Flow meter for oxygen concentrator and implementation method thereof

Abstract

The present invention discloses a flow meter for an oxygen concentrator and an implementation method thereof. The flow meter comprises a single-chip microcomputer module, a power module, an ADC data acquisition module, an oxygen flow sensor, an amplifying circuit and a display module; the single-chip microcomputer module processes the collected data and then exchanges information with the display module; the power module provides a stable voltage for the single-chip microcomputer module, the amplifying circuit and the display module, and provides a low voltage for the Wheatstone bridge at the same time; the ADC data acquisition module converts the amplified analog signal into a digital signal that can be processed by the single-chip microcomputer module; the oxygen flow sensor converts the flow information into a voltage signal; and the amplifying circuit amplifies the weak voltage value output by the oxygen flow sensor. The implementation method introduces a Kalman filtering algorithm, fits a voltage-flow rate polynomial equation through MTATLAB software, and introduces a self-correcting algorithm, and substitutes the measured voltage value into the oxygen flow rate. The present invention can realize real-time and intuitive monitoring of oxygen instantaneous flow information.

Description

Technical Field

[0001] The invention relates to a flow sensor, and in particular to a flow meter for an oxygen concentrator and an implementation method thereof. Background Art

[0002] Oxygen is an indispensable element of life for the human body and an important substance for generating energy required for the body's functional activities. Oxygen therapy is the use of supplementary oxygen to intervene in the physiological and biochemical internal environment of the human body and promote the benign cycle of metabolic processes in order to achieve the purpose of treating diseases, alleviating symptoms, promoting recovery, preventing lesions and improving health. Clinical practice has proved that oxygen therapy, with its unique therapeutic mechanism, has significant therapeutic effects on acute and chronic ischemic and hypoxic symptoms in various clinical departments and secondary diseases caused by hypoxia. Medical oxygen concentrator is an important medical device for the treatment of respiratory diseases. It can concentrate oxygen in the air and provide it to patients. It is widely used in emergency, intensive care, rehabilitation care and other fields, and plays a vital role in the life safety and health of patients. As the core component of the medical oxygen concentrator, the accuracy and stability of the flow meter of the medical oxygen concentrator are crucial to ensure the treatment effect and safety of patients.

[0003] In most oxygen concentrators on the market, float flowmeters are widely used to measure oxygen flow. However, float flowmeters also have some disadvantages in medical oxygen concentrators: ① Inaccurate measurement, with changes in oxygen supply pressure, the flow rate can change by up to 30%; ② The flow display is not intuitive; ③ It can only measure real-time flow, and cannot record the cumulative amount and oxygen inhalation time. These problems may lead to inaccurate oxygen flow, or even excessive or insufficient oxygen flow, which will affect the treatment effect and safety of patients. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a flow meter for an oxygen concentrator with high accuracy, good stability and low cost and an implementation method thereof.

[0005] Technical solution: A flow meter for an oxygen concentrator, including a single chip microcomputer module, a power module, an ADC data acquisition module, an oxygen flow sensor, an amplifying circuit and a display module;

[0006] The single chip microcomputer module processes the collected data and then exchanges information with the display module;

[0007] The power supply module provides a stable voltage for the single-chip computer module, the amplifier circuit, and the display module, and also provides a low voltage for the Wheatstone bridge;

[0008] The ADC data acquisition module converts the amplified analog signal into a digital signal that can be processed by the single-chip microcomputer module;

[0009] The oxygen flow sensor is a cavity structure, with two strain gauges inside, and the two strain gauges and external resistors form a Wheatstone bridge circuit; the two strain gauges are respectively attached to the brackets in front of the gas pipeline, when oxygen enters the cavity from the air inlet and impacts the two strain gauges through the pipeline, the two strain gauges are deformed, causing the resistance connected to the bridge to change, and the output voltage also changes accordingly;

[0010] The amplifying circuit converts the resistance change caused by the pressure of oxygen on the strain gauge into a measurable voltage change and outputs it;

[0011] The display module intuitively displays the measurement data and processing results processed by the single-chip microcomputer module.

[0012] Furthermore, in the Wheatstone bridge circuit, the first resistor and the second resistor are replaced with the first strain gauge and the second strain gauge respectively; and the first strain gauge and the second strain gauge use the same strain gauge with the same resistance value and opposite installation directions. When the first strain gauge and the second strain gauge are deformed by the airflow pressure, the resistance changes continuously, causing the output voltage to change continuously.

[0013] Furthermore, the two strain gauges are placed horizontally, and the air outlet is facing the middle position of the two strain gauges; when the two strain gauges face the air outlet, one is the front side and the other is the back side; and the gap between the strain gauge and the air outlet is less than 0.5mm, and the diameter range of the pipeline is 1.5mm to 2.5mm.

[0014] Furthermore, it also includes a Bluetooth communication module to transmit the real-time measured voltage signal to the host computer.

[0015] The implementation method of the flow meter for an oxygen concentrator described in any of the above items is as follows: through the resistance strain effect of the strain gauge, using a Wheatstone bridge circuit and an amplifier circuit, the oxygen flow rate is converted into a voltage signal; at the same time, a Kalman filter algorithm is introduced to process the voltage data and eliminate noise; a voltage-flow rate polynomial equation is fitted through MTATLAB software, and a self-correction algorithm is introduced to substitute the measured voltage value into the voltage-flow rate polynomial equation to obtain the oxygen flow rate, thereby realizing the measurement of different oxygen flow rates.

[0016] Furthermore, the self-correction algorithm is implemented as follows: After the flow meter is assembled, the output voltage value V0 at zero flow is measured and recorded once and saved in Flash; thereafter, each time the power is turned on and initialized, it is determined whether it is the first time to start working:

[0017] If it is the first measurement, measure and record the output voltage value V1 at zero flow, calculate the difference between V1 and V0 to obtain the correction coefficient ΔV, and store the correction coefficient ΔV in Flash;

[0018] If the system is not measuring for the first time, the correction factor ΔV is automatically introduced to correct the test voltage, and then substituted into the voltage-flow rate polynomial equation to obtain the oxygen flow rate.

[0019] Compared with the prior art, the present invention has the following significant effects:

[0020] 1. The flow meter in the present invention uses a strain gauge instead of a float flow meter, and then builds a corresponding software and hardware platform, which can realize real-time and intuitive monitoring of the instantaneous flow size information of oxygen;

[0021] 2. The implementation method of the present invention solves the temperature drift problem of the flow meter caused by aging of components, fatigue of strain gauges and different temperatures by adopting a self-correction program, thereby expanding the application range of the flow meter and extending the service life of the flow meter. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The figure is a cavity structure diagram of the oxygen flow sensor in the present invention;

[0023] Figure 2 The schematic diagram of the Wheatstone bridge circuit and the amplifier circuit thereof of the present invention;

[0024] Figure 3 It is a schematic diagram of the module structure of the flow meter in the present invention;

[0025] Figure 4 It is a program flow chart of the self-correction algorithm of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0027] like Figure 3 As shown, the flow meter for oxygen concentrator of the present invention comprises a single chip microcomputer module, a power module, an ADC data acquisition module, an oxygen flow sensor, an amplifier circuit and a display module. The oxygen flow sensor is connected to a Wheatstone bridge through a strain gauge, and the amplifier circuit outputs a measurable voltage signal; the ADC data acquisition module converts the voltage signal into a digital signal. The single chip microcomputer module performs algorithm processing on the digital signal, substitutes the voltage-flow rate function relationship, and obtains the corrected oxygen flow data.

[0028] The single chip microcomputer module is the core of data processing. After the collected data is processed, it interacts with the display module.

[0029] The oxygen flow sensor has a cavity structure with two strain gauges 3 and an air outlet 2 inside. The two strain gauges and the external resistor form a Wheatstone bridge circuit. The two strain gauges are respectively pasted on the bracket in front of the gas pipeline. When oxygen enters the cavity from the air inlet 1 and impacts the two strain gauges through the pipeline, the two strain gauges are deformed, causing the resistance connected to the bridge to change, and the output voltage also changes accordingly.

[0030] The power module includes a step-down module AMS1117-3.3 and an LDO chip SGM2201. The step-down module AMS1117-3.3 provides a stable voltage for the microcontroller module, the oxygen flow sensor, the amplifier circuit, and the display module. The LDO chip SGM2201 provides a low voltage of 0.8V for the Wheatstone bridge to suppress the temperature drift caused by heating.

[0031] The flow meter of the present invention is based on the resistance strain effect of the strain gauge. Through the Wheatstone bridge circuit and the amplifier circuit processing, the resistance change caused by the pressure of oxygen on the strain gauge is converted into a measurable voltage change and output through the amplifier circuit and the ADC data acquisition module. Finally, the mapping relationship between the output voltage of the strain type sensor (i.e., the oxygen flow sensor) and the external force applied thereto can be obtained.

[0032] The ADC data acquisition module converts the amplified analog signal into a digital signal that can be processed by the microcontroller.

[0033] The display module uses a 0.96-inch OLED display screen to intuitively display the measurement data and processing results processed by the microcontroller.

[0034] like Figure 1 The figure shows the cavity structure diagram of the oxygen flow sensor of the present invention. The working principle of the present invention is: the strain gauge 3 is pasted on the baffle in front of the pipe port. When oxygen enters the cavity from the air inlet 1, the oxygen impacts the strain gauge 3 through the pipe, causing the strain gauge 3 to deform, the resistance of the connected bridge changes, and the output voltage also changes accordingly. The key points of the structural design are the pasting position of the strain gauge and the diameter of the gas pipe 4. Due to the above reasons, the measurement accuracy of the oxygen flow sensor is greatly affected. In order to achieve accurate measurement and repeatability and stability of measurement data, the following issues must be considered in the structure of the oxygen flow sensor:

[0035] The pasting position of the strain gauge in the cavity has the following requirements: place the two strain gauges horizontally opposite to each other, with the short edges of the strain gauges close together, and paste and fix them on an internal bracket at the same time, with the air outlet facing the middle position of the two strain gauges. When the strain gauge faces the air outlet, one is the front side and the other is the back side, so as to ensure that when the air flow blows through, the resistance of the strain gauge after deformation becomes larger and the other becomes smaller. The gap design between the air outlet of the gas pipeline and the strain gauge must ensure that there is no shaking. In this embodiment, the gap between the air outlet and the strain gauge must be controlled within 0.5mm, otherwise it will inevitably affect the deformation of the strain gauge; the pipeline diameter must be appropriate, ranging from 1.5mm to 2.5mm. If the pipeline diameter is too large and the pipeline air pressure is too small, the strain gauge will vibrate, so the appropriate diameter can ensure the stability of the data.

[0036] like Figure 2 The figure shows the principle diagram of the Wheatstone bridge circuit and its amplifier circuit of the present invention. For the measurement of strain-type sensitive elements, a Wheatstone bridge is generally used. The Wheatstone bridge is generally composed of 4 resistors, which are used to measure the resistance of one resistor, and the other 3 resistors are known. Assuming the power supply voltage is E, the output voltage U of the bridge circuit is:

[0037]

[0038] When R1=R2=R3=R4 or R1*R3=R2*R4, no matter how large the input voltage is, the output U is always 0. This state is called the equilibrium state. If the balance is broken, an output voltage corresponding to the resistance change will be generated. In order to effectively increase the sensitivity and improve the measurement accuracy, the design adopts an improved Wheatstone bridge, and replaces the first resistor and the second resistor with the first strain gauge P1 and the second strain gauge P2; assuming that the resistance value of the first strain gauge P1 is R1, and the increment of resistance change is ΔR1; the resistance value of the second strain gauge P2 is R2, and the increment of resistance change is ΔR2; when R3=R4, the output voltage U can be obtained according to the above formula (1):

[0039]

[0040] The first strain gauge P1 and the second strain gauge P2 use the same strain gauge, have the same resistance value, and are installed in opposite directions. When the first strain gauge P1 and the second strain gauge P2 are deformed by airflow pressure, the output voltage U changes continuously due to the continuous change in resistance.

[0041] The implementation method of the flow meter for oxygen concentrator of the present invention is as follows: the flow meter accurately converts the oxygen flow rate into a voltage signal by using the resistance strain effect of the strain gauge, a Wheatstone bridge circuit and an amplifier circuit. At the same time, a Kalman filter algorithm is introduced to process the voltage data, eliminate noise, and improve the accuracy and reliability of the data. The voltage-flow rate polynomial equation is fitted by MTATLAB software, and the voltage value is substituted to obtain the oxygen flow rate. A correction coefficient ΔV is introduced in the measurement program. When the instrument leaves the factory, a standard zero flow voltage value is first recorded in the flash of the single-chip microcomputer module, and before the instrument is turned on for measurement each time, a real-time zero flow voltage value is measured and recorded. The difference between the two zero flow voltage values ​​is the correction coefficient ΔV. Before any measurement of the oxygen flow rate, the measured flow rate value is first corrected for data.

[0042] The output voltage of the Wheatstone bridge circuit measured in the experiment is about several millivolts to tens of millivolts, which is very small. In order to facilitate the subsequent detection of the voltage signal and use it as a signal source for filtering, analog-to-digital conversion and other processing, a high-precision differential amplifier composed of a high-performance operational amplifier chip SGM8276 and precision resistors is used to amplify the output voltage. The 0.8V DC voltage provided by the LDO chip SGM2201 is used to power the strain gauge bridge circuit, which can significantly suppress the temperature drift of the strain gauge when it is powered on. The LDO chip SGM2201 is a precision voltage stabilizing chip that can provide a stable reference voltage output with the characteristics of low noise, high stability and high precision. Using this power supply method, the power supply is continuously supplied at room temperature of 26℃ and zero flow, and the output voltage of the Wheatstone bridge circuit and its amplifier circuit is measured with a high-precision multimeter. The data is recorded every 5 minutes. Multiple sets of data are shown in Table 1 below.

[0043] Table 1 Output voltage record data table

[0044] Initial voltage value (mV) 5-minute voltage value 10-minute voltage value 15-minute voltage value 20 minutes voltage value 775 776 779 778 778 775 776 776 776 776 776 778 778 778 778 775 776 778 778 778 775 776 777 777 777 775 776 779 779 778 775 775 776 776 776 775 776 776 776 776 775 775 778 778 778 775 777 779 778 778

[0045] It can be seen from Table 1 that under continuous power supply, the zero point drift caused by the heating of the strain gauge causes the voltage fluctuation to be less than 4mV. The LDO chip SGM2201 can provide a stable voltage output. The voltage output in this way is very stable, so it can significantly suppress the temperature drift of the strain gauge caused by power-on heating, which is also a guarantee of low measurement error.

[0046] like Figure 3The schematic diagram of the module structure of the present invention is shown; the flow meter for the oxygen concentrator includes a single-chip microcomputer module, a power module, an ADC data acquisition module, an oxygen flow sensor, an amplifier circuit, a display module, and a Bluetooth communication module. The single-chip microcomputer module uses STM32G070 as the main chip, based on the new Arm Cortex-M0+ core, with a main frequency of 64MHz, and a built-in 12-bit AD conversion, which has the advantages of low cost, low power consumption, and high performance. The display module is a 0.96-inch OLED display. The Bluetooth communication module uses the HC-08 module to convert the serial port information of the main control chip into Bluetooth information transmission, and the real-time information of the flow meter can be transmitted to the host computer via Bluetooth.

[0047] At room temperature of 26°C, by changing the gas flow rate within the range of 0 to 10 L / min, the voltage data collected by the ADC acquisition module is recorded, and the experimental error is reduced through multiple measurements to ensure the accuracy of the experimental data. According to the experimental calibration data, the polynomial function is fitted through the software MATLAB. The functional relationship between the oxygen flow rate S and the voltage value V is fitted as follows:

[0048] S=-1.83814907391609e-15V 6 +1.26692081425345e-11V 5 -3.60770639966434e-08V 4

[0049] +5.43558039666436e-05V 3 +-0.0457199727388075V 2 +20.3757630232613V-3761.27010061790 (3)

[0051] The functional relationship between the oxygen flow rate S and the voltage value V in formula (3) is stored in the test software through code as a basis for flow rate-voltage value conversion, thereby realizing the measurement of different oxygen flow rates.

[0052] The use environment of the flow meter in the present invention, especially the temperature change, has a great influence on the result of oxygen flow rate measurement. The present invention has conducted multiple experiments under different temperature environments and obtained the measurement results shown in Table 2.

[0053] Table 2 Oxygen flow rate measurement results under different temperature environments

[0054] Oxygen flow rate (L / min) -10℃ 0℃ 15℃ 25℃ 40℃ 0 0 0 0 0 0.4 1 0.3 0.5 0.7 1.1 1.3 2 1.4 1.6 1.8 2 2.4 3 2.3 2.6 2.8 3 3.4 4 3.4 3.6 3.9 4.1 4.3 5 4.3 4.5 4.7 5 5.3

[0055] By observing the measurement data in Table 2, it is found that the measurement results are most accurate under normal temperature environment; the measurement error is large under high and low temperature environments. To solve this problem, a self-correction algorithm optimization is introduced in the software design.

[0056] like Figure 4 The flowchart of the self-correction algorithm of the present invention is shown. The working principle of the self-correction algorithm is as follows: After the flow meter is assembled, the output voltage value V0 at zero flow is measured and recorded once and saved in Flash. After that, each time the power is turned on and initialized, it is determined whether it is the first time to start working:

[0057] If it is the first measurement, measure and record the output voltage value V1 at zero flow, calculate the difference between V1 and V0 to get the correction coefficient ΔV and store it in Flash;

[0058] If the system is not measuring for the first time, the correction coefficient ΔV is automatically introduced to correct the test voltage, and then substituted into formula (3) to convert the voltage value and oxygen flow rate. After the self-correction algorithm program is introduced, the oxygen flow meter is measured at different temperatures. The measurement results are shown in Table 3.

[0059] Table 3 Oxygen flow rate measurement results under different temperature environments after introducing the correction algorithm

[0060] Oxygen flow rate (L / min) -10℃ 0℃ 15℃ 25℃ 40℃ 0 0 0 0 0 0.2 1 0.8 0.9 1 1 1 2 1.8 1.9 1.9 2 2.1 3 2.9 2.9 2.9 3 3 4 3.9 3.9 4 4.1 4.1 5 4.8 4.9 5 5 5

[0061] It can be seen from the test data in Table 3 that after the introduction of the self-correction algorithm program, the flow meter can still accurately measure the oxygen flow rate under the condition of large temperature changes, ensuring that the error is less than 0.2L / min. At the same time, the implementation method of the present invention also avoids the influence of objective factors such as long-term use of the instrument, aging of components, fatigue of strain gauges, etc. on the measurement results.

Claims

1. A flow meter for an oxygen concentrator, characterized in that: It includes a single chip microcomputer module, a power module, an ADC data acquisition module, an oxygen flow sensor, an amplifying circuit and a display module; The single chip microcomputer module processes the collected data and then exchanges information with the display module; The power supply module provides a stable voltage for the single-chip computer module, the amplifier circuit, and the display module, and also provides a low voltage for the Wheatstone bridge; The ADC data acquisition module converts the amplified analog signal into a digital signal that can be processed by the single-chip microcomputer module; The oxygen flow sensor is a cavity structure, with two strain gauges inside, and the two strain gauges and external resistors form a Wheatstone bridge circuit; the two strain gauges are respectively attached to the brackets in front of the gas pipeline, when oxygen enters the cavity from the air inlet and impacts the two strain gauges through the pipeline, the two strain gauges are deformed, causing the resistance connected to the bridge to change, and the output voltage also changes accordingly; The amplifying circuit converts the resistance change caused by the pressure of oxygen on the strain gauge into a measurable voltage change and outputs it; The display module intuitively displays the measurement data and processing results processed by the single-chip microcomputer module; In the Wheatstone bridge circuit, the two strain gauges are respectively a first strain gauge (P1) and a second strain gauge (P2), the external resistors are respectively a third resistor and a fourth resistor, the first strain gauge (P1) and the second strain gauge (P2) are connected in parallel, the third resistor and the fourth resistor are connected in parallel, one end of the amplifier circuit is connected between the first strain gauge (P1) and the second strain gauge (P2), and the other end is connected between the third resistor and the fourth resistor; and the first strain gauge (P1) and the second strain gauge (P2) use the same strain gauge, have the same resistance value, and are installed in opposite directions, and when the first strain gauge (P1) and the second strain gauge (P2) are deformed by airflow pressure, the resistance changes continuously, causing the output voltage to change continuously; The two strain gauges are placed horizontally, and the air outlet is facing the middle position of the two strain gauges; when the two strain gauges face the air outlet, one is the front side and the other is the back side; and the gap between the strain gauge and the air outlet is less than 0.5mm, and the diameter range of the pipeline is 1.5mm to 2.5mm.

2. The flow meter for oxygen concentrator according to claim 1, characterized in that: It also includes a Bluetooth communication module to transmit the real-time measured voltage signal to the host computer.

3. The method for implementing the flow meter for an oxygen concentrator according to any one of claims 1 to 2, characterized in that: Through the resistance strain effect of the strain gauge, the oxygen flow rate is converted into a voltage signal using a Wheatstone bridge circuit and an amplifier circuit. At the same time, the Kalman filter algorithm is introduced to process the voltage data and eliminate noise. The voltage-flow rate polynomial equation is fitted using the MTATLAB software, and a self-correction algorithm is introduced to substitute the measured voltage value into the voltage-flow rate polynomial equation to obtain the oxygen flow rate, thereby realizing the measurement of different oxygen flow rates.

4. The method for implementing the flow meter for an oxygen concentrator according to claim 3, characterized in that: The self-correction algorithm is implemented as follows: After the flow meter is assembled, the output voltage value V0 at zero flow is measured and recorded once and saved in Flash; after that, each time the power is turned on and initialized, it is determined whether it is the first time to start working: If it is the first measurement, measure and record the output voltage value V1 at zero flow, calculate the difference between V1 and V0 to obtain the correction coefficient ΔV, and store the correction coefficient ΔV in Flash; If the system is not measuring for the first time, the correction factor ΔV is automatically introduced to correct the test voltage, and then substituted into the voltage-flow rate polynomial equation to obtain the oxygen flow rate.

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