JPH07239351A - Frequency-analyzing apparatus - Google Patents

Abstract

PURPOSE:To measure a frequency of a to-be-measured signal in a short time by analyzing higher harmonics included in the signal. CONSTITUTION:The apparatus is constituted of a higher harmonic-selecting means for selecting a higher harmonic signal of n-th order of frequency of a to-be-measured signal, a sampling means 1 for sampling the selected higher harmonic signal for a predetermined time, an extracting means 4 for processing the sampled value by an FFT frequency analysis thereby to extract a frequency of the maximum frequency component, and a calculating means 6 for dividing the extracted frequency of the maximum frequency component by the (n) and calculating the frequency of the to-be-measured signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a fast Fourier transform (FF
TECHNICAL FIELD The present invention relates to a frequency measuring device using T: Fast Fourier Transform), and more particularly to a frequency measuring device for a target signal to be measured, for example, a railway signal containing noise of a predetermined harmonic component caused by a commercial power source.

[0002]

2. Description of the Related Art The present applicant has previously filed Japanese Patent Application Laid-Open No. 5-1368.
It is known to use FFT to analyze frequencies, as proposed in the '34 publication.

In this type of conventional frequency analysis, sampling is performed at a sampling frequency (fs / 2) which is at least twice the maximum frequency of the signal under measurement (fs), and the sampled value is subjected to FFT analysis. .

To further explain, it is assumed that the signal under measurement is based on 50H as shown in FIG. When measuring with an accuracy of 50 ± 0.1 Hz, sampling is performed for at least 1 / 0.1 = 10 (seconds) and the sample is subjected to FFT analysis.

FIG. 2 (b) is a table of the results of the FFT analysis, in which the amplitude of 49.9 Hz (1.1 V) is the largest,
Therefore, this 49.9 Hz is determined as the frequency of the signal under measurement.

[0006]

By the way, the above-mentioned conventional frequency measurement is performed when the measurement accuracy is set to 50 ± 0.1 Hz. When this is set to 50 ± 0.01 Hz, the sampling time is , At least 1 / 0.01 = 1
In addition to requiring 00 (seconds), there is a problem in that the time required for FFT analysis becomes longer as the number of samplings increases.

Therefore, the present invention has been made in order to solve such a problem. For example, when measuring the frequency of a railway signal, the signal contains known harmonic noise. It is noted that the harmonic component is used to provide a frequency measuring device that can measure with higher accuracy if the processing time is shorter than that of the conventional device or if the processing time is the same as that of the conventional device. It is an object.

[0008]

In order to achieve the above object, a frequency measuring device according to the present invention comprises a harmonic selecting means for selecting a harmonic signal having an nth frequency of the frequency of a signal under measurement, Sampling means for sampling the selected harmonic signal for a predetermined time, extracting means for performing FFT frequency analysis on the sampled value to extract the frequency of the maximum frequency component, and the frequency of the extracted maximum frequency component calculating means for calculating the frequency of the signal under measurement by dividing it by the nth order.

[0009]

In the above structure, the calculating means performs FFT frequency analysis on the value obtained by sampling the harmonic signal selected by the sampling means for a predetermined time to obtain the frequency of the maximum frequency component, The frequency of the signal under measurement is calculated by dividing by the order, that is, the nth order.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a frequency measuring device according to an embodiment, and here, an example of measuring the frequency of a signal flowing through an overhead line L is shown.

As shown in FIG. 4, the overhead line L is
It is assumed that a signal based on 50 Hz is supplied. In addition, this signal includes a plurality of harmonics of a number due to a commercial power source, for example, (100 Hz, 150 Hz, 200
It is assumed that it is known that Hz ... Is included as noise. Then, in the apparatus of this embodiment, the 10th order 500 Hz is selected from these harmonics and is used for the frequency analysis described later. It should be noted that, in general, the actual train control signal contains harmonics caused by the commercial power supply.

In the figure, T is a transformer for stepping down the signal supplied to the overhead line L to a predetermined value, and F is a harmonic wave of 500 Hz.
A bandpass filter for selecting peripheral signals, 1 is a sampling circuit for sampling the output signal of the bandpass filter 1, 2 is an A / D converter for converting the sampled analog signal into a digital value, and 3 is a digital value. The first buffer circuit, 4 is a well-known FFT frequency analyzer, 5 is a second buffer circuit for storing the result of the FFT frequency analysis, and 6 is the order of harmonics (10 in this embodiment).
It is a division circuit that divides a predetermined harmonic in (next).

Next, the frequency measuring operation of the apparatus of this embodiment will be described with reference to the flowchart of FIG.

First, it is assumed that the signal (measured signal) supplied to the overhead line L is 50 Hz, and this signal is measured with an accuracy of 50 ± 0.1 Hz. In addition, the specific harmonic to be selected is the tenth 500th of the frequency (50Hz) of the signal under measurement.
Hz is set, and the filter characteristic of the bandpass filter F and the constant of the division circuit 6 are set (step 100, step 102, hereinafter step is referred to as S).

Therefore, the sampling circuit 1 has 500
The analog signal near Hz is sampled, and the A / D converter 2 converts the sampled analog signal into a digital signal. This digital signal is stored in the first buffer circuit 3. These processes are performed for a preset time. In this example, it is 1 second (S104,
S106). The sampling frequency is at least twice the maximum frequency fs (fs / 2) as in the conventional case.

The FFT analyzer 4 analyzes the sampling value stored in the first buffer 3 according to a predetermined algorithm, and the result is obtained as a frequency component and an amplitude as shown in FIG. 2 (a). Corresponding data is stored in the second buffer circuit 5 (S108).

Next, the division circuit 6 selects the frequency with the largest amplitude among the values stored in the second buffer circuit 5, and divides this by the harmonic order (10th order). And outputs the measured value of the frequency (110, S11
2).

In the example of FIG. 2A, 499 Hz is the maximum, and this value is divided by the order (10th order) to obtain 499/10.
= 49.9 Hz is output.

The measurement result of 49.9 Hz is the sampling time of 1 second, and the sampling time of 10 seconds in FIG.
It shows that it has the same accuracy as the conventional measurement result of second.

As described above, the apparatus of this embodiment is designed to analyze the harmonics and measure the frequency, so that the processing time can be shortened. Further, if the time is the same as the conventional one, the accuracy of the measured value can be increased.

In the above-mentioned embodiment, the selected harmonic is the 10th order 500 Hz, but it may be higher or lower. If it is 10th order or more, the processing time is further shortened.

[0021]

The frequency measuring device according to the present invention comprises a harmonic selecting means for selecting a harmonic signal having an nth frequency of the frequency of the signal under measurement, and a sampling for sampling the selected harmonic signal for a predetermined time. Means for performing FFT frequency analysis on the sampled value to extract the frequency of the maximum frequency component, and dividing the frequency of the extracted maximum frequency component by the nth order to determine the frequency of the signal under measurement. Since it is composed of a calculating means for calculating, the processing time can be shortened and the frequency can be measured with the same degree of accuracy as the conventional one, and when the processing time of the same degree is satisfied, the frequency can be measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a frequency measuring device according to an embodiment of the present invention.

FIG. 2 (a) shows the FFT analysis result of the present invention,
(B) is a table showing a conventional FFT analysis result.

FIG. 3 is a flowchart showing a measurement operation.

FIG. 4 is a signal waveform diagram that flows through an overhead line.

[Explanation of symbols]

 1 A / D converter 2 Sampling circuit 3 1st buffer circuit 4 FFT analysis circuit 5 2nd buffer circuit 6 Division circuit T transformer F Bandpass filter l Overhead line

Claims (1)

[Claims] 1. Harmonic selection means for selecting a harmonic signal having an nth frequency of the frequency of the signal under measurement, sampling means for sampling the selected harmonic signal for a predetermined time, and FFT of the sampled value. Extraction means for performing frequency analysis to extract the frequency of the maximum frequency component; and calculation means for dividing the frequency of the extracted maximum frequency component by the nth order to calculate the frequency of the signal under measurement. A frequency measuring device characterized by.