Thermistor flow sensor with multiple temperature points

Abstract

A gas flow rate sensing system can be configured to operate in at least two different target temperature modes based on a measured gas flow temperature. In some embodiments, the gas flow rate sensing system can have a voltage divider including a thermistor. The gas flow rate can be determined based on a voltage output and the measured gas flow temperature, the voltage output indicating an amount of power required to maintain the thermistor at a target temperature specified by the target temperature mode.

Description

[0001] This application is a divisional application of the Chinese invention patent application with international application number PCT / NZ2017 / 050119, national application number 201780065615.4, application date September 13, 2017, and name “Thermistor flow sensor with multiple temperature points”. Technical Field

[0002] The present disclosure relates to methods and systems for sensing flow rate in a flow therapy device for delivering gas to a patient. Background Art

[0003] Respiratory assistance devices are used to deliver gas flows to users or patients in different environments (e.g., hospitals, medical facilities, boarding care, or home environments). A respiratory assistance device or flow therapy device may include an oxygen inlet for allowing supplemental oxygen to be delivered with the gas flow, and / or a humidification device for delivering heated and humidified gas. The flow therapy device may allow adjustment and control of gas flow characteristics, including flow rate, temperature, gas concentration, humidity, pressure. Sensors such as heated temperature sensing elements and / or thermistors are used to measure these characteristics of the gas. This application claims priority to U.S. Provisional Application No. 62 / 395,890, the entire contents of which are incorporated herein by reference. Summary of the invention

[0004] The present disclosure describes a gas flow rate sensing system that can be used to sense a gas flow rate of a gas flow. In some embodiments, the gas flow rate sensing system is configured to operate in at least two different target temperature modes based on a measured flow temperature. In some embodiments, the gas flow rate sensing system can include a voltage divider including a thermistor, wherein the gas flow rate can be determined based on a voltage output and the measured gas flow temperature, the voltage output indicating an amount of power required to maintain the thermistor at a target temperature specified by the target temperature mode.

[0005] A respiratory assistance device for providing a gas flow to a patient may include at least one gas flow path, the at least one gas flow path being configured to direct the gas flow to the patient. The respiratory assistance device may further include a gas flow inlet, the gas flow inlet being configured to receive the gas flow from a gas flow source. The respiratory assistance device may further include a temperature sensor, the temperature sensor being configured to measure the temperature of the gas flow. The respiratory assistance device may further include a gas flow rate sensing system, the gas flow rate sensing system being configured to measure the gas flow rate of the gas flow, wherein the gas flow rate sensing system is configured to operate in at least two different temperature modes based on the measured gas flow temperature.

[0006] The gas flow source may include a blower.

[0007] The temperature sensor and / or the gas flow rate sensing system may be located upstream of the blower.

[0008] The temperature sensor and / or the gas flow rate sensing system may be included in a sensor assembly having a housing.The sensor assembly may be located in a sensor region before the blower within the inlet flow path.

[0009] The temperature sensor and / or the gas flow rate sensing system may be located downstream of the blower.

[0010] The blower may be included in a blower / sensor module.

[0011] The blower / sensor module may be removable and configured to be inserted into a housing of the device.

[0012] The blower / sensor module may be non-removable and configured to be inserted into a housing of the device.

[0013] The blower / sensor module may include a sensing circuit board.

[0014] At least a portion of the gas flow rate sensing system may be located on or within the sensing circuit board.

[0015] The respiratory assistance device may be a continuous positive airway pressure (CPAP) device. The respiratory assistance device may deliver a non-invasive ventilation (NIV) flow. The respiratory assistance device may deliver a nasal high flow (NHF) gas flow.

[0016] The breathing assistance apparatus may further comprise a humidifier.

[0017] The gas flow path may be a heated breathing tube.

[0018] The breathing assistance apparatus may further comprise a patient interface selected from at least one of the following: a face mask, a nasal mask, a nasal pillow mask, a tracheostomy interface, a nasal cannula or an endotracheal tube.

[0019] The gas flow rate sensing system may include a thermistor circuit.

[0020] The gas flow rate sensing system may be configured to change from a first temperature mode to a second temperature mode in response to the measured gas flow temperature satisfying a predetermined threshold.

[0021] The thermistor circuit may include a voltage divider. The voltage divider may include at least a first arm and a second arm

[0022] Changing the target temperature mode of the thermistor circuit may include changing the resistance value of an arm of the voltage divider.

[0023] Changing the resistance value of an arm of the voltage divider may include connecting or disconnecting or bypassing or not bypassing a resistor to the arm of the voltage divider. Changing the resistance value of an arm of the voltage divider may include connecting to a resistor to the arm of the voltage divider. Changing the resistance value of an arm of the voltage divider may include bypassing a resistor to the arm of the voltage divider.

[0024] The breathing assistance apparatus may include a buffer stage located between the voltage divider and the power supply.

[0025] The buffer stage may include transistors.

[0026] The voltage divider can be driven from dual supplies.

[0027] The gas flow rate sensing system may be configured to operate in two different temperature modes based on the measured gas flow temperature.

[0028] The gas flow rate sensing system may be configured to operate in more than two different temperature modes.

[0029] A system for measuring the flow rate of a gas flow may include a thermistor circuit including a thermistor. The thermistor circuit may be configured to produce a voltage output and configured to operate in at least a first temperature mode and a second target temperature mode. The system may further include a temperature sensor configured to measure the gas flow temperature. The system may further include a controller coupled to the temperature sensor and the thermistor circuit, wherein the controller is configured to adjust the thermistor circuit to change between at least the first target temperature mode and the second target temperature mode in response to a change in the measured gas flow temperature.

[0030] The thermistor circuit may be a constant temperature circuit.

[0031] The thermistor may be positioned within the gas stream.

[0032] The controller may be configured to adjust the thermistor circuit to change between at least the first target temperature mode and the second target temperature mode by connecting or bypassing a first resistor within the thermistor circuit. The controller may be configured to adjust the thermistor circuit to change between at least the first target temperature mode and the second target temperature mode by connecting a first resistor within the thermistor circuit. The controller may be configured to adjust the thermistor circuit to change between at least the first target temperature mode and the second target temperature mode by bypassing a first resistor within the thermistor circuit.

[0033] The thermistor circuit may be arranged in a Wheatstone bridge configuration comprising a first voltage divider arm and a second voltage divider arm, wherein the thermistor may be located on the second voltage divider arm.

[0034] The first resistor may be located on the first voltage divider arm.

[0035] Connecting or bypassing the first resistor may include using a switch to disconnect or connect a low resistance path in parallel with the first resistor. Connecting the first resistor may include using the switch to disconnect a low resistance path in parallel with the first resistor. Bypassing the first resistor may include using the switch to connect a low resistance path in parallel with the first resistor.

[0036] The resistance value of the second resistor located on the second arm with the thermistor in the Wheatstone bridge can be configured to correspond to a geometric mean of a first thermistor resistance of the thermistor and a second thermistor resistance of the thermistor, wherein the first thermistor resistance corresponds to the first target temperature mode and the second thermistor resistance corresponds to the second target temperature mode.

[0037] The first resistor can be located on a lower portion of the first voltage divider arm and can be configured to have a certain resistance so that: when the first resistor is bypassed, a first ratio between the upper portion and the lower portion of the first voltage divider arm substantially matches a second ratio between the second resistor and the first thermistor resistance; and when the first resistor is connected, the first ratio substantially matches a third ratio between the second resistor and the second thermistor resistance.

[0038] The Wheatstone bridge configuration may further include a buffer stage located between the first and second voltage divider arms and a power supply.

[0039] The buffer stage may include a transistor, the gate of the buffer stage being connected to the output of the operational amplifier of the Wheatstone bridge.

[0040] The Wheatstone bridge can be driven by at least two power supplies.

[0041] The voltage output of the thermistor circuit may be configured to correspond to a first voltage range when operating in the first temperature mode or the second temperature mode.

[0042] The first voltage range may be between about 1 V and about 38 V, or 2 V to 30 V, or 3 V to 25 V, or 4 V to 20 V. The first voltage range may be between about 5 V and about 15 V.

[0043] The voltage output of the thermistor circuit may be scaled and shifted from the first voltage range to a second voltage range.

[0044] The scaling and shifting may be performed by an operational amplifier (op-amp) circuit.

[0045] The second voltage range may be substantially between about 0 V and about 5 V, or 0 V to 4 V, or 0 V to 3.5 V. The second voltage range may be substantially between about 0 V and about 3.3 V.

[0046] The voltage output of the thermistor circuit may be indicative of an amount of power required to maintain the thermistor at a constant temperature corresponding to the first target temperature mode or the second target temperature mode.

[0047] The gas flow rate may be determined based on the voltage output and the measured temperature of the gas flow.

[0048] The thermistor circuit may provide a different voltage output range for each of the first temperature mode and the second temperature mode.

[0049] The voltage output of the thermistor circuit can be scaled and shifted by a scaling and shifting mechanism, wherein the scaling and shifting mechanism can be modified based on the temperature mode in which the thermistor circuit is operating so that the output voltage range of the scaling and shifting mechanism can be substantially the same in the first target temperature mode or the second target temperature mode.

[0050] The scaling and shifting mechanism may be an operational amplifier circuit.

[0051] This op amp circuit can be modified by connecting or bypassing the resistors.

[0052] The output voltage range of the scaling and shifting mechanism may be substantially between about 0V and about 5V, or 0V to 4V, or 0V to 3.5V. The output voltage range of the scaling and shifting mechanism may be substantially between about 0V and about 3.3V.

[0053] The first target temperature mode and the second target temperature mode include a lower temperature mode and a higher temperature mode, and wherein the controller may be configured to switch the thermistor circuit from operating in the lower temperature mode to operating in the higher temperature mode when the measured gas flow temperature is above a first threshold.

[0054] The controller may be configured to switch the thermistor circuit from operating in the higher temperature mode to operating in the lower temperature mode when the measured gas flow temperature is below a second threshold.

[0055] The first threshold may be higher than the second threshold.

[0056] The controller may be configured to fail to adjust the thermistor circuit between the first target temperature mode and the second target temperature mode within a predetermined period of time after a previous adjustment.

[0057] The first target temperature mode and the second target temperature mode may correspond to between about 50° C. and about 70° C., and between about 90° C. and about 110° C., respectively. The first target temperature mode and the second target temperature mode may correspond to between about 60° C. and about 67° C., and between about 95° C. and about 105° C., respectively. The first target temperature mode and the second target temperature mode may correspond to about 66° C. and about 100° C., respectively.

[0058] The first target temperature mode and the second target temperature mode may be associated with a gas flow temperature range between about 0°C and about 60°C and between about 20°C and about 100°C, respectively. The first target temperature mode and the second target temperature mode may be associated with a gas flow temperature range between about 0°C and about 50°C and between about 25°C and about 85°C, respectively. The first target temperature mode and the second target temperature mode may be associated with a gas flow temperature range between about 0°C and about 40°C and between about 30°C and about 70°C, respectively.

[0059] The controller may be a microcontroller.

[0060] The controller may include a comparator circuit.

[0061] The controller may be configured to adjust the thermistor circuit to change between more than two different target temperature modes in response to changes in the measured gas flow temperature.

[0062] A system for measuring the rate or velocity of a gas flow may include a thermistor circuit including a thermistor having a plurality of different target temperature modes. The thermistor circuit may be configured to output a certain output voltage range that is the same for each of the plurality of temperature modes.

[0063] The system may include a temperature sensor configured to measure a temperature of the gas stream.

[0064] The output voltages output by the thermistor may represent the power consumption of the thermistor circuit and indicate the rate or speed of the gas flow.

[0065] The output voltages output by the thermistor represent the power consumption of the thermistor circuit and are indicative of the flow rate of the gas flow.

[0066] The thermistor circuit may have more than two different target temperature modes.

[0067] The thermistor circuit can be configured to measure a gas flow rate between about 0 L / min and about 200 L / min. The thermistor circuit can be configured to measure a gas flow rate between about 0 L / min and about 150 L / min. The thermistor circuit can be configured to measure a gas flow rate between about 0 L / min and about 100 L / min.

[0068] The system may further include a blower.

[0069] The thermistor circuit may be located upstream of the blower.

[0070] The thermistor circuit may be located downstream of the blower.

[0071] The blower can be configured to provide high flow therapy to the patient.

[0072] The blower may be included in a blower / sensor module.

[0073] The blower / sensor module may be removable and configured to be inserted into a housing of the system.

[0074] The blower / sensor module may not be removable from the housing of the system.

[0075] The blower / sensor module may include a sensing circuit board.

[0076] At least a portion of the thermistor circuit may be located on or within the sensing circuit board.

[0077] The system may further include a patient breathing conduit configured to be coupled to a gas flow outlet of the system at one end of the conduit and to a patient interface at another end of the conduit.

[0078] The patient interface may be a nasal cannula, a full face mask, a nasal mask, a tracheostomy interface, a nasal pillow mask, or an endotracheal tube.

[0079] The patient breathing conduit may include a heating wire configured to heat gas passing through the conduit.

[0080] The system may further include a humidifier configured to humidify the flow of gas to the patient. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1A Shown in diagrammatic form is a respiratory assistance device in the form of a flow therapy device.

[0082] Figure 1B An example of a sensing circuit board including a flow rate sensor that can be used in a breathing assistance device is shown.

[0083] Figure 2 Shows an example of a thermistor circuit that can be used in a thermistor flow sensor.

[0084] Figure 3 A differential operational amplifier circuit is shown that may be used in some embodiments.

[0085] Figure 4A A modified thermistor circuit configured to operate at two different target temperatures is presented.

[0086] Figure 4B and 4C Alternative resistor arrangements in a thermistor circuit configured to operate at multiple different target temperatures are presented.

[0087] Figure 4D Another embodiment is shown that includes a buffer stage after the operational amplifier.

[0088] Figure 4E An embodiment in which the bridge is driven by dual power supplies is shown.

[0089] Figure 5 A graph is shown which illustrates the output voltage range for different temperatures and flow rates.

[0090] Figure 6 A graph is shown showing the relationship between thermistor circuit output voltage and flow rate for different combinations of target temperature and flow temperature.

[0091] Figure 7 A flow chart of a process for configuring a thermistor circuit of a thermistor flow sensor to be operable at at least a first target temperature and a second target temperature is presented.

[0092] Figure 8 A flow chart is presented of a process for operating a thermistor flow sensor capable of operating at two different target temperatures, according to some embodiments. DETAILED DESCRIPTION

[0093] Figure 1AA flow therapy device 10 is shown. The device 10 may include a main housing 100 that includes a flow generator 11 (e.g., a blower) in the form of a motor / impeller arrangement, an optional humidifier 12, a controller 13, and a user interface 14 (including, for example, a display and (multiple) input devices such as (multiple) buttons, a touch screen, etc.). The controller 13 may be configured or programmed to control the components of the device, including but not limited to: operating the flow generator 11 to generate a gas flow (gas flow) for delivery to a patient; operating the humidifier 12 (if present) to humidify and / or heat the generated gas flow; receiving user input from the user interface 14 for reconfiguration and / or user-defined operation of the device 10; and outputting information to the user (e.g., on a display). The user may be a patient, a healthcare professional, or any other person interested in using the device. As used herein, "gas flow" may refer to any gas flow that may be used in a respiratory assistance or breathing device, such as an ambient air flow, a flow comprising substantially 100% oxygen, a flow comprising some combination of ambient air and oxygen, etc.

[0094] The patient breathing conduit 16 is coupled at one end to a gas flow outlet 21 in the housing 100 of the flow therapy device 10. The patient breathing conduit 16 is coupled at the other end to a patient interface 17, such as a nasal cannula having a manifold 19 and a nasal prong 18. Additionally or alternatively, the patient breathing conduit 16 can be coupled to a mask, a nasal mask, a nasal pillow mask, an endotracheal tube, a tracheostomy interface, etc. The gas flow generated by the flow therapy device 10, which may be humidified, is delivered to the patient via the patient conduit 16 through the cannula 17. The patient conduit 16 may have a heating wire 16a to heat the gas flow passing through to the patient. The heating wire 16a may be controlled by the controller 13. The patient conduit 16 and / or the patient interface 17 may be considered as part of the flow therapy device 10, or alternatively at the periphery of the flow therapy device. The flow therapy device 10, the breathing conduit 16, and the patient interface 17 may together form a flow therapy system.

[0095] The controller 13 can control the flow generator 11 to generate a gas flow with a desired flow rate. The controller 13 can also control the supplemental oxygen inlet to allow the delivery of supplemental oxygen, control the humidifier 12 (if present) to humidify the gas flow and / or heat the gas flow to an appropriate level, etc. The gas flow is led out to the patient through the patient conduit 16 and the cannula 17. The controller 13 can also control the heating element in the humidifier 12 and / or the heating element 16a in the patient respiratory conduit 16 to heat the gas to a desired temperature to obtain a desired level of treatment and / or a desired level of comfort for the patient. The controller 13 can be programmed with or can determine a suitable target gas flow temperature.

[0096] Operational sensors 3a, 3b, 3c (such as flow, temperature, humidity and / or pressure sensors) can be placed in various locations in the flow therapy device 10. In some embodiments, additional sensors (e.g., sensors 20, 25) can be placed in various locations on the patient conduit 16 and / or cannula 17 (e.g., a temperature sensor can be present at or near the end of the inspiratory tube). The output from the sensors can be received by the controller 13 to assist the controller in operating the flow therapy device 10 in a manner that provides appropriate therapy. In some configurations, providing appropriate therapy includes meeting the patient's peak inspiratory needs. The device 10 can have a transmitter and / or receiver 15 to enable the controller 13 to receive signals 8 from the sensors and / or control various components of the flow therapy device 10, including but not limited to the flow generator 11, the humidifier 12 and the heating wire 16a, or accessories or peripherals associated with the flow therapy device 10. Additionally or alternatively, the transmitter and / or receiver 15 can deliver data to a remote server or enable remote control of the device 10.

[0097] In some embodiments, the flow treatment device 10 may include a high flow treatment device. As used herein, "high flow" treatment may involve delivering gas to the patient's airway at a relatively high flow rate. For example, for adults, the flow rate may be at least about 15L / min, or about 20L / min, or about 25L / min, or about 30L / min, or about 40L / min, or about 50L / min, or up to about 150L / min. For children and infants, the flow rate may be about 1L / min, or about 2L / min, and up to 25L / min, or about 3L / min, or about 5L / min, or about 10L / min, or about 15L / min, or about 20L / min. High flow treatment may be delivered to the user's nasal and / or oral, or via a tracheostomy interface. High flow treatment may deliver gas to the user at a flow rate that is at or exceeds the peak inspiratory flow requirement of the expected user. The high flow gas that reaches the patient's airway may be beneficial for flushing the patient's airway, which may reduce the volume of the anatomical dead space. High flow therapy can often be delivered using a non-sealing patient interface (e.g., nasal cannula). The nasal cannula can be configured to deliver breathing gas to the user's nostrils at a flow rate that exceeds the expected user's peak inspiratory flow requirement.

[0098] The term "non-sealed patient interface" as used herein may refer to an interface that does not completely occlude the patient's airway by providing a pneumatic link between the patient's airway and a source of gas flow (e.g., from flow generator 11). The non-sealed pneumatic link may include less than about 95% occlusion of the patient's airway. The non-sealed pneumatic link may include less than about 90% occlusion of the patient's airway. The non-sealed pneumatic link may include between about 40% and about 80% occlusion of the patient's airway. The airway may include one or more of the patient's nostrils or mouth.

[0099] Steering Figure 1B , shows a sensing circuit board 2200 that can be implemented in the above-mentioned flow therapy device 10. Specifically, the flow therapy device 10 may include a recess for accommodating a motor / sensor module. The motor / sensor module may include a flow generator or blower, which can bring room air into the inlet port of the blower. The inlet port may optionally include a valve through which pressurized gas can enter the flow generator or blower. The valve can control the flow of oxygen into the flow generator blower. The valve can be any type of valve, including a proportional valve or a two-position valve.

[0100] The blower can be operated at a motor speed greater than about 1,000 RPM and less than about 30,000 RPM, greater than about 2,000 RPM and less than about 21,000 RPM, or any of the foregoing values. The operation of the blower can mix the gas entering the blower through the inlet port. Using a blower as a mixer can reduce the pressure drop that would otherwise occur in a system with a separate mixer (e.g., a static mixer including baffles) because mixing requires energy.

[0101] The mixed air may exit the blower through a conduit and enter a flow path in a sensor chamber of the motor / sensor module. The sensing circuit board 2200 may be positioned in the sensor chamber such that the sensing circuit board 2200 is at least partially immersed in the gas flow. At least some of the sensors on the sensing circuit board 2200 may be positioned within the gas flow to measure gas characteristics within the flow. After passing through the flow path 2006 in the sensor chamber, the gas may exit to the humidifier 12 described above.

[0102] The sensing circuit board 2200 may be a printed sensing circuit board (PCB). Alternatively, the circuit on the board 2200 may be constructed using wires connecting electronic components, rather than printing the circuit on the circuit board. At least a portion of the sensing circuit board 2200 may be mounted outside the gas flow. The gas flow may be generated by the above-mentioned flow generator 11. The sensing circuit board 2200 may include an ultrasonic transducer 2204. The sensing circuit board 2200 may include one or more thermistors 2205. The thermistor 2205 may be configured to measure the temperature of the gas flow. The sensing circuit board 2200 may include a thermistor flow rate sensor 2206. The sensing circuit board 2200 may include other types of sensors, such as a humidity sensor (including a humidity sensor only used with a separate temperature sensor, and a combined humidity and temperature sensor), a sensor for measuring atmospheric pressure, a sensor for measuring differential pressure, and / or a sensor for measuring gauge pressure. The thermistor flow rate sensor 2206 may include a hot wire flow meter, such as a platinum wire and / or a thermistor (e.g., a negative temperature coefficient (NTC) thermistor, or a positive temperature coefficient (PTC) thermistor). Other non-limiting examples of heated temperature sensing elements include glass or epoxy encapsulated thermistors, or non-encapsulated thermistors. The thermistor flow rate sensor 2206 may be configured to measure the flow rate of the gas by supplying it with constant power, or maintaining it at a constant sensor temperature, or maintaining a constant temperature difference between the sensor and the gas flow.

[0103] The sensing circuit board 2200 may include a first portion 2201 and a second portion 2202. The first portion 2201 may be positioned within the flow path 2006 of the gas, and the second portion 2202 may be positioned outside the flow path 2006 of the gas. Figure 1B In FIG. 2 , the direction of the gas flow is indicated by arrow 2203. The direction of the gas flow can be a straight line, or Figure 1B Shown is curved.

[0104] Positioning one or more of thermistors 2205 and / or thermistor flow rate sensors 2206 downstream of the combined blower and mixer can take into account the heat supplied to the gas flow from the blower. Additionally, immersing the temperature-based flow rate sensor in the flow path can improve the accuracy of the measurement because the sensor immersed in the flow is more likely to be subject to the same conditions (e.g., temperature) as the gas flow and therefore provide a better representation of the gas properties.

[0105] An example of a flow therapy apparatus is disclosed in International Application No. PCT / NZ2016 / 050193, filed on December 2, 2016, entitled “Flow Path Sensing for Flow Therapy Apparatus,” which is incorporated herein by reference in its entirety.

[0106] Flow Measurement Using Thermistors

[0107] In many respiratory assistance devices and other devices configured to deliver a flow of gas, it is often desirable to be able to measure flow rate (e.g., the rate or velocity of gas flow) using a sensing system that includes one or more sensors (e.g., a thermistor or ultrasonic sensor arrangement). For example, in the context of a non-sealed respiratory assistance device, flow rate may be measured to determine a patient's breathing cycle.

[0108] In some embodiments, at least two different types of sensors may be used to measure gas flow rate. For example, a first type of sensor may be able to measure flow rate with better short-term or local accuracy (e.g., to detect rapid, breath-to-breath changes in flow rate) but poorer long-term accuracy (e.g., due to accumulation of small errors), while a second type of sensor may be able to measure flow rate with poorer local accuracy (e.g., due to local noise) but better average accuracy. Output readings from both the first type of sensor and the second type of sensor may be combined to determine a more accurate flow measurement. For example, in some embodiments, a previously determined flow rate and one or more outputs from a second type of sensor may be used to determine a predicted current flow rate. The predicted current flow rate may then be updated using one or more outputs from the first type of sensor in order to calculate a final flow rate.

[0109] The first type of sensor may include an ultrasonic sensor assembly (e.g., Figure 1B The second type of sensor may be based on various methods of hot-wire anemometer, which can measure flow rate by monitoring convection sleeve heat transfer between the gas flow and the sensor. As described above, examples of hot-wire anemometer sensors may include hot-wire anemometers, or thermistors (hereinafter also referred to as "thermistor flow sensors"), such as, Figure 1B The thermistor flow rate sensor 2006 is shown in FIG. Figure 1BA thermistor flow rate sensor 2206 in a sensing chamber downstream of the blower is shown with the above advantages, but in some embodiments, the thermistor flow sensor may also be located upstream of the blower. The device can have an inlet flow path before the blower. The inlet flow path can be defined by three main areas, namely the inlet area, the sensor area, and the transition area. The inlet area can be the initial part of the inlet flow path. The sensing area can be located between the inlet area and the transition area. The transition area may include an outlet port coupled to the blower. The thermistor flow sensor can be located in the sensor area of ​​the inlet flow path before the blower.

[0110] Hot wire flow rate determination can measure flow rate by monitoring the heat transfer between the gas flow and the sensor. As described above, the hot wire flow meter or thermistor can be supplied with constant power, or maintained at a constant sensor temperature or maintain a constant temperature difference between the sensor and the gas flow. For example, in a constant temperature mode, the thermistor flow sensor to which the present disclosure relates can be operated by running the thermistor at a constant target temperature in the flow as the gas flows around and through the thermistor, and measuring the amount of power required to maintain the thermistor at the target temperature. In some embodiments, the target temperature can be configured to be higher than the temperature of the gas flow, so that the higher the flow rate, the more power required to maintain the thermistor at the target temperature.

[0111] Figure 2 An example of a thermistor circuit that can be used in a thermistor flow sensor according to some embodiments is shown. In some embodiments, thermistor circuit 200 can be a constant temperature circuit, such as a Wheatstone bridge circuit, for maintaining a constant target temperature of thermistor 202. Thermistor 202 has a resistance R that is more dependent on its temperature than a standard resistor. s In some embodiments, the resistance of thermistor 202 has a negative temperature coefficient. For example, the higher the temperature of the thermistor, the higher the resistance R of the thermistor 202. s Will be lower.

[0112] In some embodiments, thermistor circuit 200 includes a bridge circuit. The bridge circuit may have a first arm having a resistor R 1 and R 2 The resistors 204 and 206 form a first voltage divider which establishes a reference voltage e 1 The bridge circuit may have a second arm having a thermistor 202 and a resistor R b The resistor 208 forms a second voltage divider which establishes a reference voltage e 2The operational amplifier 210 can provide feedback to keep the thermistor circuit 200 balanced so that the voltage e 1 Equal to voltage e 2 .

[0113] With proper biasing and circuit configuration, thermistor circuit 200 can produce a constant target temperature across thermistor 202. For example, if a gas flow is used to cool thermistor 202 (resistance R s increases, and therefore the voltage e 2 The operational amplifier 210 will be used to provide more power to the bridge circuit to keep the temperature of the thermistor 202 constant. The voltage V set in the feedback loop of the operational amplifier 210 is b indicates the amount of power supplied. Therefore, by tracking V b To determine the amount of power delivered. The measured voltage can be received by a controller (e.g., controller 13) of a sensing system of the breathing assistance device to calculate the gas flow rate. In some embodiments, the voltage is fed to an ADC associated with the controller (e.g., an ADC port of the controller) to convert the analog voltage signal into a digital signal for processing by the controller. In some embodiments, the voltage drop across the thermistor 202 can be read to determine the amount of power delivered. In some embodiments, the controller configured to control the thermistor flow sensor can be a microcontroller.

[0114] The target temperature of thermistor circuit 200 can be selected by selecting the resistors in the circuit (e.g., resistors 204, 206, and 208). For example, since according to circuit 200, the voltage e 1 =e 2 is inherent, so the resistance R of thermistor 202 s It can be calculated as:

[0115]

[0116]

[0117] In this way, the expected resistance R corresponding to the expected target temperature of thermistor 202 can be calculated based on the expected resistance R s The resistance of resistors 204 , 206 , and 208 is selected.

[0118] In some embodiments, the voltage from thermistor circuit 200 (eg, voltage V b) can have a different range than the voltage that can be accepted at the controller (e.g., the voltage range of the ADC port of the controller). As such, the voltage can be fed to a differential op amp configuration so that the voltage can be scaled and / or shifted to better match the voltage range of the ADC, thereby allowing substantially the entire range of the ADC to be used. This can allow for higher resolution and more accurate power readings. The signal produced by the differential op amp can be delivered to the ADC port of the controller for reading.

[0119] Figure 3 300 is shown which may be used in some embodiments. By selecting appropriate values ​​for resistors 302, 304, 306 and 308, an incoming signal (V b ) performs DC shift and scaling. For example, if V b output range, the differential operational amplifier circuit 300 can be configured to V b The signal is shifted and / or scaled to cover substantially the entire possible range of values ​​for the controller's ADC input. By allowing substantially the entire voltage range of the ADC to be used, the resolution of the system in reading power consumption (and therefore gas flow) can be improved.

[0120] The signal from the operational amplifier 310 can be delivered to the ADC port of the controller for reading by the controller. In addition, the controller can receive readings from a temperature sensor for sensing the temperature of the gas flow. By determining the power delivered to the thermistor 202 (based on the voltage V b ), the power lost through thermistor 202 due to the gas flow passing over thermistor 202 can be determined. Since the temperature of the gas flow is known (using a temperature sensor), the amount of gas flow passing over thermistor 202 (and therefore the gas flow rate) can be determined.

[0121] Stream temperature and flow sensor resolution

[0122] In some embodiments, the primary purpose of a thermistor flow sensor is to be able to accurately measure flow (as opposed to rapid measurements that can be performed using, for example, an ultrasonic sensor arrangement.) However, in situations where there is a large range of possible flow temperatures, the resolution requirements of the thermistor flow sensor may be stretched or compressed when the difference between the gas flow temperature and the thermistor target temperature is too small or too large.

[0123] For example, as the gas flow temperature approaches the target temperature of the thermistor, the power requirement needed to maintain the thermistor target temperature may be very small. For example, for a thermistor maintaining a target temperature of approximately 66°C, if the temperature of the gas flow is approximately 64°C, very little power will be consumed to maintain the thermistor target temperature regardless of the velocity or density of the gas flow. As such, the thermistor flow sensor may need to be extremely sensitive in order to be able to detect small changes in power requirements.

[0124] If the difference between the gas flow temperature and the thermistor target temperature is large (e.g., the thermistor target temperature is about 100°C and the gas flow temperature is about 5°C), a slight change in the gas flow rate may drastically change the amount of power required to maintain the thermistor target temperature. This may require the ADC and operational amplifier to cover a wide range of power values, sacrificing detailed resolution. In addition, if the temperature difference is too large, the power consumption required to maintain the thermistor at the target temperature may become greater than the amount of power that can be supplied. In addition, when there is a large difference between the flow temperature and the target temperature, self-convection may occur, which may make it difficult to accurately calculate the flow rate. For example, when the thermistor flow sensor has a higher target temperature relative to the gas flow temperature, convection may occur above the thermistor, producing additional gas movement, thereby distorting the readings of the thermistor flow sensor.

[0125] Therefore, as described above, it may not be desirable for the difference between the gas flow temperature and the thermistor target temperature to be too large or too small. In some embodiments, the thermistor target temperature can be associated with a desired gas flow temperature range, thereby indicating a gas flow temperature range in which the difference between the thermistor target temperature and the gas flow temperature is not too small or too large.

[0126] One way to overcome the large temperature range of the gas is to use a hot wire flow meter or thermistor that maintains a constant temperature difference between the sensor temperature and the gas temperature. A hot wire flow meter that can maintain a constant temperature difference may be expensive, prone to damage and / or failure, and / or require frequent replacement. Thermistors can be cheaper and more durable than hot wires. However, maintaining a constant temperature difference on the thermistor may make the compensation circuit of the thermistor flow sensor complex and inaccurate. As described in the present disclosure, another way to overcome the large temperature range of the gas is to maintain multiple (e.g., two, three or more) constant temperatures on the thermistor of the flow rate sensor. Multiple different temperatures can allow the thermistor flow rate sensor to be accurate over a large temperature range of the gas.

[0127] Dual Temperature Thermistor Circuit

[0128] In some embodiments, in order to avoid the difference between the gas flow temperature and the thermistor target temperature being in an undesirable range (e.g., the difference is too large or too small), the thermistor circuit can be configured to operate at multiple different target temperatures (also referred to as target temperature mode or constant temperature mode). For example, the thermistor circuit can be configured to be able to switch between two different target temperatures so that the temperature of the gas flow will always fall within a certain range relative to one of the two target temperatures (e.g., not too close or too far). For example, in one embodiment, the thermistor circuit can be configured to operate at a first target temperature of about 66°C (associated with a desired flow temperature range between about 0°C and about 40°C), and a second target temperature of about 100°C (associated with a desired flow temperature range between about 30°C and about 70°C). Although the subsequent disclosure is primarily directed to a thermistor circuit with two different target temperatures, it should be understood that in other embodiments, the thermistor circuit can be associated with more than two (e.g., three or four or five or six, etc.) different operating temperatures.

[0129] Figure 4A A modified thermistor circuit 400 configured to operate at two different target temperatures according to some embodiments is shown. Thermistor circuit 400 may be similar to thermistor circuit 200, except that a thermistor having a corresponding resistance R may be used. 2a and R 2b In some embodiments, resistors 402 and 404 may be connected in series. At least one of the two resistors (e.g., resistor 404) may be bypassed via switch 406. When connected, switch 406 may provide a low (ideally zero) resistance path in parallel with resistor 404, thereby essentially "shorting" resistor 404. In this way, the reference voltage e may be changed based on whether resistor 404 is bypassed. 1 In other embodiments, switch 406 may be placed at other locations in the Wheatstone bridge to change the ratio of the resistances in the two arms of the circuit (eg, by switching R on or off). 1 or R b ).

[0130] In some embodiments, switch 406 is not a physical switch, but instead may be a bipolar junction thermistor (BJT) or other type of switch that can be electronically turned on or off by a controller to connect or bypass resistor 406. In some embodiments, switch 406 and resistor 404 may alternatively be replaced with a voltage-controlled resistor (e.g., a field effect transistor (FET) or JFET operating in the ohmic region). In this way, multiple values ​​of resistor 404 may be selected by changing the control voltage. In some embodiments, the control voltage may be configured to switch between one or more set values, thereby enabling the value of resistor 404 to switch between one or more set resistance values.

[0131] In some embodiments, more than two different temperature modes may be implemented by increasing the number of different possible resistances that can be achieved. Figure 4B and Figure 4C Alternative configurations of resistors 402 , 404 and switches 406 are shown for implementing a greater number of different resistance values. Figure 4B A resistor 404 is shown including a plurality of resistors 404-1 through 404-n. The resistors 404-1 through 404-n may be arranged in a series arrangement. Figure 4C Shown is a resistor 404 including a plurality of resistors 404-1 to 404-n and a switch 406 including a plurality of switches 406-1 to 406-n. Resistors 404-1 to 404-n can be arranged in parallel. Switches 406-1 to 406-n can each allow corresponding resistors 404-1 to 404-n to be connected as part of a circuit or to be bypassed. By connecting or bypassing resistors 404-1 to 404-n in different combinations of disconnecting and closing switches 406-1 to 406-n, different resistances can be achieved. Different resistances can correspond to different temperature modes. In some embodiments with a parallel arrangement, additional switches 406-n+1 can be used to bypass all resistors 404-1 to 404-n.

[0132] Figure 4D Another embodiment is shown that includes a buffer stage 408 after the operational amplifier. In some embodiments, the buffer stage 408 (e.g., an NPN transistor) can be used to relieve the operational amplifier 210 and improve startup performance (e.g., in situations where the operational amplifier 210 alone cannot initially power the bridge). The buffer stage 408 can improve startup performance by reducing the current drawn during startup of the operational amplifier. Figure 4EAn embodiment is shown in which the bridge according to some embodiments is driven by a dual power supply, which can allow for greater power. The circuit can include a buffer stage 408 between the voltage divider and the voltage source Vcc and / or Vee, with the gate of the buffer stage 408 connected to the output of the operational amplifier 210. In some embodiments, other variations are also possible. For example, the buffer stage 408 can be a PNP transistor instead of an NPN transistor. In some embodiments, this can allow for higher power at the expense of stability.

[0133] In some embodiments, the controller can receive temperature measurements from a temperature sensor (not shown) that measures the temperature of the gas stream. Based on the received temperature, the controller determines at which target temperature the thermistor circuit 400 should operate (e.g., by turning switch 406 on or off). For example, when the stream temperature is within a desired range associated with the first target temperature, the thermistor circuit 400 can operate at the first target temperature. In some embodiments, when the stream temperature is within a desired range associated with a second target temperature, the thermistor circuit 400 can switch operation to the second target temperature.

[0134] During operation, the controller can read the output voltage across the thermistor flow sensor (e.g., the output voltage of the thermistor circuit that travels through a differential operational amplifier and is transmitted to an ADC port of the controller). Based on the target temperature at which the thermistor flow sensor is currently operating and the measured gas flow temperature, the controller can be configured to determine the flow rate of the gas flow.

[0135] Dual Temperature Thermistor Circuit Output Voltage Range

[0136] In some embodiments, the thermistor circuit 400 is configured to present the same voltage range to the controller (and / or differential operational amplifier circuit) regardless of which temperature mode the thermistor circuit is operating in. For example, the thermistor circuit can be configured to output a voltage between about 1V to about 38V, or between about 5V to about 15V, regardless of the target temperature at which the thermistor circuit is operating, wherein about 5V corresponds to a low flow rate and about 15V corresponds to a high flow rate. The differential operational amplifier circuit can then be used to scale and / or shift the voltage to a second voltage range (e.g., between about 0V to about 5V, or between about 0V to about 3.3V) that can be accepted by the controller.

[0137] Figure 5A graph is shown that illustrates the output voltage range for different temperatures and flow rates. Graph 500 includes curve 502 that illustrates an example relationship between flow temperature and thermistor circuit output voltage for a target temperature of 100°C and a flow rate of 0 L / min. Graph 500 includes curve 504 that illustrates an example relationship between flow temperature and thermistor circuit output voltage for a target temperature of 100°C and a flow rate of 70 L / min. Graph 500 includes curve 506 that illustrates an example relationship between flow temperature and thermistor circuit output voltage for a target temperature of 66°C and a flow rate of 0 L / min. Graph 500 includes curve 508 that illustrates an example relationship between flow temperature and thermistor circuit output voltage for a target temperature of 66°C and a flow rate of 70 L / min. As shown by comparing curves 502 and 506 and / or curves 504 and 508, for a given flow rate, when the difference between the flow temperature and the target temperature is the same, the output voltage of the thermistor circuit can be substantially the same for different target temperatures. In this way, the possible output voltage range of the thermistor circuit can remain substantially the same regardless of the target temperature at which the thermistor circuit operates.

[0138] Figure 6 A graph 600 is shown showing the relationship between thermistor circuit output voltage and flow rate for different target temperature and flow temperature combinations. Figure 6 As shown, curve 602 shows an example relationship of thermistor circuit output voltage to flow rate for a thermistor target temperature of 100°C and a gas flow temperature of 30°C. Curve 604 shows an example relationship of thermistor circuit output voltage to flow rate for a thermistor target temperature of 100°C and a gas flow temperature of 70°C. Curve 606 shows an example relationship of thermistor circuit output voltage to flow rate for a thermistor target temperature of 66°C and a gas flow temperature of 0°C. Curve 608 shows an example relationship of thermistor circuit output voltage to flow rate for a thermistor target temperature of 66°C and a gas flow temperature of 40°C. Gas flow

[0139] As illustrated by graph 600, regardless of the target temperature at which the thermistor circuit operates, the relationship between the output voltage and the flow rate can be substantially similar to a similar difference between the target temperature and the flow temperature. For example, curves 602 and 606 can illustrate example relationships of the thermistor circuit output voltage and flow rate when the difference between the target temperature and the flow temperature is 70°C and 66°C, respectively. Curves 602 and 606 can illustrate substantially similar output voltage values ​​relative to changes in flow rate. Curves 604 and 608 can illustrate example relationships of the thermistor circuit output voltage and flow rate when the difference between the target temperature and the flow temperature is 30°C and 26°C, respectively. Curves 604 and 608 can illustrate substantially similar output voltage values ​​relative to changes in flow rate. The controller can compare the target temperature to the gas flow temperature (e.g., using a comparator circuit), and can use the difference to determine the flow rate based on the voltage received from the thermistor flow sensor, regardless of the target temperature at which the thermistor flow sensor is operating.

[0140] In some embodiments, configuring the thermistor circuit to present the same voltage range regardless of the operating target temperature can be accomplished by modifying the resistor values ​​of the thermistor circuit (e.g., Figure 4A Thermistor circuit 400 is implemented by appropriately configuring the resistors 204, 208, 402, and 404 shown. Because thermistor 202 is maintained at a constant target temperature during operation, the power input (due to electrical power) of thermistor circuit 400 can be equal to the power output (from power losses). In some embodiments, the power loss due to cooling flow can be determined based on King's law, which can be expressed as:

[0141] P 损耗 =(a+bQ c )(T s -T a )

[0142] where a, b, and c are flow-related constants, Q represents the gas flow rate, and T s is the target temperature of thermistor 202, and T a is the temperature of the gas stream.

[0143] The power input (eg, the power consumed by heating thermistor 202) can be expressed as:

[0144]

[0145] Among them, V s is the voltage across thermistor 202, and R sis the resistance of thermistor 202. Since the power input is equal to the power loss, the voltage V across thermistor 202 is s It can be expressed as:

[0146]

[0147] In addition, since thermistor 202 is part of a voltage divider, the voltage V across thermistor 202 is s It can also be expressed as:

[0148]

[0149] Thus, the voltage V b The relationship between , the gas flow rate Q, the resistance of thermistor 202 of the thermistor circuit, and the resistance of resistor 208 can be expressed as:

[0150]

[0151] Based on the desired target temperature T s , the resistance R of thermistor 202 s can have different known values. Therefore, the resistance R of resistor 208 b can be configured to determine the voltage V b possible values ​​of .

[0152] In order to make the voltage value V b The range of V is the same. For the same flow rate in any target temperature scenario, V b The values ​​of should all be the same value, which can be expressed as:

[0153]

[0154] This can be simplified to:

[0155]

[0156] Expression (T s,x -T a,x ) can represent the gas flow temperature range associated with each target temperature, where T s,x corresponds to a thermistor target temperature (eg, two different possible values, where the thermistor circuit is configured to operate at one of the two different target temperatures), and T a,x In some embodiments, the thermistor circuit can be configured so that when there is the same difference between the thermistor target temperature and the gas flow temperature, regardless of the target temperature mode in which the thermistor is currently operating, the output voltage V of the thermistor circuit isb should be the same. Thus, when (T s,1 -T a,1 )=(T s,2 -T a,2 ), then:

[0157]

[0158] Therefore, the resistance R of resistor 208 b The resistance value R corresponding to different target temperatures can be determined s,1 and R s,2 The geometric mean of is as follows:

[0159]

[0160] As mentioned above, R s,1 and R s,2 can be defined by the value of the thermistor target temperature. For example, in a particular embodiment, the thermistor target temperature can be about 66°C and about 100°C, and the corresponding resistance R s,1 and R s,2 are about 550Ω and about 220Ω respectively. b It can be set to about 350Ω (or about 330Ω, which may correspond to the closest resistance value in the E12 series resistor).

[0161] In addition, because the voltages on the first voltage divider and the second voltage divider of the thermistor circuit 400 are equal (e 1 =e 2 ), so the resistance R of resistors 204, 402 and 404 can be 1 , R 2a and R 2b is configured to match the ratio between resistor 208 and the resistance of thermistor 202 for different thermistor target temperatures. In an embodiment where resistors 402 and 404 are configured in series (so that resistor 404 can be disconnected using switch 406):

[0162]

[0163]

[0164] As mentioned above, in some embodiments where the target temperature of the thermistor is about 66° C. and about 100° C., the corresponding resistance R s,1 and R s,2 are about 550Ω and about 220Ω respectively, and the resistance R of the resistor 208 is b The value of is about 350Ω. Therefore, at the first target temperature of about 66°C, R b / R s The ratio of R can be about 3 / 5. At the second target temperature of about 100°C, R b / R s The ratio of can be about 3 / 2. Therefore, the resistance R of resistors 204, 402 and 404 can be determined 1 , R 2a and R 2b For example, resistors 204, 402, and 404 may be configured to have resistances R of approximately 15 kΩ, approximately 10 kΩ, and approximately 15 kΩ, respectively. 1 , R 2a and R 2b .

[0165] Figure 7 A flow chart showing an example process for configuring a thermistor circuit of a thermistor flow sensor to operate at at least a first target temperature and a second target temperature. In some embodiments, the thermistor circuit can be configured to include a first voltage divider and a second voltage divider to provide a first reference voltage and a second reference voltage to an operational amplifier (e.g., Figure 4A ), thereby allowing the target temperature of the thermistor to be maintained.

[0166] At block 702, a gas flow temperature range may be identified. In some embodiments, different respiratory therapy devices may be associated with different gas flow temperature ranges. For example, a particular respiratory therapy device may be configured to generate a gas flow at a temperature between about 0°C and about 70°C.

[0167] At block 704, two or more thermistor target temperatures may be determined. Each thermistor target temperature may be associated with a desired gas flow temperature sub-range, such that the gas flow temperature sub-range corresponding to the two or more thermistor target temperature ranges may substantially cover the entire temperature range identified at block 702. For example, in the case where the identified gas flow temperature range is from about 0°C to about 70°C, the one or more thermistor target temperatures may include: a first thermistor target temperature of about 66°C for a desired gas flow temperature sub-range between about 0°C to about 40°C, and a second thermistor target temperature of about 100°C for a desired gas flow temperature sub-range between about 30°C to about 70°C. In some embodiments, the desired temperature sub-ranges of one or more thermistor target temperatures may overlap. Overlapping may be performed to prevent hysteresis, which will be described in more detail below.

[0168] In some embodiments, it is desirable that the output voltage range of the thermistor circuit remain the same regardless of the thermistor target temperature at which the thermistor circuit is currently operating. At block 706, one or more component values ​​of the thermistor circuit may be determined such that each of the thermistor target temperatures may be associated with the same output voltage range. For example, in Figure 4A In the thermistor circuit 400 shown, the output voltage range of the thermistor circuit 400 can be based on the resistance R of the resistor 208. b Thus, by setting the resistor 208 to a suitable value as described above, the output voltage V b The range of is set to be substantially the same regardless of the target temperature at which thermistor circuit 400 is operating.

[0169] At block 708, one or more component values ​​of the thermistor circuit may be determined so that the thermistor circuit can operate at the determined thermistor target temperature. For example, where the thermistor circuit maintains the thermistor target temperature based on one or more reference voltages generated by one or more voltage dividers, the resistance values ​​of the one or more resistors of the voltage divider may be set to have a ratio that substantially matches a ratio associated with the thermistor at a given thermistor target temperature. For example, in Figure 4A In the illustrated thermistor circuit 400, one or more ratios between the resistance of thermistor 202 and the resistance of resistor 208 may be determined for different desired target temperatures of the thermistor. The resistances of resistors 204, 402, and 408 may then be set to substantially match the ratios associated with the desired target temperatures, thereby allowing the thermistor circuit 400 to operate at the desired thermistor target temperature.

[0170] Gas Stream Temperature Range and Hysteresis

[0171] As described above, the thermistor circuit (e.g., thermistor circuit 400) can be configured to operate at a plurality of different thermistor target temperatures, each thermistor target temperature being associated with a different gas flow temperature sub-range. In some embodiments, in order to avoid rapid switching between different thermistor target temperature modes when the gas flow temperature approaches a transition point between different gas flow temperature sub-ranges, the gas flow temperature sub-ranges can overlap. For example, the thermistor circuit can be configured to operate at a low target temperature and a high target temperature corresponding to a low gas flow temperature sub-range and a high gas flow temperature sub-range, respectively. The upper limit of the low gas flow temperature sub-range can be higher than the lower limit of the high gas flow temperature sub-range. Thus, when the thermistor is operated at a low target temperature, it is switched to operate at a high target temperature only when the measured gas flow temperature exceeds the upper limit of the low gas flow temperature sub-range. On the other hand, when the thermistor is operated at a high target temperature, it is switched to operate at a low target temperature only when the measured gas flow temperature is reduced to below the lower limit of the high gas flow temperature sub-range.

[0172] As an example, if the thermistor target temperatures are set at about 66° C. and about 100° C., and the corresponding gas flow temperature ranges are about 0° C. to about 40° C. and about 30° C. to about 70° C., respectively, the thermistor may switch from operating at about 66° C. to operating at about 100° C. if the measured gas flow temperature exceeds about 40° C., and the thermistor may switch from operating at about 100° C. to operating at about 66° C. if the measured gas flow temperature is less than about 30° C. In some embodiments, switching between thermistor target temperatures may be triggered by a temperature change interrupt, a scheduled timer interrupt, etc.

[0173] In some embodiments, switching between different thermistor target temperature modes can be limited based on a timer, which can be used to prevent switching between different thermistor target temperature modes from occurring within a predetermined period of time.

[0174] Other Implementations

[0175] although Figure 4AThe thermistor circuit is shown in the case where the target temperature is controlled by connecting or disconnecting a resistor (e.g., resistor 404) to or from a voltage bridge to control the reference voltage of the voltage bridge, but it should be understood that in other embodiments, the temperature of the thermistor (e.g., thermistor 202) of the thermistor flow sensor may be controlled by other methods. For example, in some embodiments, a switchable resistor may be added in series to resistor 204 instead of resistor 402. In some embodiments, a switchable resistor may be added in series to resistor 208 or to thermistor 202. In some embodiments, a switchable resistor may be added in parallel to one of the resistors of the thermistor circuit instead of in series.

[0176] In some embodiments, the thermistor circuit can provide different voltage output ranges depending on the target temperature at which the thermistor circuit is operating. Figure 3 The illustrated embodiment of the present invention can be configured to scale, attenuate and / or shift the output voltage of the thermistor circuit to produce a voltage output of substantially the same range regardless of the target temperature mode. For example, in response to the target temperature mode switch, a resistor associated with the differential operational amplifier circuit can be switched in or out (e.g., connected or bypassed) to adjust the scaling and / or shifting performed by the differential operational amplifier so that the voltage range is the same regardless of the target temperature mode.

[0177] process

[0178] Figure 8 A flow chart of an example process for operating a thermistor flow sensor capable of operating at two different target temperatures according to some embodiments is shown. At block 802, the thermistor flow sensor may be operated at a first thermistor target temperature to measure a gas flow rate. For example, in embodiments where the thermistor flow sensor is configured to operate at about 66°C or about 100°C, the first target temperature may correspond to about 66°C.

[0179] At block 804, the gas flow temperature may be measured. In some embodiments, the gas flow temperature may be periodically measured by a temperature sensor separate from the thermistor flow sensor. At block 806, a controller (e.g., Figure 1AThe controller 13 in FIG. 10 may determine whether the measured gas flow temperature meets a threshold value associated with the first thermistor target temperature. For example, in an embodiment where the first thermistor target temperature corresponds to about 66° C., the controller may determine whether the gas flow temperature is greater than about 40° C. If the controller determines that the gas flow temperature does not meet the threshold value associated with the first thermistor target temperature, the process may return to block 802 where the thermistor flow sensor may continue to operate at the first thermistor target temperature.

[0180] If the measured gas flow temperature satisfies the threshold, then at block 808, the thermistor flow sensor may be switched to operate at a second thermistor target temperature. In some embodiments, switching the thermistor flow sensor between the first thermistor and the second thermistor target temperatures may include mechanically or electronically connecting or disconnecting a resistor to or from a voltage bridge to change a reference voltage of the voltage bridge within the thermistor flow sensor. In some embodiments, the reference voltage is configured such that the thermistor may be maintained at the first thermistor target temperature or the second thermistor target temperature depending on whether the resistor is connected or disconnected.

[0181] At block 810, the thermistor flow sensor may be used to measure the gas flow rate while operating at a second thermistor target temperature. In some embodiments, the second thermistor target temperature may be approximately 100° C. At block 812, the gas flow temperature may be measured (e.g., using a temperature sensor separate from the thermistor flow sensor).

[0182] At box 814, the controller can determine whether the measured gas flow temperature meets the threshold value associated with the second thermistor target temperature. In some embodiments, the threshold value can be different from the threshold value associated with the first thermistor target temperature. For example, in an embodiment where the second thermistor target temperature corresponds to about 100°C, if the gas flow temperature is less than about 30°C, it can be considered that the gas flow temperature meets the threshold value. In this way, the threshold values ​​associated with the first thermistor target temperature and the second thermistor target temperature can define overlapping temperature ranges. By having overlapping temperature ranges, when the gas flow temperature is at a temperature near the transition point between different temperature ranges associated with the first thermistor target temperature and the second thermistor target temperature, hysteresis can be used to avoid rapid switching between the first thermistor target temperature and the second thermistor target temperature.

[0183] If the controller determines that the gas flow temperature does not meet the second threshold, the process may return to block 810, where the thermistor flow sensor may continue to measure the gas flow while operating at the second thermistor target temperature. If the gas flow temperature meets the second threshold, the thermistor flow sensor may be switched to operate at the first thermistor target temperature at block 816. The process may then return to block 802, where the thermistor flow sensor may be used to measure the gas flow while operating at the first thermistor target temperature.

[0184] By using a thermistor flow sensor configured to operate at different thermistor target temperatures, resolution issues caused by the difference between the gas flow temperature and the thermistor target temperature being too large or too small can be mitigated. By configuring the thermistor flow sensor to return substantially the same voltage range regardless of the target temperature at which the thermistor flow sensor is operating, substantially all voltage ranges that the controller can accept can be used. This can improve the resolution of the thermistor flow sensor.

[0185] Unless the context clearly requires otherwise, the words "comprise," "comprising," and the like throughout the specification and claims should be construed in an open sense (as opposed to a closed or exhaustive sense), that is, to mean "including but not limited to."

[0186] As used herein, the terms "substantially," "approximately," and "substantially" refer to an amount that is close to the stated amount and still performs a desired function or achieves a desired result. For example, in some embodiments, the terms "substantially," "approximately," and "substantially" may refer to an amount within a range of less than or equal to 10%, less than or equal to 5%, and less than or equal to 1% of the stated amount, as the context may allow.

[0187] The reference to any prior art in this specification is not, and should not be taken as, an admission or any form of suggestion that this prior art forms part of the common general knowledge in the field in any country in the world.

[0188] The disclosed devices and systems may also be broadly said to reside in the components, elements and features referred to or indicated in the specification of this application, either individually or collectively, and in any or all combinations of two or more of the components, elements or features.

[0189] In the above description, where reference has been made to integers or components having known equivalents, these integers are herein incorporated as if individually set forth.

[0190] Depending on the embodiment, certain actions, events, or functions of any algorithm, method, or process described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary for the practice of the algorithm). In addition, in some embodiments, actions or events may be performed simultaneously rather than sequentially, for example, through multithreading, interrupt handling, or multiple processors or processor cores or on other parallel architectures.

[0191] It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the disclosed apparatus and system and without diminishing the attendant advantages thereof. For example, various components may be repositioned as desired. It is therefore contemplated that such changes and modifications are included within the scope of the disclosed apparatus and system. Furthermore, not all of these features, aspects, and advantages are necessary to practice the disclosed apparatus and system. Therefore, the scope of the disclosed apparatus and system is intended to be limited only by the appended claims.

Claims

1. A breathing assistance device for providing a gas flow to a patient, the breathing assistance device comprising: a temperature sensor configured to measure a temperature of the gas flow; as well as a gas flow rate sensing system configured to measure a gas flow rate of the gas flow, wherein the gas flow rate sensing system is configured to operate in a first target temperature mode based on the measured gas flow temperature being within a first temperature sub-range, the first temperature sub-range being defined by a first temperature value and a second temperature value, the second temperature value being greater than the first temperature value, and The gas flow rate sensing system is configured to operate in a second target temperature mode based on the measured gas flow temperature being within a second temperature sub-range, wherein the second temperature sub-range is defined by a third temperature value and a fourth temperature value, the fourth temperature value being greater than the third temperature value, and the third temperature value being less than the second temperature value and greater than the first temperature value.

2. The breathing assistance device according to claim 1, wherein: The breathing assistance apparatus is configured to operate at a given flow rate in either the first target temperature mode or the second target temperature mode.

3. A breathing assistance device according to claim 1 or 2, wherein: The second temperature value of the first temperature sub-range is 10° C. higher than the third temperature value of the second temperature sub-range.

4. The breathing assistance device according to claim 1 or 2, wherein: The first temperature value of the first temperature subrange of the first target temperature mode is 0°C, and the second temperature value is 40°C, and wherein the third temperature value of the second temperature subrange of the second target temperature mode is 30°C, and the fourth temperature value is 70°C.

5. The breathing assistance device according to claim 1 or 2, wherein: The gas flow rate sensing system includes a thermistor circuit, and wherein the thermistor circuit includes a voltage divider including at least a first arm and a second arm.

6. The breathing assistance device according to claim 5, wherein: The first target temperature mode has a first thermistor target temperature, and wherein the second target temperature mode has a second thermistor target temperature, wherein the first thermistor target temperature is lower than the second thermistor target temperature.

7. A breathing assistance device as claimed in claim 6, wherein: The first thermistor target temperature is 66°C and the second thermistor target temperature is 100°C.

8. The breathing assistance device according to claim 5, wherein: Changing the target temperature mode of the thermistor circuit includes changing a resistance value associated with the first arm of the voltage divider.

9. A breathing assistance apparatus as claimed in claim 5, further comprising a buffer stage located between the voltage divider and the power supply.

10. The breathing assistance device according to claim 1 or 2, wherein: The gas flow rate sensing system is configured to change from a first target temperature mode to a second target temperature mode in response to a measured temperature of the gas flow exceeding a second temperature value.

11. The breathing assistance device according to claim 1 or 2, wherein: The gas flow rate sensing system is configured to change from the second target temperature mode to the first target temperature mode in response to a measured temperature of the gas flow decreasing below a third temperature value.

12. The breathing assistance device according to claim 1 or 2, wherein: The gas flow rate sensing system is configured to operate in more than two different target temperature modes based on a measured temperature of the gas flow being within more than two temperature sub-ranges.

13. A breathing assistance device as claimed in claim 12, wherein: Each pair of adjacent temperature subranges overlaps such that: The lower temperature sub-range is defined by a first lower temperature limit value and a first upper temperature limit value, the first upper temperature limit value is greater than the first lower temperature limit value, and The upper temperature sub-range is defined by a second lower temperature limit value and a second upper temperature limit value, the second upper temperature limit value being greater than the second lower temperature limit value, The second lower temperature limit value is less than the first upper temperature limit value and greater than the first lower temperature limit value.

14. The breathing assistance device according to claim 1 or 2, wherein: The breathing assistance apparatus further comprises a gas flow inlet configured to receive a gas flow from a gas flow source.

15. A breathing assistance apparatus as claimed in claim 14, wherein: The gas flow source includes a blower.

16. A breathing assistance apparatus as claimed in claim 15, wherein: A temperature sensor, a gas flow rate sensing system, or both a temperature sensor and a gas flow rate sensing system are located upstream of the blower.

17. The breathing assistance apparatus of claim 15, wherein: A temperature sensor, a gas flow rate sensing system, or both are disposed within a sensor assembly having a housing that is located in a sensor region within the inlet flow path upstream of the blower.

18. The breathing assistance apparatus of claim 15, wherein: A temperature sensor, a gas flow rate sensing system, or both a temperature sensor and a gas flow rate sensing system are located downstream of the blower.

19. A breathing assistance device according to claim 1 or 2, wherein: The breathing assistance apparatus also includes at least one gas flow path configured to direct a flow of gas to a patient.

20. The breathing assistance apparatus of claim 15, wherein: The blower is included in a blower / sensor module.

21. A breathing assistance apparatus as claimed in claim 20, wherein: The blower / sensor module is removable and is configured to be inserted into the housing of the breathing assistance device.

22. The breathing assistance apparatus of claim 20, wherein: The blower / sensor module is non-removable and is configured to be inserted into the housing of the breathing assistance device.

23. The breathing assistance apparatus of claim 20, wherein: The blower / sensor module includes a sensing circuit board.

24. A breathing assistance apparatus as claimed in claim 23, wherein: At least a portion of the gas flow rate sensing system is located on the sensing circuit board.

25. A breathing assistance device as claimed in claim 1 or 2, wherein: The respiratory assistance device is a continuous positive airway pressure device, or a device for delivering a non-invasive ventilation flow, or a device for delivering a high-flow nasal gas flow.

26. A breathing assistance device as claimed in claim 1 or 2, wherein: The breathing assistance apparatus further comprises a humidifier.

27. The breathing assistance apparatus of claim 19, wherein: The gas flow path is a heated breathing tube.

28. A breathing assistance apparatus as claimed in claim 1 or 2, further comprising a patient interface selected from at least one of the following: a face mask, a nasal mask, a nasal pillow mask, a tracheostomy interface, a nasal cannula or an endotracheal tube.

29. The breathing assistance apparatus of claim 8, wherein: Changing the resistance value associated with the first arm of the voltage divider includes connecting or bypassing a resistor of the first arm of the voltage divider.

30. The breathing assistance apparatus of claim 9, wherein: The buffer stage includes transistors.

31. A breathing assistance apparatus as claimed in claim 5, wherein: The voltage divider is driven from dual supplies.

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