JP2004233208A - Current detecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current detecting apparatus capable of accurately indicating (displaying) a current passing through an electric wire even in the case that the electric wire is wound on a current transformer by a plurality of times. <P>SOLUTION: The current detecting apparatus is constituted of the current transformer, a current detecting means, and an indicated value correcting means. In the current transformer, a winding for current detection is wound on an annular core through which the electric wire for current measurement is passed. On the basis of a voltage generated in the winding for current detection, the current detecting means detects the current passing through the electric wire passed through the annular core. An indicated value of the current is determined by the current detecting means according to the number of passages N (N is a natural number) of the electric wire through the annular core, and the indicated value correcting means corrects the indicated value of the current into [1/N]. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a current detection device suitable for detecting a weak current flowing in a predetermined electric wire using a current transformer.
[0002]
[Related background art]
One of the techniques for detecting an alternating current is a current detection method using a current transformer (CT) (for example, see Non-Patent Document 1). As shown in FIG. 3 (a), this current detection is performed by using a current transformer 1 in which a current detection winding 3 is wound around a ring-shaped core 2 having high magnetic permeability. The current I generated in the current detection winding 3 when the current Io flows is detected as the generated voltage E via a load resistor 5 connected between both ends of the current detection winding 3. Things.
[0003]
By the way, the voltage E detected in this way is, when the number of turns of the current detecting winding 3 is n and the resistance value of the load resistor 5 is r,
E = (1 / n) · K · Io · r
As shown. Here, K is a proportional constant.
[0004]
[Non-patent document 1]
Electronic Communication Handbook, published by the Institute of Electronics and Communication Engineers 1979, Ohmsha, page 126
[Problems to be solved by the invention]
By the way, when the current Io flowing through the electric wire H is small, the voltage E detected as described above naturally becomes small. Therefore, in the related art, for example, as shown in FIG. 3B, the electric wire H is bent and wound around the ring-shaped core 2 N times, and the current passing through the core 2 is measured N times. That is being done.
[0006]
By the way, when the current is detected in this way, the indicated value (voltage E) of the detected current is N times the current Io actually flowing through the electric wire H. Therefore, for the operator (measurer), the indicated value is proportional. It is necessary to convert and recognize. For this reason, the measured current value is likely to be erroneously recognized. Further, when trying to control any control target device in accordance with the current value detected as described above, this may cause erroneous control data to be output. However, the mode of current measurement using the current transformer 1, that is, how many times the electric wire H is passed through the ring-shaped core 2 is left to the discretion of the operator, and the current value detected via the current transformer 1 is used as the value. It is difficult to correctly give instructions according to the form.
[0007]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to correctly indicate (output) a current value detected via a current transformer according to its use mode (current measurement mode). It is an object of the present invention to provide a current detecting device having a simple configuration capable of performing the above.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a current detection device according to claim 1 of the present invention comprises a current transformer having a current detection winding wound around a ring-shaped core through which an electric wire used for current measurement passes. A current detecting means for detecting a current flowing through the electric wire penetrating the ring-shaped core from a current or a voltage generated in the detection winding, and according to a number of times N (N is a natural number) of the electric wire penetrating the ring-shaped core And a command value correcting means for correcting the command value of the current obtained by the current detecting means to [1 / N].
[0009]
That is, the current detection device according to the present invention includes an instruction value correction unit that corrects and outputs a current value detected via the current transformer. The number of penetrations N is given to the indicated value correcting means in accordance with the use form of the current transformer, that is, how many times the electric wire to be subjected to the current measurement has been passed through the current transformer, whereby the current detection is performed. The current value detected by the means is corrected to [1 / N] and output.
[0010]
According to the current detection device provided with such an indicated value correcting means, the current value detected by the current detecting means simply by giving the indicated value correcting means the number of times N of the electric wire to be subjected to the current measurement into the current transformer. Is corrected to [1 / N], and the output is wound around the current transformer N times to increase the apparent current penetrating the current transformer N times. However, it is possible to correctly output the value of the current flowing through the electric wire. Therefore, erroneous recognition of the current measurement value can be prevented, and various controls can be executed using the measured current value as it is.
[0011]
It is sufficient that the number of times N of the electric wire penetrates the ring-shaped core is manually set in the indicated value correcting means according to the current measurement mode as described in claim 2. is there. Specifically, a plurality of push button switches corresponding to the number of times of penetration N are selectively urged to set the number of times of penetration N, or a rotary switch having a plurality of contacts corresponding to the number of times of penetration N is used. The number of penetrations N may be set by switching.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a current detection device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a current detection device 10 according to this embodiment. Reference numeral 20 denotes a current transformer in which a current detection winding 3 is wound around a ring-shaped core 2, and 30 denotes the current detection in the current transformer 20. A current detecting unit (current detecting means) for detecting a current flowing through an electric wire (not shown) penetrating the ring-shaped core 2 from a voltage generated in the use winding 3. In particular, the feature of the current detection device 10 is that the current detection unit 30 and the display 60 that displays the current value detected by the current detection unit 30 as the amount of movement of a pointer or a digital value. The point is that an instruction value correction unit (instruction value correction unit) 40 for correcting the current value detected by the current detection unit 30 is provided.
[0013]
The instruction value correction unit 40 converts the current value detected by the current detection unit 30 into [1 / N] according to a constant N (natural number) set by the penetration number setting unit 50, and converts the converted current instruction value. It plays the role of outputting to the display unit 60. Incidentally, the indicated value correction section 40 variably sets the amplification gain of an amplifier (not shown) for amplifying the input signal (current measurement value) according to the constant (number of times of penetration) N, for example, so that the indicator This is realized as converting an output signal (current indication value) to be given to 60 into [1 / N] of the input signal.
[0014]
Note that the number-of-penetrations setting unit 50 includes, for example, a plurality of push-button switches that are selectively operated, a multi-contact rotary switch, and the like. The constant (the number of penetrations) N is selectively set (specified) by manually operating these switches. Note that the constant N is set as the number of times the electric wire to be measured for current is wound around the current transformer 20, that is, the number of times N the electric wire passes through the current transformer 20.
[0015]
Thus, according to the current detecting device thus configured, the electric wire is used to increase the amount of current that should be passed through the current transformer 20 because the amount of current is small, particularly according to the current flowing through the electric wire to be measured. When the current measurement is performed by passing the current through the current transformer 20 a plurality of times, if the constant N corresponding to the number of turns N is set by using the number-of-times-through setting section 50, the current transformer 20 It is possible to convert the current value detected through the current detection unit 30 into [1 / N] and supply the converted value to the display 60. As a result, the current value flowing through the electric wire is displayed on the display 60 irrespective of the number of turns of the electric wire around the current transformer 20.
[0016]
Therefore, there is no mistake in reading the indicated value (display value) of the measured current value by the display 60, and it is not necessary for the operator to convert the indicated value (display value) and grasp it. That is, it is possible to directly read the indicated value (display value) of the measured current value by the display device 60 without error as the current value flowing through the electric wire.
Further, according to the above-described configuration, the number-of-times-of-penetration setting unit 50 that sets a constant N corresponding to the number N of turns of the electric wire with respect to the current transformer 20, and the current detection unit 30 according to the constant N set by the number-of-times-of-penetration setting unit 50 By simply providing the indicated value correction unit 40 for converting the detected current value to [1 / N], the current value according to the current transformer 20 can be determined regardless of how many times the electric wire is wound around the current transformer 20. Measurement can be performed reliably. In other words, although the mode of current measurement depends on the usage of the current transformer 20 by the operator, it is only necessary to set the above-described constant N according to the mode (the number of turns N of the electric wire). There is an effect that the measurement work load does not increase.
[0017]
The above-described current detection device 10 is suitable for incorporating, for example, a heater driven to generate heat by a minute current into a temperature controller that controls the temperature according to the drive current. FIG. 2 shows a schematic configuration of a temperature control system of a heater 90 using a temperature controller 70.
This temperature control system controls a current (amount of current) supplied to a heater 90 by a heater driving unit 80 using an SCR (silicon control element), thereby controlling a heat generation temperature of the heater 90. The current flowing through the current transformer 90 is detected using the current transformer 20. In particular, by winding a lead wire (electric wire) 91 for supplying the driving current to the heater 90 around the current transformer 20 a plurality of times, the heater current (current measurement value) detected via the current transformer 20 is reduced. The correction is performed using the indicated value correction unit 40 provided in the current detection device 10 described above, and the driving current (current indicated value) of the heater 90 obtained by the correction is controlled by the control unit 71 for the heater driving unit 80. It is configured to feed back as a value. Also in this case, it is needless to say that the constant N set in the instruction value correction unit 40 is set according to the number of turns N of the lead wire 91 around the current transformer 20 by manually operating the penetration number setting unit 50.
[0018]
According to the temperature control system configured as described above, the current for driving the heater 90 to generate heat is very small, and the lead wire 91 of the heater 90 is connected to the current transformer 20 a plurality of times in order to reliably detect this current. Even in the case of winding, since the current flowing through the heater 90 can be accurately detected, the heater driving unit 80 can be directly driven and controlled without changing the control constants and the like in the control unit 71. Therefore, it is possible to control the heat generation drive while accurately detecting the drive current of the heater 90 without changing the basic configuration of the temperature controller 70.
[0019]
By the way, in the above-described current detection device, the indicated value correction unit 40 is used to perform correction (conversion) on the detected current value in accordance with the number of turns N of the electric wire (lead wire) with respect to the current transformer 20. In the case where the device has the function of switching the current detection sensitivity, it is also possible to use the instruction value correction unit 40 to perform the correction according to the switching of the current detection sensitivity. The current detection sensitivity is switched by, for example, changing the number of turns n of the current detection winding 3 in the current transformer 20 or changing the resistance of the load resistor 5 connected between both ends of the current detection winding 3 for voltage detection. This can be achieved by changing the value r or by changing the amplification gain of an amplifier (not shown) that performs current detection.
[0020]
In this case, as shown in FIG. 1, information on the current detection sensitivity set in the current detection sensitivity setting unit 51 is given to the instruction value correction unit 40, and correction according to the current detection sensitivity is also performed. Good. Specifically, when the current detection sensitivity of the current detection unit 30 is increased by M times, the indicated value correction unit 40 converts the current detection value output from the current detection unit 30 to [1 / M] times. What is necessary is just to output to the display 60. At this time, when the number of turns of the electric wire (lead wire) to the current transformer 20 is set to N times, the current detection value output from the current detection unit 30 is adjusted to [1 / M] by combining these pieces of information. [N] times and output to the display 60.
[0021]
The number of turns of the current detection winding 3 of the normally used current transformer 20 is [n0], and the number of turns of the detection winding 3 is [n1] due to some factor (difference between manufacturers, etc.). In the case of use, if the number of turns [n1] is set by the current detection sensitivity setting unit 51 and the current detection value output from the current detection unit 30 is corrected to [n1 / n0], the correct current value can be easily obtained. Can be displayed.
[0022]
With such a configuration, it is possible to obtain an instruction value corresponding to the current detection mode, so that the value of the current flowing through the electric wire can always be detected without error, and this can be directly grasped.
Note that the present invention is not limited to the embodiment described above. In the embodiment, a description has been given of a case where a minute current flowing through the heater 90 is a detection target. Of course, the specifications of the current transformer 20 are not particularly limited, and can be variously modified and implemented without departing from the gist of the invention.
[0023]
【The invention's effect】
As described above, according to the current detection device of the present invention, the value of the current flowing through the electric wire is small, and even if the electric wire is wound around the current transformer a plurality of times in order to accurately detect the current. In addition, the value of the current flowing through the electric wire can be correctly displayed or output. In addition, the current detection value can be effectively corrected simply and effectively, and a great effect in practical use such as good handleability can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a current detection device according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a temperature control system configured using the current detection device of the present invention.
FIG. 3 is a diagram for explaining the principle of current detection by a current transformer.
[Explanation of symbols]
H Electric wire 1 Current transformer 2 Ring core 3 Current detection winding 4 Voltage detection unit 5 Load resistance 10 Current detection device 30 Current detection unit 40 Indicated value correction unit 50 Number of penetration setting unit 51 Current detection sensitivity setting unit 60 Display

Claims (2)

A current transformer in which a current detection winding is wound around a ring-shaped core through which an electric wire used for current measurement is passed;
Current detection means for detecting a current flowing through an electric wire penetrating the ring-shaped core from a current or a voltage generated in the current detection winding,
Instruction value correction means for correcting an instruction value of a current obtained by the current detection means to [1 / N] according to the number of times N (N is a natural number) of penetration of the electric wire into the ring-shaped core. Characteristic current detection device. 2. The current detection device according to claim 1, wherein the number N of times that the electric wire penetrates the ring-shaped core is manually set to the indicated value correction unit in accordance with a current measurement mode.

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