CN112697762B - High-precision dissolved oxygen meter system and special SoC - Google Patents
High-precision dissolved oxygen meter system and special SoC Download PDFInfo
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/64—Fluorescence; Phosphorescence
- G01N21/6428—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes"
- G01N21/643—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes" non-biological material
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- H—ELECTRICITY
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- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
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- H03M1/129—Means for adapting the input signal to the range the converter can handle, e.g. limiting, pre-scaling ; Out-of-range indication
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/64—Fluorescence; Phosphorescence
- G01N21/6428—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes"
- G01N2021/6432—Quenching
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Abstract
The invention belongs to the technical field of sensing and measuring instruments, and particularly relates to an oxygen dissolving instrument system and a special SoC. The dissolved oxygen instrument system comprises an emission module (RDO, FIR, current domain DAC), a sensing module (a fluorescent film, a filter and dissolved oxygen solution), a receiving module (PD, TIA, PGA and an analog phase-locked amplification module), and a signal processing and control module. The system utilizes RDO, FIR and DAC to generate sinusoidal current signals to drive red and blue LEDs, the generated fluorescence is received by PD and converted into current signals, converted into voltage signals through TIA and converted into differential signals through PGA; through the analog phase-locked amplification module, after an output signal passes through the PGA and the filter, harmonic waves are eliminated and the maximum range input of the ADC is achieved; the angle is calculated by the CORDIC algorithm after the digital signal is converted into a digital signal through the ADC and sent to the CPU. The dissolved oxygen meter system can reduce the requirement on the fluorescent film, improve the precision and eliminate the influence of noise on angle calculation.
Description
Technical Field
The invention belongs to the technical field of sensing and measuring instruments, and particularly relates to an oxygen dissolving instrument system and a special SoC.
Background
Dissolved oxygen refers to free oxygen and non-complex oxygen in water or other liquids, and is involved in various biochemical and physiological activities. The content of dissolved oxygen in water is an important index of water quality, and the measurement of the content of dissolved oxygen is an important factor for evaluating the purification of water quality. The dissolved oxygen instrument plays an important role in the fields of biomedicine, food production, industrial and agricultural production and the like. The technology for researching real-time accurate measurement of the dissolved oxygen content has practical significance.
The dissolved oxygen measurement method mainly includes an iodine titration method, an electrochemical method, and an optical method. The traditional iodine titration method and the electrochemical method have the defects of large system area, low precision and the like due to the characteristics of the inherent structure and the analysis method. The optical dissolved oxygen sensor utilizes the fluorescence quenching principle and has the advantages of small area, no oxygen consumption and high anti-interference capability. Although the maintenance frequency of the fluorescence quenching sensor is low, and continuous online detection is easy to perform, it is still difficult to realize accurate detection. The existing dissolved oxygen detection technology based on the fluorescence quenching principle, such as time domain direct fluorescence lifetime detection, cannot meet the actual requirements of different applications in terms of overall precision and real-time performance.
In practical production and application, the change of the dissolved oxygen concentration is a continuous dynamic process. Therefore, a high-precision real-time dissolved oxygen detection method and system are crucial. The fluorescent films used by some of the currently developed dissolved oxygen meters based on the fluorescence quenching principle are different and have different performances, and once the fluorescent films have problems, the fluorescent films are troublesome to replace. Therefore, a chip of the dissolved oxygen meter which has high precision and can adapt to different fluorescent films is urgently needed at present.
Disclosure of Invention
The invention aims to provide a high-precision dissolved oxygen meter and a special SoC.
The structure of the high-precision oxygen dissolving instrument system provided by the invention is shown in figure 1; the system consists of four modules as follows: the device comprises a transmitting module, a sensing module, a receiving module and a signal processing and controlling module; wherein:
the transmitting module is used for generating sine current to drive the red light LED and the blue light LED, and simultaneously generating same-frequency orthogonal signals for frequency mixing of the receiving module, and comprises the following components: RDO (digital recursive oscillator), FIR (finite long single-bit impulse response filter), current-domain DAC (digital-to-analog converter), and switches; the RDO generates a step digital sine wave, the step digital sine wave is subjected to FIR filtering and then converted into an analog sine current signal by the current domain DAC, and the switch selects the driven LED.
The frequency of the sinusoidal current signal generated by the transmitting module with the structure is adjustable, the frequency of the generated sinusoidal current signal can be changed only by changing the frequency of the main clock, and an orthogonal carrier signal with good orthogonality is generated.
The sensing module consists of a fluorescent film, an optical filter and a dissolved oxygen solution; the fluorescent film is placed in the dissolved oxygen solution and used for absorbing light emitted by the LED and exciting fluorescence; the optical filter is arranged between the fluorescent film and the photodiode and used for filtering other light. The principle of fluorescence quenching is used here: the light emitted by the blue light LED passes through the fluorescent film to generate red fluorescence, the generated red fluorescence and the original blue light have a phase shift related to dissolved oxygen, the light emitted by the red light LED passes through the fluorescent film to generate a fixed phase shift, and the red light reference is used for offsetting the influence of the phase shift of a light path and a circuit.
The receiving module consists of a PD (photodiode), a direct current elimination TIA (transimpedance amplifier), a PGA (programmable gain amplifier), an analog phase-locked amplification module and an ADC (analog-to-digital converter); the PD is used for absorbing fluorescence generated by the sensing module and converting the fluorescence into a current signal, the current signal is converted into a voltage signal through the TIA, the voltage signal is demodulated into a direct current signal related to phase shift through the PGA and the analog phase-locked amplification module, and the direct current signal is converted into a digital signal through the ADC. The receiving module can automatically eliminate the influence of the direct current of the PD on the linearity of the TIA by using the direct current elimination type TIA, and improves the receiving precision.
The signal processing and control module is used for reading the digital signal output by the ADC and using a CORDIC algorithm 1 Calculating an angle (the angle reflects the phase shift between fluorescence and exciting light), and forming a feedback network with the direct current elimination type TIA to realize automatically controlled direct current elimination; and the conduction time and sequence of the red light LED and the blue light LED are controlled, so that the angle measurement is ensured.
The invention can eliminate the influence of noise on angle calculation by utilizing an analog phase locking technology and a CORDIC algorithm.
In the invention, a digital recursive oscillator (RDO), a finite-length single-bit impulse response Filter (FIR) and a current source DAC are used for generating sinusoidal current signals to drive red light and blue light LEDs, light emitted by the blue light LEDs passes through a fluorescent film to generate red fluorescence, the generated red fluorescence and blue excitation light have phase shift related to dissolved oxygen, light emitted by the red light LEDs passes through the fluorescent film to generate fixed phase shift, and the influence of the phase shift of a light path and a circuit can be counteracted by using red light reference. The generated red fluorescent light and red light emitted by the red LED are received by a Photodiode (PD) and converted into current signals, the current signals are converted into voltage signals through a direct current elimination type trans-impedance amplifier (TIA), and the voltage signals are converted into differential signals through a Programmable Gain Amplifier (PGA). And then, a differential local oscillator signal of a mixer of the phase-locked amplification module is derived from the RDO module through the analog phase-locked amplification module, so that the basic same frequency is ensured. The basic principle of the phase-locked amplification module is as follows:
the input differential signal of the mixer is:
wherein the phase isθNoise isn(t). The output signal from the mixer is obtained by the following equation:
the output signal is filtered by a filter to remove higher harmonics and the input signal itself, and is output as a low frequency signal related to amplitude and phase. Where the average value of the noise is 0. The signals finally input to the ADC are respectively
。
Therefore, the signal output by the phase-locked amplification module passes through the PGA, the filter and the buffer, and then the harmonic wave is eliminated and the maximum range input of the ADC is achieved. The angle is calculated by CORDIC algorithm after the digital signal is converted into digital signal by ADC and sent to CPU for division.
The invention also relates to an oxygen dissolution instrument SoC comprising: the device comprises a signal generating module, a signal collecting module and a signal processing and controlling module; wherein:
the signal generating module structurally comprises: RDO, FIR, current domain DAC (digital to analog converter);
the signal acquisition module structurally comprises: PD, direct current elimination TIA, PGA, an analog phase-locking amplification module and ADC;
the signal processing and control module is composed of a CPU.
In the signal generation module, the frequency of the generated sinusoidal current signal is adjustable, the frequency of the generated sinusoidal current signal can be changed only by changing the frequency of the main clock, and an orthogonal carrier signal with good orthogonality can be generated.
In the signal acquisition module, the direct current elimination type TIA is a feedback type TIA, and the current input to the TIA is controlled by detecting the amplitude range of the output voltage of the TIA, so that the TIA can ensure good linearity. The reason for this structure is that the PD has a direct current. The PGA converts the TIA output to a differential output and converts the common mode level. The analog phase-locked module consists of a mixer, a PGA and a filter, can convert a phase signal into a direct-current voltage signal, and can eliminate the influence of noise; an ADC (analog-to-digital converter) converts an analog signal into a digital signal.
In the signal processing and control module, the digital signal output by the ADC is read
After division, the angle is calculated by using a CORDIC algorithm, and a feedback network is formed with the direct current elimination type TIA, so that automatic control direct current elimination is realized. And the conduction time and sequence of the red light LED and the blue light LED are controlled, so that the angle measurement is ensured.
The invention has the advantage that the transmitting module of the system generates a sinusoidal current signal by using digital RDO, FIR and current domain DAC. The frequency of the generated sinusoidal current signal can be adjusted, and the requirement on the fluorescent film is reduced. The frequency of the generated sinusoidal current signal can be changed by only changing the frequency of the master clock and quadrature carrier signals with good orthogonality can be generated. The receiving module can automatically eliminate the influence of the direct current of the PD on the linearity of the TIA by using the direct current elimination type TIA, and the precision is improved. The influence of noise on the angle calculation can be eliminated by utilizing an analog phase locking technology and a CORDIC algorithm.
Reference to the literature
1.Zhu H, Ge Y, Jiang B. Modified CORDIC algorithm for computation ofarctangent with variable iterations[C]. IEEE International Conference on SignalProcessing. IEEE, 2016。
Drawings
FIG. 1 is a schematic representation of the structure of an oxygen dissolving instrument.
Reference numbers in the figures: 1 is a direct current elimination TIA,2 is a mixer, 3 is a low-pass filter, 4 is a buffer,5 is a comparator, and 6 is a sine current generator (composed of RDO + FIR + current domain DAC); 7 is a special SoC,8 is a signal processing and control module, 9 is an optical filter, 10 is a fluorescent film, 11 is a dissolved oxygen solution, 12 is a red light LED,13 is a blue light LED, and 14 is a PD.
Detailed Description
Detailed description of the drawings technical solutions in the embodiments of the present invention are specifically and specifically described below with reference to the drawings. The described embodiment is only one embodiment of the present invention, not all embodiments, and other embodiments without inventive labor, which are obtained by the ordinary skilled person in the art, are within the protection scope of the present invention.
The emission module generates a sinusoidal current to drive the red LED12 and the blue LED 13. The transmitting module consists of a sinusoidal current generator 6 and a switch. The conduction of the two LEDs is controlled by a signal processing and control module 8 driving switch. The RDO shown therein is a digital domain recursive oscillator that produces a sinusoidal waveform, FIR filters for filtering, and a current domain DAC for converting the digital sinusoidal waveform to an analog current signal, where a digital counter is used to produce orthogonal carrier signals at the same frequency as the RDO for mixing.
The sensing module consists of a fluorescent film 10, an optical filter 9 and a dissolved oxygen solution 11, and the fluorescence quenching principle is utilized: the light emitted by the blue light LED13 passes through the fluorescent film to generate red fluorescent light, the fluorescent light and the exciting light have phase shift, wherein the size of the phase shift is related to the dissolved oxygen amount of the solution, the light emitted by the red light LED12 passes through the fluorescent film to generate fixed phase shift, and the influence of the phase shift of a light path and a circuit can be counteracted by using red light reference.
The receiving module consists of a PD 14, a direct current elimination TIA 1, a PGA, an analog phase-locked amplifying module and an ADC. The direct current elimination type TIA is a feedback type TIA, and the current input to the TIA is controlled by detecting the amplitude range of the output voltage of the TIA 1, so that the TIA can ensure good linearity. The reason for this structure is that the PD 14 has a direct current. The PGA shown converts the TIA output to a differential output and common mode signal to 2.5V. The analog phase-locked module consists of a mixer 2, a PGA and a filter 3, and can convert a phase signal into a direct-current voltage signal and eliminate the influence of noise. The ADC shown converts an analog signal to a digital signal.
The signal processing and control module 8 reads the digital signal output by the ADC
And after division, calculating the angle by using a CORDIC algorithm, and simultaneously forming a feedback network with the direct current elimination type TIA 1 to realize automatically controlled direct current elimination. And the conduction time and sequence of the red light LED and the blue light LED are controlled, so that the angle measurement is ensured. Preferably, the signal processing and control module 8 may be implemented on the basis of a processor (CPU).
Claims (2)
1. The high-precision dissolved oxygen meter system is characterized by comprising the following four modules: the device comprises a transmitting module, a sensing module, a receiving module and a signal processing and controlling module; wherein:
the transmitting module is used for generating sine current to drive the red light LED and the blue light LED, and simultaneously generating same-frequency orthogonal signals for frequency mixing of the receiving module, and comprises the following components: the device comprises a digital recursive oscillator (RDO), a finite-length single-bit impulse response Filter (FIR), a current-domain digital-to-analog converter (DAC) and a switch; the RDO generates a step digital sine wave, the step digital sine wave is converted into an analog sine current signal by the current domain DAC after FIR filtering, and the LED driven by the current domain DAC is selected by the switch; the frequency of the sinusoidal current signal generated by the transmitting module is adjustable, namely the frequency of the main clock is changed, so that the frequency of the generated sinusoidal current signal can be changed, and an orthogonal carrier signal with good orthogonality is generated;
the sensing module consists of a fluorescent film, an optical filter and a dissolved oxygen solution; the fluorescent film is placed in the dissolved oxygen solution and used for absorbing light emitted by the blue LED and exciting fluorescence; the optical filter is arranged between the fluorescent film and the photodiode and is used for filtering other light; the light emitted by the blue light LED passes through the fluorescent film to generate red fluorescent light, the generated red fluorescent light and the blue light exciting light have a phase shift related to dissolved oxygen, the light emitted by the red light LED passes through the fluorescent film to generate a fixed phase shift, and the influence of the phase shift of a light path and a circuit can be counteracted by using red light reference;
the receiving module consists of a photodiode PD, a direct current elimination type trans-impedance amplifier TIA, a programmable gain amplifier PGA, an analog phase-locked amplifying module and an analog-to-digital converter ADC; the PD is used for absorbing fluorescence generated by the sensing module and converting the fluorescence into a current signal, converting the current signal into a voltage signal through the TIA, and demodulating the voltage signal into a direct current signal related to phase shift through the PGA and the analog phase-locked amplification module; the analog phase-locked amplification module is formed by sequentially connecting a frequency mixer, a programmable gain amplifier PGA, a low-pass filter and a buffer; after the signal input into the phase-locked amplification module passes through the mixer, the PGA, the low-pass filter and the buffer, harmonic waves are eliminated and the maximum range input of the ADC is achieved; then the digital signals are converted into digital signals through an ADC;
the signal processing and control module is used for reading the digital signal output by the ADC, calculating an angle reflecting the phase shift between fluorescence and exciting light by using a CORDIC algorithm, and forming a feedback network with the direct current elimination TIA to realize automatically controlled direct current elimination; the conduction time and sequence of the red light LED and the blue light LED are controlled, and angle measurement is guaranteed;
the method comprises the following steps that a sinusoidal current signal is generated by using RDO, FIR and a current domain DAC to drive a red LED and a blue LED, light emitted by the blue LED passes through a fluorescent film to generate red fluorescence, the generated red fluorescence and blue excitation light have a phase shift related to dissolved oxygen, light emitted by the red LED passes through the fluorescent film to generate a fixed phase shift, and red light reference is used for offsetting the influence of the phase shift of a light path and a circuit; the generated red fluorescence and red light emitted by the red LED are received by the PD and converted into current signals, the current signals are converted into voltage signals through the TIA, and the voltage signals are converted into differential signals through the PGA; and then, through the analog phase-locked amplification module, a differential local oscillator signal of a mixer of the analog phase-locked amplification module comes from the RDO module, so that the basic same frequency is ensured.
2. A dedicated SoC based on the dissolved oxygen meter system of claim 1, comprising: the device comprises a signal generating module, a signal collecting module and a signal processing and controlling module; wherein:
the signal generating module structurally comprises: RDO, FIR, current domain DAC and switch;
the signal acquisition module structurally comprises: PD, direct current elimination TIA, PGA, an analog phase-locking amplification module and ADC;
the signal processing and control module consists of a CPU;
in the signal generation module, the frequency of the generated sinusoidal current signal is adjustable, namely, the frequency of the generated sinusoidal current signal can be changed only by changing the frequency of the main clock, and an orthogonal carrier signal with good orthogonality can be generated;
in the signal acquisition module, the current input to the TIA is controlled by detecting the amplitude range of the output voltage of the TIA, so that the TIA can ensure good linearity; the PGA converts the output of the TIA into differential output and converts a common mode level; the analog phase-locked module consists of a frequency mixer, a PGA, a low-pass filter and a buffer, can convert a phase signal into a direct-current voltage signal, and can eliminate the influence of noise; the ADC converts the analog signal into a digital signal;
in the signal processing and control module, the digital signal output by the ADC is read
After the division, calculating an angle by using a CORDIC algorithm, and simultaneously forming a feedback network with a direct current elimination type TIA to realize automatically controlled direct current elimination; and the conduction time and sequence of the red light LED and the blue light LED are controlled, so that the angle measurement is ensured.
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| CN117147517B (en) * | 2023-10-31 | 2024-03-22 | 青岛海研电子有限公司 | Circuit for detecting dissolved oxygen |
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| CN201974383U (en) * | 2011-01-19 | 2011-09-14 | 高国强 | Pulse optical source fibre oxygen detector |
| CN102579012A (en) * | 2012-03-15 | 2012-07-18 | 天津大学 | Dynamic fluorescence-optical breast tomography device on basis of phase locking photon counting measurement |
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