JPS6046854B2 - How to correct distortion in electrical signals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for correcting distortion in electrical signals having linearity or amplitude distortion.

For example, in an eddy current inspection device, especially in an eddy current inspection device that excites multiple test coils in a time-sharing manner and performs signal processing by combining the output signals from each test coil into a temporally continuous signal, each eddy current detection section The output signal from
Since it is switched at time intervals of about 10-0 seconds,
If this output signal is amplified to a high degree due to the effects of switching elements or capacitance components in the circuit, the beginning of the signal waveform may become non-linear, or the amplitude may be distorted, as shown in Figure 1. Sometimes.

If such distortion exists in the signal waveform, various problems will occur in signal processing, such as the inability to perform signal processing using the amplitude component of the signal, resulting in the problem of not being able to perform highly sensitive detection. be. Conventionally, the commonly used method for correcting signals with distortion as described above is to use a band-pass filter. A number of stages must be used, and in this case there is a problem that the level of the signal after correction becomes very small, and there is also the disadvantage that amplitude distortion cannot be removed.

The present invention provides a signal correction method that solves such problems, and is particularly useful in the above-mentioned eddy current inspection equipment, in which the output signals from each inspection coil are combined into a temporally continuous signal. However, since the signal is a periodic signal with a constant frequency, an effective signal correction method was devised by paying attention to the characteristics of such a signal.

The gist of the present invention is to provide a method for correcting distortion of an electrical signal whose linearity has distortion in amplitude, and in which a signal to be corrected which is a synchronous signal having a constant frequency and a phase of the signal to be corrected are adjusted by approximately 1800 degrees. There is a method for correcting the distortion of an electrical signal, which is characterized by correcting the distortion of the electrical signal by using a circuit that causes the signal to change, and a circuit that outputs the difference between the output signal of the circuit and the correction signal as an output signal.

Hereinafter, the present invention will be explained in detail based on examples.

FIG. 2 is an example of an electrical block diagram of an apparatus for implementing the present invention.

A signal to be corrected having a distortion as shown in FIG. 1 is first input to a first low-pass filter 1 to remove high frequency components and pulse-like noise components contained in the signal to be corrected.

The waveform of the output signal of this first low-pass filter 1 is shown at 1 in FIG. Next, the first low-pass filter 1
The output signal is input to the second low-pass filter 3. The cutoff frequency of the second low-pass filter 3 is
The frequency is adjusted to be approximately equal to the excitation frequency of the test coil of the eddy current test device. FIG. 4 is a diagram showing the phase relationship between the input signal and the output signal with respect to the ratio between the frequency of the input signal and the cutoff frequency in the second low-pass filter 3. In addition, if the cutoff frequency of the second low-pass filter 3 is adjusted to a frequency approximately equal to the frequency of the input signal (i.e., the excitation frequency of the test coil), the output for the input signal of the second low-pass filter 3 is The signals will have a phase difference of approximately 180 degrees.

The waveform of the output signal of this second low-pass filter 3 is shown at 2 in FIG. The output signal of the second low-pass filter is input to the voltage adjustment circuit 4, and after the voltage is adjusted,
It is input to one input terminal of the differential amplifier 2. On the other hand, a part of the output signal of the first low-pass filter 1 is directly input to the other input terminal of the differential amplifier 2. Of the two signals input to the differential amplifier 2, that is, the signal waveforms 1 and 2 in FIG. ，
The excitation frequency components of both signals of 2 are such that the signal waveforms of 1 and 2 are 1.
Since they have a phase difference of 80 degrees, they are eventually added and amplified, and at this time, the amplitude distortion (
(the amplitude is different on the positive and negative sides) will be deposited in equal amounts on the positive and negative sides, and will eventually be removed. In this way, a signal with good linearity and little distortion as shown in 3 in FIG. 3 is obtained on the output side of the differential amplifier 2. In this example, the second low-pass filter was used to obtain a signal that delayed the phase of the signal to be corrected by about 180 degrees, but in addition to this, delay lines used in oscilloscopes, charge transfer, etc. A CCD analog delay line using a CCD shift register (for example, Nikkei Electronics 1977.9-5N0168p44)
It is described in.

) etc., it is also possible to obtain a signal with a delayed phase. However, in this case, the phases of all signals change in the same way, so if the excitation frequency of the eddy current test coil is low, the time corresponding to the phase difference of 180 vortices will be longer, resulting in non-linearity at the start of switching. This tends to make it difficult to remove severe distortions. As described above, the present invention provides a method for effectively removing distortions in signals having distortions in linearity and amplitude, and in an eddy current inspection apparatus using a plurality of eddy current inspection sections as described above, seconds~10-
This is a useful invention that can effectively remove distortion in the output signal of the eddy current inspection section that is switched at time intervals of about 5 seconds.

[Brief explanation of drawings]

Figure 1 shows an example of a signal waveform with distortion, Figure 2 shows an example of a signal waveform with distortion.
The figure is a block diagram of the signal correction circuit according to the embodiment of the present invention, FIG. 3 is a diagram showing the waveforms of the output signals of each part of the signal correction circuit of FIG. 2, and FIG. FIG. 3 is a diagram showing the phase characteristics of an output signal in a filter. 1, 3...Low pass filter, 2...
・Differential amplifier, 4... Voltage adjustment circuit.

Claims (1)

[Claims] 1. A method for correcting distortion of an electrical signal having linearity or amplitude distortion, which includes a circuit that shifts the phase of the corrected signal by 180 degrees from a signal to be corrected, which is a synchronous signal having a constant frequency, and a circuit output signal. A method for correcting distortion of an electrical signal, comprising correcting distortion of the electrical signal using a circuit that outputs a difference from the signal to be corrected.