Water quality monitoring circuit and water quality analyzer

Abstract

The present application relates to a kind of water quality monitoring circuit and water quality analyzer, water quality monitoring circuit, for the monitoring of coliform group in water quality, comprising: colorimetric light source control circuit unit, for using gain adjustment control the stable output of colorimetric light source;Ultraviolet light source control circuit unit, for using gain adjustment control the stable output of ultraviolet light source;Colorimetric detection circuit unit, for detecting the target light signal after colorimetric light source irradiation coliform group culture tank, and it is converted into first voltage signal;Fluorescence detection circuit unit, for detecting the fluorescence signal generated after ultraviolet light source irradiation coliform group culture tank, and it is converted into second voltage signal;ADC data acquisition circuit unit, for converting first voltage signal and second voltage signal into corresponding digital signal respectively, to obtain the concentration of coliform group.The present application can simultaneously carry out colorimetric and fluorescence detection, not only high efficiency, and high precision.

Description

Technical Field

[0001] This invention belongs to the field of analytical testing technology, specifically relating to a water quality monitoring circuit and a water quality analyzer. Background Technology

[0002] Escherichia coli is ubiquitous in the intestines of humans and animals. The presence of Escherichia coli in the natural environment indicates fecal contamination and the potential presence of other intestinal pathogens. Therefore, the determination of coliform bacteria can serve as an indicator of fecal contamination in water or food.

[0003] In microbiological testing, coliform bacteria are the most abundant bacteria in feces. Furthermore, after being excreted in feces, their survival time is roughly similar to that of major intestinal pathogens. In terms of testing methods, counting coliform bacteria is also simple and easy to perform. Therefore, using coliform bacteria as an indicator of fecal contamination is quite appropriate.

[0004] In practical applications, common methods for measuring *E. coli* include: enzyme substrate method, multiple-tube fermentation method, membrane filtration method, and PCR (gene fragmentation). According to the national standard GB / T4789.32-2002, analyzers generally use the enzyme substrate method. The main principle is that total coliforms, fecal coliforms, and *Escherichia coli* can produce β-galactosidase under specific culture conditions. This β-galactosidase can decompose the colorless substrate o-nitrophenyl-β-D-galactopyranoside in the selective culture medium into yellow o-nitrophenol, thus turning the culture medium yellow. The concentration of total *E. coli* can be obtained by colorimetric measurement. *Escherichia coli* also produces β-glucuronidase, which can decompose 4-methylumbelliferone-β-D-glucuronide in the selective culture medium into 4-methylumbelliferone. This 4-methylumbelliferone fluoresces under ultraviolet light, and the concentration of *E. coli* can be determined by measuring the fluorescence intensity. Therefore, the concentrations of total coliforms, fecal coliforms, and *Escherichia coli* can be obtained.

[0005] Existing detection circuits suffer from unstable light source driving and the inability to perform colorimetric and fluorescence detection simultaneously, resulting in low detection accuracy and efficiency. Summary of the Invention

[0006] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a water quality monitoring circuit and a water quality analyzer that meet one or more of the aforementioned requirements.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A water quality monitoring circuit for monitoring coliform bacteria in water, comprising:

[0009] The colorimetric light source control circuit unit is used to control the stable output of the colorimetric light source by adjusting the gain.

[0010] The ultraviolet light source control circuit unit is used to control the stable output of the ultraviolet light source by adjusting the gain.

[0011] The colorimetric detection circuit unit is used to detect the target light signal emitted after the colorimetric light source irradiates the coliform culture tank, and convert it into a first voltage signal.

[0012] The fluorescence detection circuit unit is used to detect the fluorescence signal generated after the coliform bacteria culture vessel is irradiated by an ultraviolet light source and convert it into a second voltage signal.

[0013] The ADC data acquisition circuit unit is used to convert the first voltage signal and the second voltage signal into corresponding digital signals to obtain the concentration of coliform bacteria.

[0014] As a preferred embodiment, the colorimetric light source control circuit unit includes a colorimetric light source, a first light source constant current driving circuit module, a first reference detector feedback circuit module, and a first gain adjustment circuit module. The first light source constant current driving circuit module is used to drive the colorimetric light source to emit light. The first reference detector feedback circuit module is used to detect the light signal of the colorimetric light source and convert it into a voltage signal. The first gain adjustment circuit module is used to dynamically adjust the driving current output by the first light source constant current driving circuit module by comparing the voltage signal with a preset input voltage.

[0015] As a preferred embodiment, the ultraviolet light source control circuit unit includes an ultraviolet light source, a second light source constant current drive circuit module, a second reference detector feedback circuit module, and a second gain adjustment circuit module. The second light source constant current drive circuit module is used to drive the ultraviolet light source to emit light. The second reference detector feedback circuit module is used to detect the light signal of the ultraviolet light source and convert it into a voltage signal. The second gain adjustment circuit module is used to dynamically adjust the drive current output by the second light source constant current drive circuit module by comparing the voltage signal with a preset input voltage.

[0016] As a preferred embodiment, the first gain adjustment circuit module or the second gain adjustment circuit module includes resistors R16 and R25, operational amplifier U7, resistor R30, capacitor C36, operational amplifier U12, capacitor C30, capacitor C31, resistors R28 and R29. Resistor R16 is connected to the non-inverting input of the first or second reference detector feedback circuit module and operational amplifier U7, respectively. Resistor R25 is connected to the inverting input and the output input of operational amplifier U7, respectively. Resistors R16, R25, and operational amplifiers... U7 forms a voltage follower; resistor R30 and capacitor C36 form an RC filter. The voltage output of the microcontroller is connected to the inverting input of operational amplifier U12 after passing through the RC filter. The non-inverting input of operational amplifier U12 is connected to the output of operational amplifier U7 through resistor R29. The output of operational amplifier U12 is connected to either the first light source constant current drive circuit module or the second light source constant current drive circuit module. Capacitors C30 and C31, resistors R28 and R29 are connected in series and form a loop with the non-inverting input and output of operational amplifier U12 for loop compensation.

[0017] Op-amps U7 and U12 are powered by a power supply.

[0018] As a preferred embodiment, the first or second light source constant current driving circuit module includes a current feedback resistor R40, a transistor Q1, an operational amplifier U15, a resistor R39, and a capacitor C39. The non-inverting input of the operational amplifier U15 is connected to the output of the operational amplifier U12, and the output of the operational amplifier U15 is connected to the base of the transistor Q1. The collector of the transistor Q1 is connected to the positive terminal of the power supply, and the emitter of the transistor Q1 is connected to the positive terminal of the colorimetric light source or the ultraviolet light source. The negative terminal of the colorimetric light source or the ultraviolet light source and the inverting input of the operational amplifier U15 are respectively connected to the negative terminal of the power supply through the current feedback resistor R40. The resistor R39 and the capacitor C39 are connected in series and between the negative terminal of the colorimetric light source or the ultraviolet light source and the inverting input of the operational amplifier U15 to form a loop compensation.

[0019] Op-amp U15 is powered by a power supply.

[0020] As a preferred embodiment, the first or second reference detector feedback circuit module includes a photodetector D2, a resistor R20, an operational amplifier U11, and a feedback capacitor C25. The positive terminal of the photodetector D2 is connected to the non-inverting input of the operational amplifier U11, and the negative terminal of the photodetector D2 is connected to the inverting input of the operational amplifier U11. The resistor R20 and the feedback capacitor C25 are connected in parallel and are respectively connected to the inverting input and the output terminal of the operational amplifier U11. The output terminal of the operational amplifier U11 is connected to the resistor R16.

[0021] Among them, resistor R20 and operational amplifier U11 form a transimpedance amplifier; operational amplifier U11 is powered by a power supply.

[0022] As a preferred embodiment, the colorimetric detection circuit unit or fluorescence detection circuit unit includes a photodetector D3, an operational amplifier U10, a resistor R22, a feedback capacitor C26, resistors R17, R26, R24, and an operational amplifier U6. The positive terminal of the photodetector D3 is connected to the non-inverting input of the operational amplifier U10, and the negative terminal of the photodetector D3 is connected to the inverting input of the operational amplifier U10. Resistor R22 is connected in parallel with the feedback capacitor C26 and is connected to the inverting input and the output terminal of the operational amplifier U10, respectively. Resistor R17 is connected to the non-inverting input of the operational amplifier U6 and the output terminal of the operational amplifier U10, respectively. Resistor R26 is connected to the output terminal and the inverting input of the operational amplifier U6, respectively. Resistor R24 ​​is connected to the inverting input of the operational amplifier U6 and the negative power supply terminal, respectively.

[0023] Among them, resistor R22 and operational amplifier U10 constitute a transimpedance amplifier, and operational amplifiers U6 and U10 are powered by the power supply.

[0024] As a preferred embodiment, the colorimetric detection circuit unit is electrically connected to the ADC data acquisition circuit unit through the first filter circuit unit.

[0025] As a preferred embodiment, the fluorescence detection circuit unit is electrically connected to the ADC data acquisition circuit unit via an integration circuit unit and a second filter circuit unit in sequence.

[0026] The present invention also provides a water quality analyzer that employs the water quality monitoring circuit described in any of the above embodiments.

[0027] Compared with the prior art, the beneficial effects of this invention are:

[0028] (1) The brightness of the light source can be set; the brightness of the light-emitting diode of the light source can be controlled by the microcontroller controlling the initial input voltage, which is flexible and convenient for detecting samples of different concentrations.

[0029] (2) The light source has high stability and is automatically adjusted in real time; the entire circuit uses a circuit to perform negative feedback, automatically adjusts and controls the current of the light-emitting diode, has a fast response speed, stable output, and the measured fluctuation is less than 0.5‰.

[0030] (3) Low system drift; the temperature drift of the entire drive circuit is less than 1‰ in the full temperature range of the instrument (0-50℃); the time drift is less than 5‰ in long-term testing;

[0031] (4) Long lifespan of the light source. As is well known, the luminous intensity of LED light sources will weaken as the usage time increases, and the measurement accuracy of instruments will be difficult to guarantee in the long run. However, the present invention changes the driving current by automatically adjusting the gain of the hardware, so that the light source can still maintain the same luminous intensity as the initial state after weakening.

[0032] (5) High measurement efficiency; The design of two measurement circuits can simultaneously measure colorimetry and fluorescence, which reduces the time by half compared to traditional measurement circuits.

[0033] (6) High measurement accuracy: Since there is a big difference between the colorimetric light intensity and the fluorescence light intensity, it is difficult to coordinate the two different light signals with a fixed amplification factor using the same detection circuit. However, using two detection circuits can amplify the two different signals to a suitable range for detection, which is more accurate. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the water quality monitoring circuit according to an embodiment of the present invention;

[0035] Figure 2 This is a circuit diagram of the colorimetric light source control circuit unit according to an embodiment of the present invention;

[0036] Figure 3 This is a circuit diagram of the colorimetric detection circuit unit, fluorescence detection circuit unit, and ADC data acquisition circuit unit according to an embodiment of the present invention. Detailed Implementation

[0037] To more clearly illustrate the embodiments of the present invention, specific implementation methods will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0038] Example 1:

[0039] like Figure 1 As shown, the water quality monitoring circuit of this embodiment includes a colorimetric light source control circuit unit (i.e., colorimetric light source control circuit), an ultraviolet light source control circuit unit (i.e., ultraviolet light source control circuit), a colorimetric detection circuit unit (i.e., colorimetric detection circuit), a fluorescence detection circuit unit (i.e., fluorescence detection circuit), and an ADC data acquisition circuit unit (abbreviated as ADC), which realizes the determination of the concentration of total coliforms, fecal coliforms, and Escherichia coli in water.

[0040] The colorimetric light source control circuit unit in this embodiment is used to control the stable output of the colorimetric light source using gain adjustment. Specifically, the colorimetric light source control circuit unit includes a colorimetric light source, a first light source constant current driving circuit module (hereinafter referred to as the light source driving circuit), a first reference detector feedback circuit module (hereinafter referred to as the reference detector), and a first gain adjustment circuit module (hereinafter referred to as the gain adjustment circuit). The first light source constant current driving circuit module is used to drive the colorimetric light source to emit light. The first reference detector feedback circuit module is used to detect the light signal of the colorimetric light source and convert it into a voltage signal. The first gain adjustment circuit module is used to dynamically adjust the driving current output by the first light source constant current driving circuit module by comparing the voltage signal with a preset input voltage.

[0041] like Figure 2 As shown, the first gain adjustment circuit module includes resistors R16 and R25, operational amplifier U7, resistor R30, capacitor C36, operational amplifier U12, capacitor C30, capacitor C31, resistors R28 and R29. Resistor R16 is connected to the first reference detector feedback circuit module and the non-inverting input of operational amplifier U7. Resistor R25 is connected to the inverting input and output of operational amplifier U7. Resistors R16, R25, and operational amplifier U7 constitute a voltage follower. One end of resistor R30 is connected to the voltage output terminal MCU_Vout of the microcontroller, and the other end is connected to... Connect the inverting input of op-amp U12 and capacitor C36. Capacitor C36 is also connected to the negative terminal of the power supply. Resistor R30 and capacitor C36 form an RC filter. The voltage output of the microcontroller is connected to the inverting input of op-amp U12 after passing through the RC filter. The non-inverting input of op-amp U12 is connected to the output of op-amp U7 through resistor R29. The output of op-amp U12 is connected to the first light source constant current drive circuit module. Capacitor C30, capacitor C31, resistor R28 and resistor R29 are connected in series and form a loop with the non-inverting input and output of op-amp U12 for loop compensation.

[0042] Among them, operational amplifiers U7 and U12 are powered by a power supply.

[0043] The first light source constant current drive circuit module includes a current feedback resistor R40, a transistor Q1, an operational amplifier U15, a resistor R39, and a capacitor C39. The non-inverting input of the operational amplifier U15 is connected to the output of the operational amplifier U12. The output of the operational amplifier U15 is connected to the base 1 of the transistor Q1. The collector 3 of the transistor Q1 is connected to the positive terminal VCC of the power supply. The emitter 2 of the transistor Q1 is connected to the positive terminal of the colorimetric light source (i.e., light-emitting diode) D4. The negative terminal of the colorimetric light source D4 and the inverting input of the operational amplifier U15 are respectively connected to the negative terminal of the power supply through the current feedback resistor R40. The resistor R39 and the capacitor C39 are connected in series and between the negative terminal of the colorimetric light source D4 and the inverting input of the operational amplifier U15 to form a loop compensation.

[0044] The operational amplifier U15 is powered by a power supply.

[0045] The first reference detector feedback circuit module includes a photodetector D2, a resistor R20, an operational amplifier U11, and a feedback capacitor C25. The positive terminal of the photodetector D2 is connected to the non-inverting input of the operational amplifier U11, and the negative terminal of the photodetector D2 is also connected to the inverting input of the operational amplifier U11 and the negative power supply terminal, respectively. The resistor R20 and the feedback capacitor C25 are connected in parallel and are connected to the inverting input and the output terminal of the operational amplifier U11, respectively. The output terminal of the operational amplifier U11 is connected to a resistor R16.

[0046] Among them, resistor R20 and operational amplifier U11 form a transimpedance amplifier; operational amplifier U11 is powered by a power supply.

[0047] The working principle of the colorimetric light source control circuit unit in this embodiment is as follows:

[0048] 1. The initial input voltage MCU_Vout of the first gain adjustment circuit module is set by the microcontroller. After RC filtering, it is input to the inverting input of the operational amplifier U12. At this time, since the light-emitting diode D4 is not lit, the output of the first reference detector feedback circuit module is 0V, and the voltage input to the non-inverting input of the operational amplifier U12 is also 0V. The voltage at the inverting input is greater than that at the non-inverting input, and the operational amplifier U12 outputs the maximum value (power supply voltage VCC) to the non-inverting input of the operational amplifier U15. The first light source constant current drive circuit module starts to work.

[0049] 2. At this time, since the input of the first light source constant current drive circuit module is at its maximum value, the operational amplifier U15 controls the transistor Q1 to generate the maximum current value, the light-emitting diode D4 generates the maximum light intensity, and the brightness reaches the maximum. The loop compensation network R39 and C39 make the light source constant current drive circuit work stably and will not oscillate.

[0050] 3. In the first reference detector feedback circuit module, the photodetector D2 detects the light from the LED D4, generating a corresponding current. The transimpedance amplifier, composed of resistor R20 and operational amplifier U11, converts this current value into a corresponding voltage value, which is then output to the next stage circuit for gain adjustment. Feedback capacitor C25 limits the bandwidth to maintain circuit stability. Specifically, since the output voltage is obtained by multiplying the current output by the photodetector by resistor R20, a low-temperature drift resistor with a precision of one-thousandth is used, and capacitor C25 is also a low-temperature drift capacitor made of NP0 material. Gain adjustment compares this voltage signal with the microcontroller-controlled voltage MCU_Vout, providing negative feedback: when the voltage signal is greater than MCU_Vout, the current output of the constant current source is reduced, thus weakening the light intensity of LED D4; when the voltage signal is less than MCU_Vout, the current output of the constant current source is increased, thus strengthening the light intensity of LED D4. Through dynamic adjustment, a very stable light source can be obtained, which directly improves the stability and accuracy of subsequent colorimetric measurements and fluorescence detection.

[0051] 4. The voltage follower circuit composed of resistors R16 and R25 and operational amplifier U7 buffers the output voltage of the previous stage circuit. The output of this circuit is equal to the input. It is mainly used to increase the impedance of the input to operational amplifier U12 and prevent the transimpedance amplifier from affecting the loop compensation network of U12.

[0052] 5. The voltage output from operational amplifier U7 passes through resistor R29 and enters the non-inverting input of operational amplifier U12. At this point, the voltage at the non-inverting input is greater than that at the inverting input, causing the output value of operational amplifier U12 to decrease from its maximum value. This reduces the control current of the first light source constant current drive circuit module, consequently reducing the luminous intensity of LED D4. The output voltage of the first reference detector feedback circuit module also decreases until the voltage at the non-inverting input of operational amplifier U12 equals that at the inverting input, achieving equilibrium. Specifically, the loop compensation composed of capacitors C30 and C31, resistors R28 and R29 ensures that the entire adjustment circuit quickly and stably reaches equilibrium during negative feedback adjustment, preventing oscillation. All operational amplifiers in the circuit are low-offset, low-drift precision operational amplifiers to guarantee the stability of each stage's output.

[0053] The ultraviolet light source control circuit unit in this embodiment is used to control the stable output of the ultraviolet light source using gain adjustment. Specifically, the ultraviolet light source control circuit unit includes an ultraviolet light source, a second light source constant current drive circuit module, a second reference detector feedback circuit module, and a second gain adjustment circuit module. The second light source constant current drive circuit module is used to drive the ultraviolet light source to emit light. The second reference detector feedback circuit module is used to detect the light signal of the ultraviolet light source and convert it into a voltage signal. The second gain adjustment circuit module is used to dynamically adjust the drive current output by the second light source constant current drive circuit module by comparing the voltage signal with a preset input voltage.

[0054] In this embodiment, the specific circuit of the ultraviolet light source control circuit unit is the same as the circuit structure of the colorimetric light source control circuit unit described above. It is only necessary to replace the colorimetric light source with an ultraviolet light source, which will not be described in detail here.

[0055] The light emitted by the light-emitting diode D4 is shone into the coliform culture tank (referred to as the culture tank) for colorimetric measurement and fluorescence excitation.

[0056] like Figure 3 As shown, the colorimetric detection circuit unit in this embodiment is used to detect the target light signal emitted after the colorimetric light source irradiates the coliform culture tank, and convert it into a first voltage signal.

[0057] Specifically, the colorimetric detection circuit unit includes a photodetector D3, an operational amplifier U10, a resistor R22, a feedback capacitor C26, resistors R17, R26, R24, and an operational amplifier U6. The positive terminal of the photodetector D3 is connected to the non-inverting input of the operational amplifier U10, and the negative terminal of the photodetector D3 is connected to the inverting input of the operational amplifier U10. Resistor R22 is connected in parallel with the feedback capacitor C26 and is connected to the inverting input and the output terminal of the operational amplifier U10, respectively. Resistor R17 is connected to the non-inverting input of the operational amplifier U6 and the output terminal of the operational amplifier U10, respectively. Resistor R26 is connected to the output terminal and the inverting input of the operational amplifier U6, respectively. Resistor R24 ​​is connected to the inverting input of the operational amplifier U6 and the negative power supply terminal, respectively.

[0058] Among them, resistor R22 and operational amplifier U10 constitute a transimpedance amplifier, and feedback capacitor C26, resistor R17, resistor R26, resistor R24 ​​and operational amplifier U6 constitute the first stage non-inverting amplifier circuit; operational amplifier U6 and operational amplifier U10 are powered by the power supply.

[0059] In addition, the colorimetric detection circuit unit in this embodiment is electrically connected to the ADC data acquisition circuit unit through the first filter circuit unit.

[0060] Specifically, the first filter circuit unit includes a first-stage active low-pass filter composed of capacitors C24, C27, and C29, resistors R19, R18, R23, and R27, and operational amplifier U8, which is also the second-stage non-inverting amplifier circuit. It also includes a second-stage passive filter composed of resistor R21 and capacitor C28.

[0061] The working principle of the colorimetric detection circuit unit in this embodiment is as follows:

[0062] The photodetector D3 detects the colorimetric light absorbed by the sample and generates a current signal, which is converted into a corresponding voltage by a transimpedance amplifier. Feedback capacitor C26 limits the bandwidth to maintain circuit stability. The voltage signal enters the first-stage non-inverting amplifier composed of operational amplifier U6 for amplification. This stage converts and amplifies the weak light signal into a processable electrical signal before entering the next stage. Specifically, since the output voltage at this stage is obtained by multiplying the current output from the photodetector by the resistor R22, a low-temperature drift resistor with a precision of one-thousandth is used, and capacitor C26 is also a low-temperature drift capacitor made of NP0 material. The first filtering circuit unit amplifies the amplified signal again and performs two stages of filtering to remove most of the interference and fluctuations in the signal, facilitating subsequent measurements.

[0063] The fluorescence detection circuit unit in this embodiment is used to detect the fluorescence signal generated after the coliform bacteria culture tank is irradiated by an ultraviolet light source, and convert it into a second voltage signal.

[0064] Specifically, the fluorescence detection circuit unit includes a photodetector D5, an operational amplifier U17, a resistor R32, a feedback capacitor C34, a resistor R31, a resistor R38, a resistor R42, and an operational amplifier U13. The positive terminal of the photodetector D5 is connected to the non-inverting input of the operational amplifier U17, and the negative terminal of the photodetector D5 is connected to the inverting input of the operational amplifier U17. The resistor R32 is connected in parallel with the feedback capacitor C34 and is connected to the inverting input and the output terminal of the operational amplifier U17, respectively. The resistor R31 is connected to the non-inverting input of the operational amplifier U13 and the output terminal of the operational amplifier U17, respectively. The resistor R38 is connected to the output terminal and the inverting input of the operational amplifier U13, respectively. The resistor R42 is connected to the inverting input of the operational amplifier U13 and the negative power supply terminal, respectively.

[0065] Among them, resistor R32 and operational amplifier U17 constitute a transimpedance amplifier, and feedback capacitor C34, resistor R31, resistor R42, resistor R38 and operational amplifier U13 constitute the first stage non-inverting amplifier circuit; operational amplifier U13 and operational amplifier U17 are powered by the power supply.

[0066] In addition, the fluorescence detection circuit unit is electrically connected to the ADC data acquisition circuit unit through the integration circuit unit and the second filter circuit unit in sequence.

[0067] The integrating circuit in this embodiment includes a resistor R33, a capacitor C33, and an operational amplifier U14. One end of the resistor R33 is connected to the output terminal of the operational amplifier U13, and the other end is connected to one end of the capacitor C33 and the inverting input of the operational amplifier U14. The other end of the capacitor C33 is connected to the output terminal of the operational amplifier U14, and the non-inverting input of the operational amplifier U14 is connected to the negative terminal of the power supply.

[0068] The second filter circuit unit in this embodiment includes a first-stage active low-pass filter composed of capacitors C32, C35, and C38, resistors R34, R37, R41, and R35, and operational amplifier U8, which is also a second-stage non-inverting amplifier circuit. It also includes a second-stage passive filter composed of resistor R36 and capacitor C37.

[0069] The working principle of the fluorescence detection circuit unit in this embodiment is as follows:

[0070] The photodetector D5 in the fluorescence detection circuit detects the fluorescence generated by the sample and produces a current signal. This signal is converted into a corresponding voltage by a transimpedance amplifier. Feedback capacitor C34 limits the bandwidth to maintain circuit stability. The voltage signal is then amplified by the first-stage non-inverting amplifier formed by U13. This stage converts and amplifies the weak light signal into a processable electrical signal, which then enters the next stage circuit. Specifically, since the output voltage at this stage is obtained by multiplying the current output from the photodetector by the resistor R32, a low-temperature drift resistor with a precision of one-thousandth is used, and capacitor C34 is also a low-temperature drift capacitor made of NP0 material.

[0071] Because the fluorescence signal is too weak, even after amplification by operational amplifier U13, the amplitude is still too small. Directly setting an excessively large amplification factor may lead to waveform distortion and severe interference. Compared to the colorimetric signal, the fluorescence signal adds an integrating circuit to integrate the unstable fluorescence signal generated by excitation, making the signal a smooth DC signal.

[0072] The second filtering circuit unit amplifies the integrated signal again and performs two stages of filtering. This removes most of the interference and fluctuations in the signal, facilitating subsequent measurements. The amplification factor of the fluorescence section is set higher than that of the colorimetric section, making the fluorescence signal easier to measure.

[0073] The ADC data acquisition circuit unit in this embodiment is used to convert the first voltage signal and the second voltage signal into corresponding digital signals to obtain the concentration of coliform bacteria.

[0074] Specifically, the ADC data acquisition circuit unit uses a microcontroller-controlled 24-bit high-precision ADC chip U9 with two inputs. The microcontroller can simultaneously convert two analog electrical signals into 24-bit digital signals for subsequent data calculation.

[0075] The working principle of the water quality monitoring circuit in this embodiment is as follows:

[0076] (1) When the colorimetric light source is irradiated into the culture tank, the yellow o-nitrophenol produced by the coliform bacteria will absorb the colorimetric light, making the emitted light weaker. That is to say, the detected light intensity is inversely proportional to the o-nitrophenol concentration. After the colorimetric detector receives the light signal, the transimpedance amplifier U10 converts it into the corresponding voltage signal. After passing through the in-phase amplifier U6 and the filter circuit, the corresponding value is obtained by the ADC sampling, thereby calculating the concentration of o-nitrophenol and estimating the concentration of total coliform bacteria.

[0077] (2) When ultraviolet light is irradiated into the culture vessel, it excites the 4-methylumbelliferone in the vessel to produce fluorescence. The intensity of the fluorescence is proportional to the concentration of 4-methylumbelliferone. After the fluorescence detector receives the fluorescence signal, the transimpedance amplifier U17 converts it into a corresponding voltage signal. Since the fluorescence is weak, U14 integrates the voltage signal and then filters and amplifies it. The corresponding value is obtained by the ADC sampling, thereby calculating the concentration of 4-methylumbelliferone and estimating the concentration of Escherichia coli.

[0078] (3) Subtract the values ​​from (1) and (2) to obtain the concentration of fecal coliforms.

[0079] The water quality analyzer in this embodiment uses the water quality monitoring circuit described above, which not only has high analysis efficiency but also high analysis accuracy.

[0080] In this embodiment, the connection to the negative terminal of the power supply is grounded.

[0081] Example 2:

[0082] The water quality monitoring circuit in this embodiment differs from that in Embodiment 1 in that:

[0083] The integrator circuit and filter circuit in Embodiment 1 can also be replaced with existing common integrator circuits and filter circuits to meet the needs of different applications.

[0084] Other circuit architectures can be referred to in Example 1;

[0085] The water quality analyzer in this embodiment uses the water quality monitoring circuit described above, which not only has high analysis efficiency but also high analysis accuracy.

[0086] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A water quality monitoring circuit for monitoring coliform bacteria in water, characterized in that, include: The colorimetric light source control circuit unit is used to control the stable output of the colorimetric light source by adjusting the gain. The ultraviolet light source control circuit unit is used to control the stable output of the ultraviolet light source by adjusting the gain. The colorimetric detection circuit unit is used to detect the target light signal emitted after the colorimetric light source irradiates the coliform culture tank, and convert it into a first voltage signal. The fluorescence detection circuit unit is used to detect the fluorescence signal generated after the coliform bacteria culture vessel is irradiated by an ultraviolet light source and convert it into a second voltage signal. The ADC data acquisition circuit unit is used to convert the first voltage signal and the second voltage signal into corresponding digital signals to obtain the concentration of coliform bacteria. The colorimetric light source control circuit unit includes a colorimetric light source, a first light source constant current driving circuit module, a first reference detector feedback circuit module, and a first gain adjustment circuit module. The first light source constant current driving circuit module is used to drive the colorimetric light source to emit light. The first reference detector feedback circuit module is used to detect the light signal of the colorimetric light source and convert it into a voltage signal. The first gain adjustment circuit module is used to compare the voltage signal with a preset input voltage to dynamically adjust the driving current output by the first light source constant current driving circuit module. The first gain adjustment circuit module includes resistors R16 and R25, operational amplifier U7, resistor R30, capacitor C36, operational amplifier U12, capacitor C30, capacitor C31, resistors R28 and R29. Resistor R16 is connected to the first or second reference detector feedback circuit module and the non-inverting input of operational amplifier U7. Resistor R25 is connected to the inverting input and output of operational amplifier U7. Resistor R16, resistor R25, and operational amplifier U7 constitute a voltage follower. Resistor R30 and capacitor C36 are connected to the first reference detector feedback circuit module or the second reference detector feedback circuit module and the non-inverting input of operational amplifier U7. Resistor R25 is connected to the inverting input and output of operational amplifier U7. Resistor R16, resistor R25, and operational amplifier U7 constitute a voltage follower. Capacitor C36 forms an RC filter. The voltage output of the microcontroller is connected to the inverting input of operational amplifier U12 after passing through the RC filter. The non-inverting input of operational amplifier U12 is connected to the output of operational amplifier U7 through resistor R29. The output of operational amplifier U12 is connected to either the first or second light source constant current drive circuit module. Capacitors C30 and C31, resistors R28 and R29 are connected in series and form a loop with the non-inverting input and output of operational amplifier U12 for loop compensation. Operational amplifiers U7 and U12 are powered by a power supply.

2. The water quality monitoring circuit according to claim 1, characterized in that, The ultraviolet light source control circuit unit includes an ultraviolet light source, a second light source constant current drive circuit module, a second reference detector feedback circuit module, and a second gain adjustment circuit module. The second light source constant current drive circuit module is used to drive the ultraviolet light source to emit light. The second reference detector feedback circuit module is used to detect the light signal of the ultraviolet light source and convert it into a voltage signal. The second gain adjustment circuit module is used to compare the voltage signal with a preset input voltage to dynamically adjust the drive current output by the second light source constant current drive circuit module.

3. The water quality monitoring circuit according to claim 1, characterized in that, The first light source constant current drive circuit module includes a current feedback resistor R40, a transistor Q1, an operational amplifier U15, a resistor R39, and a capacitor C39. The non-inverting input of the operational amplifier U15 is connected to the output of the operational amplifier U12, and the output of the operational amplifier U15 is connected to the base of the transistor Q1. The collector of the transistor Q1 is connected to the positive terminal of the power supply, and the emitter of the transistor Q1 is connected to the positive terminal of the colorimetric light source or the ultraviolet light source. The negative terminal of the colorimetric light source or the ultraviolet light source and the inverting input of the operational amplifier U15 are respectively connected to the negative terminal of the power supply through the current feedback resistor R40. The resistor R39 and the capacitor C39 are connected in series and between the negative terminal of the colorimetric light source or the ultraviolet light source and the inverting input of the operational amplifier U15 to form a loop compensation. Op-amp U15 is powered by a power supply.

4. The water quality monitoring circuit according to claim 3, characterized in that, The first reference detector feedback circuit module includes a photodetector D2, a resistor R20, an operational amplifier U11, and a feedback capacitor C25. The positive terminal of the photodetector D2 is connected to the non-inverting input of the operational amplifier U11, and the negative terminal of the photodetector D2 is connected to the inverting input of the operational amplifier U11. The resistor R20 and the feedback capacitor C25 are connected in parallel and are respectively connected to the inverting input and the output terminal of the operational amplifier U11. The output terminal of the operational amplifier U11 is connected to the resistor R16. Among them, resistor R20 and operational amplifier U11 form a transimpedance amplifier; operational amplifier U11 is powered by a power supply.

5. The water quality monitoring circuit according to any one of claims 1-4, characterized in that, The colorimetric detection circuit unit includes a photodetector D3, an operational amplifier U10, a resistor R22, a feedback capacitor C26, resistors R17, R26, R24, and an operational amplifier U6. The positive terminal of the photodetector D3 is connected to the non-inverting input of the operational amplifier U10, and the negative terminal of the photodetector D3 is connected to the inverting input of the operational amplifier U10. Resistor R22 is connected in parallel with the feedback capacitor C26 and is connected to the inverting input and the output terminal of the operational amplifier U10, respectively. Resistor R17 is connected to the non-inverting input of the operational amplifier U6 and the output terminal of the operational amplifier U10, respectively. Resistor R26 is connected to the output terminal and the inverting input of the operational amplifier U6, respectively. Resistor R24 ​​is connected to the inverting input of the operational amplifier U6 and the negative power supply terminal, respectively. Among them, resistor R22 and operational amplifier U10 constitute a transimpedance amplifier, and operational amplifiers U6 and U10 are powered by the power supply.

6. The water quality monitoring circuit according to any one of claims 1-4, characterized in that, The colorimetric detection circuit unit is electrically connected to the ADC data acquisition circuit unit through the first filter circuit unit.

7. The water quality monitoring circuit according to any one of claims 1-4, characterized in that, The fluorescence detection circuit unit is electrically connected to the ADC data acquisition circuit unit through an integration circuit unit and a second filter circuit unit in sequence.

8. A water quality analyzer, characterized in that, The water quality monitoring circuit described in any one of claims 1-7 is adopted.

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