A dual lock-in amplifier used in water quality monitoring equipment, its signal processing method, and water quality monitoring equipment

Abstract

The invention discloses a double-phase-lock amplifier used in water quality monitoring equipment. The double-phase-lock amplifier used in the water quality monitoring equipment comprises a signal conversion unit, a signal regulation unit, a double-phase-lock amplifier unit and a microprogrammed control unit (MCU). The signal conversion unit comprises an electro-optical conversion module, a goal response module, a photovoltaic conversion module and an alternative current (AC) amplifier, wherein the electro-optical conversion module is connected with the photovoltaic conversion module through the goal response module, and the photovoltaic conversion module is connected with the AC amplifier. The signal regulation unit comprises a band-pass filter, an AC amplifier and a following and opposition module, wherein an output end of the AC amplifier is connected with the band-pass filter, and the band-pass filter is connected with the following and opposition module through the AC amplifier. The double-phase-lock amplifier unit comprises an analog switch, a low-pass filter and a direct current (DC) amplifier, wherein an output end of the following and opposition module is connected with the analog switch, and the analog switch is connected with the DC amplifier through the low-pass filter. The MCU comprises an analog-digital (AD) sampling module and an MCU, wherein the AD sampling module is connected with an output end of the DC amplifier, and an output end of the AD sampling module is connected with the MCU. The double-phase-lock amplifier used in the water quality monitoring equipment is capable of accurately and stably measuring the amplitude of extracted useful signals.

Description

Technical field [0001] The invention belongs to the field of analog circuit and instrument design, and in particular relates to a double lock-in amplifier used in water quality monitoring equipment and its signal processing method and water quality monitoring equipment. Background technique [0002] Lock-in Amplifier (LIA) is mainly used to detect weak signals with low signal-to-noise ratio. Even if the useful signal is submerged in the noise signal, the noise signal is much larger than the useful signal, as long as the frequency of the useful signal is known Value, the amplitude value of this signal can be accurately measured. The lock-in amplifier is actually an analog Fourier transformer. The output of the lock-in amplifier is a DC voltage, which is proportional to the signal amplitude of a certain frequency (the frequency of the reference signal) in the input signal, and other frequencies in the input signal The component will not make any contribution to the output voltage;...

AI Technical Summary

Problems solved by technology

Therefore, the existing lock-in amplifier needs to know the frequency of the input signal during application, and must keep the phase difference of the input signal and the reference signal constant; , changes in temperature and humidity, changes in optical signals caused by chemical reagents) will cause changes in the phase of useful signals in the input signal, and this change is not estimable and measurable. Therefore, to extract weak useful signals from noise, Even if the frequency of the useful signal is known, once the phase difference between the useful signal and the reference signal changes, the DC voltage value output by the lock-in amplifier will be inaccurate and unstable, which will directly lead to inaccurate and unstable measurement results of the monitoring instrument

In addition, the existing water quality monitoring equipment and instruments, especially the online water quality monitoring instruments, generally have problems such as large indication error and repeatability error of the measurement results due to poor anti-interference ability and poor environmental adaptability.

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