JPH0915273A - Measuring method for fundamental frequency and measuring device - Google Patents

Abstract

PURPOSE: To provide a measuring method and a device for it of fundamental wave component frequency, in which the measuring accuracy of this fundamental wave component frequency of input signal has been improved. CONSTITUTION: This measuring device is provided with a waveform shaping means 13 imparting a high harmonic component without varying a fundamental wave component frequency in an input signal, an FFT processing means 20 processing an output signal of the waveform shaping means 13 into a fast Fourier transform(FFT), and an operational means 20 measuring the frequency of N-th (integers of more than 2) order higher harmonic constituent data among output data of this FFT processing means 20, dividing this measured value with (n) and seeking the frequency of a fundamental wave component in the input signal, respectively. Therefore, measuring errors is reducible to 1/n.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fundamental wave component frequency measuring method and measuring apparatus suitable for an FFT analyzer.

[0002]

2. Description of the Related Art An FFT (Fast Fourier Transform) analyzer is
It is a typical device for analyzing the frequency component of an input signal. FIG. 3 is a block diagram showing the configuration of a conventional FFT analysis device. An analog input signal is supplied to an ADC (analog / digital converter) 14 via an input terminal 10 and an input circuit 12, converted into time domain waveform data, and stored in a memory 16. The waveform data in the time domain is sent to the μP 20 via the bus 18 and the FFT operation is executed. The system memory 22 is a ROM storing software for the μP 20 and a RAM required for operation.
Contains. The frequency domain data obtained by the FFT calculation is sent to the display memory in the display circuit 24, and the frequency component of the input signal is displayed on the display 26 such as a CRT based on the data in the display memory. The user operates the operation panel 28 to control the operation of this device.

[0003]

Since the frequency value of the data in the frequency domain obtained by the FFT operation processing processing includes a certain error determined by the sampling frequency, the frequency of the fundamental wave component of the input signal can be accurately determined. It was difficult to measure.

An object of the present invention is to provide a method and a device for measuring the frequency of the fundamental wave component, which improves the measurement accuracy of the frequency of the fundamental wave component of the input signal.

[0005]

SUMMARY OF THE INVENTION The present invention is a fundamental frequency measuring method using an FFT analysis technique, in which a fundamental frequency component of an input signal is not changed and is shaped into a signal waveform to which a harmonic component is added. , Of the data obtained by FFT processing of this signal, the frequency of the harmonic component data of the n (integer of 2 or more) order is measured, and this measured value is divided by the above n to obtain the fundamental wave component of the above input signal. It is characterized by measuring the frequency of.

Further, the fundamental wave component frequency measuring apparatus of the present invention includes a waveform shaping means for imparting a harmonic component without changing the fundamental frequency component of the input signal, and an FFT processing of the output signal of the waveform shaping means. Of the output data of the FFT processing means, and the frequency of the harmonic component data of the n (integer of 2 or more) order among the output data of the FFT processing means.
And a calculating means for calculating the frequency of the fundamental wave component of the input signal.

[0007]

1 is a block diagram showing the configuration of an embodiment of an FFT analysis apparatus suitable for applying the fundamental wave frequency measuring method and measuring apparatus of the present invention. Elements corresponding to the conventional example in FIG. 3 are denoted by the same reference numerals. The difference between the conventional device of FIG. 3 and the device of FIG. 1 is that the waveform shaping circuit 13 is inserted between the input circuit 12 and the ADC 14. The waveform shaping circuit 13 may be, for example, a circuit that compares the output signal of the input circuit 12 with a predetermined reference level and supplies a rectangular wave pulse train that is the comparison output to the ADC 14. When the analog input signal is a pure sine wave signal, the frequency component is only the fundamental wave component. Therefore, if the frequency of the fundamental wave component is measured, the measurement error Δfo determined by the sampling frequency is inevitable. Therefore, when the waveform shaping circuit 13 is inserted to shape the waveform into the rectangular wave pulse train, the higher-order harmonic components are added without changing the frequency fo of the fundamental wave component.
The data in the frequency domain obtained by the calculation includes not only the fundamental wave component data but also higher order harmonic component data.

FIG. 2 is a graph showing frequency domain data obtained by FFT calculation of a rectangular wave pulse train. The frequency component of the rectangular wave pulse includes a frequency component (3fo, 5fo, 7fo, ...) That is an odd multiple of the fundamental wave frequency fo as a higher-order component. The measurement error of the frequency of these higher-order frequency components is also Δf, which is the same as the error of the fundamental wave frequency component. Therefore, for example, if the frequency of the 9th-order frequency component is measured, the measured value is 9fo + Δf
It can be expressed as. When this measured value is divided by the order n = 9, the result of the fundamental wave component frequency is fo + Δf / 9. So, in this case,
It should be noted that the measured value of the fundamental wave frequency fo has a one-ninth error compared to the conventional one. Thus, it can be seen that the higher the order n is, the smaller the term of the measurement error of the fundamental wave frequency fo is, so that the accuracy is improved. In general, the measured frequency value of the nth-order frequency component is nfo + Δ
Therefore, if this measured value is divided by n, the value of the frequency of the fundamental wave component fo is fo + Δf / n, which is 1 / n of the conventional error Δf.
This means that the measurement accuracy has improved significantly.

The preferred embodiment of the present invention has been described above.
It will be apparent to those skilled in the art that the present invention is not limited to only the above-described embodiments, and that various changes and modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, an example using a simple comparator was described as the waveform shaping circuit, but any circuit that gives a harmonic component without changing the frequency of the fundamental wave component A circuit that forms a waveform may be used.

[0010]

EFFECTS OF THE INVENTION By performing a waveform shaping process for imparting a harmonic component to a fundamental wave component of an input waveform, an nth (integer of 2 or more) order frequency is measured from frequency domain data obtained by FFT calculation, By dividing the measured value by the order n, the error can be reduced to 1 / n as compared with the conventional case.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing an example of frequency components for explaining the operation of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional FFT analysis device.

[Explanation of symbols]

 13 waveform shaping means 20 FFT processing means (μP) 20 computing means (μP)

Claims (2)

[Claims] 1. A fundamental frequency measuring method using an FFT analysis technique, wherein a fundamental wave component of an input signal is not changed, a signal waveform having a harmonic component is formed, and the signal is FFT processed. Among the obtained data, the frequency of the harmonic component data of the nth (integer of 2 or more) order is measured, and the measured value is divided by the above n to measure the frequency of the fundamental wave component of the input signal. Measuring method of fundamental wave component frequency. 2. A waveform shaping means for applying a harmonic component without changing a fundamental frequency component of an input signal, an FFT processing means for FFT processing an output signal of the waveform shaping means, and an output of the FFT processing means. Among the data, an arithmetic means for measuring the frequency of the nth (integer of 2 or more) harmonic component data and dividing the measured value by the n to obtain the frequency of the fundamental wave component of the input signal. Measuring device of fundamental wave component frequency.