CN111025983A

CN111025983A - Weak signal detection device with strong anti-interference performance

Info

Publication number: CN111025983A
Application number: CN201911330978.3A
Authority: CN
Inventors: 张庆乐; 李智强; 林鹏; 李凡贡
Original assignee: China Institute of Radio Wave Propagation CETC 22 Research Institute
Current assignee: China Institute of Radio Wave Propagation CETC 22 Research Institute
Priority date: 2019-12-21
Filing date: 2019-12-21
Publication date: 2020-04-17

Abstract

The invention discloses a weak signal detection device with strong anti-interference performance, which comprises a filter circuit, a pre-amplification circuit, a lock-in amplifier, a multi-channel amplification circuit, a multi-channel AD acquisition circuit, a DSP, a CAN box and an upper computer which are electrically connected together in sequence, wherein the filter circuit receives signals, and the lock-in amplifier comprises a modulation module. For a dc signal or a slowly varying signal with a small amplitude, the device disclosed in the present invention generally uses a modulator or a chopper to convert the dc signal or the slowly varying signal into an ac signal, amplify and process the ac signal, and then demodulate and low-pass filter the ac signal to obtain an amplified signal to be measured, in order to prevent the adverse effects of 1/f noise and dc amplified dc drift (e.g., temperature drift of input offset voltage of operational amplifier). The weak signal detection device designed based on the lock-in amplifier shows excellent performance in the aspect of weak signal detection.

Description

Weak signal detection device with strong anti-interference performance

Technical Field

The invention belongs to the field of oil field logging, and particularly relates to a weak signal detection device with strong anti-interference performance in the field.

Background

In hydrocarbon evaluation, a weak signal not only means that the amplitude of the signal is small, but also mainly refers to a signal submerged by noise. For various weak signals to be measured, for example, weak light, weak magnetism, micro pressure, micro vibration, micro temperature difference, etc., they are generally converted into micro current or low voltage by corresponding sensors, and then amplified by an amplifier to indicate the measured magnitude. However, because the measured signal is weak, the background noise of the sensor, the intrinsic noise of the amplifying circuit and the measuring instrument, and the external interference noise are often much larger than the amplitude of the useful signal, the noise is amplified during the process of amplifying the measured signal, and extra noise such as the internal intrinsic noise and the external interference noise of the amplifier is inevitably added, so that the weak signal cannot be detected only by amplification. The useful signal can be extracted only by increasing the amplitude of the weak signal under the condition of effectively suppressing the noise.

Disclosure of Invention

The invention aims to provide a weak signal detection device with strong anti-interference performance.

The invention adopts the following technical scheme:

the improvement of a weak signal detection device with strong interference resistance is that: the locking amplifier comprises a filter circuit, a pre-amplification circuit, a locking amplifier, a multi-channel amplification circuit, a multi-channel AD acquisition circuit, a DSP, a CAN box and an upper computer which are sequentially and electrically connected together, wherein the filter circuit receives signals, the locking amplifier comprises a modulation module, one input end of the modulation module is electrically connected with the pre-amplification circuit, the other input end of the modulation module is electrically connected with a square wave generation circuit, the output end of the modulation module is sequentially and electrically connected with a high-pass filter module and an amplification circuit and a demodulation module, in addition, the square wave generation circuit is also electrically connected with the demodulation module through a phase-shifting circuit, the output end of the demodulation module is respectively and electrically connected with each channel in the multi-channel amplification circuit, each channel comprises an amplification circuit and a low-pass filter module which are sequentially and electrically.

Furthermore, the multi-channel AD acquisition circuit is communicated with the DSP through an SPI interface.

Furthermore, the DSP communicates with the CAN box through a CAN bus.

Furthermore, the CAN box and the upper computer are communicated through a CAN bus.

Furthermore, all the amplifying circuits in the multi-channel amplifying circuit are program-controlled amplifying circuits.

The invention has the beneficial effects that:

for a dc signal or a slowly varying signal with a small amplitude, the device disclosed in the present invention generally uses a modulator or a chopper to convert the dc signal or the slowly varying signal into an ac signal, amplify and process the ac signal, and then demodulate and low-pass filter the ac signal to obtain an amplified signal to be measured, in order to prevent the adverse effects of 1/f noise and dc amplified dc drift (e.g., temperature drift of input offset voltage of operational amplifier). The weak signal detection device designed based on the lock-in amplifier shows excellent performance in the aspect of weak signal detection.

The modulator is used to shift the frequency harmonic of the dc or slowly varying signal to w0 of the modulation frequency and then amplify to avoid the adverse effects of 1/f noise.

The phase-sensitive detector is used for realizing the demodulation process of the modulation signal, the frequency and the phase angle can be simultaneously used for detection, and the probability that the noise and the signal have the same frequency and phase is very low.

The broadband noise is suppressed with a low-pass filter instead of a band-pass filter. The low-pass filter has a narrow frequency band, the frequency bandwidth of the low-pass filter is not influenced by the modulation frequency, and the stability of the low-pass filter is far better than that of the band-pass filter.

After AD acquisition, software filtering is added in the DSP, which is favorable for inhibiting white noise, and digital band-pass filters with different bandwidths are arranged in the data processing process, so that out-of-band signals can be inhibited to a greater extent.

And selecting digital filters with different orders according to different sampling sample quantities. In the actual use process, a corresponding filtering algorithm can be selected according to different conditions, the operation speed is improved, and the signal-to-noise ratio is increased to the maximum extent.

Different instructions can be sent through upper computer software to control different channel amplification factors, sampling points and the like, so that curves of all channels can be displayed, and curve processing and combination are convenient to carry out.

Drawings

FIG. 1a is a schematic diagram of a process for modulating a signal spectrum by a lock-in amplifier;

FIG. 1b is a schematic diagram of a phase sensitive detection process of a signal spectrum by a lock-in amplifier;

FIG. 2 is a block diagram showing the components of the detecting device disclosed in embodiment 1 of the present invention;

fig. 3 is a block diagram of the detecting device disclosed in embodiment 2 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

For a few tested signals with very low frequency and extremely weak signals close to direct current signals, 1/f noise at the low frequency generates very large interference on received signals, if a low-noise preamplifier is directly selected, the circuit design is simple, but the self noise and the 1/f noise of a receiving circuit appear at the output end of a post-stage amplifier with very large amplitude after being amplified, and when the amplitude of a useful signal is very small, the signal cannot be detected at all. The embodiment provides a weak signal detection device with strong anti-interference performance, which can effectively solve the problems.

The weak signal detection device with strong interference resistance is designed to reduce noise interference in a received signal, improve the noise suppression capability, enhance the amplification degree of a received useful weak signal and achieve the purpose of improving the signal-to-noise ratio of the received signal.

The working principle of the detection device disclosed by the embodiment is as follows: the process of shifting the signal spectrum by the lock-in amplifier is shown in fig. 1a, 1 b. The modulation process multiplies the low frequency signal Vs by a square wave carrier with frequency w0, thereby shifting its frequency spectrum to the modulation frequency w0, and then performs frequency selective amplification, so as not to amplify the 1/f noise and low frequency drift, as shown in fig. 1(a), wherein the dashed line represents the power spectral density of the 1/f noise and white noise. After ac amplification, the spectrum is shifted to dc (w =0) by a Phase Sensitive Detector (PSD), and noise is filtered by a Low Pass Filter (LPF), so as to obtain an amplified signal with high signal-to-noise ratio, as shown in fig. 1 (b).

Embodiment 1, as shown in fig. 2, in the detection apparatus disclosed in this embodiment, a received signal converted by a converter is first amplified by a first-stage low-pass filter circuit and then by a pre-low-noise amplifier circuit, then is chopped and modulated by a lock-in amplifier, and is modulated to a certain frequency (the frequency is determined according to a square wave generating circuit) and then is subjected to high-pass filtering, at this time, dc voltage offset CAN be removed again, then the signal is recovered by a demodulator, and is amplified by different multiples by a multi-channel amplifier circuit, and then enters an AD acquisition circuit after passing through the low-pass filter circuit, the AD acquisition circuit CAN simultaneously acquire signals of different channels, and finally, the signals are processed by a DSP, a software filtering function is added inside the DSP, the signals are digitally filtered, and finally, a CAN communication protocol is adopted and transmitted to upper computer software through a CAN box, and displaying curves of all channels in real time. The upper computer controls the control circuit to send different instructions such as a collecting command, a sampling point number, a stopping command and the like through software.

Embodiment 2, as shown in fig. 3, the amplification circuit factor in embodiment 1 can be changed only by changing the circuit resistance once determined. Embodiment 2 is to change the amplifying circuit in embodiment 1 into a program-controlled amplifying circuit, so that the amplifying times can be changed in real time by sending commands through an upper computer.

Claims

1. A weak signal detection device with strong anti-interference performance is characterized in that: the locking amplifier comprises a filter circuit, a pre-amplification circuit, a locking amplifier, a multi-channel amplification circuit, a multi-channel AD acquisition circuit, a DSP, a CAN box and an upper computer which are sequentially and electrically connected together, wherein the filter circuit receives signals, the locking amplifier comprises a modulation module, one input end of the modulation module is electrically connected with the pre-amplification circuit, the other input end of the modulation module is electrically connected with a square wave generation circuit, the output end of the modulation module is sequentially and electrically connected with a high-pass filter module and an amplification circuit and a demodulation module, in addition, the square wave generation circuit is also electrically connected with the demodulation module through a phase-shifting circuit, the output end of the demodulation module is respectively and electrically connected with each channel in the multi-channel amplification circuit, each channel comprises an amplification circuit and a low-pass filter module which are sequentially and electrically.

2. The weak signal detection device with strong interference immunity according to claim 1, wherein: and the multi-channel AD acquisition circuit is communicated with the DSP through an SPI interface.

3. The weak signal detection device with strong interference immunity according to claim 1, wherein: and the DSP communicates with the CAN box through a CAN bus.

4. The weak signal detection device with strong interference immunity according to claim 1, wherein: the CAN box and the upper computer are communicated through a CAN bus.

5. The weak signal detection device with strong interference immunity according to claim 1, wherein: and all the amplifying circuits in the multi-channel amplifying circuit are program-controlled amplifying circuits.