Turbidity measuring circuit

Abstract

The utility model discloses a turbidity measuring circuit, and relates to the field of measuring circuits. According to the specific implementation scheme, the device comprises a sensitive element, an amplifying circuit arranged at the output end of the sensitive element and a gain adjusting module used for controlling the gain of the amplifying circuit; the amplification circuit comprises a first amplification circuit, a second amplification circuit and a third amplification circuit which have different gains, and the first amplification circuit, the second amplification circuit and the third amplification circuit are sequentially connected in series; the first amplifying circuit, the second amplifying circuit and the third amplifying circuit are electrically connected with the gain adjusting module. According to the utility model, the effect of adjusting the measuring range is realized by adjusting the gain of the amplifying circuit, and the problems that the precision of a low-measuring-range range is low and high-precision measurement cannot be realized are solved.

Description

Technical Field

[0001] The utility model relates to the technical field of measurement circuits, in particular to a turbidity measurement circuit. Background Art

[0002] The 90° scattering method stipulated by the international standard has good linearity in the turbidity range of 0 - 4000 NTU (as shown in Figure 1 ), but when the turbidity is higher than 4000 NTU, due to reasons such as multiple reflections, its linearity will deteriorate rapidly. Therefore, the measurement range of turbidity sensors using the 90° scattering method is usually between 0 - 4000 NTU. However, due to the limited number of bits of the analog-to-digital converter ADC used in the sensor (usually 12 bits), this also results in a reduction in resolution when the sensor has a large measurement range. Therefore, turbidity sensors with a large measurement range often cannot be applied to scenarios with low turbidity and high resolution due to insufficient resolution. Content of the Utility Model

[0003] Based on this, in order to solve the problem of low precision in the low measurement range and inability to achieve high-precision measurement, the utility model provides a turbidity measurement circuit.

[0004] The utility model provides a turbidity measurement circuit, including:

[0005] A sensitive element, an amplification circuit arranged at the output end of the sensitive element, and a gain adjustment module for controlling the gain of the amplification circuit;

[0006] The amplification circuit includes a first amplification circuit, a second amplification circuit, and a third amplification circuit with different gain magnitudes. The first amplification circuit, the second amplification circuit, and the third amplification circuit are connected in series in sequence;

[0007] The first amplification circuit, the second amplification circuit, and the third amplification circuit are all electrically connected to the gain adjustment module.

[0008] The sensitive element outputs a signal to be processed. After the signal to be processed is filtered, a signal to be amplified is obtained, and the signal to be amplified is amplified by a multi-stage amplification circuit composed of the first amplification circuit, the second amplification circuit, and the third amplification circuit to obtain a gain signal and convert it into a measurement value.

[0009] By connecting the multi-stage amplification circuits in series, the amplification multiple of the signal can be greatly improved.

[0010] Among them, the amplification gains of the first amplifier circuit, the second amplifier circuit, and the third amplifier circuit are different and can be used to amplify the signal to be amplified. Among them, the first amplifier circuit and the second amplifier circuit are in-phase proportional amplifier circuits, and the third amplifier circuit is an inverting proportional amplifier circuit. The gain adjustment module is used to adjust the amplification multiple of the signal to be amplified to achieve the function of adjusting the measurement range. For the water body to be measured with lower turbidity, a small measurement range mode is adopted to detect its turbidity, and the turbidity signal obtained is amplified in multiple stages by a high-gain amplifier circuit.

[0011] Both the first amplifier circuit and the second amplifier circuit are in-phase proportional amplifier circuits;

[0012] The first amplifier circuit includes a second operational amplifier, a second capacitor, a first feedback resistor, and a first resistor. One end of the second capacitor is connected to the inverting input terminal of the second operational amplifier, and the other end of the second capacitor is connected to the output terminal of the second operational amplifier. The first feedback resistor is connected in parallel with the second capacitor. The non-inverting input terminal of the second operational amplifier is grounded via the first resistor, and the non-inverting input terminal of the second operational amplifier is electrically connected to the output terminal of the sensitive element;

[0013] The first amplifier circuit further includes a first adjustment resistor, and the inverting input terminal of the second operational amplifier is electrically connected to the gain adjustment module via the first adjustment resistor;

[0014] The second amplifier circuit includes a third operational amplifier, a third capacitor, a second feedback resistor, and a second resistor. One end of the third capacitor is connected to the inverting input terminal of the third operational amplifier, and the other end of the third capacitor is connected to the output terminal of the third operational amplifier. The second feedback resistor is connected in parallel with the third capacitor. The non-inverting input terminal of the third operational amplifier is grounded via the second resistor, and the non-inverting input terminal of the third operational amplifier is electrically connected to the output terminal of the second operational amplifier;

[0015] The second amplifier circuit further includes a second adjustment resistor, and the inverting input terminal of the second operational amplifier is electrically connected to the gain adjustment module via the second adjustment resistor.

[0016] Further, the amplification gains of the first amplification circuit and the second amplification circuit are different. When the gain adjustment module inputs a low level to the inverting input terminal of the second operational amplifier, the first adjustment resistor works and the first amplification circuit is in the working state. When the gain adjustment module inputs a high level to the inverting input terminal of the third operational amplifier or the end of the second adjustment resistor not connected to the inverting input terminal of the third operational amplifier is floating, the second amplification circuit is in the following state; when the gain adjustment module inputs a high level to the inverting input terminal of the second operational amplifier or the end of the first adjustment resistor not connected to the inverting input terminal of the second operational amplifier is floating, the first amplification circuit is in the following state. When the gain adjustment module inputs a low level to the inverting input terminal of the third operational amplifier, the second adjustment resistor works and the second amplification circuit is in the amplification state; when the gain adjustment module inputs a high level to the inverting input terminal of the second operational amplifier or the end of the first adjustment resistor not connected to the inverting input terminal of the second operational amplifier is floating, and the gain adjustment module inputs a high level to the inverting input terminal of the third operational amplifier or the end of the second adjustment resistor not connected to the inverting input terminal of the third operational amplifier is floating, both the first amplification circuit and the second amplification circuit are in the following state; since the amplification gains of the first amplification circuit and the second amplification circuit are different, when the first amplification circuit and the second amplification circuit work, the generated amplification factors are different, and the amplification circuit can be selected according to the requirement of the amplification factor.

[0017] The turbidity measurement circuit further includes a filtering unit, and the sensitive element is connected to the non-inverting input terminal of the first amplification circuit via the filtering unit;

[0018] The filtering unit includes a filtering resistor, a filtering capacitor, a first capacitor, and a first operational amplifier. The non-inverting input terminal of the first operational amplifier is grounded, and the inverting input terminal of the first operational amplifier is connected to the output terminal of the sensitive element;

[0019] One end of the filtering resistor is connected to the inverting input terminal of the first operational amplifier, the other end of the filtering resistor is connected to the output terminal of the first operational amplifier, and the filtering resistor and the filtering capacitor are in parallel; the output terminal of the first operational amplifier is electrically connected to the non-inverting input terminal of the second operational amplifier via the first capacitor.

[0020] Further, the filtering unit is an RC filtering circuit, which is used to receive the signal to be processed, filter out the DC component in the signal to be processed, and output the signal to be amplified that only retains the AC component to the amplification circuit.

[0021] The third amplification circuit is an inverting proportional amplification circuit;

[0022] The third amplification circuit includes a fourth operational amplifier, a fourth capacitor, a third feedback resistor, a third resistor, and a fourth resistor. One end of the fourth capacitor is connected to the inverting input terminal of the fourth operational amplifier, and the other end of the fourth capacitor is connected to the output terminal of the fourth operational amplifier. The third feedback resistor is connected in parallel with the fourth capacitor. The non-inverting input terminal of the fourth operational amplifier is grounded via the third resistor. One end of the fourth resistor is electrically connected to the inverting input terminal of the fourth operational amplifier, and the other end of the fourth resistor is electrically connected to the output terminal of the third operational amplifier;

[0023] The third amplification circuit further includes a third adjustment resistor. The inverting input terminal of the third operational amplifier is electrically connected to the gain adjustment module via the third adjustment resistor.

[0024] The inverting proportional amplification circuit has the function of phase compensation; since the filtering unit has already generated a 180-degree phase shift, by adding the third amplification circuit, when the third adjustment resistor is connected in parallel between the inverting input terminal and the output terminal of the fourth operational amplifier, the total resistance value of the feedback loop can be reduced, the required gain of the signal to be processed can be achieved, and the phase of the output gain signal and the signal to be processed remains unchanged (i.e., in-phase output).

[0025] The gain adjustment module includes a first switching element, a second switching element, and a third switching element. The inverting input terminal of the first amplification circuit is grounded via a first adjustment resistor and the first switching element. The inverting input terminal of the second amplification circuit is grounded via a second adjustment resistor and the second switching element. The third adjustment resistor is connected in series with the third switching element and then connected in parallel between the inverting input terminal and the output terminal of the third amplification circuit.

[0026] Further, when the first switching element / second switching element is closed, the inverting input terminal of the first amplification circuit / second amplification circuit receives a low level, and the first amplification circuit / second amplification circuit is in the working state. When the first switching element and the second switching element are open, the first amplification circuit / second amplification circuit is in the following state.

[0027] When the third switching element is closed, the third adjustment resistor and the third feedback resistor are connected in parallel, and the total resistance value of the feedback loop of the third amplification circuit is reduced. When the third switching element is open, the gain of the third amplification circuit is: - third feedback resistor / fourth resistor.

[0028] The gain adjustment module includes a first switching element, a second switching element, a third switching element, and a control unit. The first switching element, the second switching element, and the third switching element are all electrically connected to the control unit. The inverting input terminal of the first amplification circuit is grounded via a first adjustment resistor and the first switching element. The inverting input terminal of the second amplification circuit is grounded via a second adjustment resistor and the second switching element. The third adjustment resistor is connected in series with the second switching element and then connected in parallel between the inverting input terminal and the output terminal of the third amplification circuit.

[0029] Further, when the control module controls the first switching element / second switching element to close, the inverting input terminal of the first amplifying circuit / second amplifying circuit receives a low level, and the first amplifying circuit / second amplifying circuit is in an operating state. When the control module controls the first switching element / second switching element to open, the first amplifying circuit / second amplifying circuit is in a following state.

[0030] When the control module controls the third switching element to close, the third adjusting resistor and the third feedback resistor are in parallel, and the total resistance value of the feedback loop of the third amplifying circuit decreases. When the control module controls the third switching element to open, the gain of the third amplifying circuit is: - the third feedback resistor / the fourth resistor.

[0031] The gain adjustment module includes a third switching element and a control unit. The inverting input terminal of the first amplifying circuit is electrically connected to the control unit via a first adjusting resistor. The inverting input terminal of the second amplifying circuit is electrically connected to the control unit via a second adjusting resistor. The third adjusting resistor is connected in series with the third switching element and then in parallel between the inverting input terminal and the output terminal of the third amplifying circuit. The third switching element is electrically connected to the control unit.

[0032] Further, when the control module gives a low level to the inverting input terminal of the first amplifying circuit / second amplifying circuit, the first amplifying circuit / second amplifying circuit is in an operating state. When the control module gives a high level to the inverting input terminal of the first amplifying circuit / second amplifying circuit, the inverting input terminal of the first amplifying circuit / second amplifying circuit receives a high level, and the first amplifying circuit / second amplifying circuit is in a following state.

[0033] When the control module controls the third switching element to close, the third adjusting resistor and the third feedback resistor are in parallel, and the total resistance value of the feedback loop of the third amplifying circuit decreases. When the control module controls the third switching element to open, the gain of the third amplifying circuit is - the third feedback resistor / the fourth resistor.

[0034] The sensitive element is a photosensitive diode. The anode of the photosensitive diode is connected to the inverting input terminal of the first amplifying circuit, and the cathode of the photosensitive diode is grounded.

[0035] Further, the photosensitive diode is used to detect the light intensity of 90° scattered light and convert the light intensity into an electrical signal to be processed.

[0036] The turbidity measurement circuit includes an ADC module. The input terminal of the ADC module is electrically connected to the output terminal of the fourth operational amplifier.

[0037] The ADC module is an analog-to-digital converter, which is used to convert the gain signal from analog to digital. The measured value of the digital quantity is an N-bit binary code, where N is the number of bits of the ADC module. Taking a 12-bit ADC module with 12 bits as an example, the ADC output value is 4096 binary codes at this time. The 4096 binary codes correspond to 4096 uniformly distributed measured values within the turbidity measurement range. The difference between the two measured values corresponding to two adjacent binary codes is the resolution of the turbidity measurement circuit.

[0038] Beneficial effects: The present invention realizes the function of adjusting the range by adjusting the gain of the amplifier circuit. For the water body to be measured with low turbidity, a small-range mode is adopted to detect its turbidity. The obtained turbidity signal is amplified in multiple stages by a high-gain amplifier circuit, and then the amplified signal is converted by an analog-to-digital converter to obtain a measurement result with higher resolution; for the water body to be measured with high turbidity, a large-range mode is adopted to detect it, so that the large-range turbidity sensor can also be applied to the scenario of low turbidity and high resolution.

[0039] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. Description of the Drawings

[0040] The drawings are used to better understand the solution and do not limit the present invention. Among them:

[0041] Figure 1 is a flowchart provided according to the present invention;

[0042] Figure 2 is a schematic circuit diagram of the signal gain module provided according to the present invention;

[0043] Figure 3 is a schematic circuit diagram of the switching of the switching element provided according to the present invention;

[0044] Figure 4 is a schematic circuit diagram of the MCU controlling the state of the switching element provided according to the present invention;

[0045] Figure 5 is a schematic circuit diagram of the MCU controlling the amplifier circuit provided according to the present invention. Detailed Embodiments

[0046] The following describes exemplary embodiments of the present invention in conjunction with the accompanying drawings. Various details of the embodiments of the present invention are included to facilitate understanding, and they should be considered merely exemplary. Therefore, those of ordinary skill in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, descriptions of well-known functions and structures are omitted below for clarity and conciseness.

[0047] As Figure 1 shown, Figure 1 it includes a sensitive element, an amplification circuit, a gain adjustment module, and an ADC module;

[0048] The sensitive element is a photosensitive diode PD, which is used to detect the light intensity of 90° scattered light and convert the light intensity into an electrical signal to be processed. The signal to be processed is filtered to remove the DC component in the signal to be processed and output only the AC component of the signal to be amplified to the amplification circuit. The gain adjustment module is used to adjust the gain of the amplification circuit, and the ADC module is used to convert the gain signal from an analog quantity to a digital quantity to obtain the resolution of the turbidity measurement circuit.

[0049] As Figure 2 shown, the turbidity measurement circuit further includes a filtering unit 1. The filtering unit 1 is an RC filtering circuit. The filtering unit 1 includes a filtering resistor R1, a filtering capacitor C11, a first operational amplifier OP1, and a first capacitor C12. The non-inverting input terminal of the first operational amplifier OP1 is grounded, and the inverting input terminal of the first operational amplifier OP1 is electrically connected to the anode of the photosensitive diode PD.

[0050] The filtering unit 1 is used to filter the signal to be processed output by the photosensitive diode PD to obtain the AC component in the signal to be processed and use the AC component as the signal to be amplified.

[0051] In the present invention, the amplification circuit includes a first amplification circuit 2, a second amplification circuit 3, and a third amplification circuit 4, where:

[0052] The first amplification circuit 2 includes a second operational amplifier OP2, a second capacitor C2, a first feedback resistor R21, a first adjustment resistor R22, and a first resistor R23. The first amplification circuit 2 is a non-inverting proportional amplification circuit. One end of the second capacitor C2 is connected to the inverting input terminal of the second operational amplifier OP2, and the other end of the second capacitor C2 is connected to the output terminal of the second operational amplifier OP2. The first feedback resistor R21 is connected in parallel with the second capacitor C2. The inverting input terminal of the second operational amplifier OP2 is electrically connected to the gain adjustment module via the first adjustment resistor R22. The non-inverting input terminal of the second operational amplifier OP2 is grounded via the first resistor R23, and the non-inverting input terminal of the second operational amplifier OP2 is electrically connected to the output terminal of the first operational amplifier OP1.

[0053] When the gain adjustment module inputs a low level to the inverting input terminal of the second operational amplifier OP2, the first adjustment resistor R22 operates, and the first amplifier circuit 2 is in the operating state. When the gain adjustment module inputs a high level to the inverting input terminal of the second operational amplifier OP2 or one end of the first adjustment resistor R22 that is not connected to the non-inverting input terminal of the second operational amplifier OP2 is floating, the first amplifier circuit 2 is in the follow state.

[0054] The second amplifier circuit 3 includes a third operational amplifier OP3, a third capacitor C3, a second feedback resistor R31, a second adjustment resistor R32, and a second resistor R33. The second amplifier circuit 3 is a non-inverting proportional amplifier circuit; between the inverting input terminal and the output terminal of the third operational amplifier OP3 are respectively connected in parallel with the third capacitor C3 and the second feedback resistor R31. The inverting input terminal of the third operational amplifier OP3 is electrically connected to the gain adjustment module via the second adjustment resistor R32. The non-inverting input terminal of the third operational amplifier OP3 is grounded via the first resistor R33, and the non-inverting input terminal of the third operational amplifier OP3 is electrically connected to the output terminal of the second operational amplifier OP2.

[0055] When the gain adjustment module inputs a low level to the inverting input terminal of the third operational amplifier OP3, the second adjustment resistor R32 operates, and the second amplifier circuit 3 is in the operating state. When the gain adjustment module inputs a high level to the inverting input terminal of the third operational amplifier OP3 or one end of the second adjustment resistor R32 that is not connected to the inverting input terminal of the third operational amplifier OP3 is floating, the second amplifier circuit 3 is in the follow state.

[0056] The difference between the first amplifier circuit 2 and the second amplifier circuit 3 is that the gain magnitudes of the first amplifier circuit 2 and the second amplifier circuit 3 are different, that is, R21 / R22 ≠ R31 / R32.

[0057] The third amplifier circuit 4 includes a fourth operational amplifier OP4, a fourth capacitor C4, a third feedback resistor R41, a third adjustment resistor R43, a third resistor R44, and a fourth resistor R42. One end of the fourth capacitor C4 is connected to the inverting input terminal of the fourth operational amplifier OP4, and the other end of the fourth capacitor C4 is connected to the output terminal of the fourth operational amplifier OP4. The third feedback resistor R41 is connected in parallel with the fourth capacitor C4. The inverting output terminal of the fourth operational amplifier OP4 is connected to the gain adjustment module via the third adjustment resistor R43. The non-inverting input terminal of the fourth operational amplifier OP4 is grounded via the third resistor R44. The inverting input terminal of the fourth operational amplifier OP4 is electrically connected to the output terminal of the second operational amplifier. One end of the fourth resistor R42 is electrically connected to the inverting input terminal of the fourth operational amplifier OP4, and the other end of the fourth resistor R42 is connected to the output terminal of the second operational amplifier OP2.

[0058] When the third adjusting resistor R43 is connected in parallel between the inverting input terminal and the output terminal of the fourth operational amplifier OP4, the total resistance value of the feedback loop can be reduced, avoiding signal distortion caused by excessive gain, achieving the required gain of the signal to be processed, and keeping the phase of the output gain signal the same as that of the signal to be processed (i.e., in-phase output).

[0059] Let the signal to be amplified output from the output terminal of the filtering unit 1 be u1, the signal to be amplified output from the first amplifier circuit be u2, the signal to be amplified output from the second amplifier circuit be u3, and the gain signal output from the third amplifier circuit be u4.

[0060] When the gain adjustment module outputs a low level to the inverting input terminal of the second operational amplifier OP2 of the first amplifier circuit 2, the first amplifier circuit 2 enters the working state, amplifying the signal to be amplified u1 input from the first operational amplifier OP1 to the non-inverting input terminal of the second operational amplifier OP2 into the signal to be amplified u2, where u2 = (1 + R21 / R22) × u1; when the gain adjustment module outputs a high level to the inverting input terminal of the second operational amplifier OP2 of the first amplifier circuit 2 or when the first adjusting resistor R22 is not connected to one end of the second operational amplifier OP2 and is left floating, the first amplifier circuit 2 enters the follow-up state, and the signal to be amplified u2 output by the second operational amplifier OP2 is u2 = u1.

[0061] When the gain adjustment module outputs a low level to the inverting input terminal of the third operational amplifier OP3 of the second amplifier circuit 3, the second amplifier circuit 3 enters the working state, amplifying the signal to be amplified u2 input from the second operational amplifier OP2 to the non-inverting input terminal of the third operational amplifier OP3 into the signal to be amplified u3, where u3 = (1 + R31 / R32) × u2; when the gain adjustment module outputs a high level to the inverting input terminal of the third operational amplifier OP3 of the second amplifier circuit 3 or when the second adjusting resistor R32 is not connected to one end of the third operational amplifier OP3 and is left floating, the second amplifier circuit 3 enters the follow-up state, and the output voltage u3 of the third operational amplifier OP3 is u3 = u2.

[0062] When the third adjusting resistor R43 is not connected between one end of the fourth operational amplifier OP4 and the gain adjustment module, the on-off state of the circuit between the third adjusting resistor R43 and the inverting input terminal of the fourth operational amplifier OP4 is controlled by the gain adjustment module. When the gain adjustment module controls the circuit between the third adjusting resistor R43 and the inverting input terminal of the fourth operational amplifier OP4 to be disconnected, only the third feedback resistor R41 and the fourth capacitor C4 are connected to the circuit in the feedback loop. At this time, the gain of the third amplifier circuit 4 is -R41 / R42, and u4 = (-R41 / R42) × u3. When the gain adjustment module controls the circuit between the third adjusting resistor R43 and the inverting input terminal of the fourth operational amplifier OP4 to be conductive, the total resistance value in the feedback loop decreases, that is, the absolute value of the gain of the third amplifier circuit 4 decreases. At this time, the gain of the third-stage amplifier circuit 4 is -(R41 / / R43) / R42, and u4 = -(R41 / / R43) / R42 × u3.

[0063] The first switching element K2, the second switching element K3, and the third switching element K4 can also be controllable switching elements such as triodes, MOS transistors, and switching ICs. The control unit can select logic control elements such as MCU, CPU, PLC, or FPGA. The following uses MCU as the control unit.

[0064] It is defined that R21 / R22 > R31 / R32, that is, the amplification factor of the first amplifier circuit 2 is greater than that of the second amplifier circuit 3.

[0065] The gain adjustment module specifically includes the following three situations:

[0066] ① When the gain adjustment module includes the first switching element K2, the second switching element K3, and the third switching element K4, the first switching element K2, the second switching element K3, and the third switching element K4 can be switching elements with the function of switching the on-off state of the circuit, such as toggle switches and DIP switches (as Figure 3 shown).

[0067] When using this turbidity measurement circuit to detect turbidity, first select a suitable range according to the requirements, and then control the on-off state of the switching element according to the required range. The specific details are as follows:

[0068] When the turbidity range is 0 - 20 NTU, close the first switching element K2 corresponding to the first amplifier circuit 2 and the third switching element K4 corresponding to the third amplifier circuit 4, and keep the second switching element K3 corresponding to the second amplifier circuit 3 in the off state. At this time, the first amplifier circuit 2 is in the amplification state, the second amplifier circuit 3 is in the follower state, and the third amplifier circuit 4 is in the amplification state with a relatively small gain. The reason for choosing to let the third amplifier circuit 4 be in the amplification state with a relatively small gain is to avoid signal distortion caused by excessive gain. The signal to be amplified u1 is amplified by the first amplifier circuit 2 and the third amplifier circuit 4 and then the amplified signal u4 is output to the ADC module (that is, u2 = (1 + R21 / R22) × u1, u3 = u2, u4 = -(R41 / / R43) / R42 × u3). The ADC module converts the amplified signal u4 from analog quantity to digital quantity, so that the analog measurement values within the turbidity range of 0 - 20 NTU are converted into digital quantities by the ADC module. The measured value of the digital quantity is an N-bit binary code, where N is the number of bits of the ADC module. Taking a 12-bit ADC module with 12 bits as an example, at this time the ADC output value is 4096 binary codes. The 4096 binary codes correspond to 4096 evenly distributed measurement values within the range of 0 - 20 NTU. The difference between the two measurement values corresponding to two adjacent binary codes is the resolution of this turbidity measurement circuit.

[0069] When the turbidity range is 0 - 100 NTU, close the second switching element K3 corresponding to the second amplifier circuit 3 and the third switching element K4 corresponding to the third amplifier circuit 4, and keep the first switching element K2 corresponding to the first amplifier circuit 2 in the off state. At this time, the first amplifier circuit 2 is in the follower state, the second amplifier circuit 3 is in the amplification state, and the third amplifier circuit 4 is in the amplification state with a relatively small gain. The signal to be amplified u1 is amplified by the second amplifier circuit 3 and the third amplifier circuit 4 and then the amplified signal u4 is output to the ADC module (that is, u2 = u1, u3 = (1 + R31 / R32) × u2, u4 = -(R41 / / R43) / R42 × u3). The ADC module converts the amplified signal u4 from analog quantity to digital quantity, so that the analog measurement values within the turbidity range of 0 - 100 NTU are converted into digital quantities by the ADC module. The measured value of the digital quantity is an N-bit binary code, where N is the number of bits of the ADC module. Taking a 12-bit ADC module with 12 bits as an example, at this time the ADC output value is 4096 binary codes. The 4096 binary codes correspond to 4096 evenly distributed measurement values within the range of 0 - 100 NTU. The difference between the two measurement values corresponding to two adjacent binary codes is the resolution of this turbidity measurement circuit.

[0070] When the turbidity range is 100 - 2000 NTU, close the third switching element K4, and keep the first switch K2 corresponding to the first amplifier circuit 1 and the second switching element K3 corresponding to the second amplifier circuit 3 in the off state. At this time, the first amplifier circuit 2 is in the follower state, the second amplifier circuit 3 is in the follower state, and the third amplifier circuit 4 is in the amplification state with a smaller gain. The signal to be amplified u1 is amplified by the third amplifier circuit 4 and then the amplified signal u4 is output to the ADC module (i.e., u3 = u2 = u1, u4 = -(R41 / / R43) / R42 × u3). The ADC module converts the amplified signal u4 from analog quantity to digital quantity, so that the analog measurement values within the turbidity range of 100 - 2000 NTU are converted into digital quantities by the ADC module. The measurement value of the digital quantity is an N-bit binary code, where N is the number of bits of the ADC module. Taking a 12-bit ADC module with 12 bits as an example, at this time, the ADC output value is 4096 binary codes. The 4096 binary codes correspond to 4096 evenly distributed measurement values within the range of 100 - 2000 NTU. The difference between the two measurement values corresponding to two adjacent binary codes is the resolution of this turbidity measurement circuit.

[0071] ② When the gain adjustment module includes the first switching element K2, the second switching element K2, the third switching element K4 and the control unit (as Figure 4 shown):

[0072] When the MCU controls the first switching element K2 to close, the pin connected to the first adjusting resistor R22 outputs a low level, and the first amplifier circuit 2 is in the amplification state. When the MCU controls the first switching element K2 to open, the first amplifier circuit 2 is in the follower state;

[0073] When the MCU controls the second switching element K3 to close, the pin connected to the second adjusting resistor R32 outputs a low level, and the second amplifier circuit 3 is in the amplification state. When the MCU controls the second switching element K3 to open, the second amplifier circuit 3 is in the follower state;

[0074] When the MCU controls the third switch K4 to close, the circuit between the third adjusting resistor R43 and the inverting input terminal of the fourth operational amplifier OP4 is turned on, and the third amplifier circuit 4 is in the amplification state with a smaller gain.

[0075] ③ When the gain adjustment module includes the third switching element K2 and the control unit (as Figure 5 shown):

[0076] When the MCU controls the pin connected to the first adjusting resistor R22 to output a low level, the first amplifier circuit 2 is in the amplification state. When the MCU controls the pin connected to the first adjusting resistor R22 to output a high level, the first amplifier circuit 2 is in the follower state;

[0077] When the MCU controls the pin connected to the second adjusting resistor R32 to output a low level, the second amplifier circuit 3 is in the amplification state. When the MCU controls the pin connected to the second adjusting resistor R32 to output a high level, the second amplifier circuit 3 is in the follower state;

[0078] When the MCU controls the third switch K4 to close, the circuit between the third adjusting resistor R43 and the inverting input terminal of the fourth operational amplifier OP4 is turned on, and the third amplifier circuit 4 is in the amplification state with a small gain.

[0079] In summary, the current signal output by the photosensitive diode PD is converted into a voltage signal, and then the voltage signal is amplified by different multiples. In the scenario where a small measurement range is required, the to-be-processed electrical signal output by the photosensitive diode is amplified by a higher multiple, and then sampled through the ADC module to output a measurement result with higher resolution, meeting the requirement of high resolution for the small measurement range; in the scenario where a large measurement range is required, the to-be-processed signal output by the photosensitive diode PD is amplified by a lower multiple, and then sampled through the ADC module to output a measurement result corresponding to a larger measurement range. At this time, the resolution required for the large measurement range can still be satisfied.

[0080] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A turbidity measurement circuit, characterized in that, Including: A sensitive element, an amplification circuit disposed at an output end of the sensitive element, and a gain adjustment module for controlling a gain of the amplification circuit; The amplification circuit includes a first amplification circuit, a second amplification circuit, and a third amplification circuit with different gain magnitudes, and the first amplification circuit, the second amplification circuit, and the third amplification circuit are connected in series in sequence; The first amplification circuit, the second amplification circuit, and the third amplification circuit are all electrically connected to the gain adjustment module.

2. The turbidity measurement circuit according to claim 1, wherein: Both the first amplification circuit and the second amplification circuit are non-inverting proportional amplification circuits; The first amplification circuit includes a second operational amplifier, a second capacitor, a first feedback resistor, and a first resistor. One end of the second capacitor is connected to an inverting input end of the second operational amplifier, the other end of the second capacitor is connected to an output end of the second operational amplifier, the first feedback resistor is connected in parallel with the second capacitor, a non-inverting input end of the second operational amplifier is grounded via the first resistor, and the non-inverting input end of the second operational amplifier is electrically connected to an output end of the sensitive element; The first amplification circuit further includes a first adjustment resistor, and an inverting input end of the second operational amplifier is electrically connected to the gain adjustment module via the first adjustment resistor; The second amplification circuit includes a third operational amplifier, a third capacitor, a second feedback resistor, and a second resistor. One end of the third capacitor is connected to an inverting input end of the third operational amplifier, the other end of the third capacitor is connected to an output end of the third operational amplifier, the second feedback resistor is connected in parallel with the third capacitor, a non-inverting input end of the third operational amplifier is grounded via the second resistor, and the non-inverting input end of the third operational amplifier is electrically connected to an output end of the second operational amplifier; The second amplification circuit further includes a second adjustment resistor, and an inverting input end of the second operational amplifier is electrically connected to the gain adjustment module via the second adjustment resistor.

3. The turbidity measurement circuit according to claim 2, wherein: The turbidity measurement circuit further includes a filtering unit, and the sensitive element is connected to a non-inverting input end of the first amplification circuit via the filtering unit; The filtering unit includes a filtering resistor, a filtering capacitor, a first capacitor, and a first operational amplifier. A non-inverting input end of the first operational amplifier is grounded, and an inverting input end of the first operational amplifier is connected to an output end of the sensitive element; One end of the filtering resistor is connected to the inverting input end of the first operational amplifier, the other end of the filtering resistor is connected to an output end of the first operational amplifier, and the filtering resistor and the filtering capacitor are connected in parallel; An output end of the first operational amplifier is electrically connected to a non-inverting input end of the second operational amplifier via the first capacitor.

4. The turbidity measurement circuit according to claim 3, wherein: The third amplification circuit is an inverting proportional amplification circuit; The third amplifier circuit includes a fourth operational amplifier, a fourth capacitor, a third feedback resistor, a third resistor, and a fourth resistor. One end of the fourth capacitor is connected to the inverting input terminal of the fourth operational amplifier, and the other end of the fourth capacitor is connected to the output terminal of the fourth operational amplifier. The third feedback resistor is connected in parallel with the fourth capacitor. The non-inverting input terminal of the fourth operational amplifier is grounded via the third resistor. One end of the fourth resistor is electrically connected to the inverting input terminal of the fourth operational amplifier, and the other end of the fourth resistor is electrically connected to the output terminal of the third operational amplifier; The third amplifier circuit further includes a third adjusting resistor. The inverting input terminal of the third operational amplifier is electrically connected to the gain adjustment module via the third adjusting resistor.

5. The turbidity measurement circuit according to claim 4, characterized in that: The gain adjustment module includes a first switching element, a second switching element, and a third switching element. The inverting input terminal of the first amplifier circuit is grounded via the first adjusting resistor and the first switching element. The inverting input terminal of the second amplifier circuit is grounded via the second adjusting resistor and the second switching element. The third adjusting resistor is connected in series with the third switching element and then connected in parallel between the inverting input terminal and the output terminal of the third amplifier circuit.

6. A turbidity measurement circuit according to claim 4, characterized in that: The gain adjustment module includes a first switching element, a second switching element, a third switching element, and a control unit. The first switching element, the second switching element, and the third switching element are all electrically connected to the control unit. The inverting input terminal of the first amplifier circuit is grounded via the first adjusting resistor and the first switching element. The inverting input terminal of the second amplifier circuit is grounded via the second adjusting resistor and the second switching element. The third adjusting resistor is connected in series with the second switching element and then connected in parallel between the inverting input terminal and the output terminal of the third amplifier circuit.

7. A turbidity measurement circuit according to claim 4, characterized in that: The gain adjustment module includes a third switching element and a control unit. The inverting input terminal of the first amplifier circuit is electrically connected to the control unit via the first adjusting resistor. The inverting input terminal of the second amplifier circuit is electrically connected to the control unit via the second adjusting resistor. The third adjusting resistor is connected in series with the third switching element and then connected in parallel between the inverting input terminal and the output terminal of the third amplifier circuit. The third switching element is electrically connected to the control unit.

8. A turbidity measurement circuit according to any one of claims 3-7, characterized in that: The sensing element is a photodiode. The anode of the photodiode is connected to the inverting input terminal of the first amplifier circuit, and the cathode of the photodiode is grounded.

9. The turbidity measurement circuit according to claim 4, wherein: The turbidity measurement circuit includes an ADC module. The input terminal of the ADC module is electrically connected to the output terminal of the fourth operational amplifier.

Images