Direct-powered multi-functional flue gas emission detection circuit

Abstract

This invention discloses a directly powered multifunctional flue gas emission detection circuit, comprising: a flue gas volumetric flow rate sensor, a flue gas carbon dioxide concentration sensor, a flue gas pressure sensor, a flue gas humidity sensor, a flue gas temperature sensor, a detection controller, and a power supply circuit. The power supply circuit provides power to the flue gas volumetric flow rate sensor, the flue gas carbon dioxide concentration sensor, the flue gas pressure sensor, the flue gas humidity sensor, the flue gas temperature sensor, and the detection controller. The output terminals of the flue gas volumetric flow rate sensor, the flue gas pressure sensor, the flue gas humidity sensor, and the flue gas temperature sensor are all connected to the input terminal of the detection controller. This directly powered multifunctional flue gas emission detection circuit solves the problem in existing technologies where the installation steps cannot be simplified by removing the installation positions of the first and second pressure sensors.

Description

Technical Field

[0001] This invention relates to flue gas emission detection, and more specifically to a direct-powered multifunctional flue gas emission detection circuit. Background Technology

[0002] Flue gas emissions are an important target for environmental protection monitoring, so how to detect the carbon emission rate in flue gas emissions is the topic discussed in this application.

[0003] Chinese patent application number CN202120391426.X discloses an apparatus for testing the oxidation rate and carbon emissions of gas turbine fuels. This apparatus mainly includes a flue gas analyzer, a flue gas flow meter, a data calculation module, a field gas chromatograph, an NDIR non-dispersive infrared spectroscopy analyzer, and a gas flow meter. This invention utilizes the high-precision results of gas chromatography to correct the low-precision results of NDIR non-dispersive infrared spectroscopy, and leverages the continuous real-time measurement advantage of NDIR non-dispersive infrared spectroscopy to avoid the risk of fuel composition fluctuations under long-time interval testing conditions in gas chromatography.

[0004] Gas flow meter testing typically uses the Pitot tube differential pressure method to calculate the gas flow rate in the flue gas pipe under test. The gas flow meter includes a first pressure sensor and a second pressure sensor. The first pressure sensor detects the total pressure in the flue gas pipe under test, and the second pressure sensor detects the static pressure in the flue gas pipe under test. Then, the volumetric flow rate of the flue gas in the flue gas pipe under test is calculated using the total pressure and static pressure according to Bernoulli's formula. However, during the installation of the first and second pressure sensors, it is necessary to check the installation positions of the first and second pressure sensors to determine whether they are detecting the total pressure or the static pressure. Therefore, simplifying the installation steps of the first and second pressure sensors is an urgent problem to be solved. Summary of the Invention

[0005] The present invention provides a direct-powered multi-functional flue gas emission detection circuit, which solves the problem that the installation steps of the first and second pressure sensors cannot be simplified in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The present invention discloses a direct-powered multifunctional flue gas emission detection circuit, comprising: a flue gas volume flow rate sensor, a flue gas carbon dioxide concentration sensor, a flue gas pressure sensor, a flue gas humidity sensor, a flue gas temperature sensor, a detection controller, and a power supply circuit. The power supply circuit supplies power to the flue gas volume flow rate sensor, the flue gas carbon dioxide concentration sensor, the flue gas pressure sensor, the flue gas humidity sensor, the flue gas temperature sensor, and the detection controller. The output terminals of the flue gas volume flow rate sensor, the flue gas pressure sensor, the flue gas humidity sensor, and the flue gas temperature sensor are all connected to the input terminal of the detection controller. The flue gas volume flow rate detection sensor includes: a first pressure sensor, a second pressure sensor, a first signal processing circuit, a second signal processing circuit, and a subtraction processing circuit. The first pressure sensor is used to test the first pressure in the flue gas emission pipe under test, and the second pressure sensor is used to test the second pressure in the flue gas emission pipe under test. One of the first pressure and the second pressure is the total pressure, and the other is the static pressure. The output terminal of the first pressure sensor is connected to the input terminal of the first signal processing circuit, which amplifies the first pressure to obtain a first amplified pressure signal. The output terminal of the second pressure sensor is connected to the input terminal of the second signal processing circuit, which amplifies the second pressure to obtain a second amplified pressure signal. The output terminal of the first signal processing circuit is connected to the in-phase input terminal of the subtraction processing circuit, and the output terminal of the second signal processing circuit is connected to the inverting input terminal of the subtraction processing circuit. The subtraction processing circuit subtracts the first amplified pressure signal from the second amplified pressure signal to obtain a first differential pressure signal.

[0007] Preferably, the output of the first signal processing circuit is connected to the non-inverting input of the subtraction processing circuit via the first switch switching unit, and the output of the second signal processing circuit is connected to the inverting input of the subtraction processing circuit via the second switch switching unit. The first switch switching unit and the second switch switching unit belong to a master control switch. The master control switch is powered by a power supply circuit through a switch power supply circuit. The control terminal of the switch power supply circuit is connected to the output of a switching control circuit. The non-inverting input of the switching control circuit is connected to the output of the first signal processing circuit, and the inverting input of the switching control circuit is connected to the output of the second signal processing circuit. The switching control circuit is used to control whether the switch power supply circuit is turned on according to the magnitude of the first amplified air pressure signal and the second amplified air pressure signal.

[0008] Preferably, the switching control circuit includes: a subtraction processing unit, a current-limiting voltage input unit, a comparison unit, and a reference voltage supply unit. The non-inverting input terminal of the subtraction processing unit is the non-inverting input terminal of the switching control circuit, the inverting input terminal of the subtraction processing unit is the inverting input terminal of the switching control circuit, the output terminal of the subtraction processing unit is connected to the input terminal of the current-limiting voltage input unit, the output terminal of the current-limiting voltage input unit is connected to the inverting input terminal of the comparison unit, the reference voltage supply unit is powered by the power supply circuit, the output terminal of the reference voltage supply unit is connected to the non-inverting input terminal of the comparison unit, and the output terminal of the comparison unit is the output terminal of the switching control circuit.

[0009] Preferably, the current-limiting voltage access unit includes: a resistor R18 and a diode D2, the anode of the diode D2 is the input terminal of the current-limiting voltage access unit, the cathode of the diode D2 is the output terminal of the current-limiting voltage access unit, and the cathode of the diode D2 is grounded through the resistor R18.

[0010] Preferably, the flue gas carbon dioxide concentration detection sensor includes: an infrared emitter, an infrared receiver, a first amplification circuit, and a second amplification circuit. The infrared emitter emits infrared rays into the flue gas emission pipe to be tested. An infrared receiver is arranged opposite to the infrared emitter. The output terminal of the infrared receiver is connected to the input terminal of the first amplification circuit. The output terminal of the first amplification circuit is connected to the input terminal of the second amplification circuit. The output terminal of the second amplification circuit is the output terminal of the flue gas carbon dioxide concentration detection sensor.

[0011] Preferably, the output of the power supply circuit supplies power to the anode of the infrared transmitter and grounds the cathode of the infrared transmitter. The output of the power supply circuit supplies power to the positive terminal of the infrared receiver and grounds the negative terminal of the infrared receiver. The negative terminal of the infrared receiver is grounded through the load, and the negative terminal of the infrared receiver is the output terminal of the infrared receiver.

[0012] Preferably, the amplification ratio of the first signal processing circuit is equal to that of the second signal processing circuit.

[0013] Compared with the prior art, the present invention has the following beneficial effects: In this application, firstly, the first air pressure and the second air pressure are amplified by the same first signal processing circuit and second signal processing circuit respectively. One of the first air pressure and the second air pressure is the total pressure (when the total pressure is detected: the Pitot tube is installed in the flue gas emission pipe to be tested, and the direction of the Pitot tube connecting to the gas is parallel to the direction of gas flow in the flue gas emission pipe to be tested), and the other is the static pressure (when the total pressure is detected: the direction of the Pitot tube connecting to the gas is perpendicular to the direction of gas flow in the flue gas emission pipe to be tested). Then, in order to reduce the influence of interference signals such as power frequency on the first air pressure and the second air pressure, a subtraction processing circuit is added to the flue gas volume flow detection sensor. The subtraction processing circuit subtracts the amplified first air pressure signal from the second amplified air pressure signal, removes the common interference signal added to both the first amplified air pressure signal and the second amplified air pressure signal, thereby obtaining the first pressure difference signal. Based on the first pressure difference signal... The pressure difference is obtained, and the flue gas volumetric flow rate is then calculated using Bernoulli's formula (this principle is based on the measurement of flue gas volumetric flow rate using a differential pressure Pitot tube, which is existing technology; this calculation method is implemented in the detection controller program). Furthermore, to ensure that the first differential pressure signal output by the subtraction processing circuit is a positive voltage value, and to avoid the need to check the installation positions of the first and second pressure sensors before installation, a master control switch with a first and a second switching section is designed. This master control switch operates under the control of the switch power supply circuit and the switching control circuit. The switching control circuit automatically controls the switch power supply circuit based on the outputs of the first and second signal processing circuits, thereby automatically ensuring that the larger of the first and second amplified pressure signals is connected to the non-inverting input of the subtraction processing circuit, and the smaller of the first and second amplified pressure signals is connected to the inverting input, thus guaranteeing that the subtraction processing circuit outputs a positive voltage. Throughout the circuit, there is no need for manual identification of the installation positions of the first and second pressure sensors, simplifying the installation process, improving installation efficiency, and ensuring that: the non-inverting input of the subtraction processing circuit is connected to the larger of the first and second amplified pressure signals, and the inverting input of the subtraction processing circuit is connected to the smaller of the first and second amplified pressure signals.

[0014] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0015] Figure 1 The circuit block diagram is for a direct-powered multi-functional flue gas emission detection circuit.

[0016] Figure 2 This is a circuit diagram of the first signal processing circuit in the flue gas volume flow rate detection sensor.

[0017] Figure 3 This is a circuit diagram of the switching control circuit and the subtraction processing circuit in the flue gas volume flow detection sensor.

[0018] Figure 4 This is a circuit block diagram of a flue gas carbon dioxide concentration detection sensor. Detailed Implementation

[0019] To make the technical means, creative features, objectives, and effects of this invention clearer and easier to understand, the invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0020] like Figure 1 As shown, this invention discloses a direct-powered multifunctional flue gas emission detection circuit, comprising: a flue gas volume flow rate sensor, a flue gas carbon dioxide concentration sensor, a flue gas pressure sensor, a flue gas humidity sensor, a flue gas temperature sensor, a detection controller, and a power supply circuit. The power supply circuit provides power to the flue gas volume flow rate sensor, the flue gas carbon dioxide concentration sensor, the flue gas pressure sensor, the flue gas humidity sensor, the flue gas temperature sensor, and the detection controller. The output terminals of the flue gas volume flow rate sensor, the flue gas pressure sensor, the flue gas humidity sensor, and the flue gas temperature sensor are all connected to the input terminal of the detection controller.

[0021] like Figure 2 as well as Figure 3As shown, the flue gas volume flow rate detection sensor includes: a first pressure sensor, a second pressure sensor, a first signal processing circuit, a second signal processing circuit, and a subtraction processing circuit. The first pressure sensor is used to test the first pressure in the flue gas emission pipe under test, and the second pressure sensor is used to test the second pressure in the flue gas emission pipe under test. One of the first pressure and the second pressure is the total pressure, and the other is the static pressure. The output terminal of the first pressure sensor is connected to the input terminal of the first signal processing circuit, which amplifies the first pressure to obtain a first amplified pressure signal. The output terminal of the second pressure sensor is connected to the input terminal of the second signal processing circuit, which amplifies the second pressure to obtain a second amplified pressure signal. The output terminal of the first signal processing circuit is connected to the in-phase input terminal of the subtraction processing circuit, and the output terminal of the second signal processing circuit is connected to the inverting input terminal of the subtraction processing circuit. The subtraction processing circuit subtracts the first amplified pressure signal from the second amplified pressure signal to obtain a first differential pressure signal. The subtraction processing circuit is used to subtract the first amplified air pressure signal and the second amplified air pressure signal. During the subtraction, the common interference signal in the first amplified air pressure signal and the second amplified air pressure signal is subtracted, avoiding the need for the program to remove the common interference signal, improving the accuracy of the first pressure difference signal, thereby improving the accuracy of the flue gas volume flow rate, and also improving the accuracy of the final carbon emission rate.

[0022] Both the first and second signal processing circuits include: capacitor C1, resistors R1, R2, R3, R4, R5, R6, and R7, a sliding resistor RV1, amplifier U1:A, and amplifier U1:B. The positive terminal of capacitor C1 is connected to the positive output terminal of either the first or second pressure sensor. The negative terminal of capacitor C1 is connected to the first terminals of resistors R1 and R3. The second terminal of resistor R1 is connected to the first terminal of resistor R4 and the non-inverting input terminal of amplifier U1:A. The second terminals of resistors R3 and R4 are grounded. The inverting input terminal of amplifier U1:A is connected to the first terminal of resistor R2, and the second terminal of resistor R2 is connected to the first pressure sensor. The negative output terminal of either the pressure sensor or the second pressure sensor is connected to the negative output terminal of amplifier U1:A. The inverting input terminal of amplifier U1:A is connected to the first terminal of resistor R5. The output terminal of amplifier U1:A is connected to the first terminals of resistors R5 and R6. The second terminal of resistor R6 is connected to the non-inverting input terminal of amplifier U1:B. The inverting input terminal of amplifier U1:B is connected to the sliding terminal and the first stationary terminal of sliding resistor RV1. The second stationary terminal of sliding resistor RV1 is grounded. The first stationary terminal of sliding resistor RV1 is connected to the first terminal of resistor R7. The output terminal of amplifier U1:B is connected to the second terminal of resistor R7. The output terminal of amplifier U1:B is the output terminal of either the first or second signal processing circuit. Capacitor C1, resistors R1, R2, R3, and R4 are all for voltage regulation. Amplifiers U1:A and U1:B can use the LM324 amplifier chip, or other amplifier chips.

[0023] In this application, the output terminal of the first signal processing circuit is connected to the non-inverting input terminal of the subtraction processing circuit through the first switch switching unit, and the output terminal of the second signal processing circuit is connected to the inverting input terminal of the subtraction processing circuit through the second switch switching unit. The first switch switching unit and the second switch switching unit belong to a master control switch. The master control switch is powered by a power supply circuit through a switch power supply circuit. The control terminal of the switch power supply circuit is connected to the output terminal of a switching control circuit. The non-inverting input terminal of the switching control circuit is connected to the output terminal of the first signal processing circuit, and the inverting input terminal of the switching control circuit is connected to the output terminal of the second signal processing circuit. The switching control circuit is used to control whether the switch power supply circuit is turned on according to the magnitude of the first amplified air pressure signal and the second amplified air pressure signal.

[0024] The switching control circuit includes: a subtraction processing unit, a current-limiting voltage input unit, a comparison unit, and a reference voltage supply unit. The non-inverting input of the subtraction processing unit is the non-inverting input of the switching control circuit, and the inverting input of the subtraction processing unit is the inverting input of the switching control circuit. The output of the subtraction processing unit is connected to the input of the current-limiting voltage input unit, and the output of the current-limiting voltage input unit is connected to the inverting input of the comparison unit. The reference voltage supply unit is powered by the power supply circuit, and its output is connected to the non-inverting input of the comparison unit. The output of the comparison unit is the output of the switching control circuit.

[0025] When the first pressure sensor detects the total pressure (the second pressure sensor detects the static pressure), the first pressure output by the first pressure sensor is greater than the second pressure output by the second sensor. The subtraction processing unit outputs a positive pressure value. At this time, the current-limiting voltage input unit is turned on, and the current-limiting voltage input unit has a higher voltage output. The voltage connected to the inverting input terminal of the comparison unit is greater than the voltage connected to the non-inverting input terminal of the comparison unit. At this time, the comparison unit outputs a low level, and the switch power supply circuit is not connected. At this time, both the first and second switch switching parts in the main control switch remain in the unpowered state. At this time, the non-inverting input terminal of the subtraction processing circuit is connected to the first signal processing circuit, and the inverting input terminal of the subtraction processing circuit is connected to the second signal processing circuit. At this time, the first differential pressure signal output by the subtraction processing circuit is a positive pressure value. When the first pressure sensor detects static pressure (the second pressure sensor detects total pressure), the first pressure output by the first pressure sensor is less than the second pressure output by the second sensor. The subtraction processing unit outputs a negative pressure value. At this time, the current-limiting voltage input unit is not conducting, and the current-limiting voltage input unit outputs a smaller voltage. The voltage at the inverting input terminal of the comparison unit is smaller than the voltage at the non-inverting input terminal of the comparison unit. At this time, the comparison unit outputs a high level, and the switch power supply circuit is closed. At this time, both the first and second switch switching parts in the main control switch remain in the energized state. The circuit switches to the inverting input terminal of the subtraction processing circuit connected to the first signal processing circuit, and the non-inverting input terminal of the subtraction processing circuit connected to the second signal processing circuit. At this time, the first differential pressure signal output by the subtraction processing circuit is still a positive pressure value.

[0026] The main control switch is a relay RL1 with a first switch switching section SW1 and a second switch switching section SW2. Both the first switch switching section SW1 and the second switch switching section SW2 are single-pole double-throw switches. The stationary terminal of the first switch switching unit SW1 is connected to the non-inverting input terminal of the subtraction processing circuit. The normally closed terminal of the first switch switching unit SW1 (when the coil of the main control switch is not energized, the stationary terminal and the normally closed terminal of the first switch switching unit SW1 are closed) is connected to the output terminal of the first signal processing circuit. The normally open terminal of the first switch switching unit SW1 (when the coil of the main control switch is energized, the stationary terminal and the normally open terminal of the first switch switching unit SW1 are closed) is connected to the output terminal of the second signal processing circuit. The stationary terminal of the second switch switching unit SW2 is connected to the inverting input terminal of the subtraction processing circuit. The normally closed terminal of the second switch switching unit SW2 (when the coil of the main control switch is not energized, the stationary terminal and the normally closed terminal of the second switch switching unit SW2 are closed) is connected to the output terminal of the second signal processing circuit. The normally open terminal of the second switch switching unit SW2 (when the coil of the main control switch is energized, the stationary terminal and the normally open terminal of the second switch switching unit SW2 are closed) is connected to the output terminal of the first signal processing circuit.

[0027] The switching power supply circuit includes: diode D1 and NPN transistor Q1. The anode of diode D1 is connected to the output terminal of the power supply circuit, the cathode of diode D1 is connected to the collector of NPN transistor Q1, the emitter of NPN transistor Q1 is grounded, and the base of NPN transistor Q1 is the control terminal of the switching power supply circuit.

[0028] Both the subtraction processing circuit and the subtraction processing unit include: resistor R10, resistor R11, capacitor C2, and differential chip U2. The first terminal of resistor R10 is either the non-inverting input of the subtraction processing circuit or the non-inverting input of the subtraction processing unit. The first terminal of resistor R11 is either the inverting input of the subtraction processing circuit or the inverting input of the subtraction processing unit. The second terminal of resistor R10 is connected to the non-inverting input of differential chip U2, the second terminal of resistor R11 is connected to the inverting input of differential chip U2, the second terminal of resistor R10 is connected to the positive terminal of capacitor C2, and the second terminal of resistor R11 is connected to the negative terminal of capacitor C2. The function of resistors R10, R11, and capacitor C2 is voltage regulation. Differential chip U2 can be an AD626 model differential chip, but other models can also be used.

[0029] In this application, the current-limiting voltage input unit includes a resistor R18 and a diode D2. The anode of diode D2 is the input terminal of the current-limiting voltage input unit, and the cathode of diode D2 is the output terminal of the current-limiting voltage input unit. The cathode of diode D2 is grounded through resistor R18. When the subtraction processing unit outputs a negative voltage value, no current flows through diode D2, and there is no voltage at the cathode of diode D2. When the subtraction processing unit outputs a positive voltage value, current flows through diode D2, and there is voltage at the cathode of diode D2.

[0030] The comparison unit includes: comparator U3, the non-inverting input of comparator U3 is the non-inverting input of the comparison unit, the inverting input of comparator U3 is the inverting output of the comparison unit, and the output of comparator U3 is the output of the comparison unit.

[0031] The reference voltage providing unit includes resistors R8 and R9. The output terminal of the power supply circuit is connected to the first terminal of resistor R8, and the second terminal of resistor R8 is grounded through resistor R9. Resistor R8 is the output terminal of the reference voltage providing unit. After voltage division by resistors R8 and R9, a reference voltage output is formed.

[0032] like Figure 4 As shown, the flue gas carbon dioxide concentration detection sensor includes: an infrared emitter, an infrared receiver, a first amplification circuit, and a second amplification circuit. The infrared emitter emits infrared rays into the flue gas emission pipe to be tested. An infrared receiver is arranged opposite to the infrared emitter. The output terminal of the infrared receiver is connected to the input terminal of the first amplification circuit. The output terminal of the first amplification circuit is connected to the input terminal of the second amplification circuit. The output terminal of the second amplification circuit is the output terminal of the flue gas carbon dioxide concentration detection sensor.

[0033] The power supply circuit output provides power to the anode of the infrared transmitter and grounds the cathode. The power supply circuit output also provides power to the positive terminal of the infrared receiver and grounds the negative terminal. The negative terminal of the infrared receiver is grounded through load R13, and the negative terminal of the infrared receiver is the output terminal of the infrared receiver.

[0034] Both the infrared emitter and receiver are located in a silicon controlled rectifier (SCR) optocoupler. In the SCR optocoupler, the light-emitting diode (LED) acts as the infrared emitter, with its anode and cathode serving as the infrared emitter's anode and cathode, respectively. In the SCR optocoupler, the thyristor acts as the infrared receiver, with its positive terminal being the positive electrode and its negative terminal being the negative electrode. Because different carbon dioxide concentrations result in varying intensities of infrared radiation reaching the receiver, changes in infrared intensity are detected by measuring these changes in intensity.

[0035] The amplification ratio of the first signal processing circuit is equal to that of the second signal processing circuit. This ensures that the first and second air pressures are amplified proportionally.

[0036] The basic principle of the carbon emission velocity line monitoring method in flue gas emissions studied is to monitor parameters such as CO2 concentration, flue gas velocity, temperature, and pressure at the tail end of the flue. The total carbon emission rate is calculated using these parameters from the tail end of the flue gas emission pipe under test. The formula for calculating the carbon emission rate is as follows:

[0037]

[0038] In the above formula: M is the carbon emission rate, and the unit of M is kg / h; P ct For flue gas pressure, P ct The units are Pa; V s M represents the flue gas volumetric flow rate, with Nm³ as the unit. 3 / h; w is the unit of flue gas humidity, in %; R is the standard molar gas constant, R equals 8.314 J / (mol·K); T is the flue gas temperature, in K; This represents the volume fraction of CO2 in the flue gas. The unit is %. Among them, the two most critical parameters are and V s .

[0039] V s The flue gas volumetric flow rate is obtained using Bernoulli's formula based on the first pressure difference signal. The flue gas carbon dioxide concentration sensor detects the carbon dioxide concentration, and then the CO2 volume fraction in the flue gas is calculated based on this concentration. .

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A direct powered flue gas emission multi-functional detection circuit, characterized in that, The flue gas volume flow detection sensor, the flue gas carbon dioxide concentration detection sensor, the flue gas pressure detection sensor, the flue gas humidity sensor, the flue gas temperature sensor and the detection controller are powered by the power supply circuit. The flue gas volume flow detection sensor output end, the flue gas pressure detection sensor output end, the flue gas humidity sensor output end and the flue gas temperature sensor output end are all connected to the detection controller input end. The flue gas volume flow detection sensor includes a first air pressure sensor, a second air pressure sensor, a first signal processing circuit, a second signal processing circuit and a subtraction processing circuit. The first air pressure sensor is used to test the first air pressure in the flue gas discharge pipe to be tested, and the second air pressure sensor is used to test the second air pressure in the flue gas discharge pipe to be tested. One of the first air pressure and the second air pressure is total pressure, and the other is static pressure. The output end of the first air pressure sensor is connected to the input end of the first signal processing circuit. The first signal processing circuit is used to amplify and process the first air pressure to obtain a first amplified air pressure signal. The output end of the second air pressure sensor is connected to the input end of the second signal processing circuit. The second signal processing circuit is used to amplify and process the second air pressure to obtain a second amplified air pressure signal. The output end of the first signal processing circuit is connected to the same-phase input end of the subtraction processing circuit, and the output end of the second signal processing circuit is connected to the opposite-phase input end of the subtraction processing circuit. The subtraction processing circuit is used to subtract the first amplified air pressure signal from the second amplified air pressure signal to obtain a first pressure difference signal. The output end of the first signal processing circuit is connected to the same-phase input end of the subtraction processing circuit through a first switch switching part, and the output end of the second signal processing circuit is connected to the opposite-phase input end of the subtraction processing circuit through a second switch switching part. The first switch switching part and the second switch switching part belong to a total control type switch. The total control type switch is powered by a switch power supply circuit of the power supply circuit. The control end of the switch power supply circuit is connected to the output end of the switching control circuit. The same-phase input end of the switching control circuit is connected to the output end of the first signal processing circuit, and the opposite-phase input end of the switching control circuit is connected to the output end of the second signal processing circuit. The switching control circuit is used to control whether the switch power supply circuit is turned on according to the size of the first amplified air pressure signal and the second amplified air pressure signal. The switching control circuit includes a subtraction processing unit, a current-limiting voltage access unit, a comparison unit and a reference voltage providing unit. The same-phase input end of the subtraction processing unit is the same-phase input end of the switching control circuit, and the opposite-phase input end of the subtraction processing unit is the opposite-phase input end of the switching control circuit. The output end of the subtraction processing unit is connected to the input end of the current-limiting voltage access unit. The output end of the current-limiting voltage access unit is connected to the opposite-phase input end of the comparison unit. The reference voltage providing unit is powered by the power supply circuit. The output end of the reference voltage providing unit is connected to the same-phase input end of the comparison unit. The output end of the comparison unit is the output end of the switching control circuit. ​ 2. The direct powered flue gas emission multi-functional detection circuit according to claim 1, characterized in that, The current-limiting voltage access unit comprises a resistor R18 and a diode D2, the anode of the diode D2 is the input end of the current-limiting voltage access unit, the cathode of the diode D2 is the output end of the current-limiting voltage access unit, and the cathode of the diode D2 is grounded through the resistor R18.

3. The direct powered flue gas emission multi-functional detection circuit according to claim 1 or 2, characterized in that, The flue gas carbon dioxide concentration detection sensor comprises an infrared emitter, an infrared receiver, a first amplification circuit and a second amplification circuit, the infrared emitter is used for emitting infrared rays in the flue gas discharge pipe to be tested, the infrared receiver is arranged opposite to the infrared emitter, the output end of the infrared receiver is connected to the input end of the first amplification circuit, the output end of the first amplification circuit is connected to the input end of the second amplification circuit, and the output end of the second amplification circuit is the output end of the flue gas carbon dioxide concentration detection sensor.

4. The direct powered flue gas emission multi-functional detection circuit according to claim 3, characterized in that, The output end of the power supply circuit is used for supplying power to the anode of the infrared emitter, the cathode of the infrared emitter is grounded, the output end of the power supply circuit is used for supplying power to the positive electrode of the infrared receiver, the negative electrode of the infrared receiver is grounded, the negative electrode of the infrared receiver is grounded through a load, and the negative electrode of the infrared receiver is the output end of the infrared receiver.

5. The direct powered flue gas emission multi-functional detection circuit according to claim 4, wherein, The amplification ratio of the first signal processing circuit is equal to the amplification ratio of the second signal processing circuit.

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