CN111641411B - Signal acquisition method and system - Google Patents
Signal acquisition method and system Download PDFInfo
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- CN111641411B CN111641411B CN202010348400.7A CN202010348400A CN111641411B CN 111641411 B CN111641411 B CN 111641411B CN 202010348400 A CN202010348400 A CN 202010348400A CN 111641411 B CN111641411 B CN 111641411B
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- 238000012952 Resampling Methods 0.000 claims abstract description 16
- 238000012805 post-processing Methods 0.000 claims abstract description 7
- 230000004044 response Effects 0.000 claims description 13
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
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Abstract
The invention discloses a signal acquisition method and a system, and relates to the technical field of signal acquisition. The signal acquisition method of the invention comprises the following steps: collecting a data signal, and performing second-order anti-aliasing filtering on the data signal; AD sampling is carried out on the anti-aliasing filtered signal to obtain a digital signal; according to the required signal sampling frequency, digital anti-aliasing filtering is carried out on the digital signal, and then digital resampling is carried out on the digital anti-aliasing filtered signal; and carrying out post-processing on the digital resampled signal to obtain a required sampling data signal, and storing the required sampling data signal. The invention reduces the order of the anti-aliasing filter on the premise of ensuring the data acquisition precision, simplifies the circuit and achieves the purpose of reducing the volume of data acquisition equipment.
Description
Technical Field
The present invention relates to the field of signal acquisition technologies, and in particular, to a signal acquisition method and system.
Background
When the mechanical structure is excited by vibration and impact force, the mechanical structure can generate response in a very wide frequency range, and the dynamic analysis is carried out in the concerned frequency range for measuring the structural response, so that the data acquisition equipment is generally used for measuring the vibration and impact sensor signals. The structure vibration and impact response measurement requires higher measurement precision, and in a considerable amount of motion mechanisms, the data acquisition equipment is required to be small in size, so that the data acquisition equipment can be conveniently integrated into the structure. The measurement accuracy is high, and besides the AD conversion accuracy of the data acquisition equipment is improved, the higher anti-aliasing filtering accuracy is also required. However, the complex anti-aliasing filter circuit design is contradictory to the requirement of the smallest possible volume of the data acquisition equipment.
At present, tracking sampling of different signal frequencies mostly adopts a switched capacitor integrated filter, and the switching noise is large. In order to achieve anti-aliasing precision, a higher filter order is often used, so that a circuit is complex, and the volume of acquisition equipment is larger. It is difficult to meet the real-time measurement requirements of small space structure vibrations and impulse response signals.
Disclosure of Invention
The invention provides a signal acquisition method and a system, which can simplify a circuit as much as possible and reduce the volume of data acquisition equipment while ensuring the data signal acquisition precision.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a signal acquisition method, which comprises the following steps:
collecting a data signal, and performing second-order anti-aliasing filtering on the data signal;
AD sampling is carried out on the anti-aliasing filtered signal to obtain a digital signal;
digital anti-aliasing filtering is carried out on the digital signal according to the required signal sampling frequency, and digital resampling is carried out on the digital anti-aliasing filtered signal according to the required signal sampling frequency;
and carrying out post-processing on the digital resampled signal to obtain a required sampling data signal, and storing the required sampling data signal.
Compared with the prior art, the invention combines a second-order analog filter with digital filtering to realize signal acquisition under different sampling frequencies. The powerful real-time computing capability of the current data processing chip can be fully applied after signal acquisition to carry out numerical resampling and signal post-processing after sampling, and the signal detection precision is improved. The invention reduces the order of the anti-aliasing filter, simplifies the circuit and achieves the purpose of reducing the volume of the data acquisition equipment. Meanwhile, the digital anti-aliasing filtering and the digital resampling can achieve the effect of randomly setting the sampling frequency to track and sample the signal frequency.
Preferably, the post-processing process of the invention further comprises numerical correction of the amplitude attenuation caused by the filter, so that higher data acquisition accuracy can be obtained.
The invention also provides a signal acquisition system corresponding to the method, which comprises the following steps:
the signal acquisition unit acquires vibration data signals;
the low-pass filter is used for performing anti-aliasing filtering on the vibration data signals and reducing aliasing noise signals;
an AD converter converting the anti-aliasing filter signal into a digital signal;
a digital filter and a digital resampling filter for performing digital anti-aliasing filtering and digital resampling on the digital signal;
and the post-processing software unit performs Fourier transformation, amplitude correction and inverse Fourier transformation on the digital resampled signal to obtain a required sampling data signal and stores the required sampling data signal.
The signal acquisition system disclosed by the invention has the advantages of high data acquisition precision, simple circuit and small volume of data acquisition equipment, can randomly set the sampling frequency to track and sample the signal frequency, and meets the real-time measurement requirements of small-space structure vibration and impact response signals.
Drawings
Fig. 1 is a flow chart of a signal acquisition method of the present invention.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the invention is further described in detail below. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
At present, tracking sampling of different signal frequencies is performed, so that higher filter orders are often used for achieving anti-aliasing precision, a circuit is complex, and the volume of acquisition equipment is larger. The invention provides a signal acquisition method for solving the contradiction between the high precision requirement of data signal acquisition and the small volume of acquisition equipment, which comprises the following steps:
collecting a data signal, and performing second-order anti-aliasing filtering on the data signal;
AD sampling is carried out on the anti-aliasing filtered signal to obtain a digital signal;
according to the required signal sampling frequency, digital anti-aliasing filtering is carried out on the digital signal, and then digital resampling is carried out on the digital anti-aliasing filtered signal;
and carrying out post-processing on the digital resampled signal to obtain a required sampling data signal, and storing the required sampling data signal.
Because the mechanical structure is excited by vibration and impact force, response can be generated in a very wide frequency range, and dynamic analysis is carried out in the concerned frequency range for measuring the structure response, the data acquisition equipment is generally used for measuring the vibration and impact sensor signals. The invention first collects the above signals generated by the mechanical structure, and the data collection device may use devices known in the art to convert the analog signals to digital signals.
In data sampling systems, frequency components above one-half the sampling rate are "aliased" (shifted) to the useful frequency band. Most of the time, aliasing is a detrimental side effect, so the higher frequencies of "undersampling" are simply filtered out before the analog-to-digital (AD) conversion stage. Generally, under the condition of the same cut-off frequency, the higher the order is, the better the detection precision is, but the dynamic response speed is affected. And the higher the order, the more complex the computation. The invention carries out second-order anti-aliasing filtering on the acquired data signals and reduces anti-aliasing frequency components.
In general, when selecting filters, the goal is to provide a cut-off frequency that eliminates or at least attenuates unwanted signals from the ADC input to the point that they do not adversely affect the circuit. An anti-aliasing filter is a low pass filter that meets this requirement. The filter design principle is that the cut-off frequency is low, the dynamic response is fast, and the delay is as small as possible. The anti-aliasing filter of the present invention employs a low-pass anti-aliasing filter. As an alternative embodiment, the present invention employs a second order butterworth low pass filter. Characteristics of the second order butterworth low pass filter: the order is low, the amount of data is small, the passband region is flattest, meaning that attenuation is minimal in the corresponding frequency range. Under the condition of reasonable parameter selection, smooth filtering can be achieved without overshoot.
Key parameters that the filter needs to consider include, but are not limited to, the amount of attenuation (or ripple) in the passband, the expected filter roll-off in the stopband, the steepness of the transition region, etc. As an alternative embodiment, the filter cut-off frequency of the second order anti-aliasing filter of the present invention is set to 39kHz, the maximum analysis frequency of the structural dynamics response. The filter amplitude-frequency characteristic is set as:
wherein f 0 Is the filter cut-off frequency. The filter steepness of the second-order anti-aliasing filter is optionally set as follows:
R＝40dB/dec (2)
i.e. 40dB down per 10 octaves. With 10 times the oversampling rate, the aliased noise signal amplitude is no higher than-40 dB.
The invention performs AD sampling on the anti-aliasing filtered signal to obtain a digital signal. The person skilled in the art performs AD sampling according to techniques known in the art, according to the parameter settings required for AD sampling. As a specific implementation mode, the AD sampling frequency is set to be 2.56MHz optionally, and the amplitude of the aliased noise signal is not more than-100 dB.
After AD sampling is completed, the invention carries out digital anti-aliasing filtering on the digital signal according to the required signal sampling frequency, and then carries out digital resampling on the signal after the digital anti-aliasing filtering, thus realizing data acquisition with different sampling frequencies according to different sampling frequency requirements. As an alternative implementation mode, the invention designs a ten-second-order digital anti-aliasing filter, the cut-off frequency of the digital filter is 1/2.56 of the sampling frequency of the required signal, and the digital filtered signal is digitally resampled according to the required sampling frequency of the signal.
As can be seen from the formula (1), the signal filtered by the second-order anti-aliasing filter has larger amplitude attenuation, and the amplitude correction is required to obtain higher data acquisition accuracy. Thus, the present invention post-processes the digitally resampled signal. Specifically, the invention carries out Fourier transform on the signals after digital resampling, corrects the amplitude of the Fourier spectrum of the signals (the amplitude of the Fourier spectrum of each frequency point is divided by k (f)) by using a formula (1), carries out inverse Fourier transform on the Fourier spectrum after amplitude correction, and restores the Fourier spectrum into a time domain signal. This results in the desired sampling frequency signal and stores this signal in memory. This process may also be performed in post-processing software.
The signal acquisition method can randomly set the sampling frequency to carry out signal frequency tracking sampling. In addition, the invention can obtain higher data acquisition precision by carrying out numerical correction on the amplitude attenuation caused by the filter. The invention applies the powerful real-time computing capability of the current data processing chip, designs numerical resampling and amplitude correction, reduces the order of the anti-aliasing filter, simplifies the circuit, and achieves the purpose of reducing the volume of the data acquisition equipment.
As one embodiment, the present invention provides a signal acquisition system comprising: the signal collector collects vibration data signals, the collected signals are input into the second-order Butterworth low-pass filter to conduct anti-aliasing filtering on the vibration data signals, and aliasing noise signals are reduced. The filter cut-off frequency was set to 39kHz, the maximum analysis frequency of the structural dynamics response. The amplitude-frequency characteristic of the filter is as follows:
f 0 is the filter cut-off frequency. The steepness of the filter is as follows:
R＝40dB/dec (2)
i.e. 40dB down per 10 octaves. With 10 times the oversampling rate, the aliased noise signal amplitude is no higher than-40 dB.
The output signal in the filter enters an AD converter to be converted into a digital signal. The AD sampling frequency is set to 2.56MHz, and the amplitude of the aliased noise signal is not more than-100 dB. After AD sampling is completed, the digital signal is input into a digital anti-aliasing filter of the tenth order, the cut-off frequency of the digital anti-aliasing filter is set to be 1/2.56 of the required signal sampling frequency, and then the digital resampling is carried out on the digitally filtered signal by using a digital resampling filter according to the required signal sampling frequency. The digitally resampled signal is fourier transformed by a post-processing software unit and the magnitude of the fourier spectrum of the signal is modified by equation (1) (the magnitude of the fourier spectrum at each frequency point divided by k (f)). And performing inverse Fourier transform on the Fourier spectrum with the corrected amplitude, and restoring the Fourier spectrum into a time domain signal. This results in the desired sampling frequency signal and stores this signal in memory.
The signal acquisition system of the invention uses the powerful real-time computing capability of the current data processing chip to carry out numerical resampling and amplitude correction, reduces the order of the anti-aliasing filter, simplifies the circuit, achieves the purpose of reducing the volume of the data acquisition equipment, and meets the real-time measurement requirements of small space structure vibration and impact response signals.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (9)
1. A signal acquisition method, comprising:
collecting a data signal, and performing second-order anti-aliasing filtering on the data signal; the amplitude-frequency characteristic of the second-order anti-aliasing filter is as follows:f 0 is the filter cut-off frequency;
AD sampling is carried out on the anti-aliasing filtered signal to obtain a digital signal;
according to the required signal sampling frequency, digital anti-aliasing filtering is carried out on the digital signal, and then digital resampling is carried out on the digital anti-aliasing filtered signal;
and carrying out post-processing on the digital resampled signal to obtain a required sampling data signal, and storing the required sampling data signal.
2. The signal acquisition method of claim 1, wherein the cut-off frequency of the second order anti-aliasing filter is set to 39kHz, the maximum analysis frequency of the structural dynamics response.
3. The signal acquisition method of claim 1, wherein the second order anti-aliasing filter steepness is: r=40 dB/dec.
4. The signal acquisition method of claim 1, wherein the AD sampling frequency is 2.56MHz and the aliased noise signal amplitude is no greater than-100 dB.
5. The signal acquisition method of claim 1, wherein the digital anti-aliasing filter has a cut-off frequency of 1/2.56 of the desired signal sampling frequency.
6. The signal acquisition method of claim 1, wherein the post-processing comprises: and carrying out Fourier transformation, amplitude correction and inverse Fourier transformation on the digital resampled signal.
7. The method of claim 6, wherein the amplitude correction is a fourier spectrum amplitude of each frequency bin divided by k (f).
8. A signal acquisition system, comprising:
the signal acquisition unit acquires vibration data signals;
the low-pass filter is used for performing anti-aliasing filtering on the vibration data signals and reducing aliasing noise signals; the anti-aliasing filter is a second-order anti-aliasing filter, and the amplitude-frequency characteristic of the second-order anti-aliasing filter is as follows:f 0 is the filter cut-off frequency;
an AD converter converting the anti-aliasing filter signal into a digital signal;
a digital filter and a digital resampling filter for performing digital anti-aliasing filtering and digital resampling on the digital signal;
and the post-processing software unit performs Fourier transformation, amplitude correction and inverse Fourier transformation on the digital resampled signal to obtain a required sampling data signal and stores the required sampling data signal.
9. The signal acquisition system of claim 8 wherein the low pass filter is a second order butterworth low pass filter and the digital filter is a tenth order digital anti-aliasing filter.
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| US7133569B1 (en) * | 2000-07-31 | 2006-11-07 | Polaroid Corporation | Aliasing artifact attenuation system |
| CN204334510U (en) * | 2014-12-18 | 2015-05-13 | 天津百利机械装备集团有限公司中央研究院 | A kind of frequency overlapped-resistable filter analog circuit |
| CN106603076A (en) * | 2016-11-14 | 2017-04-26 | 江苏兆伏爱索新能源有限公司 | AD sampling signal processing method and AD sampling signal device |
| CN108199998A (en) * | 2017-12-29 | 2018-06-22 | 北京宇电科技集团有限公司 | A kind of anti-aliasing filter method, apparatus and programmable logic device |
| CN108234378A (en) * | 2018-01-19 | 2018-06-29 | 张涛 | A kind of anti-aliasing filter method, apparatus and programmable logic device |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7133569B1 (en) * | 2000-07-31 | 2006-11-07 | Polaroid Corporation | Aliasing artifact attenuation system |
| CN204334510U (en) * | 2014-12-18 | 2015-05-13 | 天津百利机械装备集团有限公司中央研究院 | A kind of frequency overlapped-resistable filter analog circuit |
| CN106603076A (en) * | 2016-11-14 | 2017-04-26 | 江苏兆伏爱索新能源有限公司 | AD sampling signal processing method and AD sampling signal device |
| CN108199998A (en) * | 2017-12-29 | 2018-06-22 | 北京宇电科技集团有限公司 | A kind of anti-aliasing filter method, apparatus and programmable logic device |
| CN108234378A (en) * | 2018-01-19 | 2018-06-29 | 张涛 | A kind of anti-aliasing filter method, apparatus and programmable logic device |
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