JP2002328145A - Method and detector for detecting change of characteristic in analog filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove a factor of a measurement error by detecting a characteristic change resulting from the secular change of an analogue filter. SOLUTION: Plural electric power system signals are input into the plural analog filters 1-n having the same characteristic to remove unnecessary frequencies therein respectively, the plural electric power system signals are selection- input in order to a reference analog filter 13 having the characteristic same to those of the analog filters hereinbefore by a second mutiplexer 12 to remove the unnecessary frequencies, output signals from the respective filters are selected in order by a first multiplexer 11 to be output, the output signals are digital-converted by an A/D-converter 15, and an obtained digital signal value from the analog filter is compared with a digital signal value from the reference analog filter to determine the presence of the characteristic change of the analog filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a characteristic change of an analog filter for removing an unnecessary frequency of a power system signal in an analog measuring circuit having an A / D conversion function, and a detector used for the method. .

[0002]

2. Description of the Related Art Various power-related signals such as current, voltage, and power are measured during normal times and when an accident occurs. Such AC signals usually include a plurality of frequencies. ing. Therefore, when performing measurement, a frequency unnecessary for measurement is always removed through a filter, and measurement is performed by selecting a basic frequency. In this case, in recent years, a digital filter based on a digital operation is used. However, since an aliasing error due to digitization is caused, an analog filter is provided before and after the A / D converter to avoid the occurrence of the error. General.

Usually, since this analog filter is composed of an analog operational amplifier and passive components, aging of the amplifier-specific characteristics and aging of the passive-component characteristics occur, which causes measurement errors. Therefore, the following analog input circuit monitoring method has been devised.

[0004] Duplicate analog input circuit, A / D
A method for comparing conversion results. In this method, an input signal is input to two sets of analog filters, and the output signal is measured and monitored by two sets of A / D converters. Therefore, it is possible to monitor the characteristic deterioration of the analog input circuit in a specific frequency band. However, there is a disadvantage that only the relative monitoring of the same input signal can be performed, and at least a double analog filter is required.

[0005] Superimpose harmonics on the analog input circuit,
After A / D conversion, the digital filter separates the superimposed signal and checks the soundness. In this method, the absolute accuracy of the analog input circuit can be monitored because the superimposed signal is known, but it cannot be said that the method is sufficient for monitoring the characteristic deterioration in the measurement frequency band because the monitoring signal is a harmonic. .

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an analog filter capable of eliminating a measurement error factor by detecting a characteristic change due to aging of an analog filter for removing unnecessary frequencies of a power system signal. An object of the present invention is to provide a filter characteristic change detection method and an analog filter characteristic change detector.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and a plurality of power system signals are respectively inputted to a plurality of analog filters having the same characteristic to remove unnecessary frequencies. The second multiplexer sequentially selects and inputs the plurality of power-system signals to a reference analog filter having the same characteristics as the analog filter to remove unnecessary frequencies, and sequentially selects output signals from these filters with the first multiplexer. These output signals are digitally converted by an A / D converter, and the obtained digital signal value from the analog filter is compared with the digital signal value from the reference analog filter to change the characteristic of the analog filter. Characteristic change detection method of an analog filter, characterized by determining the presence or absence of The reference signal of a specific frequency was raised via the second multiplexer and the reference analog filter 1
While input to the multiplexer, the reference signal is directly input to the first multiplexer to the first multiplexer, and both output signals obtained are digitally converted by the A / D converter, and the obtained digital signal values are compared. Determining whether there is a change in the characteristic of the reference analog filter, and determining whether there is a change in the characteristic of the analog filter based on the determination. A plurality of analog filters having the same characteristics for inputting and removing the respective unnecessary frequencies; and a reference having the same characteristics as the analog filters for removing the unnecessary frequencies by sequentially selecting and inputting the plurality of power-system signals by a second multiplexer. An analog filter, a first multiplexer for sequentially selecting and outputting these output signals, and an output signal for these An A / D converter for digital conversion, and a comparison / judgment device for judging whether or not there is a characteristic change by comparing the obtained digital signal value from the analog filter with the digital signal value from the reference analog filter. And a characteristic change detector for an analog filter.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to FIG.

FIG. 1 shows a circuit for measuring various power system input signals (AC signals) 1 to n such as current, voltage, and power in a normal state or when an accident occurs.
, Analog filters 1 to n having the same characteristics are provided, and the analog filters 1 to n cut off high-frequency frequencies unnecessary for measurement.

Each input signal whose high frequency has been cut off is sequentially selected by a first multiplexer 11 and A / D
Output to converter 15. Here, the signal selection switching speed of the first multiplexer 11 is synchronized with the sampling frequency of the A / D converter 15. First multiplexer 1
The frequency of the input signal at 1 is basically an integral multiple of the AC measurement signal, for example, 60 Hz when the AC measurement signal is 50 Hz.
It is performed at 0 Hz or 1200 Hz.

Digitized by the A / D converter 15,
Since the obtained digital value still contains a harmonic component unnecessary for measurement, the harmonic component is arithmetically removed by the digital filter 16, the fundamental frequency component is extracted and stored in the storage unit 17 as a measured value, Output to the output unit 18.

On the other hand, the input signals 1 to n are sequentially selected by the second multiplexer 12 and input to the reference analog filter 13 to remove unnecessary frequencies. The reference analog filter 13 has the same characteristics as the analog filters 1 to n. The obtained output signal from the reference analog filter 13 is input to another channel of the first multiplexer 11, and is sequentially selected and output together with the output signals from the analog filters 1 to n, and these output signals are A / D converted. The digital conversion is performed by the unit 15. The obtained digital value is subjected to arithmetic operation and removal of a harmonic component by a digital filter 16, a fundamental frequency component is extracted and stored in a storage unit 17 as a measured value, and output to a measurement output unit 18 to calculate the measured value.

A comparison unit 19 compares the obtained digital signal values from the analog filters 1 to n and the digital signal values from the reference analog filter 13 to determine whether or not there is a change in the characteristics of the analog filters 1 to n. . The comparison between the digital signal values from the analog filters 1 to n and the digital signal values from the reference analog filter 13 is performed for each of the input signals 1 to n.
If the digital signal value from the analog filter 13 matches the digital signal value from the reference analog filter 13, it is determined that there is no change in the characteristics of the analog filters 1 to n. This determination is made every several seconds for the purpose of monitoring the characteristic change of the analog filters 1 to n. Therefore, the switching is performed at a speed sufficiently lower than the selection speed of the first multiplexer 11, for example, 2.5 Hz. Thereby, the first multiplexer 11 and the second multiplexer 11
The problem of the switching error in the synchronization with the multiplexer 12 is avoided.

Until now, the reference analog filter 13
Indicates that there is no change in the characteristics.
Although the presence / absence of the characteristic change of n has been determined, the reference analog filter 13 also undergoes a characteristic change due to aging or the like.

Therefore, the reference signal of a specific frequency generated from the reference signal generator 14 is passed through the second multiplexer 12 and the reference analog filter 13 to the first multiplexer 1.
1, while the reference signal is directly input to the first multiplexer 11, the obtained output signals are digitally converted by the A / D converter 15, and the obtained digital signal values are compared by the comparator 19. Reference analog filter 1
It is determined whether or not there is a change in the characteristic of No. 3. If the digital signal value obtained through the reference analog filter 13 matches the digital signal value obtained without passing through the reference analog filter 13, the reference analog filter 13
It is determined that there is no change in characteristics. Therefore, it can be concluded that the determination as to whether or not there is a change in the characteristics of each of the analog filters 1 to n based on the reference analog filter 13 is correct.

However, when the digital signal value obtained through the reference analog filter 13 does not match the digital signal value obtained without passing through the reference analog filter 13, the reference analog filter 13 has a characteristic change. Is determined. Therefore, the determination as to whether or not there is a change in the characteristics of each of the analog filters 1 to n based on the reference analog filter 13 is not correct, so that it is necessary to replace the reference analog filter 13 and perform the previous operation.

The A / D converter 15 and the power supply can be monitored by inputting an A / D reference signal and a power supply monitoring signal to the first multiplexer 11.

[0018]

According to the present invention, it is possible to reliably detect a characteristic change due to aging of an analog filter for removing an unnecessary frequency of a power system signal, and to eliminate a factor of a measurement error. , Accurate measurement becomes possible.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a characteristic change detector of an analog filter according to the present invention.

[Explanation of symbols]

 1 to n analog filter 11 first multiplexer 12 second multiplexer 13 reference analog filter 14 reference signal generator 15 A / D converter 16 digital filter 17 storage unit 18 measurement output unit 19 comparison unit 20 input circuit abnormality determination unit 21 alarm output Department

Continued on the front page (72) Inventor Toshihiko Okashita 5-7-4 Rakuen-en, Saeki-ku, Hiroshima-shi, Hiroshima Rakuen-Apartment A-204 (72) Inventor Takashi Ogawa 1-1-25, Kamikodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Pref. 203 Sanko Nogawa 203 (72) Inventor Shunji Nakagawa 2-2-17-605 Koyama, Sagamihara-shi, Kanagawa F-term (reference) 2G028 AA01 BD02 CG22 FK07 GL07 2G035 AA06 AD23 AD55 AD65 2G036 AA24 BA43

Claims (3)

[Claims] 1. A plurality of power-system signals are respectively input to a plurality of analog filters having the same characteristics to remove unnecessary frequencies, and the plurality of power-system signals are supplied to a reference analog filter having the same characteristics as the analog filters. Unnecessary frequencies are removed by sequentially selecting and inputting by the second multiplexer, output signals from these filters are sequentially selected and output by the first multiplexer, and these output signals are digitally converted by the A / D converter. A method for detecting a change in the characteristic of an analog filter, comprising comparing the digital signal value from the converted analog filter with the digital signal value from the reference analog filter to determine whether or not the characteristic of the analog filter has changed. . 2. A reference signal of a specific frequency generated from a reference signal generator is input to a first multiplexer via a second multiplexer and a reference analog filter, and the reference signal is directly input to the first multiplexer. The two output signals obtained are digitally converted by an A / D converter, and the obtained two digital signal values are compared to determine whether or not there is a change in the characteristics of the reference analog filter. 2. The method according to claim 1, wherein the presence or absence of the change is determined. 3. A plurality of analog filters for inputting a plurality of power-system signals and removing respective unnecessary frequencies, and sequentially selecting and inputting the plurality of power-system signals by a second multiplexer, thereby reducing unnecessary frequencies. A reference analog filter having the same characteristics as the analog filter for removing
A first multiplexer for sequentially selecting and outputting these output signals, and an A / D for digitally converting these output signals.
An analog converter comprising: a D converter; and a comparator / determiner for comparing the obtained digital signal value from the analog filter with the digital signal value from the reference analog filter to determine whether or not there is a change in characteristics. Filter characteristic change detector.