JPH0552886A - Setting method for sampling period for measurement of harmonic by use of memory recorder - Google Patents

Abstract

PURPOSE:To execute an FFT operation accurately by a method wherein the quotient obtained by dividing the total number of data corresponding to one period by the total number of sampling data extracted from the data corresponding to one period is made to be a sampling period. CONSTITUTION:As to waveform data taken in on the body 11 of an apparatus, first the number of the data corresponding to one period is determined in accordance with a program stored in an external storage medium 20 and then a majority number of sampling data are extracted from the data at the highest sampling speed which a clock 13 in the body 11 has. Then, the quotient obtained by dividing the total number of the data corresponding to one period by the total number of the extracted sampling data is made to be a sampling period for setting the position of a sampling point for an FET operation out of the sampling data. At the position of this sampling period, the probability of existence of the sampling data corresponding exactly is high, and thereby the FET operation can be executed accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sampling period setting method for measuring harmonics by a memory recorder.

[0002]

2. Description of the Related Art Harmonic measurement is performed by Fourier transforming a waveform of one cycle to obtain frequency components. It is known that the Fourier transform in this case can be processed at high speed by using the FFT algorithm.
However, the number of sampling points of waveform data that can be efficiently calculated by the FFT algorithm is always 2
It will be limited to powers of.

Therefore, the number of sampling points (for example, data for 2 ⁷ = 128, 2 ⁸ = 256, 2 ⁹ = 512, ...) Points where the period of the waveform data to be measured corresponds to exactly a power of 2. If there is no problem.

However, when the clock frequency for sampling is fixed as in the existing memory recorder, it is difficult in most cases to match the sampled waveform data with a power of 2. there were.

On the other hand, a conventional harmonic measuring device can obtain a clock obtained by dividing an input signal frequency into an arbitrary number including a power of 2, and thus the clock frequency that determines the sampling rate can be changed. Therefore, it was possible to adjust so that the power of 2 data was sampled in one cycle.

[0006]

By the way, according to the above-mentioned harmonic measuring device, since it is possible to change the clock frequency which determines the sampling speed, one cycle is set to the number of sampling points of power of 2 They can be matched and are well adapted to FFT operations.

However, unlike the above-described harmonic measuring device, in the case of using a memory recorder, the clock frequency is fixed, so that the sampling rate cannot be varied according to the frequency of the waveform data, and a series of Waveform data 1
The sampling period T / N obtained by dividing the number T of waveform data corresponding to one period in the sampling data extracted from
The correspondence relationship as shown in FIG. 4 is shown.

That is, as shown in the figure, when the positions of the sampling data A _{1 to} A ₈ extracted from the waveform data 1 and the positions of the sampling points P _{1 to} P ₃ determined by the sampling cycle T / N do not match. As a result, for example, since the sampling data A ₂ is located at the position of the sampling point P ₁ , there is no problem, but the sampling data does not exist at the positions of the sampling points P ₂ and P ₃ , and therefore, the sampling is performed. The sampling data A ₄ for the point P _{2 and the} sampling data A ₇ for the sampling point P ₃
Will be treated as corresponding data.

Therefore, in the FFT calculation, in addition to the sampling data corresponding to the position of the sampling cycle T / N,
Inevitably, it is necessary to use data in a state in which sampling data that is close to the position of the sampling cycle T / N is also mixed, the calculation result becomes inaccurate, and some kind of posterior correction process is required. there were.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems found in the conventional method, and its structural feature is that stored data can be transmitted / received to / from a device body. In a memory recorder having a formed external storage medium, regarding the waveform data captured on the device body side, first, the number of data corresponding to one cycle is calculated according to the program stored in the external storage medium. After that, a large number of sampling data are extracted from the data corresponding to one cycle at the fastest sampling speed provided in the device main body, and the total number of sampling data extracted at this time corresponds to the data corresponding to one cycle. Is a sample for determining the position of the sampling point for FFT operation from the sampling data by dividing the total number of It is to the period.

[0011]

Therefore, a large number of sampling data can be extracted from the data corresponding to one cycle in the waveform data, and the total number of sampling data after this extraction is used to divide the total number of the data corresponding to one cycle. Since the quotient thus obtained becomes the sampling period, there is a high probability that the sampling data corresponding to the sampling period exactly exists, and the FFT calculation can be performed accurately accordingly.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing a schematic configuration of a memory recorder used for implementing the present invention. The device body 11 includes an analog unit 15 and a logic unit 16.
The input data is provided to the input unit 17, and the input data is arithmetically controlled via the CPU 12 operated by the program stored in the ROM 25 by the operation of the operation unit 19, and measured to the output unit 18 such as a printer or an LCD display. The output display of the result is possible.

An external storage medium 20 such as a RAM card, a ROM card or an IC card can be attached to the device body 11, and the device body 11 side of the data stored in the external storage medium 20 can be mounted. Is formed to allow loading into.

In the figure, reference numeral 13 indicates a clock.
4 is a frequency dividing circuit, 21 is an interface, 22 is a memory controller, 23 is a built-in RAM,
Reference numerals 24 respectively indicate trigger parts.

FIG. 1 is a flow chart showing a processing procedure as one embodiment of the present invention which is carried out via a memory recorder as shown in FIG. 2, for example. According to the figure, prior to setting the sampling cycle, the sampling speed is set and the recording length is set so that the waveform data of one cycle or more can be captured.

Next, the set sampling rate is
It is determined whether or not it is the fastest one under the clock frequency of the clock 13 in the device body 11.

In this case, when it is determined that the sampling speed is the fastest, the existing software stored in the ROM 25 is used to load the waveform data into the device main body 11 via the input unit 17.

After the waveform data is captured in this way, first, based on a program for measuring harmonics that is loaded in advance from the external storage medium 20 to the device body 11, the waveform data The total number T of data corresponding to one cycle is obtained.

Next, as shown in FIG. 3, a large number of sampling data 5, 5, ...
.. is extracted, and the total number N of the sampling data 5 extracted at this time is divided by the total number T of the data corresponding to one cycle to obtain the sampling cycle T / N.

The positions of the sampling points 6, 6, ... Are determined by the sampling cycle T / N thus obtained, and a large number of sampling data 5 having a positional relationship corresponding to the positions of these sampling points 6 are obtained. FFs are thinned out from the sampling data 5
It is secured as sampling data for T calculation.

Thus, the sampling data 5 thus thinned out and secured is used as data for performing the FFT operation, and after the processing such as the calculation necessary for the harmonic measurement is performed, the processing result is obtained. Output section 18
The process for setting the sampling period is completed by shifting to the display routine for displaying.

Since the present invention is configured as described above, the clock 13 is applied to the waveform data taken into the device main body 11 side via the input unit 17.
A large number of sampling data 5, among the data corresponding to one cycle, under the fastest sampling speed synchronized with
5, ... are extracted.

The total number T of data corresponding to one cycle that has already been determined is the number of extracted sampling data 5
Is divided by the total number N of
/ N is obtained.

The sampling data 5 required for the FFT calculation is determined by the correspondence relationship with each position of the sampling point 6 determined by the sampling cycle T / N.

That is, each of the sampling data 5 used for the FFT calculation is based on the corresponding relationship with each position of the sampling point 6 from the other several sampling data 5, 5 ,. Will be thinned out at.

Therefore, it is highly probable that the sampling data 5 as the waveform data that exactly corresponds to the sampling cycle T / N can be used in the FFT calculation, and as a result, a highly accurate calculation result can be obtained. Therefore, the accuracy of harmonic measurement by the memory recorder can be improved.

[0028]

As described above, according to the present invention, a large number of sampling data can be extracted from the data corresponding to one cycle in the waveform data even by the memory recorder of the conventional type, and a large number of the extracted data can be extracted. Since the quotient obtained by dividing the total number of data corresponding to one cycle by the total number of sampling data is the sampling cycle, it is highly probable that the sampling data corresponding to the sampling cycle exists exactly at this sampling cycle position. And F
The FT calculation can be performed accurately.

[Brief description of drawings]

FIG. 1 is a flowchart showing a processing procedure as an embodiment of the present invention.

FIG. 2 is a block diagram showing an outline of a device body used for implementing the present invention.

FIG. 3 is an explanatory diagram schematically showing a correspondence relationship between sampling data and a sampling period realized by the method of the present invention.

FIG. 4 is an explanatory diagram showing a correspondence relationship between sampling data extracted from waveform data and a sampling period by a conventional method.

[Explanation of reference numerals] 11 device main body 17 input unit 18 output unit 20 external storage medium

Claims (1)

[Claims] 1. A memory recorder comprising an external storage medium capable of transmitting and receiving stored data to and from a device body, wherein the waveform data fetched on the device body side is first stored in the external device. According to the program stored in the storage medium, determine the number of data corresponding to one cycle, and then extract a large number of sampling data from the data corresponding to one cycle at the fastest sampling speed provided in the device main body. The quotient obtained by dividing the total number of the one-cycle correspondence data by the total number of the sampling data extracted at this time is used as the sampling period for determining the position of the sampling point for FFT calculation from the sampling data. A sampling period setting method for measuring harmonics by a memory recorder.