output of the welding power source 10 into a low voltage and a large current, 12 is a welding head for flowing a welding current to an object to be welded (not shown), Reference numeral 13 is a conductor such as a cable for connecting the transformer 11 and the welding head 12.

Next, the operation of such a current measuring device will be described. FIG. 3 is a diagram showing an output waveform of each part in the current measuring device, in which the horizontal axis represents time and the vertical axis represents voltage. First, a part of the conductor 13 through which the alternating welding current I flows is branched into two as shown in FIG. At this time, the first current path 13
It is desirable that the current Ia flowing through a and the current Ib flowing through the second current path 13b be equal.

When the Hall element 1 is installed between the current paths 13a and 13b, the magnetic fields generated around the current paths 13a and 13b due to the currents Ia and Ib interlinking with the Hall element 1. When the Hall element 1 is located between the current paths 13a and 13b, the direction of the magnetic field due to the current path 13a (when the current Ia flows in the direction shown in FIG. 2 is perpendicular to the plane of the drawing and toward the other side) and the current path 13b. Since it is in the opposite direction to the direction of the magnetic field (the direction perpendicular to the paper and toward this side),
These magnetic fluxes cancel each other out and the magnetic flux density interlinking with the Hall element 1 becomes 0, and no signal is output from the Hall element 1.

Here, when the Hall element 1 is brought closer to one current path (13a in FIG. 2), a difference occurs in the magnetic flux density interlinking with the Hall element 1. Therefore, for example, when the bias current Ih is applied to the Hall element 1 in the vertical direction of FIG.
A direction perpendicular to both the bias current Ih and the magnetic field (see FIG. 2).
A Hall electromotive voltage Vh proportional to the difference in the magnetic flux density is generated in the left-right direction. The Hall electromotive voltage Vh is amplified by an amplifier (not shown) in the Hall element 1 and output as an output signal of the Hall element 1.

Next, the gain adjusting circuit 2 includes the Hall element 1
The full-wave rectification circuit 3 rectifies the output signal of the gain adjustment circuit 2 as shown in FIG.
(B)). Subsequently, the sample-hold circuit 4 samples the output of the full-wave rectifier circuit 3 with a sampling pulse (not shown) and holds the sampled value for a fixed time (FIG. 3).
(C)). Then, the A / D conversion circuit 5 converts this sample value into a digital value, and the CPU 6 stores the obtained digital value in the memory 7.

In this way, the digital value of the measurement result is stored in the memory 7, and this digital value is the current path 13.
It is a value proportional to the difference in the magnetic flux densities caused by the currents flowing through a and 13b, and also a value proportional to the current I, but since it does not directly correspond to the current I, in order to obtain the value of the current I It is necessary to perform calibration such as.

That is, although the relationship between the digital value and the current value is preset in the CPU 6 as shown in FIG. 4, the relationship between the sample value of the sample and hold circuit 4 and the digital value is A / D conversion circuit. (Determined by the characteristics of No. 5), it is not possible to determine what current value the digital value obtained from the A / D conversion circuit 5 shows unless calibration is performed.

Therefore, it is assumed that the peak value of the current I is measured by another method using a toroidal coil or the like and the value at this time is 5000A. Next, the same measurement is performed using the current measuring device according to the present embodiment, and the gain of the gain adjusting circuit 2 is adjusted so that the digital value of the measurement result becomes "10000000" (5000A). By such calibration, the digital value obtained by the A / D conversion circuit 5 corresponds to the value of the current I, and accurate measurement can be realized. In the present embodiment, in order to simplify the description of FIG. 4, the case of the 8-bit A / D conversion circuit 5 has been described, but it goes without saying that it may be 8 bits or more.

Then, the CPU 6 displays the current value (instantaneous value in this case) of the measurement result on the display 8 composed of a liquid crystal or a light emitting diode. Further, the CPU 6 calculates an effective value or an average value of the effective value over several cycles from the instantaneous value stored in the memory 7 and stores the calculated value in the memory 7, or causes the display 8 to display a current value of the calculated result. You can also

As described above, according to the present invention, the value of the current I is obtained by detecting the difference between the magnetic fields generated by the currents flowing through the first and second current paths 13a and 13b by the hall element 1.
The magnetic field (magnetic flux density) applied to the Hall element 1 becomes smaller than in the conventional case. As a result, the upper limit of the measurable current value can be set to, for example, 5000 A or more, which is larger than the conventional value.

The Hall element 1 is connected to the current paths 13a, 1
Since it suffices to install the Hall element 1 on one side between 3b, the installation location of the Hall element 1 is not restricted,
It can be easily applied to various types of measurement objects (conductors). Also, the sensitivity can be adjusted by adjusting the mounting position. In this embodiment, the AC welding current is measured, but the present invention is not limited to this, and DC may be measured.

[0017]

According to the present invention, a Hall element, a gain adjusting circuit, a sample hold circuit, an A / D conversion circuit and a C
By configuring the current measuring device from PU, the value of the current flowing in the conductor can be measured, and the magnetic field applied to the Hall element is smaller than before, so the upper limit of the measurable current value is higher than before. can do. In addition, since the installation location of the Hall element is not restricted, it is possible to easily deal with various measurement targets.

[Brief description of drawings]

FIG. 1 is a block diagram of a current measuring device according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a portion of the Hall element of FIG.

3 is a diagram showing an output waveform of each part in the current measuring device of FIG.

FIG. 4 is a diagram showing an example of a relationship between a digital value and a current value obtained by an A / D conversion circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hall element, 2 ... Gain adjustment circuit, 3 ... Full wave rectification circuit, 4 ... Sample hold circuit, 5 ... A / D conversion circuit,
6 ... CPU, 7 ... Memory, 8 ... Indicator, 10 ... Welding power source, 11 ... Transformer, 12 ... Welding head, 13 ... Conductor,
13a ... 1st electric current path, 13b ... 2nd electric current path.

Claims (1)

[Claims] 1. A conductor, a part of which is divided into a parallel first and second current paths, and a conductor which is installed at a position deviated to one side between the first and second current paths, , A Hall element that outputs a signal based on the difference between the magnetic fields generated by the current flowing through the second current path, and a gain adjustment circuit that amplifies the output signal of the Hall element to a value corresponding to the current, A sample and hold circuit that samples the output of the gain adjustment circuit and holds the sampled value for a certain period of time, an A / D conversion circuit that converts this sampled value into a digital value, and the value of the current flowing through the conductor from this digital value. A current measuring device having a CPU.