Liquid level detection circuit and system based on isolation transformer

Abstract

The invention provides a liquid level detection circuit and system based on an isolation transformer, the liquid level detection circuit is provided with an isolation transformer sub-circuit, a potential comparison sub-circuit and a signal output sub-circuit, the isolation transformer sub-circuit is provided with the isolation transformer and a liquid level switch, and the on-off state of the liquid level switch can limit the on-off state of the isolation transformer. The detection voltage and the input voltage of the isolation transformer sub-circuit are changed, and the potential comparison sub-circuit controls the signal output sub-circuit to form connection or disconnection based on the relative voltage value of the detection voltage and the input voltage, so that the output signal of the subsequent signal output device is changed. In the invention, based on the physical characteristics of the isolation transformer, the electrical isolation function of the source side loop and the secondary side loop of the isolation transformer can be realized, and the circuit safety of the source side loop of the isolation transformer is effectively guaranteed in the process of realizing liquid level height detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid level detection, and in particular relates to a liquid level detection circuit and system based on an isolation transformer. Background Art

[0002] Liquid level detection refers to a technology that measures the position or depth of the liquid surface in a container. It is usually used to monitor the liquid level in storage tanks, water tanks, pipes and other containers to ensure the correct storage, transportation and use of the liquid. It is now widely used in production operations in various industries such as chemical, food, water treatment, and pharmaceuticals. By realizing automated monitoring of the liquid level, abnormal liquid level conditions can be detected in a timely manner, ensuring operational safety, improving production efficiency, ensuring production quality, and improving the level of automation in production operations.

[0003] Under the existing technology, conventional liquid level detection operations are mostly implemented by radar liquid level detection, capacitive liquid level switch or frequency signal liquid level detection. Among them, compared with the non-contact detection scheme, the radar liquid level meter can transmit very low energy and extremely short microwave pulses through the antenna system to realize the liquid level detection function and output the liquid level detection data, but the radar liquid level meter has a high cost and is difficult to maintain. When used for single-point or multi-point fixed liquid level detection operations, the cost performance is low. Compared with the contact detection scheme, the capacitive liquid level meter can be based on the capacitive sensing principle. When the height of the measured medium immersing the measuring electrode changes, it will cause its capacitance to change, thereby realizing the indirect liquid level measurement function and outputting the liquid level detection data, and the tuning fork liquid level meter can use the resonance of the piezoelectric crystal to determine whether there is liquid contact, thereby realizing the indirect liquid level measurement function and outputting the liquid level detection data. However, when facing some special liquids, such as conductive liquids, the capacitive liquid level meter and the tuning fork liquid level meter do not have the function of isolation detection, so the use safety is poor and the measurement accuracy is low. Summary of the invention

[0004] The present invention provides a liquid level detection circuit and system based on an isolation transformer to solve the technical problems in the prior art that conventional liquid level detection operations cannot achieve isolation detection, have high use costs, and have low measurement accuracy.

[0005] To solve the above problems, the technical solution of the present invention is: a liquid level detection circuit based on an isolation transformer, comprising: An isolation transformer subcircuit, wherein the isolation transformer subcircuit is provided with an isolation transformer, wherein a source side output terminal of the isolation transformer is connected in series with a ninth resistor and then connected to a ground terminal, a source side input terminal of the isolation transformer is connected to a common node of the ninth resistor and the ground terminal, a secondary side input terminal of the isolation transformer is connected to a first interface of a liquid level switch, and a secondary side output terminal of the isolation transformer is connected to a second interface of the liquid level switch; The loop voltage at the output terminal side of the isolation transformer source side is set as the detection voltage, and the loop voltage at the input terminal side of the isolation transformer source side is set as the input voltage; A potential comparison subcircuit, wherein the potential comparison subcircuit is provided with an operational amplifier, wherein the input voltage of the source side of the isolation transformer is input to the non-inverting input terminal of the operational amplifier, and the detection voltage of the source side of the isolation transformer is input to the inverting input terminal of the operational amplifier; A signal output subcircuit, wherein the signal output subcircuit is provided with a PMOS tube, the gate of the PMOS tube is connected to the first branch of the output end of the operational amplifier, the source of the PMOS tube is connected to the power supply, and the drain of the PMOS tube is connected to the signal output device; A liquid level detection circuit based on an isolation transformer is configured as follows: the isolation transformer subcircuit adjusts the relative voltage value of the detection voltage and the input voltage based on the open and closed state of the liquid level switch, and the potential comparison subcircuit further controls the signal output subcircuit to form a path or an open circuit based on the detection voltage and the input voltage, thereby changing the outward output signal of the subsequent signal output device.

[0006] Preferably, a liquid level detection circuit based on an isolation transformer further includes a disconnection alarm subcircuit, wherein the disconnection alarm subcircuit is provided with an NMOS tube, the gate of the NMOS tube is connected to the second branch of the output end of the operational amplifier, and an alarm device is connected in parallel between the drain and source of the NMOS tube; A liquid level detection circuit based on an isolation transformer is further configured such that the potential comparison subcircuit controls the signal output subcircuit and the disconnection alarm subcircuit to form a circuit and a disconnection respectively based on the detection voltage and the input voltage.

[0007] Preferably, the alarm device uses an LED lamp, and the disconnection alarm sub-circuit also includes a diode and a third resistor, the anode of the diode is connected to the power supply, the cathode of the diode is connected to the first end of the third resistor, the second end of the third resistor is connected to the common node formed by the drain of the NMOS tube and the anode of the LED lamp in parallel, and the common node formed by the source of the NMOS tube and the cathode of the LED lamp in parallel is connected to the source side input end point of the isolation transformer sub-circuit.

[0008] Preferably, in the isolation transformer sub-circuit, the current of the detection current loop constructed from the source side input terminal to the source side output terminal of the isolation transformer is limited to 1-24 mA.

[0009] Preferably, the signal output subcircuit is provided with an optical MOS solid-state relay, a first control port of a source side of the optical MOS solid-state relay is connected to the drain of the PMOS tube, a second control port of a source side of the optical MOS solid-state relay is connected to a ground terminal, a first output port of a secondary side of the optical MOS solid-state relay is connected to a first interface of a signal output terminal, and a second output port of a secondary side of the optical MOS solid-state relay is connected to a second interface of the signal output terminal; The optical MOS solid-state relay is configured such that, when the PMOS tube is turned on, the optical MOS solid-state relay is turned on, and the signal output terminal outputs a liquid level signal.

[0010] Preferably, a circuit breaker is provided in series in the line from the first output port of the secondary side of the optical MOS solid-state relay to the first interface of the signal output terminal, and the circuit breaker is used to prevent the signal output sub-circuit from overloading.

[0011] Preferably, a magnetic bead is also connected in series in the line from the first output port of the secondary side of the optical MOS solid-state relay to the first interface of the signal output terminal, and the magnetic bead is used to eliminate high-frequency interference of the signal in the signal output subcircuit.

[0012] Based on the same concept, the present invention also provides a liquid level detection system based on an isolation transformer, equipped with any one of the above-mentioned liquid level detection circuits based on an isolation transformer, comprising: A liquid level detection module, which is used to monitor the liquid level status of a single or multiple monitoring objects in real time and output a corresponding level signal; A main control module, which collects the level signal output by the liquid level detection module and converts it into an analog signal; A network communication module, which includes a gateway and an industrial switch. The network communication module obtains the liquid level status data processed by the main control module through a 485 communication method, and realizes data transmission and communication between local and remote locations; A remote monitoring module receives the liquid level status data output by the network communication module in real time and implements a visual monitoring function in a remote client.

[0013] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art: The present invention provides a liquid level detection circuit and system based on an isolation transformer. In addition to a conventional liquid level switch, an isolation transformer is further provided. Based on the electrical characteristics of the isolation transformer, its source winding and secondary winding have the advantage of electrical isolation, and transmit electrical energy and variable voltage through electromagnetic induction. Therefore, in the present invention, the source loop and the secondary loop are in a physically isolated state. When used for conductive liquids, the safety of the device on the source loop side can be effectively guaranteed.

[0014] At the same time, the present invention is provided with a potential comparison subcircuit, a signal output subcircuit and a disconnection alarm subcircuit. Based on the working state of the isolation transformer, the present invention can accurately and efficiently realize the adaptive sound and light warning and level signal output functions under different liquid level states. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic structural diagram of a liquid level detection circuit based on an isolation transformer provided by the present invention; Figure 2 A schematic structural diagram of a liquid level detection system based on an isolation transformer provided by the present invention. DETAILED DESCRIPTION

[0016] The following is a further detailed description of a liquid level detection circuit and system based on an isolation transformer proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and claims.

[0017] First embodiment See also Figure 1 , this embodiment provides a liquid level detection circuit based on an isolation transformer, realizing an electrically isolable liquid level detection function.

[0018] Specifically, the liquid level detection circuit based on the isolation transformer provided in this embodiment includes an isolation transformer sub-circuit, a potential comparison sub-circuit and a signal output sub-circuit.

[0019] An isolation transformer T1 is provided in the isolation transformer subcircuit, and the source side output terminal 1 of the isolation transformer T1 is connected to the first end of the ninth resistor R9, and the second end of the ninth resistor R9 is connected to an eleventh resistor R11 and a twelfth resistor R12 arranged in parallel and then grounded, and the source side input terminal 3 of the isolation transformer T1 is connected in series with a third capacitor C3 and then connected to the second end of the ninth resistor R9, wherein the loop on the side of the source side output terminal 1 of the isolation transformer T1 is set to IL1, and the loop on the side of the source side input terminal 2 of the isolation transformer T1 is set to IH1, and the loop voltage on the side of the source side output terminal 1 of the isolation transformer T1 is further set to the detection voltage, and the loop voltage on the side of the source side input terminal 2 of the isolation transformer T1 is set to the input voltage.

[0020] The secondary input terminal 8 of the isolation transformer T1 is connected to the first interface of the liquid level switch J2, and the secondary output terminal 7 of the isolation transformer T1 is connected to the second interface of the liquid level switch J2, wherein the liquid level switch J2 only needs to realize switch on / off control according to the liquid level height. In this embodiment, when the liquid level reaches a preset height, the liquid level switch J2 is closed, and at this time, the secondary circuit of the isolation transformer T1 forms a passage. Conversely, when the liquid level is lower than the preset height, the liquid level switch J2 is disconnected, and at this time, the secondary circuit of the isolation transformer T1 forms a short circuit.

[0021] The isolation transformer T1 is provided with a source winding and a secondary winding inside, and the source winding and the secondary winding themselves have electrical isolation characteristics. When the source loop of the isolation transformer T1 forms a path and there is current, a magnetic field will be generated in its source winding, and the magnetic field will cut the secondary winding of the isolation transformer T1. If the isolation transformer T1 forms a path, an induced current can be generated in the secondary loop of the isolation transformer T1. Therefore, in this embodiment, by detecting the current change in the secondary loop of the isolation transformer T1, the opening and closing state of the liquid level switch J2 in the secondary loop of the isolation transformer T1 can be determined, and further it can be determined whether the actual height of the liquid level reaches the preset height.

[0022] An operational amplifier U1 is provided in the potential comparison subcircuit. The input voltage of the source side of the isolation transformer T1 is input to the non-inverting input terminal of the operational amplifier U1, and the detection voltage of the source side of the isolation transformer T1 is input to the inverting input terminal of the operational amplifier U1.

[0023] In this embodiment, the input voltage values ​​of the non-inverting input terminal and the inverting input terminal of the operational amplifier U1 change based on the conduction conditions of the source side and the secondary side of the isolation transformer T1. Therefore, by obtaining the high and low level states of the output terminal of the operational amplifier U1, it is possible to indirectly determine whether the actual liquid level has reached the preset height.

[0024] A PMOS tube Q1 is provided in the signal output subcircuit, the gate of the PMOS tube Q1 is connected to the first branch of the output end of the operational amplifier U1, the source of the PMOS tube Q1 is connected to the power supply VCC, and the drain of the PMOS tube Q1 is connected to the signal output device. When the output end of the operational amplifier U1 outputs a high level, the PMOS tube Q1 is turned off, enabling the signal output subcircuit to be disconnected, and the signal output terminal J1 in the signal output subcircuit can output an open circuit signal, which means that the actual height of the liquid level reaches the preset height. Conversely, when the output end of the operational amplifier U1 outputs a low level, the PMOS tube Q1 is turned on, enabling the signal output subcircuit to be connected, and the signal output terminal J1 of the signal output subcircuit can output a connection signal, which means that the actual height of the liquid level does not reach the preset height.

[0025] In summary, this embodiment provides a liquid level detection circuit based on an isolation transformer. The isolation transformer subcircuit adjusts the relative voltage value of the detection voltage and the input voltage based on the opening and closing state of the liquid level switch J2. Subsequently, the potential comparison subcircuit further controls the signal output subcircuit to form a path or an open circuit based on the detection voltage and the input voltage, thereby changing the outward output level signal of the signal output terminal J1 to realize the functions of liquid level detection and detection signal output. In this process, based on the electrical isolation characteristics of the isolation transformer T1 itself, the source side loop and the secondary side loop have good insulation characteristics. When facing liquid level height detection such as conductive liquids, the use safety of the source side loop can be effectively guaranteed, thereby expanding the application scenarios of this embodiment in liquid level detection operations.

[0026] The specific circuit structure of a liquid level detection circuit based on an isolation transformer provided in this embodiment is further described in detail below: The liquid level detection circuit based on the isolation transformer provided in the present embodiment is also provided with a disconnection alarm subcircuit, in which an NMOS tube Q2 is provided, the gate of the NMOS tube Q2 is connected to the second branch of the output end of the operational amplifier U1, and an alarm device is connected in parallel between the drain and the source of the NMOS tube Q2. In the present embodiment, when the output end of the operational amplifier U1 outputs a high level, the NMOS tube Q2 is turned on, the branch where the alarm device is located is disconnected, and the alarm device does not issue an alarm, which means that the actual height of the liquid level has reached the preset height. On the contrary, when the output end of the operational amplifier U1 outputs a low level, the NMOS tube Q2 is turned off, the branch where the alarm device is located is connected, and the alarm device issues an alarm, which means that the actual height of the liquid level has not reached the preset height.

[0027] Preferably, the alarm device is selected as an LED lamp, and the disconnection alarm sub-circuit also includes a diode D1, a third resistor R3 and a fifth resistor R5. The anode of the diode D1 is connected to the power supply VCC, the cathode of the diode D1 is connected to the first end of the third resistor R3, the second end of the third resistor R3 is connected to the common node formed by the drain of the NMOS tube Q2 and the anode of the LED lamp in parallel, the cathode of the LED lamp is connected in series with the fifth resistor R5 and then connected to the source of the NMOS tube Q2, and the common node formed by the second end of the fifth resistor R5 and the source of the NMOS tube Q2 is further connected to the loop IH1 on the side of the source side input terminal 2 of the isolation transformer T1. In this embodiment, the disconnection alarm subcircuit is used in conjunction with the signal output subcircuit. When the liquid level reaches a preset height, the liquid level switch J2 is closed, the output end of the operational amplifier U1 outputs a high level, the PMOS tube Q1 is turned off, and the signal output terminal J1 of the signal output subcircuit can output an open circuit signal. At the same time, the NMOS tube Q2 is turned on, and the LED light is turned off, indicating that the liquid level has reached the preset height. Conversely, when the liquid level does not reach the preset height, the liquid level switch J2 is disconnected, the output end of the operational amplifier U1 outputs a low level, the PMOS tube Q1 is turned on, and the signal output terminal J1 of the signal output subcircuit can output a path signal. At the same time, the NMOS tube Q2 is turned off, and the LED light is turned on, indicating that the liquid level has not reached the preset height.

[0028] Further, in this embodiment, when the NMOS tube Q2 is turned on, the source side loop of the isolation transformer T1 can be understood as: power supply VCC-diode D1-third resistor R3-NMOS tube Q2-IH1-source side winding-ninth resistor R9-IL1-(eleventh resistor R11, twelfth resistor R12)-ground terminal GND. The current value of the source side loop of the isolation transformer T1 is: I 回路 =(VCC-V Q2 ) / (R3+R 绕组 +R11) / 2+R9), by adjusting the resistance value of the third resistor R3, the current value range of the source side loop of the isolation transformer T1 is limited to 1-24mA, preferably 4-20mA, so as to adapt to the analog signal transmission specifications of the industrial standard, enhance the interoperability with other devices, and ensure the quality and stability of signal transmission.

[0029] In this embodiment, the signal output subcircuit is provided with an optical MOS solid-state relay MP1, a first control port 1 on the source side of the optical MOS solid-state relay MP1 is connected to the drain of the PMOS tube Q1, a second control port 2 on the source side of the optical MOS solid-state relay MP1 is connected in series with a first resistor R1 and then connected to the ground terminal, a first output port 3 on the secondary side of the optical MOS solid-state relay MP1 is connected to the first interface of the signal output terminal J1, and a second output port 4 on the secondary side of the optical MOS solid-state relay MP1 is connected to the second interface of the signal output terminal J1.

[0030] The optical MOS solid-state relay MP1 is also provided with a source side and a secondary side. In the present embodiment, when the PMOS tube Q1 is turned on, the source side loop of the optical MOS solid-state relay MP1 forms a path and current flows, and then the source side to the secondary side of the optical MOS solid-state relay MP1 is turned on, so that the secondary side loop of the optical MOS solid-state relay MP1 also forms a path and current flows, and the enable signal output terminal J1 can output a path signal, and the path signal can be understood as a high level. Conversely, when the PMOS tube Q1 is turned off, the source side loop of the optical MOS solid-state relay MP1 forms an open circuit, and the source side to the secondary side of the optical MOS solid-state relay MP1 is electrically isolated, so that the secondary side loop of the optical MOS solid-state relay MP1 also forms an open circuit, and the enable signal output terminal J1 can output an open circuit signal, and the open circuit signal can be understood as a low level.

[0031] Furthermore, in the line from the first output port 3 of the secondary side of the optical MOS solid-state relay MP1 to the first interface of the signal output terminal J1, a circuit breaker F1 and a second resistor R2 are connected in series. The second resistor R2 is used to limit the current in the secondary side loop of the optical MOS solid-state relay MP1, and when the current in the secondary side loop of the optical MOS solid-state relay MP1 exceeds a preset value, the circuit breaker F1 will fuse and cut off the circuit to prevent overload, thereby ensuring the safety of the signal output sub-circuit.

[0032] Furthermore, a magnetic bead BL1 is also connected in series in the circuit from the first output port 3 of the secondary side of the optical MOS solid-state relay MP1 to the first interface of the signal output terminal J1. Based on the characteristics of the magnetic bead BL1 that it presents lower impedance at low frequencies and higher impedance at high frequencies, it is used to suppress high-frequency interference of the signal of the signal output sub-circuit and improve the anti-interference ability of the signal output sub-circuit, thereby ensuring that the contact signal quality output by the signal output terminal J1 is better.

[0033] Below, several voltage parameter calculation methods of a liquid level detection circuit based on an isolation transformer provided in this embodiment will be further described in detail to verify the feasibility of this embodiment: Specifically, the potential of the non-inverting input terminal of the operational amplifier U1 is calculated as follows: V 同相输入端 =I 回路 R11 / 2+VCC(R6+R15 / 2) / (R4+R6+R11 / 2)+I 运算放大器 (R6+R11 / 2), V IL1 =I 回路 R11 / 2, where I 运算放大器 It is related to the reverse current. When the current value is small, it is only a few microamperes, so the calculation can be ignored in this embodiment.

[0034] The potential of the inverting input terminal of the operational amplifier U1 is calculated as: V 反相输入端 =VIH1 R10 / (R10+R8), V IH1 =V IL1 +I 回路 R9+V 绕组 , V 绕组 =I 回路 R 绕组 , where I 回路 =(VCC-V Q2 ) / (R3+R 绕组 +R11 / 2+R9).

[0035] When there is current in the source circuit of the isolation transformer T1, if the liquid level switch J2 is closed, an induced current will be generated in the secondary circuit of the isolation transformer T1 due to the principle of electromagnetic induction. At this time, there is a difference between IH1 and IL1 by the voltage drop of the ninth resistor R9 and the transformer winding. Conversely, if the liquid level switch J2 is disconnected, a current loop cannot be formed in the secondary circuit of the isolation transformer T1, resulting in charge accumulation (induced voltage) on the source side of the isolation transformer T1 due to the difference in iron loss and copper loss in the transformer core and winding, further causing the voltage drop between IH1 and IL1 in the source circuit to increase (about 300mV, and subsequently calculated as 250mV).

[0036] Specifically, when the liquid level exceeds the preset height, the liquid level switch J2 is closed. 回路 is 1mA, then V IL1 =16.5*1mA=16.5mV, V IH1 =16.5mV+5*1mA=21.5mV. At this time, the voltage value of the non-inverting input terminal of the operational amplifier U1 is 29.6mV greater than the voltage value of the inverting input terminal. The operational amplifier U1 outputs a high level, which satisfies the NMOS tube Q2 to turn on and the PMOS tube Q1 to turn off. If I is set 回路 is 24mA, then V IL1 =16.5*24mA=384mV, V IH1 =16.5*24mA+5*24mA=504mV. At this time, the voltage value of the non-inverting input terminal of the operational amplifier U1 is 75.4mV greater than the voltage value of the inverting input terminal. The operational amplifier U1 outputs a high level, which still satisfies the NMOS tube Q2 to turn on and the PMOS tube Q1 to turn off.

[0037] Similarly, when the liquid level does not exceed the preset height, the liquid level switch J2 is disconnected. 回路 is 1mA, then V IL1 =16.5*1mA+27.3mV=43.8mV, V IH1=16.5mV+250mA=266.5mV. At this time, the voltage value of the non-inverting input terminal of the operational amplifier U1 is 131.9mV less than that of the inverting input terminal. The operational amplifier U1 outputs a low level, which satisfies the NMOS tube Q2 to turn off and the PMOS tube Q1 to turn on. If I is set 回路 is 24mA, then V IL1 =16.5*24mA+27.3mV=411.3mV, V IH1 =16.5*24mA+250mA=646mV. At this time, the voltage value of the non-inverting input terminal of the operational amplifier U1 is 14.6mV less than the voltage value of the inverting input terminal, which still satisfies the requirement that the NMOS tube Q2 is turned off and the PMOS tube Q1 is turned on.

[0038] Second embodiment Based on the same concept, the present invention also provides a liquid level detection system based on an isolation transformer, see Figure 2 , including liquid level detection module, main control module, network communication module and remote monitoring module.

[0039] The liquid level detection module is provided with a liquid level detection circuit based on an isolation transformer as described in any one of the first embodiments, realizing the liquid level monitoring function for a single or multiple monitoring objects, and converting the opening and closing action of the liquid level switch into a level signal output.

[0040] The main control module can collect the level signal output by the liquid level detection module, calculate and analyze the level signal, and convert the switch signal into an analog signal based on subsequent signal data processing requirements.

[0041] The network communication module includes a gateway and an industrial switch. The network communication module can obtain the liquid level status data processed by the main control module through 485 communication, and realize the data transmission and communication function between local and remote devices.

[0042] The remote monitoring module includes monitoring software, network PC, cloud, Android, etc. Users can realize the visual monitoring function of the liquid level status of the monitored object based on different monitoring platforms.

[0043] In summary, the present invention provides a liquid level detection circuit and system based on an isolation transformer. Based on the characteristics that the voltage drop on the source side of the isolation transformer is different in magnitude when it is on and off, a potential comparison subcircuit, a signal output subcircuit and a line break alarm subcircuit are designed. According to the on and off state of the liquid level switch under different liquid level states, the output of sound and light warnings and level signals is realized, and in this process, the insulation safety of the liquid level detection circuit is fully guaranteed. At the same time, during the signal transmission process, the switch signal of the liquid level switch is still output as a switch signal by the signal output subcircuit after isolation transmission, and is specifically output as a non-polar contact signal by the signal output terminal, so as to ensure that the signal is clear and accurate and the transmission is complete, which is convenient for the subsequent expansion of external matching functions. In addition, the main control module can further process the switch signal into an analog signal or a bus signal, and realize a one-to-many liquid level monitoring function for several monitoring objects through the computing power of the main control module.

[0044] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they still fall within the protection scope of the present invention.

[0045] As used herein, the term "including" and its variations mean open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "based at least in part on". The terms "an example embodiment" and "an embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc. may refer to different or the same objects.

Claims

1. A liquid level detection circuit based on an isolation transformer, characterized in that: include: An isolation transformer subcircuit, wherein the isolation transformer subcircuit is provided with an isolation transformer, wherein a source side output terminal of the isolation transformer is connected in series with a ninth resistor and then connected to a ground terminal, a source side input terminal of the isolation transformer is connected to a common node of the ninth resistor and the ground terminal, a secondary side input terminal of the isolation transformer is connected to a first interface of a liquid level switch, and a secondary side output terminal of the isolation transformer is connected to a second interface of the liquid level switch; The loop voltage at the output terminal side of the isolation transformer source side is set as the detection voltage, and the loop voltage at the input terminal side of the isolation transformer source side is set as the input voltage; A potential comparison subcircuit, wherein the potential comparison subcircuit is provided with an operational amplifier, wherein the input voltage of the source side of the isolation transformer is input to the non-inverting input terminal of the operational amplifier, and the detection voltage of the source side of the isolation transformer is input to the inverting input terminal of the operational amplifier; A signal output subcircuit, wherein the signal output subcircuit is provided with a PMOS tube, the gate of the PMOS tube is connected to the first branch of the output end of the operational amplifier, the source of the PMOS tube is connected to the power supply, and the drain of the PMOS tube is connected to the signal output device; A liquid level detection circuit based on an isolation transformer is configured as follows: the isolation transformer subcircuit adjusts the relative voltage value of the detection voltage and the input voltage based on the open and closed state of the liquid level switch, and the potential comparison subcircuit further controls the signal output subcircuit to form a path or an open circuit based on the detection voltage and the input voltage, thereby changing the outward output signal of the subsequent signal output device.

2. The liquid level detection circuit based on the isolation transformer as claimed in claim 1, characterized in that: It also includes a disconnection alarm subcircuit, wherein the disconnection alarm subcircuit is provided with an NMOS tube, the gate of the NMOS tube is connected to the second branch of the output end of the operational amplifier, and an alarm device is connected in parallel between the drain and source of the NMOS tube; A liquid level detection circuit based on an isolation transformer is further configured such that the potential comparison subcircuit controls the signal output subcircuit and the disconnection alarm subcircuit to form a circuit and a disconnection respectively based on the detection voltage and the input voltage.

3. The liquid level detection circuit based on the isolation transformer as claimed in claim 2, characterized in that: The alarm device uses an LED lamp, and the disconnection alarm sub-circuit also includes a diode and a third resistor. The anode of the diode is connected to the power supply, the cathode of the diode is connected to the first end of the third resistor, the second end of the third resistor is connected to the common node formed by the drain of the NMOS tube and the anode of the LED lamp in parallel, and the common node formed by the source of the NMOS tube and the cathode of the LED lamp in parallel is connected to the source side input end point of the isolation transformer sub-circuit.

4. The liquid level detection circuit based on the isolation transformer as claimed in claim 3, characterized in that: In the isolation transformer sub-circuit, the current of the detection current loop constructed from the source side input terminal to the source side output terminal of the isolation transformer is limited to 1-24 mA.

5. The liquid level detection circuit based on the isolation transformer as claimed in claim 1, characterized in that: The signal output subcircuit is provided with an optical MOS solid-state relay, the first control port of the source side of the optical MOS solid-state relay is connected to the drain of the PMOS tube, the second control port of the source side of the optical MOS solid-state relay is connected to the ground terminal, the first output port of the secondary side of the optical MOS solid-state relay is connected to the first interface of the signal output terminal, and the second output port of the secondary side of the optical MOS solid-state relay is connected to the second interface of the signal output terminal; The optical MOS solid-state relay is configured such that, when the PMOS tube is turned on, the optical MOS solid-state relay is turned on, and the signal output terminal outputs a liquid level signal.

6. The liquid level detection circuit based on the isolation transformer as claimed in claim 5, characterized in that: A circuit breaker is provided in series in the line from the first output port of the secondary side of the optical MOS solid-state relay to the first interface of the signal output terminal, and the circuit breaker is used to prevent the signal output sub-circuit from overloading.

7. The liquid level detection circuit based on the isolation transformer as claimed in claim 5, characterized in that: A magnetic bead is also arranged in series in the line from the first output port of the secondary side of the optical MOS solid-state relay to the first interface of the signal output terminal, and the magnetic bead is used to eliminate high-frequency interference of the signal in the signal output subcircuit.

8. A liquid level detection system based on an isolation transformer, characterized in that: A liquid level detection circuit based on an isolation transformer as described in any one of claims 1 to 7, comprising: A liquid level detection module, which is used to monitor the liquid level status of a single or multiple monitoring objects in real time and output a corresponding level signal; A main control module, which collects the level signal output by the liquid level detection module and converts it into an analog signal; A network communication module, which includes a gateway and an industrial switch. The network communication module obtains the liquid level status data processed by the main control module through a 485 communication method, and realizes data transmission and communication between local and remote locations; A remote monitoring module receives the liquid level status data output by the network communication module in real time and implements a visual monitoring function in a remote client.

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