Hot wire flow sensor and pressure compensation method thereof

Abstract

A hot wire type flow sensor and a pressure compensation method thereof are disclosed. The hot wire type flow sensor includes an inlet and an outlet, and further includes: a gas pressure measuring unit connected to the inlet and measuring a gas pressure value of a gas flowing into the inlet; a filter unit provided at the inlet side and filtering the gas flowing into the hot wire type flow sensor; a flow rate measuring unit provided at the outlet side and measuring an average flow rate of the gas passing through the hot wire type flow sensor; a pressure compensation unit calculating a compensation value of the gas pressure of the gas flowing into the inlet based on the average flow rate of the gas of the hot wire type flow sensor and the gas pressure value of the gas flowing into the inlet according to a predetermined pressure compensation algorithm; and a pressure regulating unit connected to the inlet and regulating the gas pressure of the gas flowing into the inlet based on the compensation value.

Description

Technical Field

[0001] This application relates to the field of medical devices, and more particularly to a flow sensor, a ventilator and anesthesia machine having the flow sensor, and a pressure compensation method thereof. Background Technology

[0002] With the development of modern medicine, ventilators, as an effective means of artificially replacing spontaneous ventilation, are widely used to treat sleep apnea or other respiratory disorders. The flow sensor, as a crucial component in the ventilator's airway structure, not only plays a decisive role in the ventilator's alarm function but also monitors the patient's inspiratory and respiratory flow rate and pressure in real time, feeding this information back to the ventilator's control system to assist in more accurate control of parameters such as patient flow rate, pressure, and tidal volume.

[0003] Flow sensors are precision electronic detection components and are core parts for monitoring gas volume and flow rate during ventilator use. Currently, due to differences in ventilator manufacturers, the structure and operating principles of ventilators vary, resulting in the use of different flow sensors. Based on their working principles, they can be broadly categorized as follows: hot-wire flow sensors, hot-film flow sensors, ultrasonic flow sensors, and pressure-measuring flow sensors.

[0004] The basic principle of a hot-wire flow sensor is to place a thin metal wire (whose resistance varies at different temperatures) in the gas stream being measured. An electric current heats the wire, raising its temperature above the fluid's temperature. When the gas flows over the hot wire, it carries away some of the wire's heat, causing the wire's temperature to drop. The amount of heat dissipated by the wire in the gas is related to the flow rate. This heat dissipation causes a change in the wire's temperature, which in turn causes a change in resistance. The flow rate signal is then converted into an electrical signal, which, after appropriate signal transformation and processing, is used to measure the gas flow rate. The hot wire, placed in the measurement channel, acts as one arm of a Wheatstone bridge. The hot wire, placed in the measurement channel, serves as one arm of a Wheatstone bridge. An operational amplifier differentially amplifies the voltage signal output from the bridge. The operational amplifier provides the bias voltage required for the transistor's operation and allows the operational amplifier's output signal to be superimposed on the transistor's bias potential, then amplified by the transistor to power the bridge. The feedback loop, consisting of the bridge circuit, operational amplifier, and transistor, ensures the hot wire operates at a constant temperature. Upon power-on, the hot wire resistor rapidly heats up, and its resistance immediately increases, quickly bringing the bridge to equilibrium. When fluid flows through the velocity meter, the temperature and impedance of the hot wire change due to heat exchange, causing the bridge to become unbalanced. The fluid velocity can then be measured based on the output feedback voltage signal. The higher the velocity per unit cross-sectional area, the faster the hot wire cools down. Therefore, the hot wire requires more electrical energy to maintain a stable temperature (180°C). The energy required to keep the hot wire at 180°C represents the velocity of the airflow passing through the sensor and cooling the hot wire.

[0005] Hot-wire flow sensors offer significant advantages in terms of high precision, making them widely used as precision electronic detection components in medical devices such as ventilators and anesthesia machines. However, because the guide wire in a hot-wire flow sensor is extremely thin, if patient secretions or condensation adhere to the platinum wire of the flow sensor, especially residual medication after nebulization therapy, it can cause the flow sensor to malfunction. In severe cases, it can even cause the platinum wire to melt and the flow sensor to be destroyed. Summary of the Invention

[0006] In view of the above, a hot-wire flow sensor with a filter and its pressure compensation method are proposed. The filter helps to remove impurities from the gas, preventing contamination of the sensor probe and affecting its sensitivity. Furthermore, by compensating for the gas resistance caused by the filter, good sensor performance is ensured.

[0007] According to one aspect of the present invention, a hot-wire flow sensor is provided, the hot-wire flow sensor including an inlet and an outlet, characterized in that the hot-wire flow sensor further includes: a pressure measuring unit connected to the inlet, the pressure measuring unit measuring the pressure value of gas flowing into the inlet; a filtering unit disposed on the inlet side, the filtering unit filtering the gas flowing into the hot-wire flow sensor; a flow velocity measuring unit disposed on the outlet side, the flow velocity measuring unit measuring the average flow velocity of the gas passing through the hot-wire flow sensor; a pressure compensation unit, based on the average flow velocity of the gas in the hot-wire flow sensor and the pressure value of the gas flowing into the inlet, calculating a compensation value of the pressure of the gas flowing into the inlet according to a predetermined pressure compensation algorithm; and a pressure regulating unit connected to the inlet, the pressure regulating unit adjusting the pressure of the gas flowing into the inlet based on the compensation value.

[0008] Preferably, the predetermined pressure compensation algorithm includes calculating the following two fitting curves: in the absence of the filter unit, a first curve is obtained by the fitting algorithm to obtain the first gas pressure value of the gas flowing into the air inlet and the first average flow velocity of the gas in the hot wire flow sensor; and in the presence of the filter unit, a second curve is obtained by the fitting algorithm to obtain the second gas pressure value of the gas flowing into the air inlet and the second average flow velocity of the gas in the hot wire flow sensor.

[0009] Preferably, the pressure compensation unit calculates the compensation value of the gas pressure flowing into the inlet based on the average flow velocity of the gas from the hot-wire flow sensor, the gas pressure of the gas flowing into the inlet, and the target average flow velocity, according to a predetermined compensation algorithm. This includes: locating a first average flow velocity on the first curve that is the same as the value of the second average flow velocity; determining a first gas pressure value on the first curve corresponding to the located first average flow velocity; and determining the difference between the determined first gas pressure value and the second gas pressure value as the compensation value.

[0010] Preferably, the filtration unit includes a filter screen and / or filter cotton.

[0011] Preferably, the cross-section of the filter unit matches the cross-section of the air inlet, and the filter unit is fitted into the inner wall of the air inlet.

[0012] Preferably, the filter unit is detachably disposed on the air inlet side.

[0013] Preferably, a pull strap is installed on one side of the filter unit, which is used to remove the filter unit from inside the hot wire flow sensor.

[0014] According to one aspect of the present invention, a pressure compensation method for a hot-wire flow sensor is provided, the hot-wire flow sensor including an inlet, a filter unit, and an outlet, characterized in that the pressure compensation method for the hot-wire flow sensor includes: a pressure measurement step, measuring the pressure value of gas flowing into the inlet; a flow velocity measurement step, measuring the average flow velocity of gas passing through the hot-wire flow sensor; a pressure compensation step, calculating a compensation value of the gas pressure flowing into the inlet based on the average flow velocity of the gas in the hot-wire flow sensor and the pressure value of the gas flowing into the inlet according to a predetermined pressure compensation algorithm; and a pressure adjustment step, adjusting the gas pressure of the gas flowing into the inlet based on the compensation value.

[0015] Preferably, the predetermined pressure compensation algorithm includes calculating the following two fitting curves: in the absence of the filter unit, a first curve is obtained by the fitting algorithm to obtain the first gas pressure value of the gas flowing into the air inlet and the first average flow velocity of the gas in the hot wire flow sensor; and in the presence of the filter unit, a second curve is obtained by the fitting algorithm to obtain the second gas pressure value of the gas flowing into the air inlet and the second average flow velocity of the gas in the hot wire flow sensor.

[0016] Preferably, the pressure compensation step includes: locating a first average flow velocity on the first curve that has the same value as the second average flow velocity; determining a first air pressure value on the first curve corresponding to the located first average flow velocity; and determining the difference between the determined first air pressure value and the second air pressure value as the compensation value.

[0017] As can be seen from the above scheme, by setting up a filter, impurities in the gas can be effectively filtered out, preventing contamination of the sensor probe and affecting the sensor's sensitivity. Furthermore, by compensating for the gas resistance caused by the filter, good sensor performance is ensured. In addition, the new hot-wire flow sensor includes a removable filter, allowing for cleaning or replacement each time the filter is used, reducing the cost of replacement due to damage. Attached Figure Description

[0018] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which will make the above and other features and advantages of the present invention more apparent to those skilled in the art. In the drawings:

[0019] Figure 1A schematic diagram of a hot-wire flow sensor according to an embodiment of the present invention is shown;

[0020] Figure 2 A flow rate diagram of a hot-wire flow sensor without a filter unit is shown according to an embodiment of the present invention.

[0021] Figure 3 A flow rate diagram of a hot-wire flow sensor with a filter unit provided is shown according to an embodiment of the present invention.

[0022] Figure 4 A schematic diagram of a hot-wire flow sensor according to an embodiment of the present invention is shown;

[0023] Figure 5 A pressure-flow rate curve of a hot-wire flow sensor according to an embodiment of the present invention is shown;

[0024] Figure 6 A functional block diagram of a hot-wire flow sensor according to an embodiment of the present invention is shown; and

[0025] Figure 7 A flowchart of a pressure compensation method for a hot-wire flow sensor according to an embodiment of the present invention is shown. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the following embodiments are provided to further illustrate the present invention in detail.

[0027] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0029] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction of the component itself; similarly, for ease of understanding and description, "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0030] Figure 1 A schematic diagram illustrating the structure of a hot-wire flow sensor according to an embodiment of the present invention is shown. Figure 1The upper diagram shows a side view of the hot-wire flow sensor 10. As shown, the hot-wire flow sensor 10 includes an inlet 102, an outlet 104, and a thermistor platinum wire 106. When gas (e.g., in the case of a hot-wire flow sensor applied to an exhaled ventilator, the gas is the user's exhaled gas) flows from the inlet 102 to the outlet 104 in the direction of the arrow, it carries away heat as it passes over the surface of the thermistor platinum wire 106. A temperature sensor in the hot-wire control device continuously measures the temperature of the hot wire and then measures the energy required to heat the wire and maintain it at a certain fixed temperature. By measuring the amount of electricity required for heating, the gas flow rate is measured. The resistance of the thermistor platinum wire 106 changes with the gas flow rate, causing the circuit to lose its original balance and generating an unbalanced current signal. The magnitude of this signal corresponds to the gas flow rate, thus allowing the gas flow rate to be measured based on the gas's thermal conductivity. Figure 1 As shown in the lower part of the diagram, a filter unit 108 is disposed near the air inlet 102. This filter unit prevents patient secretions and condensation from adhering to the platinum wire of the flow sensor, which could cause the flow sensor to malfunction or even melt, damaging the flow sensor in severe cases. In this application, to reduce the cost of replacement due to damage, the filter unit 108 can be made as a detachable part, facilitating cleaning and replacement and reducing replacement costs. For example, a pull strap can be installed on one side of the filter unit 108, which can be used to remove the filter unit 108 from the hot-wire flow sensor when cleaning or replacement is required. The filter unit 108 includes a filter screen and / or filter cotton. The cross-section of the filter unit 108 matches the cross-section of the air inlet 102, allowing the filter unit 108 to fit into the inner wall of the air inlet 102.

[0031] Figure 2 A flow rate diagram of a hot-wire flow sensor without a filter unit is shown according to an embodiment of the present invention. Figure 2 As shown, without a filter unit, the air pressure at the inlet of the hot-wire flow sensor is P1, the air pressure at the outlet is P2, the air resistance of the pipe is R1, and the flow velocity within the pipe is F1. Since no filter unit is installed, the air pressure P1 at the inlet of the hot-wire flow sensor is equal to the air pressure P2 at the outlet. The flow velocity F1, the air pressures P1 and P2 at both ends of the air resistance, and the air resistance R1 satisfy the following conditions:

[0032]

[0033] Furthermore, when the hot-wire flow sensor is an expiratory flow sensor, P2 = 0, therefore, the above equation can be simplified to:

[0034]

[0035] Figure 3 A flow rate diagram of a hot-wire flow sensor with a filter unit provided, according to an embodiment of the present invention, is shown. Figure 3 As shown, with the filter unit installed, the air pressure at the inlet of the hot-wire flow sensor is P1', the air pressure at the outlet is P2', the air resistance of the pipe is R2, and the flow velocity within the pipe is F2. Due to the filter unit, the air pressure P1' at the inlet of the hot-wire flow sensor is greater than the air pressure P2' at the outlet. The flow velocity F2, the air pressures P1' and P2' at both ends of the air resistance, and the air resistance R2 satisfy the following conditions:

[0036]

[0037] Figure 4 A schematic diagram of a hot-wire flow sensor according to an embodiment of the present invention is shown. Figure 4 As shown, the gas source 402 supplies gas to the inlet of the hot wire flow sensor via the pressure reducing valve 404. The gas pressure measuring unit 406 measures the gas pressure value P1 of the gas flowing into the inlet, and the flow rate measuring unit 408 measures the average flow rate of the gas passing through the hot wire flow sensor.

[0038] Figure 5 As shown Figure 4 The diagram shows the pressure-velocity curve measured by the hot-wire flow sensor. Figure 4 The hot-wire flow sensor shown measures the air pressure-flow rate with and without a filter unit. Figure 5 As shown, curve A is the pressure-velocity curve obtained by a fitting algorithm when a filter unit is installed, and curve B is the pressure-velocity curve obtained by a fitting algorithm when a filter unit is not installed. Curves A and B were acquired before the hot-wire flow sensor was put into use and are stored in the control unit of the hot-wire flow sensor for use as reference values ​​for pressure compensation after the hot-wire flow sensor is put into use.

[0039] Figure 6A functional block diagram of a hot-wire flow sensor according to an embodiment of the present invention is shown. The hot-wire flow sensor includes: a pressure measuring unit 602 connected to an air inlet, which measures the pressure of gas flowing into the air inlet; a filtering unit 604 disposed on the air inlet side, which filters the gas flowing into the hot-wire flow sensor; a flow velocity measuring unit 606 disposed on the air outlet side, which measures the average flow velocity of gas passing through the hot-wire flow sensor; a pressure compensation unit 608, which calculates a compensation value for the pressure of gas flowing into the air inlet based on the average flow velocity of gas from the hot-wire flow sensor, the pressure of gas flowing into the air inlet, and a target average flow velocity, according to a predetermined pressure compensation algorithm; and a pressure regulating unit 610 connected to the air inlet, which regulates the pressure of gas flowing into the air inlet based on the compensation value. The pressure regulating unit 610 may be a pressure reducing valve. Specifically, after the flow sensor equipped with the filter unit 604 is installed on the ventilator, the pressure measurement unit 602 measures the pressure value P1' of the gas flowing into the air inlet, and the flow velocity measurement unit 606 measures the average flow velocity F2 of the gas passing through the hot-wire flow sensor. Next, in the pressure compensation unit 608, a pre-stored pressure-flow velocity curve is referenced, for example, as shown in... Figure 5 The pressure-velocity curves A and B of the hot-wire flow sensor are shown. In curve A, (P1', F2) is a point such that the average velocity of the gas passing through the hot-wire flow sensor, measured by the velocity measurement unit 606, is F2 = F1. Next, the corresponding point (P1, F1) is found in curve B; that is, P1 is used as the pressure value after pressure compensation. The pressure compensation unit 608 uses the difference between P1 and P1' as the compensation value, and the pressure regulating unit 610 adjusts the pressure of the gas flowing into the inlet according to this compensation value.

[0040] Figure 7 A flowchart illustrating a pressure compensation method for a hot-wire flow sensor according to an embodiment of the present invention is shown. Figure 7 As shown, the pressure compensation method for a hot-wire flow sensor includes: a pressure measurement step 702, measuring the pressure value of the gas flowing into the inlet; a flow velocity measurement step 704, measuring the average flow velocity of the gas passing through the hot-wire flow sensor; a pressure compensation step 706, calculating a compensation value for the pressure of the gas flowing into the inlet based on the average flow velocity of the gas from the hot-wire flow sensor, the pressure value of the gas flowing into the inlet, and a target average flow velocity, according to a predetermined pressure compensation algorithm; and a pressure adjustment step 708, adjusting the pressure of the gas flowing into the inlet based on the compensation value.

[0041] As can be seen from the above solutions, the hot-wire flow sensor and pressure compensation method for the hot-wire flow sensor proposed according to the present invention, by setting a filter, facilitates the filtration of impurities in the gas, avoiding contamination of the sensor probe and affecting the sensor's sensitivity. Furthermore, by compensating for the gas resistance caused by the filter, good sensor performance is ensured. In addition, the new hot-wire flow sensor includes a removable filter, allowing for cleaning or replacement each time the filter is used, reducing the cost of replacement due to damage.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A hot wire flow sensor comprising an inlet and an outlet, characterised in that, The hot-wire flow sensor further comprises: a gas pressure measuring unit connected to the gas inlet and measuring a gas pressure value of the gas flowing into the gas inlet; a filter unit provided at the gas inlet side and filtering the gas flowing into the hot-wire flow sensor; a flow rate measuring unit provided at the gas outlet side and measuring an average flow rate of the gas passing through the hot-wire flow sensor; a pressure compensation unit calculating a compensation value of the gas pressure of the gas flowing into the gas inlet according to a predetermined pressure compensation algorithm based on the average flow rate of the gas passing through the hot-wire flow sensor, the gas pressure value of the gas flowing into the gas inlet, and a target average flow rate; and a pressure regulating unit connected to the gas inlet and regulating the gas pressure of the gas flowing into the gas inlet based on the compensation value, the predetermined pressure compensation algorithm comprises calculating two fitting curves: a first curve of a first gas pressure value of the gas flowing into the gas inlet and a first average flow rate of the gas passing through the hot-wire flow sensor obtained by a fitting algorithm without the filter unit; and a second curve of a second gas pressure value of the gas flowing into the gas inlet and a second average flow rate of the gas passing through the hot-wire flow sensor obtained by a fitting algorithm with the filter unit.

2. The hot wire flow sensor of claim 1, wherein, The pressure compensation unit calculating a compensation value of the gas pressure of the gas flowing into the gas inlet according to a predetermined compensation algorithm based on the average flow rate of the gas passing through the hot-wire flow sensor, the gas pressure of the gas flowing into the gas inlet, and a target average flow rate comprises: positioning a first average flow rate with the same numerical value as the second average flow rate on the first curve, determining a first gas pressure value corresponding to the positioned first average flow rate on the first curve, and determining a difference value between the determined first gas pressure value and the second gas pressure value as the compensation value.

3. The hot wire flow sensor of claim 1, wherein, The filter unit comprises a filter screen and / or filter cotton.

4. The hot wire flow sensor of claim 3, wherein, A cross section of the filter unit matches a cross section of the gas inlet, and the filter unit is fitted to an inner wall of the gas inlet.

5. The hot wire flow sensor of claim 1, wherein, The filter unit is detachably provided at the gas inlet side.

6. The hot wire flow sensor of claim 1, wherein, A pull tab is installed at one end of a side surface of the filter unit, and the pull tab is used to take out the filter unit from inside the hot-wire flow sensor.

7. A pressure compensation method for a hot wire flow sensor comprising an inlet, a filter unit, an outlet, characterized in that, The pressure compensation method for the hot-wire flow sensor comprises: a gas pressure measuring step of measuring a gas pressure value of the gas flowing into the gas inlet; a flow rate measuring step of measuring an average flow rate of the gas passing through the hot-wire flow sensor; a pressure compensation step of calculating a compensation value of the gas pressure of the gas flowing into the gas inlet according to a predetermined pressure compensation algorithm based on the average flow rate of the gas passing through the hot-wire flow sensor measured in the flow rate measuring step, the gas pressure value of the gas flowing into the gas inlet measured in the gas pressure measuring step, and a target average flow rate; and a pressure regulating step of regulating the gas pressure of the gas flowing into the gas inlet based on the compensation value, The predetermined pressure compensation algorithm includes calculating two fitting curves: a first curve of a first gas pressure value of the gas flowing into the gas inlet and a first average flow rate of the gas passing through the hot-wire type flow sensor obtained by a fitting algorithm without the filter unit being provided; and a second curve of a second gas pressure value of the gas flowing into the gas inlet and a second average flow rate of the gas passing through the hot-wire type flow sensor obtained by a fitting algorithm with the filter unit being provided.

8. The method for pressure compensation of a hot wire flow sensor according to claim 7, wherein, The pressure compensation step includes locating a first average flow rate identical to the second average flow rate on the first curve, determining a first gas pressure value corresponding to the located first average flow rate on the first curve, and determining a difference between the determined first gas pressure value and the second gas pressure value as the compensation value.

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