JP3086039B2 - Waveform display method of waveform measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform measuring device,
More specifically, PLL (PhaseLocked)
The present invention relates to a waveform display method of a waveform measuring device that fetches data with a sampling signal synchronized with a signal under measurement by a Loop circuit and performs, for example, harmonic analysis based on the data for one wavelength.

[0002]

2. Description of the Related Art The configuration of a waveform measuring apparatus of this type will be schematically described with reference to FIG. 1. First, a signal under measurement is converted into an analog signal of a level that can be input at an input unit 1. FIG.

[0003] The analog signal is passed through an A / D conversion circuit 3 through an anti-aliasing filter 2 having a variable cut-off frequency for passing a fundamental wave and a harmonic contained in the analog signal.
And converted into a digital signal by the circuit 3,
Stored in the memory 4.

The sampling timing of the A / D conversion circuit 3 and the data writing timing of the memory 4 are controlled by the storage control circuit 5. In this case, these timings are synchronized with the signal to be measured by the PLL circuit 6. It has become.

That is, the analog signal of the input unit 1 is converted by the waveform shaping circuit 7 into a rectangular wave signal. The phase difference between the rectangular wave signal and the sampling signal of the A / D conversion circuit 3 is detected in the PLL circuit 6 and the storage control circuit 5
Controls the sampling signal synchronously based on the phase difference detection signal.

In this example, the sampling frequency is set to 512 times the signal under measurement, that is, one wavelength is sampled at 512 points, and its frequency spectrum can be accurately obtained by FFT (Fast Fourier Transform) processing.

Therefore, the PLL circuit 6 compares the phase of the signal whose sampling frequency is 1/512 with the rectangular wave signal from the waveform shaping circuit 7, and varies the voltage of the internal VCO according to the phase difference. Then, a signal of a predetermined frequency is given to the storage control circuit 5.

Note that the rectangular wave signal from the waveform shaping circuit 7 is also supplied to a frequency measuring circuit 8, which measures the frequency of the signal under measurement.

The memory 4 and the circuits 5, 6, 8 are connected to a central processing unit (CPU) 10 via a bus line 9. In addition to the RAM 11 and the ROM 12, the bus line 9 of the CPU 10 is a digital signal processor that performs high-speed calculation of a fundamental wave included in the signal under measurement and harmonics of a predetermined order (for example, up to the 49th order) by FFT calculation. A (DSP) 13 and a CRT 14 as a display device are connected.

In this conventional example, since the sampling frequency is set to 512 times that of the signal under measurement, 512 data are taken into the memory 4 per wavelength. Note that the sampling frequency changes continuously depending on the input frequency range (for example, 5 Hz to 150 Hz) of the PLL circuit 6.

This data is subjected to arithmetic processing according to a program stored in the ROM 12 or subjected to processing appropriate for the display device, and is output to the CRT 14 as numerical values or waveforms.

FIG. 5 shows an example of displaying a waveform on the CRT 14. In this case, the X-axis (horizontal axis) of the screen is 5
The pixel is composed of 12 dots / 1 wavelength, and based on the sample value data, the corresponding pixel emits light as illustrated in the enlarged view of FIG. In this example, a vertical scale is set at a position where one wavelength is divided into eight (every 64 dots) as a standard of the time axis.

[0013]

According to this waveform device, since the sampling timing can be varied and data for one wavelength can be sampled accurately and in a fixed number,
This is advantageous for calculating a frequency spectrum by FT processing.

However, the displayed waveform is PLL
The input frequency range of the circuit 6 (for example, 5 Hz to 150 H
Since all the waveforms are the same in z), the image of the frequency is not visually (intuitively) recognized.

If the displayed waveform contains, for example, pulse-like noise, the position of the noise in the time axis direction must be calculated from, for example, the frequency displayed on another part of the screen. There was annoyance that it did not become. For example, if the frequency is 50 Hz and the noise is on the third vertical scale from the left, the position in the time axis direction is (1/50) × (3/8) seconds.

[0016]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional drawbacks, and has a structural feature that converts an analog signal under test into a digital signal based on a sampling signal of a predetermined frequency. An A / D conversion circuit for conversion, a storage unit for storing the digital signal converted by the A / D conversion circuit, and a sampling signal of the A / D conversion circuit output in synchronization with the signal under measurement; A storage control circuit that controls a write timing of the storage unit; and a PLL circuit that detects a phase difference between the signal under measurement and the sampling signal and provides a synchronization control signal to the storage control circuit. In the circuit, a digital signal for one wavelength of the signal under measurement is obtained from the sampling signal having a predetermined frequency, and the signal under measurement is obtained based on the digital signal. In a waveform measuring apparatus that displays a waveform on a display unit such as a CRT or a printer, a frequency measurement value of the digital signal is converted into absolute time axis coordinates and displayed on the display unit. .

In the case where the signal to be measured is displayed in dots on the display unit, the frequency of the signal to be measured is f, the number of samples of data to be extracted at one wavelength of the signal to be measured is N, and one division of the time axis coordinate. The time per unit is Dt, and the number of display dots per division is Dn.
Then, the position on the time axis coordinate of the data whose sampling order is n-th is (n · Dn) / (f · ND ·
t).

[0018]

According to the above arrangement, the data acquired at the sampling timing by the PLL circuit is converted from the measured frequency value into absolute time axis coordinates and displayed, so that reading in the time axis direction is easy. Become.

[0019]

In this embodiment, the same apparatus as that of FIG. 4 described above is used, and the description of the same apparatus will be omitted.

FIG. 1 shows a display example of a waveform on the time axis coordinate according to the present invention, which will be described in comparison with a waveform display example by the PLL of FIG.

First, in the waveform output example of FIG. 5, for a point n dots away from the sample point number 1 (see FIG. 6, start point), the time difference Tn from the start point is determined by setting the frequency of the waveform to fHz. For example, Tn = (n / f) × 512 seconds.

On the other hand, in the waveform output of FIG.
Assuming that the position of the same sample value as in FIG. 5 (the number of dots from the start point) is m, the time difference Tm is obtained. Here, the time per DIV (division) is D
Assuming that the number of display dots per t and 1 DIV is Dn, Tm = m × Dt / Dn seconds.

Since n and m are assumed to be the same sample value,
Tn = Tm. Therefore, from (n / f) × 512 = m × Dt / Dn, m = (n × Dn) / (f × 512 × Dt) is derived.

As an example, sampling data by a PLL having a frequency of 50 Hz is 1 DIV for 5 ms and 1 DIV.
When the number of display dots per unit is converted to a time axis display of 60, m = {n / (50 × 512)} × {60 / (5/1)
0 ³ )｝ = 0.46875n, Table 1 shows an example of conversion of each sample point to the time axis, and FIG. 2 shows a dot display example of the same data.

[0025]

[Table 1] In this way, by converting the frequency measurement value into arbitrary time axis data, reading of the time axis becomes extremely easy. As shown in FIG. 2, for example, two data are displayed on the same time axis, and the identity with the output waveform by the PLL is slightly impaired. Since there is a surface which cannot completely follow the fluctuation, if the PLL is locked, it can be regarded as practically the same.

For reference, FIG. 3 shows a flowchart of a waveform display method according to the present invention. In addition to the CRT 14, a printer, an LCD, and the like can be applied as the display device.

[0027]

As described above, according to the present invention, it is possible to convert the data acquired at the sampling timing by the PLL circuit into absolute time axis coordinate values and to display the data. The output waveform reflects the frequency of the signal under measurement, and its time axis position can be read very easily.

[Brief description of the drawings]

FIG. 1 is a waveform chart showing a waveform display example according to the display method of the present invention.

FIG. 2 is an explanatory view showing a dot display state by enlarging a part of the waveform diagram of FIG. 1;

FIG. 3 is a flowchart of a display method according to the present invention.

FIG. 4 is a block diagram of a waveform measuring device.

FIG. 5 is an output waveform diagram based on data sampled by a PLL.

FIG. 6 is an explanatory view showing a dot display state by enlarging a part of the waveform diagram of FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input part 2 Filter 3 A / D conversion circuit 4 Memory 5 Storage control circuit 6 PLL circuit 7 Waveform shaping circuit 8 Frequency measurement circuit 9 Bus line 10 CPU 13 Digital signal processor 14 CRT

Claims (2)

(57) [Claims] An A / D conversion circuit for converting an analog signal under measurement into a digital signal based on a sampling signal of a predetermined frequency; a storage unit for storing the digital signal converted by the A / D conversion circuit; The sampling signal of the A / D conversion circuit is output in synchronization with the signal under measurement,
A storage control circuit that controls a write timing of the storage unit; and a PLL circuit that detects a phase difference between the signal under measurement and the sampling signal and provides a synchronization control signal to the storage control circuit. A circuit that obtains a digital signal corresponding to one wavelength of the signal under measurement with the sampling signal having a predetermined frequency, and displays the waveform of the signal under measurement on a display unit such as a CRT or a printer based on the digital signal; In the measuring apparatus, a frequency measurement value of the digital signal is converted into an absolute time axis coordinate and displayed on the display unit. 2. When the measured signal is displayed as dots on the display unit, the frequency of the measured signal is f, the number of samples of data extracted for one wavelength of the measured signal is N, and the time axis coordinate is Dt is the time per division, and Dn is the number of dots displayed per division.
Then, the position on the time axis coordinate of the data whose sampling order is n-th is (n × Dn) / (f × N × D
2. The waveform display method according to claim 1, wherein t).