JP3975647B2

JP3975647B2 - Analog input circuit monitoring method

Info

Publication number: JP3975647B2
Application number: JP2000141207A
Authority: JP
Inventors: 進森谷; 弘晃長阪
Original assignee: Meidensha Corp
Current assignee: Meidensha Corp
Priority date: 2000-05-15
Filing date: 2000-05-15
Publication date: 2007-09-12
Anticipated expiration: 2020-05-15
Also published as: JP2001327062A

Description

【０００１】
【発明の属する技術分野】
本発明は、アナログ入力回路の動作の正常／異常を監視する監視方式に関する。
【０００２】
【従来の技術】
電力系統の保護継電装置は、例えば、系統の電圧や電流を検出し、これら信号を基に送配電線の地絡や短絡事故を判定し、系統保護出力を得る。このような保護継電装置は、アナログ方式とディジタル方式があるが、いずれの方式にしても電流や電圧の検出にはアナログ入力回路が必要となる。
【０００３】
この種のアナログ入力回路の故障は、事故検出不能になるし、事故波及の原因になるため、従来から監視回路や点検回路が設けられている。
【０００４】
図４は、従来の監視方式を示し、ディジタル方式の保護継電装置に適用されるものである。電圧等の検出信号になる外部入力は、電力系統の一定周波数ｆを有して補助変流器等から取り込まれ、この入力信号をアナログ入力回路（Ａ／Ｉ）１で適当な電圧信号に変換およびサンプル・ホールドされ、Ａ／Ｄ変換器２によってディジタル値に変換され、このディジタル値を保護継電用コンピュータに１つの検出データとして保護演算に供する。
【０００５】
このアナログ入力回路の監視には、基本周波数ｆになる外部入力に対し、監視入力信号としてその高調波（図示では第３高調波ｆ₃）を重畳させてアナログ入力回路１に注入し、Ａ／Ｄ変換器２のディジタル出力に対してコンピュータのソフトウェア構成などで構成するディジタルフィルタ３を通すことで、Ａ／Ｄ変換器２のディジタル出力に含まれる第３高調波成分を取り出し、ソフトウェア構成などにされる判定部４によりフィルタ３の出力ｆ_3OUTと注入した第３高調波信号ｆ_3INとの絶対値差分が監視幅εより小さいか否かの判定、すなわち
【０００６】
【数１】
｜ｆ_3OUT−ｆ_3IN｜≦ε
からアナログ入力回路１の正常／異常を監視する。
【０００７】
なお、アナログ方式の保護継電装置の監視の場合、アナログ入力回路１の出力からアナログフィルタ回路を使用して第３高調波を取り出し、監視入力信号との絶対値差分を得る構成になる。
【０００８】
【発明が解決しようとする課題】
電力系統では避雷動作や負荷状態などによっては、外部入力ｆに第３高調波ｆ_3IN’が含まれることがある。この場合、注入した監視入力ｆ_3INに第３高調波ｆ_3IN’がランダムな位相で加算されることになる。このとき、フィルタ３の出力もｆ_3OUTからｆ_3OUT’に変化する。このときの判定は、
【０００９】
【数２】
｜ｆ_3OUT−（ｆ_3IN±ｆ_3IN’）｜≦ε
から正常／異常を判定することになり、アナログ入力回路が正常にもかかわらず異常と判定したり、逆に異常にもかかわらず正常と判定する問題があった。
【００１０】
本発明の目的は、外部入力に含まれる高調波信号と監視入力信号とが同等の周波数成分をもつ場合にもアナログ入力回路の正常／異常を確実に判定できる監視方式を提供することにある。
【００１１】
【課題を解決するための手段】
本発明は、監視入力になる高調波信号を一時的に取り除き、この状態でアナログ入力回路の出力に含まれる高調波信号を取り出すことで外部入力に含まれる高調波信号の有無やレベルを求め、この高調波信号で判定部の判定結果の真偽判定や正常な判定ができるようにしたもので、以下の方式を特徴とする。
【００１２】
一定の基本周波数の外部入力をもつアナログ入力回路の入力に高調波の監視入力を重畳させておき、該アナログ入力回路の出力に含まれる該高調波の有無またはレベルから前記アナログ入力回路の正常／異常を監視するアナログ入力回路の監視方式であって、
前記アナログ入力回路の入力に重畳させる前記監視入力を遮断できるスイッチ手段と、
前記アナログ入力回路の正常／異常の判定結果が異常になったとき、前記スイッチ手段により監視入力を一時的に遮断させ、この遮断時の該アナログ入力回路の出力から前記外部入力に前記監視入力と同じ高調波が含まれるか否か、または高調波レベルを判定し、この判定により前記判定結果の真／偽を判定する監視処理手段とを備えたことを特徴とする。
【００１３】
また、一定の基本周波数の外部入力をもつアナログ入力回路の入力に高調波の監視入力を重畳させておき、該アナログ入力回路の出力に含まれる該高調波の有無またはレベルから前記アナログ入力回路の正常／異常を監視するアナログ入力回路の監視方式であって、
前記アナログ入力回路の入力に重畳させる前記監視入力を遮断できるスイッチ手段と、
前記スイッチ手段により監視入力を定期的に遮断させ、この遮断時の該アナログ入力回路の出力から前記外部入力に前記監視入力と同じ高調波が含まれるか否か、または高調波レベルを判定しておき、前記アナログ入力回路の正常／異常の判定結果が異常になったとき、前記高調波の有無またはレベルにより該判定結果の真／偽を判定する監視処理手段とを備えたことを特徴とする。
【００１４】
また、一定の基本周波数の外部入力をもつアナログ入力回路の入力に高調波の監視入力を重畳させておき、該アナログ入力回路の出力に含まれる該高調波の有無またはレベルから前記アナログ入力回路の正常／異常を監視するアナログ入力回路の監視方式であって、
前記アナログ入力回路の入力に重畳させる前記監視入力を遮断できるスイッチ手段と、
前記スイッチ手段により監視入力を定期的に遮断させ、この遮断時の該アナログ入力回路の出力から前記監視入力と同じ高調波のレベルを判定し、この高調波レベルを前記アナログ入力回路の正常／異常の判定のための監視幅に含ませておく監視処理手段とを備えたことを特徴とする。
【００１５】
また、一定の基本周波数の外部入力をもつアナログ入力回路の入力に高調波の監視入力を重畳させておき、該アナログ入力回路の出力に含まれる該高調波の有無またはレベルから前記アナログ入力回路の正常／異常を監視するアナログ入力回路の監視方式であって、
前記アナログ入力回路の入力に重畳させる前記監視入力を遮断できるスイッチ手段と、
前記スイッチ手段により監視入力を定期的に遮断させ、この遮断時の該アナログ入力回路の出力から前記監視入力と同じ高調波のレベルを判定し、この高調波レベルを前記監視入力に含ませておく監視処理手段とを備えたことを特徴とする。
【００１６】
【発明の実施の形態】
図１は、本発明の実施形態を示す監視回路であり、図４と同等の部分は同一符号で示す。
【００１７】
図１において、スイッチ部５は、外部信号に重畳させる監視入力ｆ_3INを一時的に遮断するためのものである。ソフトウェア構成される監視処理部６は、判定部４の判定結果が異常になった場合に、スイッチ部５を一時的にオフ（遮断）制御し、このときにフィルタ３の出力から外部入力ｆに含まれる第３高調波ｆ_3IN’を取り出し、この第３高調波ｆ_3IN’の有無またはレベルをチェックし、このチェックで判定部４の判定結果の真／偽を判定、つまりアナログ入力回路１の正常／異常を監視する。
【００１８】
図２は、監視処理部６による監視処理タイムチャートを示す。監視処理部６は、通常時にはスイッチ部５をオンさせておき、この状態で判定部４の判定結果がアナログ入力回路１の異常とする判定になったとき、スイッチ部５をオンからオフに切り替える。この状態で、監視処理部６は、フィルタ３の出力ｆ_3OUTを取り出す。このときのフィルタ３の出力ｆ_3OUTは、外部入力に含まれる第３高調波ｆ_3IN’になり、この信号ｆ_3IN’のレベルから監視処理部６が判定部４の判定結果の真／偽を判定する。
【００１９】
すなわち、外部入力に含まれる第３高調波ｆ_3IN’のレベルがある値以上に高いときは、判定部４の判定結果が「偽」と判定し、判定部４の出力を「正常」に復帰させると共に、スイッチ部５をオフからオンに戻し、アナログ入力回路１の監視を再開させる。逆に、外部入力に含まれる第３高調波ｆ_3IN’のレベルがある値に満たない場合、判定部４の判定結果が「真」と判定し、アナログ入力回路１の異常として判定部４の出力を有効にする。
【００２０】
監視処理部６による判定部４の出力の有効／無効の処理は、例えば、フラグを使用してコンピュータ側に転送したり、判定部４の判定出力に抑止回路を設ける構成で実現される。
【００２１】
また、監視処理は、判定部４の判定結果が異常になる度に行い、「偽」の判定が一定回数継続するか否かで有効／無効の処理を行うことで、外部入力に一時的に第３高調波が含まれる場合の誤った判定を防止できる。
【００２２】
図３は、他の実施形態を示す監視処理タイムチャートである。同図では、判定部４の判定が「正常」にある状態で定期的に監視処理を実行するものである。監視処理部６は、スイッチ部５を定期的にオフさせ、この状態でフィルタ３の出力ｆ_3OUTを取り出し、この信号ｆ_3OUTのレベル、すなわち外部入力に第３高調波ｆ_3IN’がどの程度含まれているかを判定・記憶しておく。
【００２３】
これにより、その後にスイッチ部５をオンさせた監視状態で、判定部４に異常が発生したときに、監視処理部６が直前に記憶する外部入力に含まれる第３高調波ｆ_3IN’のレベルの大小から判定部４の判定結果の真／偽を判定することができる。これにより、判定部４の出力の真／偽を迅速に判定することができる。
【００２４】
なお、図３に示すタイムチャートによる監視処理において、取り出した第３高調波ｆ_3IN’を判定部４の判定式に含ませておくこともできる。つまり、監視幅εを
【００２５】
【数３】
｜ｆ_3IN＋ｆ_3IN’｜＝ε’
としておき、この監視幅ε’で判定部４が判定を行う。これにより、判定部４の出力の真／偽を迅速に判定することができるし、監視幅εを厳格に設定することで判定精度を高めることができる。
【００２６】
また、図３に示すタイムチャートによる監視処理において、取り出した第３高調波ｆ_3IN’のレベルに応じて監視入力ｆ_3INのレベルを切り替え、または連続的に変更しておくこともできる。つまり、監視幅εを
【００２７】
【数４】
｜Δｆ_3IN＋ｆ_3IN’｜＝ε’
としておき、この監視幅ε’で判定部４が判定を行う。この場合も、判定部４の出力の真／偽を迅速に判定することができるし、監視幅εを厳格に設定することで判定精度を高めることができる。
【００２８】
なお、以上までの実施形態の監視方式をアナログ方式のアナログ入力回路に適用する場合、アナログ入力回路１の出力から第３高調波を抽出するフィルタを設け、この出力から第３高調波のレベルを判定することで実現される。
【００２９】
また、監視入力は、第３高調波に限らず、第５高調波などにすることができるし、複数の高調波を組み合わせた判定とすることができる。
【００３０】
また、実施形態では、保護継電装置のアナログ入力回路に適用した場合を示すが、外部入力が系統電流など一定周波数になるアナログ入力回路、例えば各種計測装置のアナログ入力回路に適用して同等の作用を効果を得ることができる。
【００３１】
【発明の効果】
以上のとおり、本発明によれば、監視入力になる高調波信号を一時的に取り除き、この状態でアナログ入力回路の出力に含まれる高調波信号を取り出すことで外部入力に含まれる高調波信号の有無やレベルを求め、この高調波信号で判定部の判定結果の真偽判定や正常な判定ができるようにしたため、外部入力に含まれる高調波信号と監視入力信号とが同等の周波数成分をもつ場合にもアナログ入力回路の正常／異常を確実に判定できる。
【図面の簡単な説明】
【図１】本発明の実施形態を示す監視回路の構成図。
【図２】実施形態における監視処理タイムチャート。
【図３】他の実施形態における監視処理タイムチャート。
【図４】従来の監視方式の例。
【符号の説明】
１…アナログ入力回路
２…Ａ／Ｄ変換器
３…フィルタ
４…判定部
５…スイッチ部
６…監視処理部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a monitoring method for monitoring normal / abnormal operation of an analog input circuit.
[0002]
[Prior art]
The power system protective relay device detects, for example, the voltage and current of the system, determines a ground fault and a short-circuit accident of the transmission and distribution lines based on these signals, and obtains a system protection output. Such a protective relay device includes an analog system and a digital system, but an analog input circuit is required for detection of current and voltage in any system.
[0003]
A failure of this type of analog input circuit makes it impossible to detect an accident and causes an accident to spread, so a monitoring circuit and an inspection circuit are conventionally provided.
[0004]
FIG. 4 shows a conventional monitoring method, which is applied to a digital protective relay device. An external input that becomes a detection signal such as a voltage has a constant frequency f of the power system and is taken in from an auxiliary current transformer or the like, and this input signal is converted into an appropriate voltage signal by the analog input circuit (A / I) 1. The digital value is sampled and held and converted into a digital value by the A / D converter 2, and this digital value is supplied to the protective relay computer as one detection data for a protection operation.
[0005]
For monitoring the analog input circuit, the harmonic (as shown in the figure, the third harmonic f ₃ ) is superimposed on the external input having the fundamental frequency f and injected into the analog input circuit 1 as the monitoring input signal. The third harmonic component contained in the digital output of the A / D converter 2 is extracted by passing the digital filter 3 configured by the software configuration of the computer with respect to the digital output of the D converter 2, and the software configuration or the like is obtained. The determination unit 4 determines whether the absolute value difference between the output f _3OUT of the filter 3 and the injected third harmonic signal f _3IN is smaller than the monitoring width ε, that is,
[Expression 1]
| F _3OUT −f _3IN | ≦ ε
The analog input circuit 1 is monitored for normality / abnormality.
[0007]
In the case of monitoring of the analog type protective relay device, the third harmonic is extracted from the output of the analog input circuit 1 using an analog filter circuit, and an absolute value difference from the monitoring input signal is obtained.
[0008]
[Problems to be solved by the invention]
In the electric power system, the third harmonic f _3IN ′ may be included in the external input f depending on the lightning protection operation or the load state. In this case, the third harmonic f _3IN ′ is added to the injected monitoring input f _3IN with a random phase. At this time, the output of the filter 3 is also changed from f _3Out to f _3Out '. The judgment at this time is
[0009]
[Expression 2]
| F _3OUT − (f _3IN ± f _3IN ') | ≦ ε
Therefore, there is a problem that it is determined that the analog input circuit is abnormal even if the analog input circuit is normal, or conversely, it is determined that the analog input circuit is normal regardless of the abnormality.
[0010]
An object of the present invention is to provide a monitoring system that can reliably determine whether the analog input circuit is normal or abnormal even when the harmonic signal included in the external input and the monitoring input signal have equivalent frequency components.
[0011]
[Means for Solving the Problems]
The present invention temporarily removes the harmonic signal that becomes the monitoring input, and in this state takes out the harmonic signal included in the output of the analog input circuit to obtain the presence or level of the harmonic signal included in the external input, This harmonic signal can be used to determine whether the determination result of the determination unit is authentic or normal, and is characterized by the following method.
[0012]
A harmonic monitoring input is superimposed on the input of an analog input circuit having an external input of a fixed fundamental frequency, and the analog input circuit is detected from the presence / absence or level of the harmonic included in the output of the analog input circuit. An analog input circuit monitoring method for monitoring abnormalities,
Switch means capable of interrupting the monitoring input to be superimposed on the input of the analog input circuit;
When the normal / abnormal judgment result of the analog input circuit becomes abnormal, the monitoring input is temporarily interrupted by the switch means, and the monitoring input is connected to the external input from the output of the analog input circuit at the time of the interruption. It is characterized by comprising monitoring processing means for determining whether or not the same harmonics are included, or determining a harmonic level and determining whether the determination result is true or false.
[0013]
Further, a harmonic monitoring input is superimposed on an input of an analog input circuit having an external input of a constant fundamental frequency, and the presence or level of the harmonic contained in the output of the analog input circuit is used to determine whether the analog input circuit An analog input circuit monitoring method for monitoring normality / abnormality,
Switch means capable of interrupting the monitoring input to be superimposed on the input of the analog input circuit;
The monitoring input is periodically interrupted by the switch means, and whether the same harmonics as the monitoring input are included in the external input from the output of the analog input circuit at the time of the interruption, or the harmonic level is determined. And a monitoring processing means for determining true / false of the determination result based on the presence / absence or level of the harmonic when the analog input circuit normal / abnormal determination result is abnormal. .
[0014]
Further, a harmonic monitoring input is superimposed on an input of an analog input circuit having an external input of a constant fundamental frequency, and the presence or level of the harmonic contained in the output of the analog input circuit is used to determine whether the analog input circuit An analog input circuit monitoring method for monitoring normality / abnormality,
Switch means capable of interrupting the monitoring input to be superimposed on the input of the analog input circuit;
The monitoring input is periodically interrupted by the switch means, and the same harmonic level as the monitoring input is determined from the output of the analog input circuit at the time of the interruption, and this harmonic level is determined as normal / abnormal in the analog input circuit. And a monitoring processing means included in the monitoring width for the determination.
[0015]
Further, a harmonic monitoring input is superimposed on an input of an analog input circuit having an external input of a constant fundamental frequency, and the presence or level of the harmonic contained in the output of the analog input circuit is used to determine whether the analog input circuit An analog input circuit monitoring method for monitoring normality / abnormality,
Switch means capable of interrupting the monitoring input to be superimposed on the input of the analog input circuit;
The monitoring means is periodically interrupted by the switch means, the same harmonic level as the monitoring input is determined from the output of the analog input circuit at the time of the interruption, and this harmonic level is included in the monitoring input. And a monitoring processing means.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a monitoring circuit showing an embodiment of the present invention, and parts equivalent to those in FIG. 4 are denoted by the same reference numerals.
[0017]
In FIG. 1, a switch unit 5 is for temporarily blocking a monitoring input f _3IN to be superimposed on an external signal. When the determination result of the determination unit 4 becomes abnormal, the monitoring processing unit 6 configured by software temporarily controls the switch unit 5 to be turned off (blocked). At this time, the output of the filter 3 is changed to the external input f. The third harmonic f _3IN ′ included is taken out and the presence or level of the third harmonic f _3IN ′ is checked, and the true / false of the determination result of the determination unit 4 is determined by this check, that is, the analog input circuit 1 Monitor normal / abnormal.
[0018]
FIG. 2 shows a monitoring processing time chart by the monitoring processing unit 6. The monitoring processing unit 6 normally turns on the switch unit 5, and switches the switch unit 5 from on to off when the determination result of the determination unit 4 is determined to be abnormal in the analog input circuit 1 in this state. . In this state, the monitoring processing unit 6 takes out the output f _{3OUT of the} filter 3. The output f _3OUT of the filter 3 at this time becomes the third harmonic f _3IN ′ included in the external input, and the monitoring processing unit 6 determines _whether the determination result of the determination unit 4 is true / false from the level of the signal f _3IN ′. judge.
[0019]
That is, when the level of the third harmonic f _3IN ′ included in the external input is higher than a certain value, the determination result of the determination unit 4 is determined to be “false”, and the output of the determination unit 4 is returned to “normal”. At the same time, the switch unit 5 is returned from off to on, and the monitoring of the analog input circuit 1 is resumed. On the other hand, when the level of the third harmonic f _3IN ′ included in the external input is less than a certain value, the determination result of the determination unit 4 is determined to be “true” and the analog input circuit 1 is regarded as abnormal. Enable output.
[0020]
The processing for validating / invalidating the output of the determination unit 4 by the monitoring processing unit 6 is realized by, for example, a configuration in which a flag is used to transfer to the computer side or a determination circuit is provided for the determination output of the determination unit 4.
[0021]
In addition, the monitoring process is performed every time the determination result of the determination unit 4 becomes abnormal, and a valid / invalid process is performed depending on whether or not the “false” determination continues for a certain number of times, thereby temporarily receiving an external input. An erroneous determination when the third harmonic is included can be prevented.
[0022]
FIG. 3 is a monitoring processing time chart showing another embodiment. In the figure, the monitoring process is periodically executed in a state where the determination of the determination unit 4 is “normal”. The monitoring processing unit 6 periodically turns off the switch unit 5 and _takes out the output f _3OUT of the filter 3 in this state, and the level of this signal f _3OUT , that is, how much the third harmonic f _3IN ′ is included in the external input Judgment is made and memorized.
[0023]
As a result, the level of the third harmonic f _3IN ′ included in the external input stored immediately before by the monitoring processing unit 6 when an abnormality occurs in the determination unit 4 in the monitoring state in which the switch unit 5 is subsequently turned on. The true / false of the determination result of the determination unit 4 can be determined from the size of. Thereby, the true / false of the output of the determination part 4 can be determined rapidly.
[0024]
In the monitoring process using the time chart shown in FIG. 3, the extracted third harmonic f _3IN ′ can be included in the determination formula of the determination unit 4. That is, the monitoring width ε is
[Equation 3]
| F _3IN + f _3IN '| = ε'
Then, the determination unit 4 performs the determination with the monitoring width ε ′. Thereby, the true / false of the output of the determination part 4 can be determined rapidly, and determination accuracy can be improved by setting the monitoring width | variety strict.
[0026]
In the monitoring process using the time chart shown in FIG. 3, the level of the monitoring input f _3IN can be switched or continuously changed according to the level of the extracted third harmonic f _3IN ′. In other words, the monitoring width ε
[Expression 4]
| Δf _3IN + f _3IN '| = ε ′
Then, the determination unit 4 performs the determination with the monitoring width ε ′. Also in this case, the true / false of the output of the determination unit 4 can be quickly determined, and the determination accuracy can be improved by strictly setting the monitoring width ε.
[0028]
In addition, when applying the monitoring method of the above embodiment to an analog type analog input circuit, a filter for extracting the third harmonic from the output of the analog input circuit 1 is provided, and the level of the third harmonic is determined from this output. It is realized by judging.
[0029]
In addition, the monitoring input is not limited to the third harmonic, but may be a fifth harmonic or the like, or may be determined by combining a plurality of harmonics.
[0030]
In addition, the embodiment shows a case where the present invention is applied to an analog input circuit of a protective relay device. The effect can be obtained.
[0031]
【The invention's effect】
As described above, according to the present invention, the harmonic signal serving as the monitoring input is temporarily removed, and in this state, the harmonic signal included in the external input is extracted by extracting the harmonic signal included in the output of the analog input circuit. Presence / absence and level are obtained, and the determination result of the determination unit can be determined with this harmonic signal, and normal determination can be performed. Even in this case, it is possible to reliably determine whether the analog input circuit is normal or abnormal.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a monitoring circuit showing an embodiment of the present invention.
FIG. 2 is a monitoring processing time chart according to the embodiment.
FIG. 3 is a monitoring processing time chart according to another embodiment.
FIG. 4 shows an example of a conventional monitoring method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Analog input circuit 2 ... A / D converter 3 ... Filter 4 ... Determination part 5 ... Switch part 6 ... Monitoring processing part

Claims

A harmonic monitoring input is superimposed on the input of an analog input circuit having an external input of a fixed fundamental frequency, and the analog input circuit is detected from the presence / absence or level of the harmonic included in the output of the analog input circuit. An analog input circuit monitoring method for monitoring abnormalities,
Switch means capable of interrupting the monitoring input to be superimposed on the input of the analog input circuit;
When the normal / abnormal judgment result of the analog input circuit becomes abnormal, the monitoring input is temporarily interrupted by the switch means, and the monitoring input is connected to the external input from the output of the analog input circuit at the time of the interruption. A monitoring method for an analog input circuit, comprising: monitoring processing means for determining whether or not the same harmonic is included, or determining a harmonic level and determining whether the determination result is true or false.

A harmonic monitoring input is superimposed on the input of an analog input circuit having an external input of a fixed fundamental frequency, and the analog input circuit is detected from the presence / absence or level of the harmonic included in the output of the analog input circuit. An analog input circuit monitoring method for monitoring abnormalities,
Switch means capable of interrupting the monitoring input to be superimposed on the input of the analog input circuit;
The monitoring input is periodically interrupted by the switch means, and whether the same harmonics as the monitoring input are included in the external input from the output of the analog input circuit at the time of the interruption, or the harmonic level is determined. And a monitoring processing means for determining true / false of the determination result based on the presence / absence or level of the harmonic when the analog input circuit normal / abnormal determination result is abnormal. Analog input circuit monitoring method.

A harmonic monitoring input is superimposed on the input of an analog input circuit having an external input of a fixed fundamental frequency, and the analog input circuit is detected from the presence / absence or level of the harmonic included in the output of the analog input circuit. An analog input circuit monitoring method for monitoring abnormalities,
Switch means capable of interrupting the monitoring input to be superimposed on the input of the analog input circuit;
The monitoring input is periodically interrupted by the switch means, and the same harmonic level as the monitoring input is determined from the output of the analog input circuit at the time of the interruption, and this harmonic level is determined as normal / abnormal in the analog input circuit. A monitoring method for an analog input circuit, comprising: a monitoring processing unit included in a monitoring width for the determination.

A harmonic monitoring input is superimposed on the input of an analog input circuit having an external input of a fixed fundamental frequency, and the analog input circuit is detected from the presence / absence or level of the harmonic included in the output of the analog input circuit. An analog input circuit monitoring method for monitoring abnormalities,
Switch means capable of interrupting the monitoring input to be superimposed on the input of the analog input circuit;
The monitoring means is periodically interrupted by the switch means, the same harmonic level as the monitoring input is determined from the output of the analog input circuit at the time of the interruption, and this harmonic level is included in the monitoring input. An analog input circuit monitoring method, comprising: a monitoring processing means.