JP2929197B2 - Insulation resistance measurement method that compensates for the effect of ground resistance - Google Patents
Insulation resistance measurement method that compensates for the effect of ground resistanceInfo
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- JP2929197B2 JP2929197B2 JP23696488A JP23696488A JP2929197B2 JP 2929197 B2 JP2929197 B2 JP 2929197B2 JP 23696488 A JP23696488 A JP 23696488A JP 23696488 A JP23696488 A JP 23696488A JP 2929197 B2 JP2929197 B2 JP 2929197B2
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- insulation resistance
- frequency
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- resistance
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Description
【発明の詳細な説明】 （産業上の利用分野） 本発明は電路等の絶縁抵抗を測定する方法，殊に対地
浮遊容量大なる場合無視し得なくなる接地抵抗の影響を
補償した絶縁抵抗測定方法に関する。The present invention relates to a method for measuring the insulation resistance of an electric circuit or the like, and more particularly to a method for measuring the insulation resistance which compensates for the influence of ground resistance which cannot be ignored when the stray capacitance to ground is large. About.
（従来技術） 従来，漏電等の早期発見の為には第２図に示す如き電
路の絶縁抵抗測定方法を用いるのが一般的であった。(Prior Art) Conventionally, a method of measuring insulation resistance of an electric circuit as shown in FIG. 2 has been generally used for early detection of electric leakage or the like.
即ち,Zなる負荷を有する受電変圧器Ｔの第２種接地線
LEを介して発振器OSCから商用周波数と異なった周波数
１なる測定用低周波信号電圧を電路L1及びL2に印加
し，前記接地線LEを貫通する変流器ZCTによって絶縁抵
抗Ｒ及び浮遊容量Ｃを介して帰還する漏洩電流を検出す
る。That is, the second-class ground wire of the receiving transformer T having a load of Z
Commercial frequency and different frequency from the oscillator OSC via the L E
Applying a low-frequency signal voltage 1 becomes measurement paths L 1 and L 2, the current transformer ZCT that passes through the ground line L E detects a leakage current is fed back through the insulation resistance R and the stray capacitance C.
この際前記変流器ZCTの出力に含まれる周波数１の
成分をフィルタFILTにて検出しその漏洩電流を例えば前
記発振器OSCの出力を用いて掛算器MULTで同期検波して
有効分電流を分離して得，これによって電路の絶縁抵抗
を測定するものであった。At this time, the component of frequency 1 contained in the output of the current transformer ZCT is detected by the filter FILT, and the leakage current is synchronously detected by the multiplier MULT using, for example, the output of the oscillator OSC to separate an effective current. This was used to measure the insulation resistance of the circuit.
その測定理論を第３図の等価回路を用いて更に説明す
るならば前記接地線LEの接地点Ｅを介して前記発振器OS
Cに帰還する電流をＩとすると であるから印加する測定信号電圧と同相の成分，即ち上
記（１）式右辺第１項に比例した値を同期検波等の手法
を用いて検出すれば絶縁抵抗Ｒに逆比例した測定値を得
るものである。The oscillator OS through the ground point E of the measurement theory third the ground line if further described with reference to the equivalent circuit of Figure L E
If the current returning to C is I Therefore, if a component in phase with the applied measurement signal voltage, that is, a value proportional to the first term on the right side of the above equation (1) is detected by using a technique such as synchronous detection, a measured value inversely proportional to the insulation resistance R is obtained. Things.
しかしながら上記（１）式からも明らかな如くこの測
定法は接地線LEに大地を介して帰還する電流を測定する
にも拘らず接地抵抗を無視しているので対地浮遊容量Ｃ
が大きくなると接地抵抗の影響が現われ測定値が現実の
電路の絶縁抵抗とはなはだしくかけ離れたものとなる，
即ち正確な絶縁抵抗の測定が不可能になるという欠陥が
あった。However, since this measurement technique as is apparent from the above equation (1) is ignored even though not ground resistance to measure the current fed back through the earth to the ground line L E ground stray capacitance C
Becomes larger, the effect of the grounding resistance appears, and the measured value is far from the actual insulation resistance of the electric circuit.
That is, there is a defect that accurate measurement of insulation resistance becomes impossible.
（発明の目的） 本発明は上記欠点に鑑みなされたものであって，対地
浮遊容量Ｃの影響を受けることなく正確な絶縁抵抗測定
を行なう絶縁抵抗測定方法を提供することを目的とす
る。(Object of the Invention) The present invention has been made in view of the above-mentioned drawbacks, and has as its object to provide an insulation resistance measuring method for performing an accurate insulation resistance measurement without being affected by the stray capacitance C to the ground.
（発明の概要） この目的を達成するために本発明の絶縁抵抗測定方法
は電路に商用周波数と異なる周波数１なる低周波の測
定信号電圧を印加し，接地線に帰還する周波数１の漏
洩電流中の有効分並びに無効分を検出すると共に上記電
路と大地間の周波数１の電圧を検出し，該周波数１
の電圧と上記測定信号電圧との位相差を得，前記有効分
に前記無効分と前記位相差との積を加算することにより
絶縁抵抗を測定するよう手段を講ずる。(Summary of the Invention) In order to achieve this object, the insulation resistance measuring method of the present invention applies a low-frequency measurement signal voltage having a frequency 1 different from the commercial frequency to an electric circuit, and returns the frequency 1 leakage current to the ground line. detects the active component and reactive component detects the voltage of the frequency 1 between the path and the ground, the frequency 1
Means for measuring the insulation resistance by obtaining the phase difference between the above-mentioned voltage and the measurement signal voltage, and adding the product of the above-mentioned ineffective part and the above-mentioned phase difference to the above-mentioned effective part.
（実施例） 以下本発明を図面に示す実施例とに基づいて詳細に説
明する。(Examples) Hereinafter, the present invention will be described in detail based on examples shown in the drawings.
先ず，本発明に係る絶縁抵抗測定方法を説明する前
に，その理解を助ける為従来の手法の欠陥を少しく詳細
に説明する。First, before describing the insulation resistance measuring method according to the present invention, the defects of the conventional method will be described in some detail in order to help the understanding.
第４図は接地抵抗γを考慮した場合の等価回路図であ
る。FIG. 4 is an equivalent circuit diagram when the ground resistance γ is considered.
この場合接地点Ｅを介して発振器OSCに帰還する電流
をI1としこれを とする。このとき， であり（２）式で接地抵抗γを無視すれば前記（１）式
と同一になることはいうまでもない。A current feedback to the oscillator OSC through this grounding point E and I 1 to this And At this time, It goes without saying that if the ground resistance γ is neglected in the equation (2), it becomes the same as the equation (1).
さて，（３）式において，対地浮遊容量Ｃ＝０のとき
Ａは となるが一般にＲ≫γであるからＡは1/Rと考えてよく
前記（２）式の同相分はV/Rとなり，同相分を検出する
ことにより絶縁抵抗を測定することができる。しかし浮
遊容量Ｃが大きいときには同相分を検出しても（３）式
で示される如く正しく絶縁抵抗を測定していないことに
なる。Now, in equation (3), when stray capacitance to ground C = 0, A is However, since R≫γ generally, A can be considered as 1 / R, and the in-phase component in the above equation (2) becomes V / R, and the insulation resistance can be measured by detecting the in-phase component. However, when the stray capacitance C is large, even if the in-phase component is detected, the insulation resistance is not correctly measured as shown by the equation (3).
このような誤差が実際上どの程度になるかを以下に示
す。The following shows how much such an error actually occurs.
一般にＲ≫γであるから（３）式においてＲ＋γ→Ｒ
とすると と表し得る。In general, since R≫γ, in equation (3), R + γ → R
Then It can be expressed as
ここで例えば１＝20Hz,C＝５μF,γ＝100Ωとする
と （ω1Cγ）２＝（２π×20×５×10-6×100）２ 3.95×10-3 となり（ω1Cγ）２≪１である。Here, for example, if 1 = 20 Hz, C = 5 μF, γ = 100Ω, (ω 1 Cγ) 2 = (2π × 20 × 5 × 10 −6 × 100) 2 3.95 × 10 -3 and (ω 1 Cγ) 2 ≪ It is one.
したがって（４）式は とみなしてよい。Therefore, equation (4) is May be considered.
従って，例えば１＝20Hz,C＝５μF,R＝100KΩ，γ
＝100Ωの場合前記（５）式の｛ ｝内は １＋（ω1C）2Rγ＝4.95 となり，同相分から検出されるべき絶縁抵抗値100KΩは
100KΩ/4.95＝20.2KΩ として測定されてしまうこと
になる。Therefore, for example, 1 = 20 Hz, C = 5 μF, R = 100 KΩ, γ
In the case of = 100Ω, the value in {} of the above equation (5) is 1+ (ω 1 C) 2 Rγ = 4.95, and the insulation resistance value 100KΩ to be detected from the in-phase component is
It will be measured as 100KΩ / 4.95 = 20.2KΩ.
斯くの如く，従来の接地抵抗を無視した絶縁抵抗測定
方法では対地浮遊容量が大きい場合極めて測定誤差が大
きくなる欠陥を有すること前述の通りである。更に対地
浮遊容量には一般電子機器の電源回路に付加されるノイ
ズフィルタのキャパシタンスも含まれるので今後対地浮
遊容量は大きくなっていく傾向にあるから従来の方法で
はますます正確な測定結果が得られないことになる。As described above, as described above, the conventional insulation resistance measurement method ignoring the ground resistance has a defect that the measurement error becomes extremely large when the ground stray capacitance is large. Furthermore, since the stray capacitance to the ground includes the capacitance of the noise filter added to the power supply circuit of general electronic equipment, the stray capacitance to the ground tends to increase in the future, so that more accurate measurement results can be obtained by the conventional method. Will not be.
この問題を解決する為本発明に於いては以下の如き手
法をとる。In order to solve this problem, the present invention employs the following method.
即ち、周波数f1の印加信号によって得られる漏洩電流
の同相分をig1とすると前記（２）式及び（５）式から が得られる。That is, the in-phase component of the leakage current obtained by applying the signal of frequency f 1 from the to and ig 1 (2) and Formula (5) Is obtained.
一方，（３）式から印加信号と90゜位相のずれた成分
Ｂは であり，又，一般にＲ≫γであるため と表わされ，更には（ω1Cγ）２≪１であるので Ｂω1C ………（７） となるので接地抵抗γの影響は実用上ほとんど受けない
ことになる。On the other hand, from the equation (3), the component B shifted by 90 ° from the applied signal is And because in general R≫γ Further, since (ω 1 Cγ) 2 ≪1, Bω 1 C (7) is satisfied, so that the effect of the ground resistance γ is hardly practically affected.
従って周波数f1の印加信号によって得られる漏洩電流
の無効分をig2とすれば（２）式及び（７）式から ig2＝VB sinω1t ＝ω1CV sinω1t ………（８） ところで電路と大地間に存在する周波数１の電圧Ｅ
は Ｅ＝Ｖ−I1γ ………（９） であり，（６），（８）式から漏洩電流I1は と表されるから（10）式を（９）式に代入すると となり，γ/R≪1,（ω1Cγ）２≪１であるので Ｅ＝（１−ｊω1Cγ）Ｖ ………（12） が得られる。電路と大地間に存在する周波数１の電圧
Ｅと測定信号電圧Ｖとの位相差は tan＝−ω1Cγでありω1Cγ≪１であるため ＝−ω1Cγ ………（13） となる。Therefore, if the reactive component of the leakage current obtained by applying the signal of frequency f 1 and ig 2 (2) ig from the equation and (7) 2 = VB sinω 1 t = ω 1 CV sinω 1 t ......... (8 By the way, the voltage E of frequency 1 existing between the electric circuit and the ground
Is E = V−I 1 γ (9). From equations (6) and (8), the leakage current I 1 is Substituting equation (10) into equation (9) Since γ / R≪1, (ω 1 Cγ) 2 ≪1, E = (1−jω 1 Cγ) V (12) is obtained. The phase difference between the voltage E of frequency 1 existing between the electric circuit and the ground and the measurement signal voltage V is tan = −ω 1 Cγ and ω 1 Cγ≪1, so that = −ω 1 Cγ (13) Become.
したがって，（６）式のig1に（８）式のig2と（13）
式のの積を加算すると となるので接地抵抗γの影響なく絶縁抵抗を測定しうる
ことが分かる。Therefore, ig 1 in Eq. (6) is replaced with ig 2 in Eq.
Adding the products of the expressions It can be seen that the insulation resistance can be measured without being affected by the ground resistance γ.
上述したような理論に基づいて測定を実際に行なうた
めには以下の如くすればよい。In order to actually perform the measurement based on the above-described theory, the following may be performed.
第１図は本発明に係る絶縁抵抗測定方法を実現する為
の回路の一実施例を示す図である。FIG. 1 is a diagram showing one embodiment of a circuit for realizing the insulation resistance measuring method according to the present invention.
即ち，接地線LEに周波数１なる低周波信号発生用の
発振器OSCを直列に接続して、電圧Ｖなる電圧を印加す
る。一方前記零相変流器ZCT出力を周波数１成分を検
出するフィルタFILTに印加して，商用周波成分と分離し
該フィルタFILTの出力を第１の同期検波回路MULT1の一
方の入力端に入力せしめると共に前記発振器OSCの出力
を第１の同期検出回路MULT1の第２の入力端に入力せし
める。かくして第１の同期検波回路MULT1の出力から前
述の（６）式に相当する漏洩電流の有効分ig1が得ら
れ、この出力を第１のローパスフィルタLPF1に印加し直
流分のみを得れば、 が得られる。That is, by connecting the oscillator OSC for low-frequency signal generator comprising a frequency 1 to the ground line L E in series to apply a voltage composed voltage V. On the other hand, the output of the zero-phase current transformer ZCT is applied to a filter FILT for detecting one frequency component, separated from the commercial frequency component, and the output of the filter FILT is input to one input terminal of a first synchronous detection circuit MULT1. At the same time, the output of the oscillator OSC is input to the second input terminal of the first synchronization detection circuit MULT1. Thus, from the output of the first synchronous detection circuit MULT 1 , an effective component ig 1 of the leakage current corresponding to the above equation (6) is obtained, and this output is applied to the first low-pass filter LPF 1 to obtain only the DC component. If Is obtained.
一方，前記フィルタFILTの出力を分岐して第２の同期
検波回路MULT2の一方の入力端に入力せしめると共に前
記発振器OSCの出力を移送器PSに印加して90゜位相を推
移せしめその出力を第２の同期検波回路MULT2の第２の
入力端に入力せしめる。かくして、第２の同期検波回路
MULT2出力から前述の（８）式に相当する漏洩電流の無
効分ig2が得られ、この出力を第２のローパスフィルタL
PF2に印加し直流分のみを得れば、 ▲▼＝ω1CV ………（16） なる。On the other hand, the second with inputting the imagewise signal to one input terminal of the synchronous detection circuit MULT 2 is applied the output of the oscillator OSC to the conveying device PS and allowed changes the phase by 90 degrees the output branches the output of the filter FILT allowed to input to the second synchronous second input of the detection circuit MULT 2. Thus, the second synchronous detection circuit
An ineffective component ig2 of the leakage current corresponding to the above equation (8) is obtained from the MULT 2 output, and this output is used as the second low-pass filter L
If applied to the PF 2 you get only the DC component, ▲ ▼ = ω 1 CV ......... (16) made.
更に接地側電路L2と大地E3との間の電圧Ｅを高入力イ
ンピーダンス増幅器Ａで検出し，その出力を位相差検出
のためのかけ算器MULT3の一方の入力端に印加し，他方
の入力端には発振器OSC出力を印加する。Further it detects a voltage E between the ground-side electrical path L 2 and the ground E 3 with a high input impedance amplifier A, and applies the output to one input terminal of the multiplier MULT 3 for phase difference detection, the other An oscillator OSC output is applied to the input terminal.
斯くして前記かけ算器MULT3の出力をローパスフィル
タLPF3に加えることにより得る直流分は−1/2 ωCrV2と
なり、（13）式に相当する位相差φに比例した値とな
る。これは（12）式からも明らかなように電圧Ｅの振幅
は〔１＋（ω1Cγ）２〕1/2１であるから電路と大地
間に存在する周波数１の電圧Ｅと測定用低周波信号電
圧Ｖとの大きさは変わらないが位相のみだけシフトし
ているので、発振器OSC出力と高入力インピーダンス増
幅器Ａの出力に得られる周波数f1の電圧Ｅとを用いるこ
とにより位相差φを得るものである。Thus to DC component is -1/2 ωCrV 2 next obtained by adding an output of said multiplier MULT3 low-pass filter LPF 3, a value proportional to the phase difference φ corresponding to (13). This is because the amplitude of the voltage E is [1+ (ω 1 Cγ) 2 ] 1/2 1 as is apparent from the equation (12), so that the voltage E of the frequency 1 existing between the electric circuit and the ground and the low frequency for measurement Since the magnitude of the signal voltage V does not change but is shifted only by the phase, the phase difference φ is obtained by using the output of the oscillator OSC and the voltage E of the frequency f 1 obtained at the output of the high input impedance amplifier A. Things.
次に図示を省略するがローパスフィルタLPF3の出力を
予め1/2 V2で割ることにより位相差φを求め、これをか
け算器MULT4の一入力端に印加し、他の入力端にはロー
パスフィルタLPF2の出力を印加すれば該MULT4の出力は
▲▼×となり該MULT4出力を加算器ADDに印加す
ると共に更に該加算器ADDにローパスフィルタLPF1の出
力を加えることにより加算器ADDの出力OUTは となるので絶縁抵抗を測定することが可能となる。Next, although not shown, the output of the low-pass filter LPF 3 is divided in advance by 1/2 V 2 to obtain a phase difference φ, which is applied to one input terminal of the multiplier MULT 4 and is applied to the other input terminals. low pass output by applying the output of the filter LPF 2 the MULT 4 is ▲ ▼ further adder by adding the output of the low pass filter LPF 1 to the adder ADD as well as applied to the adder ADD to × next the MULT 4 output ADD output OUT is Therefore, the insulation resistance can be measured.
尚，実施例に於いては説明簡単の為単相２線の場合を
示したが本発明はこれに限定る必然性は全くなく一端接
地の単相３線或は３相３線の場合であっても同一の原理
に基づいて実施可能なことは明らかであろう。In the embodiment, the case of a single-phase two-wire is shown for the sake of simplicity. However, the present invention is not necessarily limited to this case. However, it is apparent that the present invention can be implemented based on the same principle.
なお，上記実施例においては零相電流の検出に零相変
流器を用いているが接地線LEを切断しこれを低抵抗を直
列接続しこの抵抗の両端電圧をもって零相電流を検出し
てもよい。また電路への低周波電圧の印加に当っては接
地線LEを切断しこれに発振器を直列に挿入接続するので
はなく，接地線を発振器出力のトランスを貫通させる等
してもよい。高入力インピーダンス増幅器Ａの出力に大
きな商用周波成分が含まれるときは，商用周波成分除去
フィルタを増幅器Ａと同期検波器MULT3の一方の入力間
に入れることがのぞましい。Incidentally, to detect the zero-phase current with detecting is used the zero-phase current transformer disconnect the ground line L E low resistance which are connected in series to the voltage across the resistance of the zero-phase current in the above embodiments You may. Also, instead of the hitting to the application of the low-frequency voltage to the electric path to insert connecting the oscillator to cut the ground line L E in series, may be such as to penetrate the transformer oscillator output ground line. When a large commercial frequency component included in the output of the high input impedance amplifier A, it is desirable to put the commercial frequency component removal filter between one input of the amplifier A and the synchronous detector MULT 3.
（発明の効果） 本発明は以上説明した如き手法によって電路の絶縁抵
抗を測定するものであるから接地抵抗の影響を完全にキ
ャンセルすることが可能となるのみならず発振器等の出
力抵抗の影響をも接地抵抗に加味して補償するので対地
浮遊容量が大きい電路等の絶縁抵抗を正確に測定する上
で著しい効果を発揮する。(Effects of the Invention) Since the present invention measures the insulation resistance of the electric circuit by the method described above, it is possible not only to completely cancel the influence of the ground resistance but also to reduce the influence of the output resistance of the oscillator and the like. Also, the compensation is performed in consideration of the ground resistance, so that a remarkable effect is exhibited in accurately measuring the insulation resistance of an electric circuit or the like having a large floating capacitance to the ground.
第１図は本発明に係る絶縁抵抗測定方法を実現する為の
一実施例を示すブロック図，第２図は従来の絶縁抵抗測
定方法を説明する図，第３図は等価回路図，第４図は接
地抵抗を考慮した場合の等価回路図である。 Ｔ……変圧器,L1及びL2……電路,LE……接地線,OSC……
発振器,LPF1,2,3……ローパスフィルタ,ADD……加算器,
FILT……フィルタ,PS……90゜移相器,A……高入力イン
ピーダンス増幅器。FIG. 1 is a block diagram showing an embodiment for realizing an insulation resistance measuring method according to the present invention, FIG. 2 is a diagram for explaining a conventional insulation resistance measuring method, FIG. 3 is an equivalent circuit diagram, FIG. The figure is an equivalent circuit diagram when the ground resistance is considered. T ...... transformer, L 1 and L 2 ...... paths, L E ...... ground line, OSC ......
Oscillator, LPF 1 , 2 , 3 …… Low-pass filter, ADD …… Adder,
FILT …… Filter, PS …… 90 ° phase shifter, A …… High input impedance amplifier.
Claims (1)
周波の測定信号電圧を印加し、前記測定信号電圧及びこ
れを90゜位相シフトしたものにて接地線から抽出した信
号を同期検波して接地線に帰還する漏洩電流中の有効分
並びに無効分をそれぞれ検出すると共に上記電路と大地
間の電圧と上記測定信号電圧との位相差を検出し、前記
有効分に前記無効分と前記位相差との積を加算すること
により絶縁抵抗を測定することを特徴とした接地抵抗の
影響を補償した絶縁抵抗測定方法。1. A low-frequency measurement signal voltage having a frequency f1 different from the commercial frequency is applied to an electric circuit, and the measurement signal voltage and a signal obtained by shifting the phase of the measurement signal voltage by 90.degree. The effective component and the ineffective component in the leakage current that returns to the ground line are detected, and the phase difference between the voltage between the electric circuit and the ground and the measurement signal voltage is detected, and the ineffective component and the phase difference are detected in the effective component. And measuring the insulation resistance by adding the product of the two.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23696488A JP2929197B2 (en) | 1988-09-21 | 1988-09-21 | Insulation resistance measurement method that compensates for the effect of ground resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23696488A JP2929197B2 (en) | 1988-09-21 | 1988-09-21 | Insulation resistance measurement method that compensates for the effect of ground resistance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0283461A JPH0283461A (en) | 1990-03-23 |
| JP2929197B2 true JP2929197B2 (en) | 1999-08-03 |
Family
ID=17008376
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP23696488A Expired - Fee Related JP2929197B2 (en) | 1988-09-21 | 1988-09-21 | Insulation resistance measurement method that compensates for the effect of ground resistance |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2929197B2 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103713198A (en) * | 2014-01-08 | 2014-04-09 | 国家电网公司 | Method for measuring phase to phase mutual impedance of long-distance extra-high voltage common-tower double-circuit transmission line |
| CN103713198B (en) * | 2014-01-08 | 2016-11-30 | 国家电网公司 | A kind of distance extra-high voltage same tower double circuit transmission line of electricity mutual impedance measuring method |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4914233B2 (en) | 2007-01-31 | 2012-04-11 | 富士重工業株式会社 | Outside monitoring device |
-
1988
- 1988-09-21 JP JP23696488A patent/JP2929197B2/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103713198A (en) * | 2014-01-08 | 2014-04-09 | 国家电网公司 | Method for measuring phase to phase mutual impedance of long-distance extra-high voltage common-tower double-circuit transmission line |
| CN103713198B (en) * | 2014-01-08 | 2016-11-30 | 国家电网公司 | A kind of distance extra-high voltage same tower double circuit transmission line of electricity mutual impedance measuring method |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0283461A (en) | 1990-03-23 |
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