Aspirating smoke fire detector, fire protection system, air flow detection circuit and method

Abstract

The present disclosure provides an airflow detection circuit, including: a first thermistor, one end of which is coupled to a first resistor and a first switch, and the other end of which is coupled to a first input end of a first operational amplifier; a second thermistor, one end of which is coupled to the first resistor and the first switch, and the other end of which is coupled to a second input end of the first operational amplifier; a voltage source, coupled to the first resistor and the first switch, and configured to provide a power supply voltage to the first thermistor and the second thermistor in a corresponding power supply path based on the on or off of the first switch; a controller, coupled to the output end of the first operational amplifier, configured to collect an output signal of the first operational amplifier, and determine the airflow velocity based on the output signal. The airflow detection circuit of the present disclosure senses temperature through the first thermistor and the second thermistor, and determines the airflow velocity through the output signal of the first operational amplifier, which can improve the stability, reliability and broad spectrum of the airflow detection result.

Description

Technical Field

[0001] The present disclosure generally relates to the field of fire protection, and in particular to an airflow detection circuit, an airflow detection method, an aspirating smoke fire detector and a fire protection system. Background Art

[0002] Some existing aspirating smoke fire detectors use ultrasonic waves for detection, using the Doppler effect generated when ultrasonic waves propagate in the gas and encounter airflow. The speed and direction of the airflow are determined by measuring the Doppler frequency shift of ultrasonic waves. However, this detection method has some defects, such as the detection results are not stable and reliable enough, and the broad spectrum is not good enough. How to improve the stability, reliability and broad spectrum of the detection results of aspirating smoke fire detectors is a demand that needs to be improved in the fire protection field.

[0003] The contents of the background technology section are merely the technologies known to the inventors and do not necessarily represent the prior art in the field. Summary of the invention

[0004] In view of one or more problems existing in the prior art, the present disclosure provides an airflow detection circuit, which can improve the stability, reliability and broad spectrum of the detection results of the aspirating smoke fire detector.

[0005] The airflow detection circuit includes:

[0006] A first thermistor, one end of which is coupled to the first resistor and the first switch, and the other end of which is coupled to the first input terminal of the first operational amplifier;

[0007] a second thermistor, one end of which is coupled to the first resistor and the first switch, and the other end of which is coupled to the second input terminal of the first operational amplifier;

[0008] a voltage source coupled to the first resistor and the first switch, and configured to provide a supply voltage to the first thermistor and the second thermistor through corresponding power supply paths based on the on or off state of the first switch;

[0009] The controller is coupled to the output terminal of the first operational amplifier and is configured to collect an output signal of the first operational amplifier and determine the air flow rate based on the output signal.

[0010] Optionally, when the first switch is opened, the voltage source is configured to provide a supply voltage to the first thermistor and the second thermistor via the first resistor.

[0011] Optionally, when the first switch is turned on, the voltage source is configured to provide a supply voltage to the first thermistor and the second thermistor via the first switch.

[0012] Optionally, the airflow detection circuit further includes: a second operational amplifier, wherein a first input terminal of the second operational amplifier is coupled to the first thermistor, and a second input terminal of the second operational amplifier is coupled to the second thermistor.

[0013] Optionally, the airflow detection circuit also includes: a second switch, which is coupled to the output terminal of the second operational amplifier and the first switch and is configured to control the on or off of the first switch based on the output signal of the second operational amplifier.

[0014] Optionally, when the output signal of the second operational amplifier is higher than a first threshold, the second switch is turned on; when the second switch is turned on, the first switch is turned on.

[0015] Optionally, when the output signal of the second operational amplifier is lower than a second threshold, the second switch is disconnected; when the second switch is disconnected, the first switch is disconnected.

[0016] Optionally, the first switch includes a metal oxide semiconductor field effect transistor, and the second switch includes a transistor, and the collector of the transistor is coupled to the gate of the first switch.

[0017] Optionally, the thermistor includes a platinum resistor; the first thermistor includes PT100; and the second thermistor includes PT1000.

[0018] Optionally, the controller is configured to determine a duty cycle of an output signal of the first operational amplifier, and determine the airflow rate based on the duty cycle.

[0019] Optionally, the controller is configured to determine the air flow rate based on the duty cycle and flow rate comparison table.

[0020] Optionally, the controller is coupled to a master controller, and the controller is configured to determine a state of the detection pipeline based on the airflow velocity, and feed the state back to the master controller.

[0021] The optional airflow detection circuit further includes: a second resistor, a third resistor and a fourth resistor, wherein the second resistor is coupled to the first thermistor, the third resistor and the fourth resistor are connected in series and coupled to the second thermistor, and the second resistor, the third resistor and the fourth resistor satisfy the following relationship:

[0022]

[0023] Among them, VCC is the voltage of the voltage source, VDS is the on-state voltage drop of the first switch, RPT1 is the resistance value of the first thermistor, RPT2 is the resistance value of the second thermistor, ΔRPT1 is the resistance change value of the first thermistor with temperature, ΔR PT2 is the resistance change value of the second thermistor with temperature, T is temperature, R2 is the resistance value of the second resistor, R3 is the resistance value of the third resistor, and R4 is the resistance value of the fourth resistor.

[0024] The optional airflow detection circuit also includes: a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor and an eleventh resistor, wherein one end of the fifth resistor is coupled to the first resistor and the first switch, and the other end is coupled to the collector of the second switch; one end of the sixth resistor is coupled to the output of the second operational amplifier, and the other end is coupled to the base of the second switch; one end of the seventh resistor is coupled between the sixth resistor and the base of the second switch, and the other end is coupled to the emitter of the second switch; one end of the eighth resistor is coupled to the output of the first operational amplifier, and the other end is coupled to the controller; one end of the ninth resistor is coupled between the eighth resistor and the controller, and the other end is grounded; one end of the tenth resistor is coupled to the second input of the first operational amplifier, and the other end is coupled between the output of the first operational amplifier and the eighth resistor; one end of the eleventh resistor is coupled to the second input of the first operational amplifier, and the other end is grounded.

[0025] The optional airflow detection circuit also includes: a first capacitor, a second capacitor, a third capacitor and a fourth capacitor, wherein one end of the first capacitor is coupled between the first thermistor and the first input terminal of the second operational amplifier, and the other end is coupled to the emitter of the second switch; one end of the second capacitor is coupled between the third resistor and the fourth resistor, and coupled to the second input terminal of the second operational amplifier, and the other end is coupled to the emitter of the second switch; the third capacitor is connected in parallel to the seventh resistor, one end is coupled to the base of the second switch, and the other end is coupled to the emitter of the second switch; the fourth capacitor is connected in parallel to the ninth resistor, and the other end is grounded.

[0026] The present disclosure also provides an aspirating smoke fire detector, comprising the airflow detection circuit as described above.

[0027] The present disclosure also provides a fire fighting system, comprising:

[0028] General controller; and

[0029] The aspirating smoke fire detector as described above is communicatively connected to the master controller, and is configured to detect the airflow velocity, determine the state of the detection pipeline based on the airflow velocity, and report the state to the master controller.

[0030] The present disclosure also provides an airflow detection method, comprising:

[0031] Collect the airflow to be measured;

[0032] Based on the airflow to be measured, collecting an output signal of an airflow detection circuit;

[0033] Based on the output signal, determining a duty cycle; and

[0034] determining an air flow rate based on the duty cycle;

[0035] The airflow detection method is implemented by the aspirating smoke fire detector as described above.

[0036] Optionally, the airflow detection method further includes: determining a state of the detection pipeline based on the airflow velocity, and reporting the state to the main controller.

[0037] The present disclosure also provides a computer-readable storage medium, including computer-executable instructions stored thereon, and when the executable instructions are executed by a processor, the airflow detection method as described above is implemented.

[0038] The airflow detection circuit disclosed in the present invention has a simple circuit, a simple algorithm, low requirements on the controller, and takes into account both real-time performance and stability. The temperature is sensed by a first thermistor and a second thermistor, and the airflow velocity is determined by the output signal of the first operational amplifier, thereby improving the stability, reliability and broad spectrum of the airflow detection results.

[0039] The airflow detection circuit disclosed in the present invention determines the airflow velocity by the duty cycle of the output signal of the first operational amplifier, and determines the state of the detection pipeline based on the airflow velocity, thereby improving the accuracy and reliability of the detection result.

[0040] The airflow detection circuit disclosed in the present invention controls the second switch and the first switch through the output signal of the second operational amplifier, and can control the power supply path of the first thermistor and the second thermistor, thereby reducing the adverse effect of the peak signal of the output signal of the first operational amplifier, so that the peak operational amplifier output is converted into a uniform switching time, making the output signal of the first operational amplifier more stable, and making the output signal collected by the controller more stable, and can more accurately determine the duty cycle of the output signal of the first operational amplifier, which is conducive to improving the accuracy of the airflow detection result. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the embodiments of the present disclosure, they are used to explain the present disclosure and do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0042] Figure 1 A schematic block diagram of an airflow detection circuit according to some embodiments of the present disclosure is shown.

[0043] Figure 2 A schematic block diagram of an airflow detection circuit according to some other embodiments of the present disclosure is shown.

[0044] Figure 3 A circuit schematic diagram of an airflow detection circuit according to some embodiments of the present disclosure is shown.

[0045] Figure 4 A schematic diagram showing comparison curves of flow rate, sampling duty cycle, and fitting duty cycle according to some embodiments of the present disclosure is shown.

[0046] Figure 5 A schematic diagram showing whether the period of the output signal of the first operational amplifier is abnormal according to some embodiments of the present disclosure.

[0047] Figure 6 A schematic diagram of an aspirating smoke fire detector according to some embodiments of the present disclosure is shown.

[0048] Figure 7 A schematic diagram of a fire protection system according to some embodiments of the present disclosure is shown.

[0049] Figure 8 A flow chart of an airflow detection method according to some embodiments of the present disclosure is shown. DETAILED DESCRIPTION

[0050] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present disclosure. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0051] In the description of the present disclosure, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present disclosure. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present disclosure, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0052] In the description of the present disclosure, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "coupled" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances.

[0053] In the present disclosure, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0054] Many different embodiments or examples are provided below to implement different structures of the present disclosure. In order to simplify the present disclosure, the components and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present disclosure. In addition, the present disclosure may repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present disclosure provides various specific examples of processes and materials, but those of ordinary skill in the art may be aware of the application of other processes and / or the use of other materials.

[0055] The preferred embodiments of the present disclosure are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0056] The present disclosure provides an airflow detection circuit, which uses a thermistor for detection and indirectly detects the flow rate of the airflow by measuring the cooling effect of the airflow on its surface.

[0057] Figure 1 FIG. 2 shows a schematic block diagram of an airflow detection circuit according to some embodiments of the present disclosure. Figure 1 As shown, the airflow detection circuit 100 includes a voltage source VCC, a first resistor R1, a first switch K1, a first thermistor T1, a second thermistor T2, a first operational amplifier U1 and a controller C. One end of the first thermistor T1 is coupled to the first resistor R1 and the first switch K1, and the other end is coupled to the first input end (e.g., the positive input end) of the first operational amplifier U1. One end of the second thermistor T2 is coupled to the first resistor R1 and the first switch K1, and the other end is coupled to the second input end (e.g., the negative input end) of the first operational amplifier U1. The voltage source VCC is coupled to the first resistor R1 and the first switch K1, and can provide a power supply voltage to the first thermistor T1 and the second thermistor T2 in a corresponding power supply path based on the conduction or disconnection of the first switch K1. The controller C is coupled to the output end of the first operational amplifier U1, and can collect the output signal of the first operational amplifier U1, and determine the airflow velocity based on the output signal of the first operational amplifier U1. The specific method for determining the airflow velocity will be described below.

[0058] In some embodiments, the first resistor R1 can be used as a bias resistor. When the first switch K1 is disconnected, the voltage source VCC provides a supply voltage to the first thermistor T1 and the second thermistor T2 via the first resistor R1. When the first switch K1 is turned on, the voltage source VCC provides a supply voltage to the first thermistor T1 and the second thermistor T2 via the first switch K1.

[0059] Figure 2FIG. 2 shows a schematic block diagram of an airflow detection circuit according to some other embodiments of the present disclosure. Figure 2 As shown, the airflow detection circuit 200 also includes a second operational amplifier U2. The first input terminal (e.g., the positive input terminal) of the second operational amplifier U2 is coupled to the first thermistor T1, and the second input terminal (e.g., the negative input terminal) of the second operational amplifier U2 is coupled to the second thermistor T2. The airflow detection circuit 300 also includes a second switch K2, which is coupled to the output terminal of the second operational amplifier U2 and the first switch K1. The second switch K2 can control the conduction or disconnection of the first switch K1 based on the output signal of the second operational amplifier U2. When the output signal of the second operational amplifier U2 is higher than the first threshold (e.g., outputting a high level), the second switch K2 is turned on. When the second switch K2 is turned on, the first switch K1 is turned on. When the output signal of the second operational amplifier U2 is lower than the second threshold (e.g., outputting a low level), the second switch K2 is turned off, and the first threshold is greater than the second threshold. When the second switch K2 is turned off, the first switch K1 is turned off.

[0060] In some embodiments, the first switch K1 includes a field-effect transistor (MOSFET, FET) switch, for example, a metal-oxide-semiconductor field-effect transistor (MOSFET). Preferably, the first switch K1 can be a P-channel metal-oxide-semiconductor field-effect transistor (PMOS) or an N-channel metal-oxide-semiconductor field-effect transistor (NMOS). The first switch K1 can also be any other component that can play an equal or similar role, including but not limited to a switching device such as a bipolar junction transistor (BJT) and a relay.

[0061] In some embodiments, the second switch K2 includes a transistor (BJT), for example, the second switch K2 can be an NPN transistor or a PNP transistor. The second switch K2 can be any other component that can play an equal or similar role, including but not limited to FET, MOSFET, PMOS, NMOS, RELAY and other switch devices.

[0062] Figure 3 FIG. 2 shows a circuit diagram of an airflow detection circuit according to some embodiments of the present disclosure. Figure 3 As shown, the first switch K1 is a MOSFET, the second switch K2 is a triode, and the collector c of the second switch K2 is coupled to the gate g of the first switch K1. When the second switch K2 is turned on, the second switch K2 can provide a driving voltage to the gate g of the first switch K1 to drive the first switch K1 to turn on.

[0063] In some embodiments, the first thermistor T1 and the second thermistor T2 include a platinum resistance thermometer (PRT), or any other components that can play an equal or similar role, including but not limited to a thermistor diode, a thermistor capacitor, etc. Preferably, the first thermistor T1 is PT100, and the second thermistor T2 is PT1000. It is understandable that when different types of first thermistors T1, second thermistors T2, first switches K1, and second switches K2 are used, the airflow detection circuit can be adaptively adjusted, for example, some components can be appropriately increased or decreased, depending on actual needs.

[0064] When the temperature rises to a value greater than the temperature conversion point, the resistance of the first thermistor T1 and the second thermistor T2 increases, the voltage of the first thermistor T1 and the second thermistor T2 increases, the voltage of the first input terminal and the second input terminal of the first operational amplifier U1 and / or the second operational amplifier U2 decreases, the voltage of the output terminal of the first operational amplifier U1 and / or the second operational amplifier decreases, and the first operational amplifier U1 and / or the second operational amplifier outputs a low level.

[0065] When the temperature drops to less than the temperature conversion point, the resistance of the first thermistor T1 and the second thermistor T2 decreases, the voltage of the first thermistor T1 and the second thermistor T2 decreases, the voltage of the first input terminal and the second input terminal of the first operational amplifier U1 and / or the second operational amplifier U2 increases, the voltage of the output terminal of the first operational amplifier U1 and / or the second operational amplifier increases, and the first operational amplifier U1 and / or the second operational amplifier outputs a high level.

[0066] In some embodiments, Figure 3 As shown, the airflow detection circuit 300 also includes a second resistor R2, a third resistor R3 and a fourth resistor R4, and the circuit connection relationship is as follows: Figure 3As shown. The second resistor R2 is coupled to the first thermistor T1, and the third resistor R3 and the fourth resistor R4 are connected in series and coupled to the second thermistor T2. By reasonably setting the second resistor R2, the third resistor R3, and the fourth resistor R4, the airflow detection circuit 300 is in an initial state (for example, when it is just powered on), the first input terminal (for example, the positive input terminal) of the second operational amplifier U2 is at a high potential (high level), the second input terminal (for example, the negative input terminal) is at a low potential (low level), and the output of the second operational amplifier U2 is at a high level.

[0067] When the output of the second operational amplifier U2 is at a high level, the second switch K2 is turned on, the first switch K1 is turned on, and the voltage source VCC provides a supply voltage to the first thermistor T1 and the second thermistor T2 via the first switch K1.

[0068] When the output of the second operational amplifier U2 is at a low level, the second switch K2 is turned off, the first switch K1 is turned off, and the voltage source VCC provides a supply voltage to the first thermistor T1 and the second thermistor T2 via the first resistor R1.

[0069] In some embodiments, a temperature transition point may be defined, and the temperature transition point is a critical temperature at which the second operational amplifier U2 outputs a high level or a low level. When the temperature is less than the temperature transition point, the operational amplifier of the second operational amplifier U2 outputs a high level. When the temperature is greater than the temperature transition point, the operational amplifier of the second operational amplifier U2 outputs a low level. When the temperature is equal to the temperature transition point, the operational amplifier output of the second operational amplifier U2 maintains the previous or current level state.

[0070] In some embodiments, the second resistor R2, the third resistor R3 and the fourth resistor R4 satisfy the following relationship:

[0071]

[0072] Among them, V CC is the voltage of the voltage source, V DS is the conduction voltage drop of the first switch K1, R PT1 is the resistance value of the first thermistor, R PT2 is the resistance value of the second thermistor, ΔR PT1 is the resistance change of the first thermistor with temperature, ΔR PT2 is the resistance change value of the second thermistor with temperature, T is temperature, R2 is the resistance value of the second resistor, R3 is the resistance value of the third resistor, R4 is the resistance value of the fourth resistor, and T is the operating temperature conversion point. It should be noted that the present invention does not limit the specific temperature of the operating temperature conversion point T, and it can be preset according to requirements in actual applications.

[0073] Assume that the temperature conversion point is set to 70°C, the first thermistor T1 is PT100, and the second thermistor T2 is PT1000. When the temperature conversion point T is reached, there are:

[0074] R PT1 +T×ΔR PT1 =127.49Ω, R PT2 +T×ΔR PT2 =1270.751Ω,

[0075] According to formula 1, there is the following relationship:

[0076]

[0077] In this case, the resistance values ​​of the second resistor R2 , the third resistor R3 , and the fourth resistor R4 can be flexibly configured to satisfy the relationship of Formula 1.

[0078] It should be noted that the resistance values ​​of the second resistor R2, the third resistor R3, and the fourth resistor R4 can be selected to be at the same level as the first thermistor T1 and the second thermistor T2 to avoid a significant impact on their power, so that the entire airflow detection circuit works stably. For example, the second resistor R2 is of the same order of magnitude as the first thermistor T1 (for example, one hundred or several hundred ohms, etc.), and the third resistor R3 and the fourth resistor R4 are of the same order of magnitude as the second thermistor T2 (for example, one thousand or several thousand ohms, etc.).

[0079] It should be noted that, in Formula 1, all parameters except temperature T are constants and can be flexibly configured according to the temperature requirements of the application scenario. In some embodiments, the second resistor R2 = 130Ω, the third resistor R3 = 200Ω, and the fourth resistor R4 = 1500Ω.

[0080] In the present disclosure, the first thermistor and the second thermistor can sense the temperature change of the air duct. The first thermistor and the second thermistor are placed in the air duct, and the airflow will have a cooling effect on them. The voltage level of the appropriate voltage source can be selected for the first thermistor and the second thermistor to ensure their power, so as to avoid the situation where the temperature rise is offset by the temperature drop and the operating temperature conversion point cannot be reached. In some embodiments, the voltage level of the voltage source VCC can be 10 to 20V. However, the present disclosure is not limited to this.

[0081] In some embodiments, the thermal sensitivity of the first thermistor T1 is different from that of the second thermistor T2, the second resistor R2 is coupled to the first thermistor T1, the third resistor R3 and the fourth resistor R4 are connected in series and coupled to the second thermistor T2, and the resistance values ​​of the second resistor R2, the third resistor R3 and the fourth resistor R4 are reasonably set so that the ratio of the resistance value of the first thermistor T1 to the sum of the resistance values ​​of the first thermistor T1 and the second resistor R2 changes faster than the ratio of the resistance value of the second thermistor T2 to the sum of the resistance values ​​of the second thermistor T2, the third resistor R3 and the fourth resistor R4. In other words, T1 / (T1+R2) changes faster with temperature than T2 / (T2+R3+R4). For convenience, it is referred to as the resistance ratio hereinafter.

[0082] When the ambient air temperature rises to a value greater than the temperature conversion point, the resistance ratio of the first thermistor T1 (e.g., PT100) increases faster than the resistance ratio of the second thermistor T2 (e.g., PT1000) (specifically, although the resistance ratio of the first thermistor T1 caused by the ambient temperature increases less than the resistance ratio of the second thermistor T2, the total resistance of the branch of the first thermistor T1 is significantly smaller than the total resistance of the branch of the second thermistor T2, and therefore the thermal power generated by the current passing through the first thermistor T1 is significantly greater than the thermal power generated by the current passing through the second thermistor T2). Thermistor T2 generates thermal power, so the resistance ratio of the first thermistor T1 increases faster than that of the second thermistor T2), the voltage at the first input terminal of the second operational amplifier U2 decreases faster than that of the second input terminal of the second operational amplifier U2. When the voltage at the first input terminal of the second operational amplifier U2 is less than the voltage at the second input terminal, the operational amplifier output of the second operational amplifier U2 is low. At this time, the second switch K2 is disconnected, the first switch K1 is disconnected, and the voltage source VCC provides a power supply voltage to the first thermistor T1 and the second thermistor T2 via the first resistor R1.

[0083] When the temperature drops to less than the temperature conversion point, the resistance ratio of the first thermistor T1 (for example, PT100) decreases faster than that of the second thermistor T2 (for example, PT1000), and the voltage at the first input terminal of the second operational amplifier U2 increases faster than that of the second input terminal of the second operational amplifier U2. When the voltage at the first input terminal of the second operational amplifier U2 is greater than the voltage at the second input terminal, the operational amplifier output of the second operational amplifier U2 is high. At this time, the second switch K2 is turned on, the first switch K1 is turned on, and the voltage source VCC provides a supply voltage to the first thermistor T1 and the second thermistor T2 via the first switch K1.

[0084] In this way, the second switch K2 can be turned on or off based on the high or low level signal output by the second operational amplifier U2, thereby controlling the on or off of the first switch K1, thereby realizing different power supply paths of the voltage source VCC to the first thermistor T1 and the second thermistor T2.

[0085] It should be noted that when the ambient air temperature is equal to the temperature conversion point, the first operational amplifier, the second operational amplifier, the first switch and the second switch maintain the previous or current state.

[0086] When the temperature does not reach the temperature conversion point (the temperature is less than the temperature conversion point), the second operational amplifier U2 outputs a high level, the second switch K2 is turned on, the first switch K1 is turned on, the voltage source VCC provides a supply voltage to the first thermistor T1 and the second thermistor T2 via the first switch K1, the first input terminal of the first operational amplifier U1 inputs a high level, and the first operational amplifier U1 outputs a high level. The controller C can collect the high level output by the first operational amplifier U1.

[0087] When the temperature reaches the temperature conversion point (temperature is greater than the temperature conversion point), the second operational amplifier U2 outputs a low level, the second switch K2 is disconnected, the first switch K1 is disconnected, the voltage source VCC provides a supply voltage to the first thermistor T1 and the second thermistor T2 via the first resistor R1, the first input terminal of the first operational amplifier U1 inputs a low level, and the first operational amplifier U1 outputs a low level. The controller C can collect the low level output by the first operational amplifier U1.

[0088] It can be seen that the temperature transition point may also be a critical temperature at which the first operational amplifier U1 outputs a high level or a low level.

[0089] In some embodiments, the controller C can collect the output voltage of the first operational amplifier U1, determine the resistance of the first thermistor T1 and the second thermistor T2 based on the output voltage of the first operational amplifier U1, determine the airflow temperature or the change in airflow temperature, and then determine the airflow velocity. For example, when the output voltage of the first operational amplifier U1 is higher than the third threshold, it is determined that the resistance of the first thermistor T1 and the second thermistor T2 is smaller, the temperature is lower, and the airflow velocity is faster. When the output voltage of the first operational amplifier U1 is lower than the fourth threshold, it is determined that the resistance of the first thermistor T1 and the second thermistor T2 is larger, the temperature is higher, and the airflow velocity is slower. The third threshold is greater than the fourth threshold. Optionally, the airflow temperature can be determined by a temperature sensor. The temperature sensor can be coupled to the controller or integrated into the controller.

[0090] In some preferred embodiments, the controller C can determine the duty cycle of the output signal of the first operational amplifier U1, and determine the airflow velocity based on the duty cycle. For example, the controller C can read the high and low level pulse widths of the output signal of the first operational amplifier U1 through the input edge capture interrupt, and calculate the duty cycle of a single pulse. When the duty cycle is greater than a fifth threshold value (e.g., 50%, 60%, etc.), it is determined that the airflow velocity is fast. When the duty cycle is lower than a sixth threshold value (e.g., 30%, 20%, etc.), it is determined that the airflow velocity is slow. The fifth threshold value is greater than the sixth threshold value.

[0091] Table 1 shows an example of the controller C determining the duty cycle based on the output signal of the first operational amplifier U1 according to some embodiments of the present disclosure.

[0092] Table 1

[0093]

[0094] As shown in Table 1, the sampling pulse width in the first column is the pulse width of the output signal of the first operational amplifier U1 collected by the controller C. The full pulse width in the second column is the full pulse width period. The duty cycle in the third column is the duty cycle of the output signal of the first operational amplifier U1.

[0095] The duty cycle is calculated as: Duty cycle = pulse width * 100% / full pulse width.

[0096] In some preferred embodiments, the controller C can process the output signal of the first operational amplifier U1 to obtain a stable duty cycle of the output signal, thereby improving the accuracy of the airflow detection result. For example, the controller C can filter the clutter of the output signal of the first operational amplifier U1 by using a median, a mean, etc., thereby improving the accuracy.

[0097] As shown in Table 1, for example, the average duty cycle is: (58.4+57.8+58.1) / 3=58.1%. The average pulse width period is (88218+89828+87597) / 3=88.55 ms.

[0098] When the airflow velocity increases, the duty cycle increases (for example, increases to 61.29%), and the pulse width period becomes shorter (for example, shortens to 83.76ms). When the airflow velocity slows down, the duty cycle decreases (for example, decreases to 54.4%), and the pulse width period becomes longer (for example, becomes longer to 91.89ms). It should be understood that the full pulse width period is related to the first operational amplifier U1, and there may be a certain margin, for example, it is allowed to vary within the range of 400us to 200ms. However, the present invention is not limited to this, and it depends on actual needs.

[0099] In some embodiments, the controller C may determine the air flow rate based on a comparison table of the duty cycle of the output signal of the first operational amplifier U1 and the flow rate.

[0100] In some embodiments, a standard anemometer may be used to establish a duty cycle and flow rate (wind speed) comparison table using a large amount of experimental data.

[0101] In some embodiments, the controller C can be coupled to a fan (not shown in the figure), and the fan speed can be adjusted by adjusting the fan duty cycle to achieve different wind speeds. The larger the fan duty cycle, the faster the fan speed and the faster the wind speed. The smaller the fan duty cycle, the smaller the fan speed and the smaller the wind speed. The fan duty cycle can be 50-100%.

[0102] In some embodiments, different wind speeds can be achieved by adjusting the number of openings in the pipeline under test while keeping the fan speed (or fan duty cycle) fixed. The more openings in the pipeline under test, the greater the wind speed. The fewer openings in the pipeline under test, the lower the wind speed.

[0103] In some embodiments, different wind speeds can be achieved by adjusting the speed of the fan (or the fan duty cycle) and the number of openings in the inspected pipeline.

[0104] In some embodiments, multiple fans may be used to achieve different wind speeds, which may improve efficiency.

[0105] In some embodiments, the controller C may collect the output voltage of the first operational amplifier U1 multiple times at different wind speeds, and determine the duty cycle of the output voltage, thereby establishing a wind speed and duty cycle comparison table.

[0106] Preferably, the controller C can also fit the duty cycle to obtain a fitted duty cycle, which is conducive to establishing a more stable and reliable comparison relationship between wind speed and duty cycle.

[0107] Table 2 shows a comparison table of the duty cycle of the output signal of the first operational amplifier and the flow rate (wind speed) according to some embodiments of the present disclosure. Figure 4 A schematic diagram of a comparison curve of flow rate, sampling duty cycle and fitting duty cycle according to some embodiments of the present disclosure is shown. As shown in Table 2, the first column is the flow rate (wind speed or flow rate). The second column is the sampling duty cycle, which is the duty cycle determined by the controller C based on the output signal of the first operational amplifier U1. The third column is the fitting duty cycle, which is the duty cycle obtained by the controller C fitting the sampling duty cycle. Figure 4 As shown, the horizontal axis represents the sampling point number, the vertical axis represents the flow rate (m / s), the blue curve L1 represents the flow rate; the gray curve L2 represents the sampling duty cycle; and the green curve L3 represents the fitting duty cycle. Figure 4It can be seen that each sampling point number corresponds to the sampling duty cycle and the fitting duty cycle in the vertical direction, and the flow rate is positively correlated with the duty cycle as a whole. When the duty cycle increases, the flow rate increases. When the duty cycle decreases, the flow rate decreases. Therefore, the airflow velocity can be detected based on the duty cycle of the output signal of the first operational amplifier. It should be noted that Figure 4 An example of a flow rate (blue curve L1 ) with a fan duty cycle of 75% is illustrated, which does not constitute a limitation of the present disclosure.

[0108] Table 2

[0109]

[0110]

[0111] In some embodiments, a comparison table of duty cycle and flow rate (wind speed) (e.g., experimental data, comparison table, comparison curve, etc.) can be stored in a memory. The controller can collect the output signal of the first operational amplifier, determine the duty cycle of the output signal, call the stored comparison table of duty cycle and flow rate (wind speed) to determine the airflow velocity, and realize airflow monitoring.

[0112] For example, when the controller determines that the duty cycle (eg, fitting duty cycle) of the output signal of the first operational amplifier is 58.1%, it can be known from the duty cycle and flow rate comparison table that the air flow rate is approximately 2.66 m / s.

[0113] For another example, when the controller determines that the duty cycle (eg, fitting duty cycle) of the output signal of the first operational amplifier is 66%, it can be known from the duty cycle and flow rate comparison table that the air flow rate is approximately 4.03 m / s.

[0114] In some embodiments, the controller C may be coupled to the master controller C0 , and the controller C may determine the state of the detection pipeline based on the airflow velocity, and feed the state back to the master controller C0 .

[0115] In some embodiments, the controller C can determine the state of the detection pipeline based on the relationship between the airflow velocity and the threshold. For example, when the airflow velocity is between the seventh threshold and the eighth threshold (for example, 3.15-6 m / s), the detection pipeline is determined to be normal. For example, when the airflow velocity is higher than the seventh threshold (for example, 6 m / s), and / or lower than the eighth threshold (for example, 3.15 m / s), the detection pipeline is determined to be abnormal. Specifically, when the airflow velocity is higher than the seventh threshold (for example, 6 m / s), the detection pipeline is determined to be open (leaky); when the airflow velocity is lower than the eighth threshold (for example, 3.15 m / s), the detection pipeline is determined to be blocked (blocked). The seventh threshold is greater than the eighth threshold.

[0116] It should be noted that the specific sizes of various thresholds involved in the present disclosure can be flexibly adjusted according to actual needs.

[0117] In some embodiments, the controller C can perform a fault alarm based on the airflow velocity. For example, when the airflow velocity is lower than 20% of the eighth threshold value (i.e., the airflow velocity is 80% or less of the lower limit of the normal velocity), the controller C can perform a low airflow (blocked pipe, blockage) fault alarm. When the airflow velocity is higher than 30% of the seventh threshold value (i.e., the airflow velocity is 130% or more of the upper limit of the normal velocity), the controller C can perform a high airflow (open pipe, broken leak) fault alarm.

[0118] For example, if the normal flow rate is 4m / s, when the airflow rate is lower than 20% of the normal flow rate, that is, 4m / s*80%=3.24m / s and below, the controller C determines that the detected pipeline is blocked and can issue a low airflow (blocked, blocked) fault alarm. When the airflow rate is higher than 30% of the normal flow rate, that is, 4m / s*130%=5.2m / s and above, the controller C determines that the detected pipeline is open and can issue a high airflow fault alarm.

[0119] Optionally, the controller C can perform a graded fault alarm based on the airflow velocity. The graded fault alarm may include three levels: a minor fault alarm, a general fault alarm, and a serious fault alarm. For example, when the airflow velocity is lower than 0-20% of the eighth threshold, the controller C may perform a minor fault alarm of low airflow (blocked pipe, blockage). When the airflow velocity is lower than 20-50% of the eighth threshold, the controller C may perform a general fault alarm of low airflow (blocked pipe, blockage). When the airflow velocity is lower than 50%-100% of the eighth threshold, the controller C may perform a serious fault alarm of low airflow (blocked pipe, blockage). For another example, when the airflow velocity is higher than 0-30% of the seventh threshold, the controller C may perform a minor fault alarm of high airflow (open pipe, broken leak). When the airflow velocity is higher than 30-50% of the seventh threshold, the controller C may perform a general fault alarm of high airflow (open pipe, broken leak). When the airflow velocity is higher than 50%-100% of the seventh threshold, the controller C may perform a serious fault alarm of high airflow (open pipe, broken leak).

[0120] Optionally, the graded fault alarm may include two levels: abnormal alarm and fault alarm. For example, when the airflow velocity is lower than 0-50% of the eighth threshold, the controller C may perform a low airflow (blocked pipe, blockage) abnormal alarm. When the airflow velocity is lower than 50%-100% of the eighth threshold, the controller C may perform a low airflow (blocked pipe, blockage) fault alarm. For another example, when the airflow velocity is higher than 0-50% of the seventh threshold, the controller C may perform a high airflow (open pipe, broken leak) abnormal alarm. When the airflow velocity is higher than 30-50% of the seventh threshold, the controller C may perform a high airflow (open pipe, broken leak) fault alarm. It should be noted that the present invention does not limit the specific level of the graded fault alarm and its corresponding threshold percentage. In practical applications, they can be set according to requirements. In addition, the present invention does not limit the specific values ​​of normal flow rate, abnormal flow rate, percentage, etc. In practical applications, they can be set according to requirements, which are all within the scope of protection of the present invention.

[0121] In some embodiments, the controller C may also monitor whether the period of the output signal of the first operational amplifier U1 is abnormal. For example, the controller C may determine whether the period of the output signal of the first operational amplifier U1 is abnormal by whether the period of the output signal of the first operational amplifier U1 conforms to the calibration period. When it is monitored that the period of the output signal of the first operational amplifier U1 conforms to the calibration period, it is determined that the period of the output signal of the first operational amplifier U1 is normal. When it is monitored that the period of the output signal of the first operational amplifier U1 does not conform to the calibration period, for example, when it is monitored that the period of the output signal of the first operational amplifier U1 is less than half of the calibration period, it is preliminarily determined that the period of the output signal of the first operational amplifier U1 is abnormal. Preferably, the controller may continuously monitor multiple periods of the output signal of the first operational amplifier U1 for re-judgment. If it is still monitored that the period of the output signal of the first operational amplifier U1 is less than half of the calibration period, it may be determined that the period of the output signal of the first operational amplifier U1 is abnormal. Preferably, the controller C may perform compensation correction processing on the signal of the abnormal period. Figure 5 A schematic diagram showing whether the period of the output signal of the first operational amplifier is abnormal according to some embodiments of the present disclosure. Figure 5 Figure a shows an example in which the period of the output signal of the first operational amplifier is normal. Figure 5 Figure b in the figure shows an example of an abnormal period of the output signal of the first operational amplifier. During the compensation correction process, the controller can combine pulse 2 and pulse 3 to perform compensation correction, which is beneficial to improve the accuracy of the detection result.

[0122] like Figure 3As shown, the airflow detection circuit 300 also includes a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10 and an eleventh resistor R11. One end of the fifth resistor R5 is coupled to the first resistor R1 and the first switch K1, and the other end is coupled to the collector c of the second switch K2. One end of the sixth resistor R6 is coupled to the output end of the second operational amplifier U2, and the other end is coupled to the base b of the second switch K2. The sixth resistor R6 is a current limiting resistor. One end of the seventh resistor R7 is coupled between the sixth resistor R6 and the base b of the second switch K2, and the other end is coupled to the emitter e of the second switch K2. The seventh resistor R7 is a bias resistor, which can provide a bias voltage to the base b of the second switch K2, control the second switch K2 to be turned on, and the collector c of the second switch K2 is coupled to the gate of the first switch K1. When the second switch K2 is turned on, the second switch K2 provides a driving voltage to the gate g of the first switch K1. The gate of the first switch K1 receives an enable signal from the second switch K2, the first switch K1 is turned on, and the power supply voltage of the voltage source VCC is applied to the first thermistor T1 and the second thermistor T2 through the first switch K1. One end of the eighth resistor R8 is coupled to the output end of the first operational amplifier U1, and the other end is coupled to the controller C. One end of the ninth resistor R9 is coupled between the eighth resistor R8 and the controller C, and the other end is grounded. One end of the tenth resistor R10 is coupled to the second input end of the first operational amplifier U1, and the other end is coupled between the output end of the first operational amplifier U1 and the eighth resistor R8. One end of the eleventh resistor R11 is coupled to the second input end of the first operational amplifier U1, and the other end is grounded.

[0123] In some embodiments, the controller C collects the voltage signal at the output end of the first operational amplifier U1, which can be amplified by the tenth resistor R10 and the eleventh resistor R11, and then divided by the eighth resistor R8 and the ninth resistor R9 to adjust the output signal of the first operational amplifier U1 to a voltage level that the controller C can withstand. The output end of the first operational amplifier U1 can be coupled to the sampling pin of the controller C. The controller C can detect the output signal of the first operational amplifier U1 in real time, calculate the duty cycle by the length of time the output signal of the first operational amplifier U1 is in the high and low level states, and determine the flow rate information of the airflow according to the flow rate duty cycle comparison table.

[0124] like Figure 3As shown, the airflow detection circuit 300 also includes a first capacitor C1, a second capacitor C2, a third capacitor C3 and a fourth capacitor C4. One end of the first capacitor C1 is coupled between the first thermistor T1 and the first input terminal of the second operational amplifier U1, and the other end is coupled to the emitter e of the second switch K2. One end of the second capacitor C2 is coupled between the third resistor R3 and the fourth resistor R4, and is coupled to the second input terminal of the second operational amplifier U2, and the other end is coupled to the emitter e of the second switch K2. The third capacitor C3 is connected in parallel to the seventh resistor R7, one end is coupled to the base b of the second switch K2, and the other end is coupled to the emitter e of the second switch K2. The fourth capacitor C4 is connected in parallel to the ninth resistor R9, one end is coupled to the output terminal of the eighth resistor R8, and the other end is grounded. The first capacitor C1, the second capacitor C2, the third capacitor C3 and the fourth capacitor C4 are filter capacitors. The present disclosure does not limit the specific capacitance value, and can be flexibly adjusted according to the signal quality received by the controller C and the EMC effect.

[0125] The airflow detection circuit disclosed in the present invention has a simple circuit, a simple algorithm, low requirements on the controller, and takes into account both real-time performance and stability. The temperature is sensed by a first thermistor and a second thermistor, and the airflow velocity is determined by the output signal of the first operational amplifier, thereby improving the stability, reliability and broad spectrum of the airflow detection results.

[0126] The airflow detection circuit disclosed in the present invention determines the airflow velocity by the duty cycle of the output signal of the first operational amplifier, and determines the state of the detection pipeline based on the airflow velocity, thereby improving the accuracy and reliability of the detection result.

[0127] The airflow detection circuit disclosed in the present invention controls the second switch and the first switch through the output signal of the second operational amplifier, and can control the power supply path of the first thermistor and the second thermistor, thereby reducing the adverse effect of the peak signal of the output signal of the first operational amplifier, so that the peak operational amplifier output is converted into a uniform switching time, making the output signal of the first operational amplifier more stable, and making the output signal collected by the controller more stable, and can more accurately determine the duty cycle of the output signal of the first operational amplifier, which is conducive to improving the accuracy of the airflow detection result.

[0128] The present disclosure also provides an aspirating smoke fire detector. Figure 6 FIG. 4 is a schematic diagram of an aspirating smoke fire detector 400 according to some embodiments of the present disclosure. Figure 6As shown, the aspirating smoke fire detector 400 includes the airflow detection circuit 100 / 200 / 300 as described above. Although not shown in the figure, it can be understood that the aspirating fire detector 400 can also include a housing, an air suction pipe, a fan, a display screen, a speaker, a buzzer and other devices. The aspirating smoke fire detector 400 can display the airflow detection result through the fan, the display screen, the speaker, the buzzer and other devices.

[0129] In some embodiments, the aspirating smoke fire detector 400 can detect the airflow velocity, determine the state of the detection pipeline based on the airflow velocity, and feed back the state to the main controller. For example, when the airflow velocity is between the seventh threshold and the eighth threshold, the detection pipeline is determined to be normal. When the airflow velocity is higher than the seventh threshold, and / or lower than the eighth threshold, the detection pipeline is determined to be abnormal. When the airflow velocity is higher than the seventh threshold, the detection pipeline is determined to be leaking; when the airflow velocity is lower than the eighth threshold, the detection pipeline is determined to be blocked. The seventh threshold is greater than the eighth threshold. When it is determined that the detection pipeline is normal, the aspirating smoke fire detector can report and / or display normal, and can also send a normal state (for example, 1) to the main controller. When it is determined that the detection pipeline is leaking, the aspirating smoke fire detector can report and / or display leaking, and can also send a leaking state (for example, 0) to the main controller. When it is determined that the detection pipeline is blocked, the aspirating smoke fire detector can report and / or display blocking, and can also send a blocking state (for example, 00) to the main controller.

[0130] In some embodiments, the aspirating smoke fire detector 400 can perform high and low airflow fault alarms based on the airflow velocity and report to the main controller. The aspirating smoke fire detector 400 can perform graded fault alarms based on the airflow velocity. The operations of performing fault alarms and graded fault alarms based on the airflow velocity can be performed by the controller in the aspirating smoke fire detector 400, which is similar or the same as the related examples of the controller C performing fault alarms and graded fault alarms, and will not be repeated here.

[0131] The aspirating smoke fire detector disclosed in the present invention can sample the flow rate in the pipeline in real time by adopting the above-mentioned airflow detection circuit, so as to determine whether there is a leak or blockage in the pipeline in the monitoring area, thereby protecting the entire monitoring area and making the detection result more stable and reliable.

[0132] In some embodiments, the aspirating smoke detector 400 includes a memory for storing a flow rate duty cycle comparison table.

[0133] The present disclosure also provides a fire fighting system. Figure 7 FIG. 5 shows a schematic diagram of a fire fighting system 500 according to some embodiments of the present disclosure. Figure 7As shown, the fire protection system 500 includes a master controller C0 and an aspirating smoke fire detector 400. The aspirating smoke fire detector 400 is in communication connection with the master controller C0. The aspirating smoke fire detector 400 includes the airflow detection circuit 100 / 200 / 300 as described above.

[0134] The aspirating smoke fire detector 400 can detect the airflow velocity, determine the state of the detection pipeline based on the airflow velocity, and report the state to the master controller C0. The master controller C0 can control the operation of the aspirating smoke fire detector 400. For example, when the aspirating smoke fire detector 400 reports a normal state to the master controller C0, the master controller C0 can control the aspirating smoke fire detector 400 to continue to work. When the aspirating smoke fire detector 400 reports an abnormal state to the master controller C0, the master controller C0 can control the aspirating smoke fire detector 400 to suspend operation.

[0135] The fire protection system of the present disclosure can achieve more stable and reliable airflow monitoring by adopting the above-mentioned aspirating smoke fire detector 400.

[0136] The present disclosure also provides an airflow detection method. Figure 8 FIG. 6 is a flow chart of an airflow detection method 600 according to some embodiments of the present disclosure. Figure 8 As shown, the airflow detection method 600 includes steps S610 to S640 , and the airflow detection method 600 can be implemented by the aspirating smoke fire detector 400 .

[0137] In step S610, the airflow to be tested is collected. The aspirating smoke fire detector can draw the air in the detection pipeline into the detector through a sampling pipe (aspirating pipe).

[0138] In step S620, based on the airflow to be measured, the output signal of the airflow detection circuit is collected. The aspirating smoke fire detector can sense the temperature change of the gas sucked into the sampling tube through the first thermistor and the second thermistor of the airflow detection circuit, and collect the output signal of the first operational amplifier through the airflow detection circuit.

[0139] In step S630, the duty cycle is determined based on the output signal. The aspirating smoke detector may determine the duty cycle based on the output signal of the first operational amplifier.

[0140] In step S640, the airflow velocity is determined based on the duty cycle. The aspirating smoke fire detector can determine the airflow velocity based on the duty cycle and a comparison table of duty cycle and velocity.

[0141] In some embodiments, the airflow detection method 600 further includes: determining the state of the detection pipeline based on the airflow velocity, and reporting the state to the master controller. The aspirating smoke fire detector can determine the state of the detection pipeline according to the airflow velocity. For example, when the airflow velocity is between the seventh threshold and the eighth threshold, the detection pipeline is determined to be normal; when the airflow velocity is higher than the seventh threshold, the detection pipeline is determined to be leaking; when the airflow velocity is lower than the eighth threshold, the detection pipeline is determined to be blocked. When the detection pipeline is determined to be normal, the aspirating smoke fire detector can send a normal state (for example, 1) to the master controller. When the detection pipeline is determined to be leaking, the aspirating smoke fire detector can send a high airflow (open pipe, leaking) state (for example, 0) to the master controller. When the detection pipeline is determined to be blocked, the aspirating smoke fire detector can send a low airflow (blocked pipe, blocked) state (for example, 00) to the master controller. The master controller can receive the detection pipeline state reported by the aspirating smoke fire detector and promptly notify relevant staff. The aspirating smoke fire detector can also broadcast and / or display the detection results by itself and promptly notify relevant personnel.

[0142] In some embodiments, the airflow detection method 600 further includes: performing a fault alarm based on the airflow velocity. In some embodiments, the airflow detection method 600 further includes: performing a graded fault alarm based on the airflow velocity. The above description is the same or similar, and will not be repeated here.

[0143] The present disclosure also provides a computer-readable storage medium, including computer-executable instructions stored thereon, and when the executable instructions are executed by a processor, the airflow detection method as described above is implemented.

[0144] In some embodiments, the memory / computer readable storage medium may be any tangible medium containing or storing a program that may be used by or in combination with an instruction execution system, apparatus, or device. Computer readable storage media include, but are not limited to, electrical, magnetic, optical, or semiconductor forms or devices, more specific examples (a non-exhaustive list) include: an electrical connection with one or more conductors, a portable computer hard disk, a hard disk, a random access memory (RAM), a non-volatile random access memory (NVRAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0145] In some embodiments, the processor / controller / general controller may include a central processing unit (CPU), a microprocessing unit (MCU), and may also include other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components and other similar devices.

[0146] It should be noted that this specification provides method operation steps as described in the embodiments or schematic diagrams, but more or fewer operation steps may be included based on conventional or non-creative labor. The order of steps listed in the embodiments is only one way of executing the order of many steps and does not represent the only execution order. When the actual system or device product is executed, it can be executed in the order or in parallel according to the method shown in the embodiments or flowcharts.

[0147] Finally, it should be noted that the above is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. Although the present disclosure is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. An airflow detection circuit, comprising: A first thermistor, one end of which is coupled to the first resistor and the first switch, and the other end of which is coupled to the first input terminal of the first operational amplifier; a second thermistor, one end of which is coupled to the first resistor and the first switch, and the other end of which is coupled to the second input terminal of the first operational amplifier; a voltage source coupled to the first resistor and the first switch, and configured to provide a supply voltage to the first thermistor and the second thermistor through corresponding power supply paths based on the on or off state of the first switch; a controller, coupled to the output terminal of the first operational amplifier, configured to collect an output signal of the first operational amplifier, and determine an airflow velocity based on the output signal; The airflow detection circuit further includes: a second operational amplifier, a first input terminal of the second operational amplifier coupled to the first thermistor, and a second input terminal of the second operational amplifier coupled to the second thermistor; The airflow detection circuit further includes a second switch coupled to the output terminal of the second operational amplifier and the first switch and configured to control the on or off state of the first switch based on an output signal of the second operational amplifier. 2 . The airflow detection circuit of claim 1 , wherein when the first switch is open, the voltage source is configured to provide a supply voltage to the first thermistor and the second thermistor via the first resistor. 3 . The airflow detection circuit of claim 1 , wherein when the first switch is turned on, the voltage source is configured to provide a supply voltage to the first thermistor and the second thermistor via the first switch.

4. The airflow detection circuit according to any one of claims 1-3, wherein when the output signal of the second operational amplifier is higher than a first threshold, the second switch is turned on; when the second switch is turned on, the first switch is turned on.

5. The airflow detection circuit according to any one of claims 1 to 3, wherein when the output signal of the second operational amplifier is lower than a second threshold, the second switch is disconnected; when the second switch is disconnected, the first switch is disconnected. 6 . The airflow detection circuit according to claim 1 , wherein the first switch comprises a metal oxide semiconductor field effect transistor, the second switch comprises a transistor, and the collector of the transistor is coupled to the gate of the first switch.

7. The airflow detection circuit according to any one of claims 1 to 3, wherein the thermistor comprises a platinum resistor; the first thermistor comprises PT100; and the second thermistor comprises PT1000.

8. The airflow detection circuit according to any one of claims 1-3, wherein the controller is configured to determine a duty cycle of the output signal of the first operational amplifier, and determine the airflow rate based on the duty cycle.

9. The airflow detection circuit of claim 8, wherein the controller is configured to determine the airflow velocity based on the duty cycle and flow velocity comparison table.

10. The airflow detection circuit according to claim 8, wherein the controller is coupled to a master controller, and the controller is configured to determine a state of the detection pipeline based on the airflow velocity, and feed back the state to the master controller.

11. The airflow detection circuit according to any one of claims 1 to 3, further comprising: a second resistor, a third resistor and a fourth resistor, wherein the second resistor is coupled to the first thermistor, the third resistor and the fourth resistor are connected in series and coupled to the second thermistor, and the second resistor, the third resistor and the fourth resistor satisfy the following relationship: Among them, V CC is the voltage of the voltage source, V DS is the conduction voltage drop of the first switch, R PT1 is the resistance value of the first thermistor, R PT2 is the resistance value of the second thermistor, ΔR PT1 is the resistance change of the first thermistor with temperature, ΔR PT2 is the resistance change of the second thermistor with temperature, T is temperature, R2 is the resistance value of the second resistor, R3 is the resistance value of the third resistor, and R4 is the resistance value of the fourth resistor.

12. The airflow detection circuit according to claim 11, further comprising: a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor and an eleventh resistor, wherein one end of the fifth resistor is coupled to the first resistor and the first switch, and the other end is coupled to the collector of the second switch; One end of the sixth resistor is coupled to the output end of the second operational amplifier, and the other end is coupled to the base of the second switch; One end of the seventh resistor is coupled between the sixth resistor and the base of the second switch, and the other end is coupled to the emitter of the second switch; One end of the eighth resistor is coupled to the output end of the first operational amplifier, and the other end is coupled to the controller; One end of the ninth resistor is coupled between the eighth resistor and the controller, and the other end is grounded; one end of the tenth resistor is coupled to the second input terminal of the first operational amplifier, and the other end is coupled between the output terminal of the first operational amplifier and the eighth resistor; one end of the eleventh resistor is coupled to the second input terminal of the first operational amplifier, and the other end is grounded.

13. The airflow detection circuit according to claim 12, further comprising: a first capacitor, a second capacitor, a third capacitor and a fourth capacitor, wherein one end of the first capacitor is coupled between the first thermistor and the first input end of the second operational amplifier, and the other end is coupled to the emitter of the second switch; One end of the second capacitor is coupled between the third resistor and the fourth resistor and coupled to the second input terminal of the second operational amplifier, and the other end is coupled to the emitter of the second switch; The third capacitor is connected in parallel to the seventh resistor, one end of which is coupled to the base of the second switch and the other end of which is coupled to the emitter of the second switch; the fourth capacitor is connected in parallel to the ninth resistor and the other end of which is grounded.

14. An aspirating smoke fire detector, comprising the airflow detection circuit according to any one of claims 1 to 13.

15. A fire fighting system, comprising: Master controller; and The aspirating smoke fire detector according to claim 14 is communicatively connected to the master controller, configured to detect the airflow velocity, determine the state of the detection pipeline based on the airflow velocity, and report the state to the master controller.

16. A method for detecting airflow, comprising: Collect the airflow to be measured; Based on the airflow to be measured, collecting an output signal of an airflow detection circuit; determining a duty cycle based on the output signal; and determining an air flow rate based on the duty cycle; The airflow detection method is implemented by the aspirating smoke fire detector as claimed in claim 14.

17. The airflow detection method according to claim 16, further comprising: Based on the airflow velocity, the state of the detection pipeline is determined, and the state is reported to the main controller. 18 . A computer-readable storage medium, comprising computer-executable instructions stored thereon, wherein the executable instructions implement the airflow detection method according to claim 16 or 17 when executed by a processor.

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