JP2661566B2 - Energy measurement circuit and digital energy meter - Google Patents
Energy measurement circuit and digital energy meterInfo
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- JP2661566B2 JP2661566B2 JP6283399A JP28339994A JP2661566B2 JP 2661566 B2 JP2661566 B2 JP 2661566B2 JP 6283399 A JP6283399 A JP 6283399A JP 28339994 A JP28339994 A JP 28339994A JP 2661566 B2 JP2661566 B2 JP 2661566B2
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- current transformer
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Description
【０００１】[0001]
【産業上の利用分野】本発明は商用電圧信号および負荷
電流信号をそれぞれディジタル化して乗算と積分をする
ことによって電力量を計測する電力量計測回路と電力量
計に関し、特に負荷電流信号を電圧信号に変換するため
に変流器を用いる電力量計測回路とディジタル電力量計
に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric energy measuring circuit and an electric energy meter for measuring an electric energy by digitizing and multiplying and integrating a commercial voltage signal and a load current signal, and more particularly, to converting a load current signal into a voltage. The present invention relates to an electric energy measurement circuit using a current transformer to convert a signal and a digital electric energy meter.
【０００２】[0002]
【従来の技術】従来用いられていたこの種の電力量計測
回路とディジタル電力量計のブロック構成図を図３に示
す。2. Description of the Related Art FIG. 3 shows a block diagram of a conventional watt-hour measuring circuit and a digital watt-hour meter.
【０００３】分圧器３１では計測する電路の３１Ｓと３
２Ｓ間に印加される電圧３Ｖ０が電子回路で扱えるレベ
ルの信号電圧３Ｖ１に分圧されてＡ／Ｄコンバータ３２
に供給される。Ａ／Ｄコンバータ３２では分圧器３１の
出力信号がディジタル信号３Ｖ２に変換されて乗算積分
回路３５に供給される。[0003] In the voltage divider 31, 31S and 3
The voltage 3V0 applied during the 2S is divided into a signal voltage 3V1 of a level that can be handled by the electronic circuit, and the A / D converter 32
Supplied to In the A / D converter 32, the output signal of the voltage divider 31 is converted into a digital signal 3V2 and supplied to the multiplication / integration circuit 35.
【０００４】変流器３３では負荷３ＺＬに応じて電路３
１Ｓと３２Ｌの間に流れる負荷電流３Ｉ０に比例した電
圧信号３Ｉ１が生成されてＡ／Ｄコンバータ３４に供給
される。Ａ／Ｄコンバータ３４では変流器３３の出力信
号がディジタル信号３Ｉ２に変換されて乗算積分回路３
５に供給される。In the current transformer 33, the electric circuit 3
A voltage signal 3I1 proportional to the load current 3I0 flowing between 1S and 32L is generated and supplied to the A / D converter 34. The A / D converter 34 converts the output signal of the current transformer 33 into a digital signal 3I2,
5 is supplied.
【０００５】乗算積分回路３５の乗算器３５ａではＡ／
Ｄコンバータ３２と３４から生成した１組のディジタル
信号３Ｖ２と３Ｉ２が乗算されて乗算結果が累積加減算
器３５ｂに出力される。累積加減算器３５ｂでは乗算回
路３５ａの乗算結果が積分されて計算回路３６に出力さ
れる。計算回路では累積加減算器の積分結果が計算され
て電力量に変換され表示部３７に出力される。The multiplier 35a of the multiplying and integrating circuit 35 uses A /
A set of digital signals 3V2 and 3I2 generated from the D converters 32 and 34 are multiplied, and the multiplication result is output to the accumulator 35b. The accumulator 35b integrates the multiplication result of the multiplication circuit 35a and outputs the result to the calculation circuit 36. The calculation circuit calculates the integration result of the accumulator, converts the result into an electric energy, and outputs the electric energy to the display unit 37.
【０００６】また、変流器の系統のＡ／Ｄコンバータで
発生する量子化雑音の影響を軽減するために、特開平２
−１７３５７７で示されているように、入力信号に電路
周波数と相関のない周波数の信号が付加されている場合
もある。In order to reduce the influence of quantization noise generated in an A / D converter of a current transformer system, Japanese Patent Laid-Open No.
As indicated by 173577, a signal having a frequency uncorrelated with the circuit frequency may be added to the input signal.
【０００７】[0007]
【発明が解決しようとする課題】従来のディジタル電力
量計では、変流器３３を励磁する励磁エネルギーが必要
でありそのため損失電力が発生し、負荷電流３Ｉ０が小
さいときにはその損失電力が相対的に大きくなって負荷
電流３Ｉ０に対応した出力信号３Ｉ１が生成されにくく
なり大きな誤差となって表示されるという問題点があっ
た。In the conventional digital watt-hour meter, the excitation energy for exciting the current transformer 33 is required, so that a loss power is generated. When the load current 3I0 is small, the loss power is relatively small. As a result, the output signal 3I1 corresponding to the load current 3I0 becomes difficult to be generated, and a large error is displayed.
【０００８】本発明の目的は、以上のような問題点を克
服し変流器の励磁エネルギーに起因する誤差を縮小し、
精度の高い電力量計測回路とディジタル電力量計を提供
することにある。SUMMARY OF THE INVENTION An object of the present invention is to overcome the above problems and reduce errors caused by the excitation energy of a current transformer.
An object of the present invention is to provide a highly accurate electric energy measuring circuit and a digital electric energy meter.
【０００９】[0009]
【課題を解決するための手段】本発明の電力量計測回路
は、分圧器と変流器と、それぞれのＡ／Ｄコンバータ
と、２系列のＡ／Ｄコンバータから生成した１組のディ
ジタル信号を乗算して積分する乗算積分回路と、積分結
果を電力量に変換する計算回路を有する電力量計測回路
において、変流器に電路の周波数と相関のない周波数の
交流磁界を生成させる回路を有し、変流器で電路の電流
によって生成した出力信号に、交流磁界によって生成し
た信号が重畳される。SUMMARY OF THE INVENTION An electric energy measuring circuit according to the present invention comprises a voltage divider, a current transformer, respective A / D converters, and a set of digital signals generated from two series of A / D converters. A power measuring circuit having a multiplying and integrating circuit for multiplying and integrating, and a calculating circuit for converting an integration result into a power amount, including a circuit for causing a current transformer to generate an AC magnetic field having a frequency uncorrelated with a frequency of an electric circuit. The signal generated by the AC magnetic field is superimposed on the output signal generated by the current in the current path in the current transformer.
【００１０】また、電力量計測回路の乗算積分回路は２
系列のＡ／Ｄコンバータから生成した１組のディジタル
信号を乗算する乗算回路と、乗算値を累積加算する累積
加減算器から構成され、計算回路が乗算積分回路の積分
が設定値に達するとパルスを発信して処理回路に出力す
るとともに累積加減算器の累積値から設定値が減算され
るパルス変換回路と、パルス変換回路から発信されたパ
ルスをカウントして計算しその結果を表示部に出力する
処理回路とから構成されている。[0010] The multiplication and integration circuit of the electric energy measuring circuit is 2
A multiplication circuit for multiplying a set of digital signals generated from a series A / D converter and a cumulative adder / subtractor for cumulatively adding the multiplied values are provided. When the integration of the multiplication / integration circuit reaches a set value, a pulse is generated. A pulse conversion circuit for transmitting and outputting to a processing circuit and subtracting a set value from a cumulative value of a cumulative adder / subtractor, and a process for counting and calculating pulses transmitted from the pulse conversion circuit and outputting the result to a display unit And a circuit.
【００１１】本発明のディジタル電力量計は前記の電力
量計測回路を有する。[0011] A digital watt-hour meter according to the present invention has the above-described power amount measuring circuit.
【００１２】[0012]
【作用】電路の周波数と相関のない周波数の電流から生
成される信号が変流器の出力信号に重畳されるので、負
荷電流によって変流器に生成した励磁エネルギーによる
損失に起因する誤差の影響が相対的に減少し、一方重畳
された信号は電路周波数と無関係な周波数なので、乗算
積分回路で電路の周波数の電圧信号との乗算と積分で平
均的には０となる。その結果電力量計算での誤差が減少
する。Since the signal generated from the current having a frequency uncorrelated with the frequency of the electric circuit is superimposed on the output signal of the current transformer, the influence of an error caused by the loss due to the excitation energy generated in the current transformer by the load current. Is relatively reduced, while the superimposed signal has a frequency irrelevant to the circuit frequency. Therefore, the multiplication and integration of the signal by the multiplication and integration with the voltage signal of the circuit frequency becomes 0 on average. As a result, errors in the calculation of the electric energy are reduced.
【００１３】[0013]
【実施例】次に、本発明の実施例について図面を参照し
て説明する。Next, embodiments of the present invention will be described with reference to the drawings.
【００１４】図１は本発明に係る実施例の電力量計測回
路と電力量計のブロック構成図である。 分圧器１０１
では計測する電路の１１Ｓと１２Ｓ間に印加される電圧
１Ｖ０が電子回路で扱えるレベルの信号電圧１Ｖ１に分
圧されて増幅回路１０２に供給される。増幅回路１０２
では分圧器１０１の出力信号が増幅されてフィルタ１０
３に供給される。フィルタ１０３では増幅回路１０２で
増幅された出力信号の不用周波数がカットされてＡ／Ｄ
コンバータ１０４に供給される。Ａ／Ｄコンバータ１０
４ではフィルタ１０３の出力信号がディジタル信号１Ｖ
２に変換されて乗算積分回路１０９に供給される。FIG. 1 is a block diagram of a watt hour meter and a watt hour meter according to an embodiment of the present invention. Voltage divider 101
Then, the voltage 1V0 applied between 11S and 12S of the electric circuit to be measured is divided into a signal voltage 1V1 of a level that can be handled by the electronic circuit and supplied to the amplifier circuit 102. Amplifier circuit 102
Then, the output signal of the voltage divider 101 is amplified and
3 is supplied. In the filter 103, unnecessary frequencies of the output signal amplified by the amplifier circuit 102 are cut and the A / D
It is supplied to a converter 104. A / D converter 10
4, the output signal of the filter 103 is a digital signal 1V
It is converted to 2 and supplied to the multiplication and integration circuit 109.
【００１５】変流器１０５では負荷１ＺＬに応じて電路
１１Ｓと１１Ｌとの間に流れる電流１Ｉ０を測定し、１
Ｉ０に比例した電圧信号１Ｉ１が生成される。The current transformer 105 measures a current 1I0 flowing between the electric circuits 11S and 11L according to the load 1ZL.
A voltage signal 1I1 proportional to I0 is generated.
【００１６】また負荷電流１Ｉ０によって変流器に生成
した励磁エネルギーにより発生する損失に起因する、電
圧信号１Ｉ１に対する誤差の影響を相対的に減少させる
目的で、交流発生回路１１２によって発生した、電路の
周波数と相関のない周波数の電流１ＩＥ０が、変流器１
０５に流されることによって交流磁界が生成される。そ
の交流磁界に対応して生成した電圧信号１ＩＥ１が電圧
信号１Ｉ１に重畳され増幅回路１０６に出力される。In order to relatively reduce the influence of an error on the voltage signal 1I1 due to the loss caused by the excitation energy generated in the current transformer due to the load current 1I0, the electric circuit generated by the AC generation circuit 112 The current 1IE0 having a frequency that is not correlated with the frequency is
05, an AC magnetic field is generated. Voltage signal 1IE1 generated corresponding to the AC magnetic field is superimposed on voltage signal 1I1 and output to amplification circuit 106.
【００１７】重畳された信号１ＩＥ１は電路周波数と無
関係の周波数なので、電路周波数の電圧信号１Ｖ２との
乗算積分回路での乗算と積分で平均的には０となり、電
力量計算には影響しない。Since the superimposed signal 1IE1 has a frequency irrelevant to the circuit frequency, the multiplication and integration of the voltage signal 1V2 of the circuit frequency by the multiplication and integration circuit becomes 0 on average, and does not affect the power amount calculation.
【００１８】増幅回路１０６では変流器１０５の出力信
号が増幅されてフィルタ１０７に供給される。フィルタ
１０７では増幅回路１０６で増幅された出力信号の不用
周波数がカットされてＡ／Ｄコンバータ１０８に供給さ
れる。Ａ／Ｄコンバータ１０８ではフィルタ１０７の出
力信号がディジタル信号１Ｉ２＋１ＩＥ２に変換されて
乗算積分回路１０９に供給される。In the amplifier circuit 106, the output signal of the current transformer 105 is amplified and supplied to the filter 107. In the filter 107, unnecessary frequencies of the output signal amplified by the amplifier circuit 106 are cut and supplied to the A / D converter 108. In the A / D converter 108, the output signal of the filter 107 is converted into a digital signal 1I2 + 1IE2 and supplied to the multiplication / integration circuit 109.
【００１９】乗算積分回路１０９の乗算器１０９ａでは
Ａ／Ｄコンバータ１０４と１０８から生成した１組のデ
ィジタル信号１Ｖ２と１Ｉ２＋１ＩＥ２が乗算されて乗
算結果が累積加減算器１０９ｂに出力される。累積加減
算器１０９ｂでは乗算器１０９ａの乗算結果が積分され
計算回路１１０に出力される。The multiplier 109a of the multiplication and integration circuit 109 multiplies a set of digital signals 1V2 and 1I2 + 1IE2 generated from the A / D converters 104 and 108, and outputs the multiplication result to the accumulator 109b. The accumulator 109b integrates the multiplication result of the multiplier 109a and outputs the result to the calculation circuit 110.
【００２０】計算回路１１０のパルス変換回路１１０ａ
では累積加減算器１０９ｂの積分値が設定値に達する
と、パルスを発信して処理回路１１０ｂに出力するとと
もに前記累積加減算器１０９ｂの積分値から前記設定値
が減算される。処理回路１１０ｂではパルス変換回路１
１０ａから発信されたパルスをカウントしてそのカウン
ト数にあらかじめ設定した係数を乗算して電力量を計算
しその結果を表示部１１１に出力する。表示部１１１で
は処理回路１１０ｂより入力した電力量を表示する。The pulse conversion circuit 110a of the calculation circuit 110
When the integrated value of the accumulator 109b reaches a set value, a pulse is transmitted and output to the processing circuit 110b, and the set value is subtracted from the integrated value of the accumulator 109b. In the processing circuit 110b, the pulse conversion circuit 1
The number of pulses transmitted from 10a is counted, and the number of counts is multiplied by a preset coefficient to calculate the amount of power, and the result is output to the display unit 111. The display unit 111 displays the amount of power input from the processing circuit 110b.
【００２１】図２は、変流器における入力電流と出力信
号の関係を示す図であり、図２（ａ）は従来例の場合
を、図２（ｂ）は実施例の場合を示す。FIG. 2 is a diagram showing the relationship between the input current and the output signal in the current transformer. FIG. 2A shows the case of the conventional example, and FIG. 2B shows the case of the embodiment.
【００２２】図２においては、比較のため電路電流によ
る磁界の振幅が磁気回路の保磁力以内の場合で説明して
いるが、保磁力以上であっても振幅の小さい場合は同種
の影響が発生する。In FIG. 2, the case where the amplitude of the magnetic field due to the electric circuit current is within the coercive force of the magnetic circuit is described for comparison. I do.
【００２３】図２（ａ）においては、電路電流３Ｉ０に
よる磁界の振幅が変流器３３の保磁力以内なので磁束は
発生せず、電路電流３Ｉ０があるのに出力信号３Ｉ１が
発生しない。In FIG. 2A, no magnetic flux is generated because the amplitude of the magnetic field due to the circuit current 3I0 is within the coercive force of the current transformer 33, and no output signal 3I1 is generated despite the presence of the circuit current 3I0.
【００２４】図２（ｂ）においては、図２（ａ）の電路
電流３Ｉ０に等しい電路電流１Ｉ０に交流発生回路１１
２によって発生した、電路の周波数と相関のない周波数
の電流１ＩＥ０が重畳されている。その結果発生する磁
界の振幅は変流器１０５の保磁力を大きく上回り、この
振幅に比例した磁束が発生し、出力信号１Ｉ１＋１ＩＥ
１も入力１Ｉ０＋１ＩＥ０に比例する。従って乗算積分
回路１０９で、重畳した１ＩＥ１成分が除去されれば、
電路電流１ＩＯに対応する出力信号１Ｉ１が生成する。In FIG. 2 (b), an AC circuit 11 is connected to a circuit current 1I0 equal to the circuit current 3I0 of FIG. 2 (a).
2, a current 1IE0 having a frequency uncorrelated with the frequency of the electric circuit is superimposed. The amplitude of the resulting magnetic field greatly exceeds the coercive force of the current transformer 105, and a magnetic flux proportional to this amplitude is generated, and the output signal 1I1 + 1IE
1 is also proportional to the input 1I0 + 1IE0. Therefore, if the superposed 1IE1 component is removed by the multiplication and integration circuit 109,
An output signal 1I1 corresponding to the circuit current 1IO is generated.
【００２５】[0025]
【発明の効果】電路の周波数と相関のない周波数から生
成される信号が、変流器の出力信号に重畳されるので、
負荷電流によって変流器に生成した励磁エネルギーによ
り発生する損失に起因する出力信号に対する誤差の影響
が相対的に減少し、一方重畳された信号は電路周波数と
無関係な周波数なので、乗算積分回路での電路周波数の
電圧信号との乗算と積分で平均的には０となり、最終的
に電力量計算での誤差が減少する。特に負荷電流の少な
い場合はその効果が大きい。According to the present invention, a signal generated from a frequency having no correlation with the frequency of an electric circuit is superimposed on an output signal of a current transformer.
The effect of the error on the output signal due to the loss caused by the excitation energy generated in the current transformer by the load current is relatively reduced, while the superimposed signal has a frequency independent of the circuit frequency, so that By multiplication and integration with the voltage signal of the circuit frequency, the average becomes 0, and finally the error in the calculation of the electric energy is reduced. In particular, when the load current is small, the effect is large.
【００２６】また、従来例で例示した特開平２−１７３
５７７で示されているように、入力信号に電路周波数と
相関のない周波数の信号が付加されると、Ａ／Ｄコンバ
ータで発生する量子化雑音の影響を軽減できるので、本
発明によってＡ／Ｄコンバータの精度も実質的に向上
し、さらに電力量計算での誤差が減少するという効果が
ある。Further, Japanese Patent Application Laid-Open No. 2-173 illustrated in the conventional example
As indicated by reference numeral 577, when an input signal is added with a signal having a frequency uncorrelated with the circuit frequency, the effect of quantization noise generated by the A / D converter can be reduced. There is an effect that the accuracy of the converter is substantially improved and the error in the calculation of the electric energy is reduced.
【図１】本発明の実施例のブロック構成図である。FIG. 1 is a block diagram of an embodiment of the present invention.
【図２】（ａ）は従来例の変流器における入力電流と出
力信号の関係を示す図である。（ｂ）は第１の実施例の
変流器における入力電流と出力信号の関係を示す図であ
る。FIG. 2A is a diagram illustrating a relationship between an input current and an output signal in a conventional current transformer. FIG. 3B is a diagram illustrating a relationship between an input current and an output signal in the current transformer according to the first embodiment.
【図３】従来例のブロック構成図である。FIG. 3 is a block diagram of a conventional example.
１０１ 分圧器 １０２ 増幅回路 １０３ フィルタ １０４ Ａ／Ｄコンバータ １０５ 変流器 １０６ 増幅回路 １０７ フィルタ １０８ Ａ／Ｄコンバータ １０９ 乗算積分回路 １０９ａ 乗算器 １０９ｂ 累積加減算器 １１０ 計算回路 １１０ａ パルス変換回路 １１０ｂ 処理回路 １１１ 表示部 １１２ 電路の周波数と相関のない周波数の交流発生
回路 ３１ 分圧器 ３２ Ａ／Ｄコンバータ ３３ 変流器 ３４ Ａ／Ｄコンバータ ３５ 乗算積分回路 ３５ａ 乗算器 ３５ｂ 累積加減算器 ３６ 計算回路 ３７ 表示部101 voltage divider 102 amplifying circuit 103 filter 104 A / D converter 105 current transformer 106 amplifying circuit 107 filter 108 A / D converter 109 multiplication / integration circuit 109a multiplier 109b accumulation adder / subtractor 110 calculation circuit 110a pulse conversion circuit 110b processing circuit 111 display Unit 112 AC generation circuit having a frequency uncorrelated with the frequency of the electric circuit 31 Voltage divider 32 A / D converter 33 Current transformer 34 A / D converter 35 Multiplication and integration circuit 35 a Multiplier 35 b Cumulative addition / subtraction unit 36 Calculation circuit 37 Display unit
Claims (2)
電流を測定する変流器と、 前記分圧器の出力信号をディジタル信号に変換する第１
のＡ／Ｄコンバータと、前記変流器の出力信号をディジ
タル信号に変換する第２のＡ／Ｄコンバータと、 前記
２系列のＡ／Ｄコンバータから生成した１組のディジタ
ル信号を乗算して積分する乗算積分回路と、積分結果を
電力量に変換する計算回路を有する電力量計測回路にお
いて、 前記変流器に前記電路の周波数と相関のない周波数の交
流磁界を生成させる回路を有し、前記変流器で電路の電
流によって生成した出力信号に、前記交流磁界によって
生成した信号が重畳されることを特徴とする電力量計測
回路。1. A voltage divider that divides a voltage of a circuit, a current transformer that measures a current in the circuit, and a first circuit that converts an output signal of the voltage divider into a digital signal.
A / D converter, a second A / D converter for converting an output signal of the current transformer into a digital signal, and a set of digital signals generated from the two series of A / D converters for integration A multiplication and integration circuit, and a power amount measurement circuit having a calculation circuit for converting an integration result into a power amount, comprising: a circuit for causing the current transformer to generate an AC magnetic field having a frequency uncorrelated with the frequency of the electric circuit, A power measurement circuit, wherein a signal generated by the AC magnetic field is superimposed on an output signal generated by a current in a current path in a current transformer.
るディジタル電力量計。2. A digital power meter with energy measurement circuit according to claim 1.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6283399A JP2661566B2 (en) | 1994-11-17 | 1994-11-17 | Energy measurement circuit and digital energy meter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6283399A JP2661566B2 (en) | 1994-11-17 | 1994-11-17 | Energy measurement circuit and digital energy meter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08146054A JPH08146054A (en) | 1996-06-07 |
| JP2661566B2 true JP2661566B2 (en) | 1997-10-08 |
Family
ID=17665023
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP6283399A Expired - Lifetime JP2661566B2 (en) | 1994-11-17 | 1994-11-17 | Energy measurement circuit and digital energy meter |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2661566B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102169139A (en) * | 2010-10-26 | 2011-08-31 | 江苏多维科技有限公司 | Independently packaged ammeter sensor |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100335136B1 (en) * | 2000-01-31 | 2002-05-04 | 이종수 | Apparatus of signal transformation |
| KR100880563B1 (en) * | 2007-06-12 | 2009-01-30 | 윤희복 | Digital Power Transducer |
| WO2009125627A1 (en) | 2008-04-11 | 2009-10-15 | 三菱電機株式会社 | Equipment state detecting apparatus, equipment state detecting method, family member accident detecting apparatus, family member accident detecting system, and family member accident detecting method |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5838747B2 (en) * | 1978-06-09 | 1983-08-25 | 三菱電機株式会社 | Electronic energy meter |
| JPH01158365A (en) * | 1987-09-24 | 1989-06-21 | Fuji Electric Co Ltd | Method and apparatus for detecting small current |
-
1994
- 1994-11-17 JP JP6283399A patent/JP2661566B2/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102169139A (en) * | 2010-10-26 | 2011-08-31 | 江苏多维科技有限公司 | Independently packaged ammeter sensor |
| CN102169139B (en) * | 2010-10-26 | 2014-04-16 | 江苏多维科技有限公司 | Independently packaged ammeter sensor |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH08146054A (en) | 1996-06-07 |
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