Liquid detection device and detection system for small pipes

Abstract

The utility model provides a kind of liquid detection device and detection system for small pipeline, it is applicable to small pipeline, not susceptible to interference, high sensitivity, and lower cost, comprising: laser emission unit, set in the side of the small pipeline to be measured, for emitting the laser beam of preset light intensity to the pipe wall of small pipeline;Optical signal receiving unit, with the laser emission unit is set in the same side of the small pipeline, the optical signal receiving unit receives the reflected light reflected by the interface formed by the inner wall of small pipeline and the medium in pipe, generates the electrical signal corresponding to the light intensity of the reflected light, compares the electrical signal with preset threshold value, for judging whether there is liquid in small pipeline.

Description

Technical Field

[0001] This utility model relates to the field of sensor technology, and in particular to a liquid detection device and detection system for small pipelines. Background Technology

[0002] In many measuring instruments, Teflon capillary tubes are commonly used as gas / liquid transmission lines. In liquid transmission lines, real-time monitoring of the liquid level is necessary, for example, to prevent reagent depletion. In gas transmission lines, under abnormal circumstances, liquid may seep into the instrument, causing malfunctions, valve corrosion and blockage, and even damage to core detection circuits. On some unattended testing equipment, real-time monitoring of the presence of liquid in the transmission lines is even more crucial to ensure the reliability of equipment operation.

[0003] Currently, the two most commonly used liquid detection solutions for small pipelines are as follows: The first type is the capacitive detection scheme. Figure 1 As shown, the principle of capacitive liquid detection is based on the significant difference in dielectric constant between water and air. An electrode inside the sensor, together with the pipe and the medium inside the pipe, forms a variable dielectric capacitor. The presence of liquid inside the pipe is determined by measuring the change in capacitance. The advantage of this method is that it is low-cost and non-contact detection. However, its disadvantages are also very prominent: low sensitivity and susceptibility to external environmental interference, such as human proximity or changes in electric field, which may cause changes in capacitance and lead to misjudgment. This is especially true for small diameter tubes, such as 1 / 8-inch Teflon tubes, where the capacitance change caused by the liquid inside the tube is very small, making it difficult to achieve stable and accurate detection.

[0004] The second method is ultrasonic testing, which detects liquids by measuring the change in the propagation time of ultrasonic waves within the pipe, such as... Figure 2 As shown, the ultrasonic transducer is placed close to the pipe. During measurement, the transducer emits short-duration ultra-high frequency (>1MHz) ultrasonic waves and records the current time T. When the ultrasonic waves encounter the pipe wall, they generate echoes, which are detected by the transducer and the echo time Tn is recorded. The first echo T1 is usually generated by the pipe wall close to the transducer. Since the speed of sound in liquids is much greater than that in gases, the time T2 for the echo generated by the second pipe wall to reach the transducer will be different. The liquid information in the pipe can be obtained by the time difference T2-T. Since the speed of sound in liquids is much faster than that in gases, the presence or absence of liquid can be determined by analyzing the time difference of the pipe wall echoes. However, the high-frequency ultrasonic transducers used in ultrasonic detection schemes are expensive and are usually suitable for large-diameter pipes or water tanks. They have limited ability to distinguish trace amounts of liquid in thin pipes and cannot meet the detection needs of small pipes. Utility Model Content

[0005] To address the aforementioned problems, this utility model provides a liquid detection device and system for small pipelines, which is suitable for small pipelines, is not easily affected by interference, has high sensitivity, and is low in cost.

[0006] The technical solution is as follows: A liquid detection device for small pipelines, characterized in that it comprises: A laser emitting unit is set on one side of the small pipe to be tested and is used to emit a laser beam of preset intensity toward the pipe wall. An optical signal receiving unit is disposed on the same side of the small pipe as the laser emitting unit. The optical signal receiving unit receives reflected light reflected from the interface formed by the inner wall of the small pipe and the medium inside the pipe, generates an electrical signal corresponding to the light intensity of the reflected light, and compares the electrical signal with a preset threshold to determine whether there is liquid inside the small pipe.

[0007] Furthermore, it also includes a laser probe, which is installed close to the outer wall of the small pipe. The laser probe contains a transmitting optical fiber and a receiving optical fiber. The transmitting optical fiber is connected to the laser transmitting unit, and the receiving optical fiber is connected to the optical signal receiving unit.

[0008] Furthermore, it also includes: a processing unit electrically connected to the optical signal receiving unit, the processing unit comparing the intensity of the received electrical signal with a preset threshold and outputting a judgment signal to indicate whether there is liquid in the small pipe; when the intensity of the electrical signal is lower than the preset threshold, it is determined that there is liquid in the small pipe; when the intensity of the electrical signal is higher than or equal to the preset threshold, it is determined that there is no liquid in the small pipe.

[0009] Furthermore, the laser emitting unit includes: Laser driving circuit, used to generate driving current; A laser diode is connected to the laser driving circuit, and the laser diode emits the laser beam under the drive current.

[0010] Furthermore, the laser driving circuit includes: A first operational amplifier, wherein the non-inverting input of the first operational amplifier is used to receive a drive voltage; Sampling resistor; A MOS transistor, wherein the gate of the MOS transistor is connected to the output terminal of the first operational amplifier, the source of the MOS transistor is grounded through a sampling resistor, and the drain of the MOS transistor is connected to the laser diode; The inverting input of the first operational amplifier is connected to the source of the MOS transistor for current feedback.

[0011] Furthermore, the optical signal receiving unit includes: A photodiode is used to receive the reflected light and generate a photocurrent corresponding to the intensity of the reflected light. A photoelectric conversion amplifier circuit, connected to the photodiode, is used to convert the photocurrent into a voltage signal as the electrical signal.

[0012] Furthermore, the photoelectric conversion amplifier circuit includes: A second operational amplifier, wherein the inverting input terminal of the second operational amplifier is connected to the output terminal of the photodiode; The feedback resistor is connected between the inverting input and the output of the second operational amplifier.

[0013] Furthermore, the laser emitting unit is configured such that the laser beam it emits is incident at an angle perpendicular or nearly perpendicular to the wall of the small pipe.

[0014] A detection system, characterized in that it comprises: Small pipes; As described above, in a liquid detection device for small pipes, the laser emitting unit and the optical signal receiving unit of the liquid detection device are located on the same side of the outside of the small pipe.

[0015] This invention relates to a liquid detection device for small pipes. By setting up a laser emitting unit and an optical signal receiving unit, and utilizing the difference in optical refractive index, the reflected light intensity signal changes significantly due to the presence or absence of liquid in the pipe. This enables accurate identification of liquid in small pipes. Furthermore, this invention uses a highly directional laser as the detection source. The design of its optical path and signal processing link makes it less susceptible to interference from external electromagnetic fields, temperature, and other environmental factors, resulting in high operational reliability. The device has a compact structure, does not have special requirements for pipe diameter, and is particularly suitable for small pipes that are difficult to handle with capacitive and ultrasonic solutions. Moreover, the overall structure is simple and the cost is low. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a capacitive detection scheme in the prior art; Figure 2 This is a schematic diagram of an existing ultrasonic testing scheme; Figure 3 This is a schematic diagram of a liquid detection device for a small pipeline in one embodiment; Figure 4 This is a schematic diagram of a liquid detection device for a small pipeline in another embodiment; Figure 5 This is a schematic diagram of a laser emitting unit in one embodiment; Figure 6 This is a schematic diagram of a laser emitting unit in another embodiment; Detailed Implementation

[0017] See Figure 3 This utility model discloses a liquid detection device for small pipelines, comprising: Laser emitting unit 1 is disposed on one side of small pipe 3 and is used to emit a laser beam of preset intensity toward the pipe wall of small pipe 3. The laser beam emitted by laser emitting unit 1 is incident at an angle perpendicular or nearly perpendicular to the pipe wall of small pipe. The optical signal receiving unit 2 is located on the same side of the small pipe 3 as the laser emitting unit 1. The optical signal receiving unit 2 receives the reflected light reflected from the interface formed by the inner wall of the small pipe 3 and the medium inside the pipe, generates an electrical signal corresponding to the intensity of the reflected light, and compares the electrical signal with a preset threshold to determine whether there is liquid inside the small pipe 3. In this embodiment, an electrical signal reading unit 6 is provided. The electrical signal reading unit 6 can be a voltmeter, multimeter, power meter, etc., to read the electrical signal. Then, by comparing the read voltage signal with a preset threshold, it is used to determine whether there is liquid in the small pipe 3. When the intensity of the electrical signal is lower than the preset threshold, it is determined that there is liquid in the small pipe; when the intensity of the electrical signal is higher than or equal to the preset threshold, it is determined that there is no liquid in the small pipe.

[0018] In one embodiment of this utility model, a laser probe can be provided. The laser probe is installed close to the outer wall of a small pipe. The laser probe contains a transmitting optical fiber 501 and a receiving optical fiber 502. The transmitting optical fiber 501 is connected to the laser transmitting unit 1, and the receiving optical fiber 502 is connected to the optical signal receiving unit 2. The front end of the laser probe is fixed close to the outer wall of the pipe. To ensure that the light path is perpendicular to the incident light, a matching slot clamp can also be designed.

[0019] See Figure 4 In one embodiment of this utility model, a processing unit 4 can be provided, electrically connected to the optical signal receiving unit 2. The processing unit 4 compares the intensity of the received electrical signal with a preset threshold and outputs a judgment signal to indicate whether liquid exists in the small pipe. When the intensity of the electrical signal is lower than the preset threshold, it is determined that liquid exists in the small pipe; when the intensity of the electrical signal is higher than or equal to the preset threshold, it is determined that no liquid exists in the small pipe. In this embodiment, the processor of the processing unit 4 is an STM32G071C8T6. In other embodiments, other processors with similar performance, such as STM32G081C8T6, can also be used. The output terminal of the processing unit 4 outputs a logic level signal, such as a high / low level, which can directly indicate whether liquid exists in the small pipe 3.

[0020] See Figure 5In one embodiment of this utility model, the laser emitting unit 1 includes: Laser driving circuit, used to generate driving current; Laser diode U1 is connected to the laser driving circuit. Laser diode 101 emits a laser beam under the drive current.

[0021] In this embodiment, the laser driving circuit includes: The first operational amplifier U4.1 has its non-inverting input terminal used to receive the drive voltage. Sampling resistor R1; MOS transistor Q1, the gate of MOS transistor Q1 is connected to the output terminal of the first operational amplifier U4.1, the source of MOS transistor Q1 is grounded through sampling resistor R1, and the drain of MOS transistor is connected to laser diode; The inverting input of the first operational amplifier U4.1 is connected to the source of the MOSFET for current feedback.

[0022] In this embodiment, the laser driving circuit further includes a capacitor C1 and a resistor R2 connected between the inverting input and output terminals of the first operational amplifier U4.1, a resistor R3 connected between the inverting input terminal of the first operational amplifier U4.1 and the source of the MOSFET Q1, a resistor R2 connected between the output terminal of the first operational amplifier U4.1 and the gate of the MOSFET Q1, a resistor R4 connected between the inverting input terminal of the first operational amplifier U4.1, and a resistor R5 connected between the non-inverting input terminal of the first operational amplifier U4.1. When the laser driving circuit is working, the driving voltage is input to the non-inverting input terminal of the first operational amplifier U4.1, and the first operational amplifier U4.1 will adjust the gate voltage of the MOSFET Q1, which can linearly control the operating current of the laser diode U1 and precisely control the emitted light power of the laser diode U1.

[0023] See Figure 6 In this embodiment, the optical signal receiving unit 2 includes: Photodiode U2 is used to receive reflected light and generate a photocurrent corresponding to the intensity of the reflected light. The photoelectric conversion amplifier circuit, connected to the photodiode U2, is used to convert the photocurrent into a voltage signal as an electrical signal, which can be output to the processing unit 4.

[0024] In this embodiment, the photoelectric conversion amplifier circuit includes: The second operational amplifier U4.2 has its inverting input terminal connected to the output terminal of the photodiode U2. The feedback resistor R6 is connected between the inverting input and output of the second operational amplifier U4.2.

[0025] In this embodiment, the photoelectric conversion amplifier circuit further includes: a supplementary capacitor C3 connected between the inverting input terminal and the output terminal of the second operational amplifier U4.2; a resistor R7 connected to the output terminal of the second operational amplifier U4.2; a capacitor C4 connected to the non-inverting input terminal of the second operational amplifier U4.2; and a reference voltage VREF connected to the non-inverting input terminal of the second operational amplifier U4.2.

[0026] In this embodiment, photodiode U2 is used to receive reflected light and convert the light intensity signal into a weak photocurrent signal I. 光电流 Based on the virtual short characteristic of operational amplifiers, the output voltage V of the second operational amplifier U4.2 is... out =I 光电流 *R6, the weak photocurrent is converted and amplified into an easily measurable voltage signal, which is an electrical signal that can be compared with a preset threshold.

[0027] The working principle of the liquid detection device for small pipelines in this embodiment is based on Fresnel's law of reflection of light at the interface between different media. When a laser beam is incident on the pipeline, reflection occurs. This invention mainly utilizes the reflection that occurs at the interface between the inner wall of the pipeline and the medium inside the pipeline. According to Fresnel's formula, when the light is incident perpendicularly, the reflectivity R of the light at this interface is as follows: R = (n1 - n2) 2 / (n1+n2) 2 Where n1 is the refractive index of the pipe wall and n2 is the refractive index of the medium inside the pipe; The refractive index of a Teflon tube wall is approximately 1.3, the refractive index of air is approximately 1, and the refractive index of pure water is approximately 1.33. Calculations show that when the Teflon tube contains air, the light reflectivity R≈0.017; when the Teflon tube contains pure water, the light reflectivity R≈0.00013. Therefore, the reflectivity of light decreases significantly when a liquid is present in the tube, and the difference in reflectivity between the presence and absence of liquid is obvious. When a beam of light is incident perpendicularly on a Teflon tube, the intensity of the reflected light can be expressed by the following formula: I 反射= I 入射 *R Where I 反射 For the intensity of reflected light, I 入射 R is the incident light intensity, and R is the reflectivity.

[0028] The reflected light enters the photodiode U2 of the optical signal receiving unit. After photoelectric conversion and amplification, the intensity of the reflected light is obtained. According to the above formula, when the tube is full of liquid, the light reflectivity decreases and the intensity of the reflected light weakens. Therefore, the intensity of the reflected light can be used to determine whether the tube is full of liquid.

[0029] Specifically, when the small pipe 3 is filled with air, the refractive index difference between the inner wall of the pipe (e.g., made of Teflon) and air is significant, resulting in strong reflected light. The optical signal receiving unit 2 receives the strong optical signal and converts it into a high-level electrical signal. When the small pipe 3 is filled with liquid, the refractive index of the inner wall of the pipe and the liquid are very similar, causing the reflected light to weaken sharply. The optical signal receiving unit 2 receives a weak optical signal and converts it into a low-level electrical signal. Therefore, the processing unit 4 can accurately determine whether there is liquid in the small pipe 3 by judging whether the electrical signal is higher or lower than a preset threshold. Typically, the preset threshold can be set near the midpoint between the electrical signal strength corresponding to the presence and absence of liquid.

[0030] As mentioned above, the reflectivity of the Teflon tube when it is filled with air is more than 100 times that when it is filled with water. The light intensity signal received by the light receiving unit differs greatly between the liquid and liquid states, making signal processing extremely simple and reliable with a very high signal-to-noise ratio. This fundamentally avoids misjudgment caused by weak signals, making it possible to detect liquids in small and micro pipes that were previously difficult to monitor reliably. This invention is based on light intensity detection and is not limited by the pipe diameter. As long as the laser spot can be focused on the pipe wall, it is sufficient. The detection process is based on optical reflection and reception and is completely unaffected by the surrounding electric and magnetic fields. The laser beam has excellent directionality and the energy is concentrated on a very small detection point, effectively eliminating the influence of stray light from the environment. Even if the operator gets close, it will not affect the reflectivity of the light. Furthermore, the laser diode, photodiode, and general operational amplifier used in this invention are all common industrial components with extremely low cost.

[0031] In one embodiment of this utility model, a detection system is further included, comprising: Small pipe 3; It also includes the aforementioned liquid detection device for small pipelines. The laser emitting unit and the optical signal receiving unit of the liquid detection device are located on the same side of the outside of the small pipeline for real-time monitoring of the small pipeline. By monitoring the liquid in the small pipeline in real time, it is possible to effectively prevent equipment failure caused by liquid leakage or reagent depletion, and it provides a strong guarantee for the safe and reliable operation of unattended equipment.

[0032] The detection system of this invention can achieve precise monitoring of liquids in pipelines, and can detect abnormal liquids in gas pipelines in a timely manner, avoiding liquid damage to expensive downstream core components, and improving the safety and service life of the equipment; it can also accurately determine whether liquid reagents are exhausted, avoiding instrument idling or generating invalid detection data, and ensuring the effectiveness of experimental or analytical procedures.

[0033] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention.

[0034] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A liquid detection device for small pipelines, characterized in that, include: A laser emitting unit is set on one side of the small pipe to be tested and is used to emit a laser beam of preset intensity toward the pipe wall. An optical signal receiving unit is disposed on the same side of the small pipe as the laser emitting unit. The optical signal receiving unit receives reflected light reflected from the interface formed by the inner wall of the small pipe and the medium inside the pipe, generates an electrical signal corresponding to the light intensity of the reflected light, and compares the electrical signal with a preset threshold to determine whether there is liquid inside the small pipe.

2. The liquid detection device for small pipelines according to claim 1, characterized in that: It also includes a laser probe, which is installed close to the outer wall of a small pipe. The laser probe contains a transmitting optical fiber and a receiving optical fiber. The transmitting optical fiber is connected to the laser transmitting unit, and the receiving optical fiber is connected to the optical signal receiving unit.

3. A liquid detection device for small pipelines according to claim 1, characterized in that: Also includes: The processing unit is electrically connected to the optical signal receiving unit. The processing unit compares the intensity of the received electrical signal with a preset threshold and outputs a judgment signal to indicate whether there is liquid in the small pipe. When the intensity of the electrical signal is lower than the preset threshold, it is determined that there is liquid in the small pipe; when the intensity of the electrical signal is higher than or equal to the preset threshold, it is determined that there is no liquid in the small pipe.

4. A liquid detection device for small pipelines according to claim 1, characterized in that: Also includes: An electrical signal reading unit is used to read the electrical signals of the optical signal receiving unit.

5. A liquid detection device for small pipelines according to claim 1, characterized in that: The laser emitting unit includes: Laser driving circuit, used to generate driving current; A laser diode is connected to the laser driving circuit, and the laser diode emits the laser beam under the drive current.

6. A liquid detection device for small pipelines according to claim 5, characterized in that: The laser driving circuit includes: A first operational amplifier, wherein the non-inverting input of the first operational amplifier is used to receive a drive voltage; Sampling resistor; A MOS transistor, wherein the gate of the MOS transistor is connected to the output terminal of the first operational amplifier, the source of the MOS transistor is grounded through a sampling resistor, and the drain of the MOS transistor is connected to the laser diode; The inverting input of the first operational amplifier is connected to the source of the MOS transistor for current feedback.

7. A liquid detection device for small pipelines according to claim 1, characterized in that: The optical signal receiving unit includes: A photodiode is used to receive the reflected light and generate a photocurrent corresponding to the intensity of the reflected light. A photoelectric conversion amplifier circuit, connected to the photodiode, is used to convert the photocurrent into a voltage signal as the electrical signal.

8. A liquid detection device for small pipelines according to claim 7, characterized in that: The photoelectric conversion amplifier circuit includes: A second operational amplifier, wherein the inverting input terminal of the second operational amplifier is connected to the output terminal of the photodiode; The feedback resistor is connected between the inverting input and the output of the second operational amplifier.

9. A liquid detection device for small pipelines according to claim 1, characterized in that: The laser emitting unit is configured such that the laser beam it emits is incident at an angle perpendicular or nearly perpendicular to the wall of the small pipe.

10. A detection system, characterized in that, include: Small pipes; The liquid detection device for a small pipeline as described in any one of claims 1 to 9, wherein the laser emitting unit and the optical signal receiving unit of the liquid detection device are disposed on the same side of the exterior of the small pipeline.

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