Liquid level detection circuit and blood purification apparatus

Abstract

This invention discloses a liquid level detection circuit and a blood purification device, comprising several operational amplifiers and several resistors. Operational amplifier U1 has its non-inverting input connected to one end of resistor R1 and one end of resistor R2, its inverting input connected to one end of resistor R3 and one end of resistor R4, and its output terminal connected to the other end of resistor R3 and the non-inverting input of operational amplifier U2. Operational amplifier U2 has its inverting input connected to one end of resistor R5 and one end of resistor R6, and its output terminal connected to the other end of resistor R5 and one end of resistor R10. Operational amplifier U3 has its non-inverting input connected to one end of resistor R7 and one end of resistor R8, its inverting input connected to one end of resistor R9 and the other end of resistor R10, and its output terminal connected to the other end of resistor R9. The other end of resistor R1 is connected to IN-1; the other end of resistor R4 is connected to IN-2; and the other ends of resistors R2, R6, and R8 are grounded.

Description

Technical Field

[0001] This invention relates to the field of blood purification technology, and in particular to a liquid level detection circuit and a blood purification device. Background Technology

[0002] Blood purification equipment removes harmful substances such as urea, creatinine, drug residues, and heavy metals from the blood through dialysis, filtration, or adsorption technologies. The fluid level detection in the venous chamber of this equipment is a core component ensuring patient safety and equipment efficiency during blood purification treatment. Real-time monitoring and dynamic adjustment can significantly reduce the incidence of serious complications such as air embolism and coagulation. However, existing fluid level detection circuits can only detect and alert on the fluid level in the venous chamber in real time, and cannot perform predictive detection and alerts. Therefore, this paper proposes a fluid level detection circuit and blood purification equipment that can predict the current fluid level and provide two alert modes—predictive alert and real-time alert—based on the predicted fluid level and switching signals. The system can automatically switch between the two alert modes based on the fluid level status without manual feedback of the switching signal. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a liquid level detection circuit and a blood purification device, comprising several operational amplifiers and several resistors. Operational amplifier U1 has its non-inverting input connected to one end of resistor R1 and one end of resistor R2, its inverting input connected to one end of resistor R3 and one end of resistor R4, and its output connected to the other end of resistor R3 and the non-inverting input of operational amplifier U2. Operational amplifier U2 has its inverting input connected to one end of resistor R5 and one end of resistor R6, and its output connected to the other end of resistor R5 and one end of resistor R10. Operational amplifier U3 has its non-inverting input connected to one end of resistor R7 and one end of resistor R8. The inverting input is connected to one end of resistor R9 and the other end of resistor R10, and the output input is connected to the other end of resistor R9; the other end of resistor R1 is connected to IN-1; the other end of resistor R4 is connected to IN-2; the other ends of resistors R2, R6, and R8 are grounded; the flow signals from the arterial output and venous input are fed back to the detection circuit through IN-1 and IN-2 respectively, and the two flow signals are fed back by the acquisition circuit. The arterial flow signal passes through resistors R1 and R2 to the ground terminal, and the signal at resistor R2 is fed back to the non-inverting input of operational amplifier U1. The output of operational amplifier U1 is connected to the inverting input of operational amplifier U1 via resistor R3 for negative feedback. The venous flow signal is fed back to the inverting input of operational amplifier U1 via resistor R4. Operational amplifier U1 outputs a flow difference signal based on the arterial and venous flow rates. This flow difference signal is fed back to the non-inverting input of operational amplifier U2. The output signal of operational amplifier U2 is connected to the ground terminal via resistors R5 and R6. The signal at the end of resistor R5 is fed back to the inverting input of operational amplifier U2. Adjusting the resistance ratio of resistors R5 and R6 adjusts the prediction time. The prediction time is 1 + resistor R5 / resistance R6, and the time unit is... The flow sensors at both ends are identical. Operational amplifier U2 outputs a total flow difference signal based on the predicted time and flow difference, using the flow difference as a reference, after the set predicted time. The current liquid level signal is fed back by the acquisition circuit. The current liquid level signal passes through resistors R7 and R8 to the ground terminal. The signal at the resistor R8 terminal is fed back to the non-inverting input of operational amplifier U3. The output terminal of operational amplifier U3 is connected to the inverting input of operational amplifier U3 through resistor R9 for negative feedback. The total flow difference signal is fed back to the inverting input of operational amplifier U3 through resistor R10. Operational amplifier U3 outputs a predicted liquid level signal based on the current liquid level and the total flow difference.

[0004] Furthermore, it also includes several operational amplifiers and several relays. Operational amplifier U4's non-inverting input is connected to the common terminal of relay S1, and operational amplifier U5's inverting input is connected to its output terminal of relay S2. The output terminal of operational amplifier U5 is connected to the common terminal of relay S3. The first terminal of relay S1 is connected to the other end of resistor R9, and the second terminal is connected to the other end of resistor R7. The first terminal of relay S2 is connected to OUT-1, and the second terminal is connected to OUT-3. The first terminal of relay S3 is connected to OUT-2, and the second terminal is connected to OUT-4. The positive terminal of relay S1 is connected to the positive terminals of relays S2 and S3. The negative terminals of relays S1, S2, and S3 are grounded. The high-limit signal of the safe liquid level threshold is fed back to the inverting input of operational amplifier U4, and the low-limit signal of the safe liquid level threshold is fed back to the non-inverting input of operational amplifier U5. The high-limit signal and the low-limit signal... The signal can be fed back from the power supply signal. The power supply signal passes through resistors R12, R11, and R13 to the ground terminal. The signal at resistor R11 is fed back to the inverting input of operational amplifier U4, and the signal at resistor R13 is fed back to the non-inverting input of operational amplifier U5. Adjusting the resistance values ​​of resistors R11, R12, and R13 sets the safe liquid level threshold. The predicted liquid level signal is fed back to the non-inverting input of operational amplifier U4 and the inverting input of operational amplifier U5 via relay S1. When the amplitude of the predicted liquid level signal is higher than the amplitude of the high limit signal, operational amplifier U4 outputs; when the amplitude of the predicted liquid level signal is lower than the amplitude of the low limit signal, operational amplifier U5 outputs. The positive terminals of relays S1, S2, and S3 input switching signals. The switching signals can be manually fed back. If no switching signal is fed back, the signal at the output of operational amplifier U4 is fed back to the alarm circuit via relay S2 and OUT-1, and operational amplifier U5... The output signal is fed back to the alarm circuit via relays S3 and OUT-2. When the alarm circuit receives a signal from the output of operational amplifier U4 / Op-amp U5, it performs a corresponding pre-judgment alarm. When a switching signal is received, the paths of relays S1, S2, and S3 are switched, and the non-inverting input of operational amplifier U4 loses the pre-judgment liquid level signal feedback. The current liquid level signal is fed back to the non-inverting input of operational amplifier U4 via relay S1. At this time, when the current liquid level signal exceeds the safe liquid level threshold, operational amplifier U4 / Op-amp U5 outputs. The signal from the output of operational amplifier U4 is fed back to relay S2. OUT-3 feeds back to the alarm circuit and protection circuit. The signal from the output of operational amplifier U5 is fed back to the alarm circuit and protection circuit via relay S3 and OUT-2. When the alarm circuit receives the signal from the output of operational amplifier U4 / Operational amplifier U5, it issues a corresponding real-time alarm. When the protection circuit receives the signal from the output of operational amplifier U4 / Operational amplifier U5, it feeds back the execution signal for anticoagulant injection / physiological saline replenishment to the actuator to ensure that the liquid level can return to the safe liquid level threshold. Based on this, two detection modes, predictive detection and real-time detection, are provided.

[0005] Furthermore, it also includes several field-effect transistors (FETs), several resistors, several diodes, and capacitors. The gate of FET Q1 is connected to the cathodes of diodes D1, D2, and D3, and the gate of FET Q2. Its source is connected to one end of resistor R16 and one end of resistor R17. Its drain is connected to one end of capacitor C1 and the drain of FET Q2. The source of FET Q2 is connected to the cathode of diode D5, the non-inverting input of operational amplifier U6, and one end of resistor R15. The output of operational amplifier U6 is connected to the positive terminal of relay S1 and the anode of diode D3. The anode of diode D1 is connected to the output of operational amplifier U4. The anode of diode D2 is connected to the output of operational amplifier U5. The anode of diode D4 is connected to OUT-4. The anode of diode D5 is connected to OUT-3. The other end of resistor R16 is connected to the power supply. The other ends of capacitor C1, resistor R15, and resistor R17 are grounded.The output signal of operational amplifier U4 is fed back to the gates of field-effect transistors Q1 and Q2 via diode D1. The output signal of operational amplifier U5 is also fed back to the gates of field-effect transistors Q1 and Q2 via diode D2. Resistor R14 discharges the parasitic capacitance of the gates of field-effect transistors Q1 and Q2. The power supply signal passes through resistors R16 and R17 to ground. The signal at resistor R17 passes through the source and drain of field-effect transistor Q1, causing the potential at capacitor C1 to match the potential at resistor R17. When operational amplifiers U4 and U5 are outputting, the voltage difference between the gate and source of field-effect transistor Q1 exceeds the conduction threshold, causing Q1 to be cut off. Similarly, the voltage difference between the gate and source of field-effect transistor Q2 exceeds the conduction threshold. When the threshold is reached, MOSFET Q2 turns on. The signal at capacitor C1 passes through the drain and source of MOSFET Q2, and resistor R15 to ground. The potential at capacitor C1 decreases, and the signal at resistor R15 is fed back to the non-inverting input of op-amp U6. The zero-bias signal is fed back to the inverting input of op-amp U6. The zero-bias signal can be fed back from the power supply signal. When MOSFET Q2 is on, the time it takes for the potential signal at capacitor C1 to drop to the amplitude of the zero-bias signal is the switching time. Adjusting the resistance value of resistor R15 sets the switching time; a higher resistance value of R15 results in a longer switching time, and vice versa. The set switching time can be the same as or slightly higher than the predicted time. The power supply signal passes through resistors R18 and R19 to ground, and the signal at resistor R19 is fed back to the inverting input of op-amp U6. Adjusting the resistance value of resistor R15 sets the switching time. Resistor R19 changes the amplitude of the zero-bias signal. When MOSFET Q2 is turned on, operational amplifier U6 outputs. The output signal of operational amplifier U6 is a switching signal. One path of the switching signal is fed back to the gates of MOSFETs Q1 and Q2 via diode D3, ensuring that the gates of MOSFETs Q1 and Q2 continuously receive the switching signal during the switching time. The other path is fed back to the positive terminals of relays S1, S2, and S3, switching the paths of relays S1, S2, and S3. At this time, the detection mode switches to real-time detection mode. When the switching time is exceeded, operational amplifier U6 is turned off, and the detection mode automatically switches back to predictive detection mode. During real-time detection mode, if the current liquid level is higher than the safe liquid level threshold, operational amplifier U4 outputs. The output signal of operational amplifier U4 is routed through relay S2, diode D5, and resistor R15 to ground. If the current liquid level is below the safe liquid level threshold, the output signal of operational amplifier U5 is routed through relay S3, diode D4, and resistor R15 to ground. This ensures that, without manual feedback switching, the initial detection mode is a predictive detection mode. In predictive detection mode, if the predicted liquid level exceeds the safe liquid level threshold, it automatically switches to real-time detection mode. After the switching time, if the current liquid level does not exceed the safe liquid level threshold, it automatically switches back to predictive detection mode. During the switching time, if the current liquid level exceeds the safe liquid level threshold, the detection mode is locked in real-time detection mode until the current liquid level is within the safe liquid level threshold for a certain period before switching back to predictive detection mode.

[0006] Furthermore, it also includes several resistors, wherein one end of resistor R11 is connected to one end of resistor R12 and the inverting input of operational amplifier U4, and the other end is connected to one end of resistor R13 and the non-inverting input of operational amplifier U5; the other end of resistor R12 is connected to the power supply; the other end of resistor R13 is grounded; the resistance values ​​of resistors R11, R12, and R13 are adjusted to set the safe liquid level threshold.

[0007] Furthermore, it also includes several resistors, one end of which, resistor R18, is connected to the power supply, and the other end is connected to one end of resistor R19 and the inverting input of operational amplifier U6; the other end of resistor R19 is grounded; adjusting resistor R19 changes the amplitude of the zero-bias signal.

[0008] Furthermore, it also includes a resistor, R14, with one end connected to the gate of the field-effect transistor Q1 and the other end grounded; resistor R14 discharges the parasitic capacitance of the gate of the field-effect transistor Q1.

[0009] Furthermore, resistors R11, R12, and R13 are adjustable resistors.

[0010] Furthermore, resistors R18 and R19 are adjustable resistors.

[0011] Furthermore, a blood purification device includes any of the liquid level detection circuits described above.

[0012] The advantages of this invention compared to the prior art are:

[0013] This invention can predict the current liquid level and provide two alarm modes, namely prediction alarm and real-time alarm, based on the predicted liquid level and switching signal. It can automatically switch between the two alarm modes based on the liquid level when the switching signal is not manually fed back. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 The circuit structure diagram provided for this invention. Detailed Implementation

[0016] To make the objectives and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or more specific embodiments of the present invention and does not strictly limit the scope of protection specifically claimed by the present invention.

[0017] This invention discloses a liquid level detection circuit and a blood purification device, comprising several operational amplifiers and several resistors. Operational amplifier U1 has its non-inverting input connected to one end of resistor R1 and one end of resistor R2, its inverting input connected to one end of resistor R3 and one end of resistor R4, and its output terminal connected to the other end of resistor R3 and the non-inverting input of operational amplifier U2. Operational amplifier U2 has its inverting input connected to one end of resistor R5 and one end of resistor R6, and its output terminal connected to the other end of resistor R5 and one end of resistor R10. Operational amplifier U3 has its non-inverting input connected to one end of resistor R7 and one end of resistor R8, its inverting input connected to one end of resistor R9 and the other end of resistor R10, and its output terminal connected to the other end of resistor R9. The other end of resistor R1 is connected to IN-1; the other end of resistor R4 is connected to IN-2; and the other ends of resistors R2, R6, and R8 are grounded.

[0018] Specifically, it also includes several operational amplifiers and several relays. Among the several operational amplifiers, the non-inverting terminal of operational amplifier U4 is connected to the common terminal of relay S1, the inverting terminal of operational amplifier U5 is connected to the common terminal of relay S2, and the output terminal of operational amplifier U5 is connected to the common terminal of relay S3. The first terminal of relay S1 is connected to the other end of resistor R9, and the second terminal is connected to the other end of resistor R7. The first terminal of relay S2 is connected to the OUT-1 terminal, and the second terminal is connected to the OUT-3 terminal. The first terminal of relay S3 is connected to the OUT-2 terminal, and the second terminal is connected to the OUT-4 terminal. The positive terminal of relay S1 is connected to the positive terminals of relay S2 and relay S3. The negative terminals of relay S1, relay S2, and relay S3 are grounded.

[0019] Specifically, it also includes several field-effect transistors (FETs), several resistors, several diodes, and capacitors. Among the several FETs, the gate of FET Q1 is connected to the cathodes of diodes D1, D2, and D3, and the gate of FET Q2; the source is connected to one end of resistor R16 and one end of resistor R17; and the drain is connected to one end of capacitor C1 and the drain of FET Q2. The source of FET Q2 is connected to the cathode of diode D5, the non-inverting input of operational amplifier U6, and one end of resistor R15. The output of operational amplifier U6 is connected to the positive terminal of relay S1 and the anode of diode D3. The anode of diode D1 is connected to the output of operational amplifier U4; the anode of diode D2 is connected to the output of operational amplifier U5; the anode of diode D4 is connected to the OUT-4 terminal; the anode of diode D5 is connected to the OUT-3 terminal; the other end of resistor R16 is connected to the power supply; and the other ends of capacitor C1, resistor R15, and resistor R17 are grounded.

[0020] Specifically, it also includes several resistors, wherein one end of resistor R11 is connected to one end of resistor R12 and the inverting input of operational amplifier U4, and the other end is connected to one end of resistor R13 and the non-inverting input of operational amplifier U5; the other end of resistor R12 is connected to the power supply; and the other end of resistor R13 is grounded.

[0021] Specifically, it also includes several resistors, one end of which, resistor R18, is connected to the power supply, and the other end is connected to one end of resistor R19 and the inverting input of operational amplifier U6; the other end of resistor R19 is grounded.

[0022] Specifically, it also includes a resistor, R14, with one end connected to the gate of the field-effect transistor Q1 and the other end grounded.

[0023] Specifically, resistors R11, R12, and R13 are adjustable resistors.

[0024] Specifically, resistors R18 and R19 are adjustable resistors.

[0025] Specifically, a blood purification device includes any of the liquid level detection circuits described above.

[0026] The flow signals from the arterial output and venous input terminals are fed back to the detection circuit via IN-1 and IN-2, respectively. The two flow signals are also fed back from the acquisition circuit. The arterial flow signal passes through resistors R1 and R2 to ground. The signal at resistor R2 is fed back to the non-inverting input of operational amplifier U1. The output of operational amplifier U1 is negatively fed back through resistor R3 and the inverting input of operational amplifier U1. The venous flow signal passes through resistor R4 to the inverting input of operational amplifier U1. Operational amplifier U1 outputs a flow difference signal based on the arterial and venous flow rates. This flow difference signal is fed back to the non-inverting input of operational amplifier U2. The output signal of operational amplifier U2 passes through resistors R5 and R6 to ground. The signal at resistor R5 is fed back to the inverting input of operational amplifier U2. At the end, adjust the resistance ratio of resistors R5 and R6 to adjust the prediction time. The prediction time is 1 + resistor R5 / resistor R6, and the time unit is consistent with the flow sensors at both ends. Based on the prediction time and flow difference, operational amplifier U2 outputs the total flow difference signal after the set prediction time, with the flow difference as the reference. The current liquid level signal is fed back by the acquisition circuit. The current liquid level signal is fed to the ground terminal through resistors R7 and R8. The signal at the resistor R8 terminal is fed back to the non-inverting terminal of operational amplifier U3. The output terminal of operational amplifier U3 is connected to the inverting terminal of operational amplifier U3 through resistor R9 and the negative feedback. The total flow difference signal is fed back to the inverting terminal of operational amplifier U3 through resistor R10. Operational amplifier U3 outputs the prediction liquid level signal based on the current liquid level and the total flow difference.

[0027] The high-limit signal of the safe liquid level threshold is fed back to the inverting input of operational amplifier U4, and the low-limit signal is fed back to the non-inverting input of operational amplifier U5. Both the high-limit and low-limit signals can be fed back from the power supply signal, which passes through resistors R12, R11, and R13 to the ground terminal. The signal at resistor R11 is fed back to the inverting input of operational amplifier U4, and the signal at resistor R13 is fed back to the non-inverting input of operational amplifier U5. Adjusting the resistance values ​​of resistors R11, R12, and R13 sets the safe liquid level threshold and allows for prediction. The liquid level signal is fed back to the non-inverting input of operational amplifier U4 and the inverting input of operational amplifier U5 via relay S1. When the predicted liquid level signal amplitude is higher than the high limit signal amplitude, operational amplifier U4 outputs; when the predicted liquid level signal amplitude is lower than the low limit signal amplitude, operational amplifier U5 outputs. Switching signals are input to the positive terminals of relays S1, S2, and S3. These switching signals can be manually fed back. If no switching signal is fed back, the signal at the output of operational amplifier U4 is fed back to the alarm circuit via relay S2 and OUT-1. The output signal is fed back to the alarm circuit via relays S3 and OUT-2. When the alarm circuit receives a signal from the output of operational amplifier U4 / Op-amp U5, it performs a corresponding pre-judgment alarm. When a switching signal is received, the paths of relays S1, S2, and S3 are switched, and the non-inverting input of operational amplifier U4 loses the pre-judgment liquid level signal feedback. The current liquid level signal is fed back to the non-inverting input of operational amplifier U4 via relay S1. At this time, when the current liquid level signal exceeds the safe liquid level threshold, operational amplifier U4 / Op-amp U5 outputs. The signal from the output of operational amplifier U4 is fed back to relay S2. OUT-3 feeds back to the alarm circuit and protection circuit. The signal from the output of operational amplifier U5 is fed back to the alarm circuit and protection circuit via relay S3 and OUT-2. When the alarm circuit receives the signal from the output of operational amplifier U4 / Operational amplifier U5, it issues a corresponding real-time alarm. When the protection circuit receives the signal from the output of operational amplifier U4 / Operational amplifier U5, it feeds back the execution signal for anticoagulant injection / physiological saline replenishment to the actuator to ensure that the liquid level can return to the safe liquid level threshold. Based on this, two detection modes, predictive detection and real-time detection, are provided.

[0028] The output signal of operational amplifier U4 is fed back to the gates of field-effect transistors Q1 and Q2 via diode D1. The output signal of operational amplifier U5 is also fed back to the gates of field-effect transistors Q1 and Q2 via diode D2. Resistor R14 discharges the parasitic capacitance of the gates of field-effect transistors Q1 and Q2. The power supply signal passes through resistors R16 and R17 to ground. The signal at resistor R17 passes through the source and drain of field-effect transistor Q1, causing the potential at capacitor C1 to match the potential at resistor R17. When operational amplifiers U4 and U5 are outputting, the voltage difference between the gate and source of field-effect transistor Q1 exceeds the conduction threshold, causing Q1 to be cut off. Similarly, the voltage difference between the gate and source of field-effect transistor Q2 exceeds the conduction threshold. When the threshold is reached, MOSFET Q2 turns on. The signal at capacitor C1 passes through the drain and source of MOSFET Q2, and resistor R15 to ground. The potential at capacitor C1 decreases, and the signal at resistor R15 is fed back to the non-inverting input of op-amp U6. The zero-bias signal is fed back to the inverting input of op-amp U6. The zero-bias signal can be fed back from the power supply signal. When MOSFET Q2 is on, the time it takes for the potential signal at capacitor C1 to drop to the amplitude of the zero-bias signal is the switching time. Adjusting the resistance value of resistor R15 sets the switching time; a higher resistance value of R15 results in a longer switching time, and vice versa. The set switching time can be the same as or slightly higher than the predicted time. The power supply signal passes through resistors R18 and R19 to ground, and the signal at resistor R19 is fed back to the inverting input of op-amp U6. Adjusting the resistance value of resistor R15 sets the switching time. Resistor R19 changes the amplitude of the zero-bias signal. When MOSFET Q2 is turned on, operational amplifier U6 outputs. The output signal of operational amplifier U6 is a switching signal. One path of the switching signal is fed back to the gates of MOSFETs Q1 and Q2 via diode D3, ensuring that the gates of MOSFETs Q1 and Q2 continuously receive the switching signal during the switching time. The other path is fed back to the positive terminals of relays S1, S2, and S3, switching the paths of relays S1, S2, and S3. At this time, the detection mode switches to real-time detection mode. When the switching time is exceeded, operational amplifier U6 is turned off, and the detection mode automatically switches back to predictive detection mode. During real-time detection mode, if the current liquid level is higher than the safe liquid level threshold, operational amplifier U4 outputs. The output signal of operational amplifier U4 is connected to ground via relay S2, diode D5, and resistor R15. If the current liquid level is lower than the safe liquid level threshold, the output signal of operational amplifier U5 is connected to ground via relay S3, diode D4, and resistor R15. In this way, when there is no manual feedback switching signal, the initial detection mode is the predictive detection mode. If the predicted liquid level exceeds the safe liquid level threshold in the predictive detection mode, it automatically switches to the real-time detection mode. After the switching time ends, if the current liquid level does not exceed the safe liquid level threshold, it automatically switches back to the predictive detection mode. If the current liquid level exceeds the safe liquid level threshold during the switching time, the detection mode is locked in the real-time detection mode until the current liquid level is at the safe liquid level threshold for a certain period of time, and then it switches back to the predictive detection mode.

[0029] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A liquid level detection circuit, characterized in that, The system includes several operational amplifiers (op-amps) and several resistors. Op-amp U1 has its non-inverting input connected to one end of resistor R1 and one end of resistor R2, its inverting input connected to one end of resistor R3 and one end of resistor R4, and its output terminal connected to the other end of resistor R3 and the non-inverting input of op-amp U2. Op-amp U2 has its inverting input connected to one end of resistor R5 and one end of resistor R6, and its output terminal connected to the other end of resistor R5 and one end of resistor R10. Op-amp U3 has its non-inverting input connected to one end of resistor R7 and one end of resistor R8, its inverting input connected to one end of resistor R9 and the other end of resistor R10, and its output terminal connected to the other end of resistor R9. The other end of resistor R1 is connected to IN-1. One end of resistor R4 is connected to the IN-2 terminal; the other ends of resistors R2, R6, and R8 are grounded; the flow signals from the arterial output terminal and the venous input terminal are fed back to the detection circuit through IN-1 and IN-2 respectively; operational amplifier U1 outputs a flow difference signal based on the flow rate at the arterial end and the flow rate at the venous end; the prediction time is adjusted by adjusting the resistance ratio of resistors R5 and R6; operational amplifier U2 outputs a total flow difference signal based on the prediction time and the flow difference, with the flow difference as the reference, after the set prediction time; operational amplifier U3 outputs a predicted liquid level signal based on the current liquid level and the total flow difference.

2. The liquid level detection circuit according to claim 1, characterized in that, It also includes several operational amplifiers and several relays. Among the several operational amplifiers, the non-inverting terminal of operational amplifier U4 is connected to the common terminal of relay S1, the inverting terminal of operational amplifier U5 is connected to the common terminal of relay S2, and the output terminal of operational amplifier U5 is connected to the common terminal of relay S3. The first terminal of relay S1 is connected to the other end of resistor R9, and the second terminal is connected to the other end of resistor R7. The first terminal of relay S2 is connected to OUT-1, and the second terminal is connected to OUT-3. The first terminal of relay S3 is connected to OUT-2, and the second terminal is connected to OUT-4. The positive terminal of relay S1 is connected to the positive terminals of relay S2 and relay S3. The negative terminals of relay S1, relay S2, and relay S3 are grounded.

3. The liquid level detection circuit according to claim 2, characterized in that, It also includes several field-effect transistors (FETs), several resistors, several diodes, and capacitors. Among the several FETs, the gate of FET Q1 is connected to the cathodes of diodes D1, D2, and D3, and the gate of FET Q2; the source is connected to one end of resistor R16 and one end of resistor R17; and the drain is connected to one end of capacitor C1 and the drain of FET Q2. The source of FET Q2 is connected to the cathode of diode D5, the non-inverting input of operational amplifier U6, and one end of resistor R15. The output terminal of operational amplifier U6 is connected to the positive terminal of relay S1 and the anode of diode D3. The anode of diode D1 is connected to the output terminal of operational amplifier U4; the anode of diode D2 is connected to the output terminal of operational amplifier U5; the anode of diode D4 is connected to the OUT-4 terminal; the anode of diode D5 is connected to the OUT-3 terminal; the other end of resistor R16 is connected to the power supply; the other end of capacitor C1, the other end of resistor R15, and the other end of resistor R17 are grounded.

4. The liquid level detection circuit according to claim 2, characterized in that, It also includes several resistors, wherein one end of resistor R11 is connected to one end of resistor R12 and the inverting input of operational amplifier U4, and the other end is connected to one end of resistor R13 and the non-inverting input of operational amplifier U5; the other end of resistor R12 is connected to the power supply; and the other end of resistor R13 is grounded.

5. The liquid level detection circuit according to claim 3, characterized in that, It also includes several resistors, one end of which, resistor R18, is connected to the power supply, and the other end is connected to one end of resistor R19 and the inverting input of operational amplifier U6; the other end of resistor R19 is grounded.

6. The liquid level detection circuit according to claim 3, characterized in that, It also includes a resistor R14, one end of which is connected to the gate of the field-effect transistor Q1, and the other end is grounded.

7. The liquid level detection circuit according to claim 4, characterized in that, The resistors R11, R12, and R13 are adjustable resistors.

8. The liquid level detection circuit according to claim 5, characterized in that, The resistors R18 and R19 are adjustable resistors.

9. A blood purification device, characterized in that, The blood purification device has a liquid level detection circuit as described in any one of claims 1-8.

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