A high-precision and high-resolution DNIR carbon dioxide sensor

Abstract

The application relates to the technical field of carbon dioxide sensors, in particular to a high-precision and high-resolution DNIR carbon dioxide sensor, which comprises a pyroelectric sensor, a direct-current isolation first-stage amplification integration circuit, a second-stage amplification band-pass filter circuit, a differential input 24-bit A / D sampling circuit, a data processor and an upper computer. A pure alternating-current sine wave signal to direct-current signal circuit, a direct-current signal generation circuit with temperature compensation, a differential amplification circuit and a full-differential output amplification circuit are arranged between the second-stage amplification band-pass filter circuit and the differential input 24-bit A / D sampling circuit, the output range of the sine wave is doubled through the improvement of the second-stage amplification band-pass filter circuit, and the common-mode interference can be inhibited and the resolution of the sensor can be further improved through the adoption of the differential input 24-bit A / D sampling circuit. The problems that the resolution and precision of the single-wavelength and single-beam DNIR carbon dioxide sensor for detecting the carbon dioxide concentration are not high in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide sensor technology, specifically to a high-precision and high-resolution DNIR carbon dioxide sensor. Background Technology

[0002] A non-dispersive (DNIR) carbon dioxide sensor, hereinafter referred to as "DNIR_CO2", is used to detect the concentration of carbon dioxide gas in the air of people's working or living environments, or the carbon dioxide content in the exhaled breath of patients undergoing rehabilitation. The acquired data is transmitted to a central processing unit for analysis, allowing control centers or medical personnel to take appropriate action. It can be divided into several types based on differences in the sensing element and structure. This invention only relates to improvements in the circuitry of a single-wavelength, single-beam DNIR_CO2 sensor. Therefore, the following description focuses only on the circuitry of a single-wavelength, single-beam DNIR_CO2 sensor.

[0003] Figure 1 This is a schematic block diagram illustrating the basic principle of existing single-wavelength, single-beam DNIR_CO2 technology. Its basic principle utilizes the selective absorption of infrared radiation at a specific wavelength (4.26µm) by carbon dioxide gas. The concentration of carbon dioxide is determined by the intensity of the infrared energy received by the infrared-sensitive element (pyroelectric). The lower the carbon dioxide concentration, the larger the amplitude of the output signal, and vice versa. The output amplitude is maximum when the carbon dioxide concentration is zero. Because this pyroelectric sensor is highly sensitive to temperature, if a DC signal is used to directly drive the light source, the received signal, after amplification, will easily drift outside the amplifier's linear region due to temperature drift, resulting in an inaccurate signal. Furthermore, since this temperature drift frequency is very low, typically less than 1Hz, a 5V pulse with a 30ms period and a 1 / 4 duty cycle is used to drive the light source. Figure 2This is a block diagram and partial circuit diagram of the signal processing part related to this invention, using a foreign single-wavelength, single-beam DNIR_CO2. It uses +5V, GND, and -5V to power the active bandpass filter circuit. The pyroelectric inductor output signal, after being processed by the first stage of DC blocking, filtering, and amplification, and then by the second stage of active bandpass filtering and amplification, becomes a pulsating sine wave signal with a period of 30ms and a zero-crossing point of 2.048V, almost unaffected by temperature drift. Because the subsequent stage uses a single-ended input 16-bit A / D sampling circuit to directly sample this sine wave signal, the output is not a pure sine wave signal with a zero-crossing point of 0V. To determine the signal strength, the peak values ​​of the positive and negative half-cycles of the sine wave must be sampled, but this type of A / D chip cannot sample negative voltage signals. Therefore, both the positive and negative peak values ​​of the sine wave must be adjusted to above 0V. The obtained data is then sent to the MCU control unit (according to the Lambert-Beer law algorithm) for processing, and then transmitted to the host computer via the communication port. Other auxiliary circuits (such as temperature control circuits, light source drivers, MCUs, etc.) are not included in the scope of this invention and will not be described here.

[0004] The analysis of the existing circuit technology above reveals three reasons for its low resolution of carbon dioxide concentration.

[0005] 1. With a constant power supply of ±5V, when the carbon dioxide concentration is zero (the minimum, equivalent to 0 calibration), infrared light is not absorbed at all, and the pyroelectric sensor receives the strongest signal. Therefore, its output signal amplitude is also the largest. At this point, the signal is transmitted to the active bandpass filter and amplifier circuit. The amplifier gain is adjusted to maximize the output amplitude without entering the nonlinear region. This is the limit of signal gain in existing technology. If carbon dioxide gas of a certain concentration and pressure is introduced into the gas chamber, some infrared light is absorbed, and the pyroelectric sensor's output signal weakens accordingly. If the carbon dioxide concentration increases, the output signal amplitude decreases, and vice versa, but it will not exceed the amplitude of zero-concentration gas. Therefore, the gain of the bandpass filter is limited by the zero-concentration gas concentration and cannot be further increased.

[0006] Second, because the zero-crossing point of the bandpass filter output signal in the existing technology is not at 0V but at 2.048V, the amplification range of the amplifier can only be within the range of 0V to +5V, rather than the entire range of -5V to +5V. Its amplification range is only half of the power supply range.

[0007] Third, in existing technologies, a single-ended input 16-bit A / D sampling chip is used. Firstly, the single-ended input cannot suppress common-mode interference from the power supply, resulting in a decrease in sampling resolution. Secondly, the effective resolution of the 16-bit A / D chip is only 13-14 bits, which is also a reason for the low resolution.

[0008] Based on this, the present invention designs a high-precision and high-resolution DNIR carbon dioxide sensor to solve the above problems. Summary of the Invention

[0009] The purpose of this invention is to provide a high-precision and high-resolution DNIR carbon dioxide sensor to solve the problem of low resolution and accuracy of single-wavelength, single-beam DNIR carbon dioxide sensors in the prior art as mentioned in the background section.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a high-precision and high-resolution DNIR carbon dioxide sensor, comprising a pyroelectric sensor, a DC blocking first-stage amplification and integration circuit, a second-stage amplification and bandpass filter circuit M1, a differential input 24-bit A / D sampling circuit M2, a data processor, and a host computer;

[0011] Between the secondary amplification bandpass filter circuit M1 and the differential input 24-bit A / D sampling circuit M2, there are respectively a pure AC sine wave signal to DC signal conversion circuit MZ1, a temperature-compensated DC signal generation circuit MZ2, a differential amplifier circuit MZ3, and a fully differential output amplifier circuit MZ4.

[0012] The pyroelectric sensor is used to collect carbon dioxide concentration voltage signals and input the collected carbon dioxide concentration voltage signals into a DC blocking first-stage amplification and integration circuit.

[0013] The DC blocking first-stage amplifier and integrator circuit converts the received carbon dioxide concentration voltage signal into a deformed pulse signal, and inputs the deformed pulse signal into the second-stage amplifier and bandpass filter circuit M1.

[0014] The secondary amplification bandpass filter circuit M1 converts the deformed pulse signal into a pure AC sine wave signal, and inputs the pure AC sine wave signal into the -IN terminal of the differential amplifier circuit MZ3.

[0015] The temperature-compensated DC signal generation circuit MZ2 uses the control of the data processor to output a DC signal, and inputs the DC signal to the +IN terminal of the differential amplifier circuit MZ3.

[0016] The differential amplifier circuit MZ3 differentially amplifies the two received DC signals and inputs the amplified DC signals to the -I terminal of the fully differential output amplifier circuit MZ4.

[0017] The fully differential output amplifier circuit MZ4 converts the received amplified DC signal into two DC signals with opposite phases. The in-phase signal is input to the -AIN terminal of the differential input 24-bit A / D sampling circuit M2, and the inverted signal is input to the +AIN terminal of the differential input 24-bit A / D sampling circuit M2.

[0018] The differential input 24-bit A / D sampling circuit M2 converts the received signal into a digital signal and communicates the digital signal with the data processor through the SPI1 port. The data processor performs calculations according to the Beer-Lambert theorem and converts the signal into a digital quantity that corresponds exactly to the concentration of the carbon dioxide sensor, which is then transmitted to the host computer through the communication port.

[0019] Preferably, the second-stage amplification bandpass filter circuit M1 includes an operational amplifier U401A. Pin 6 of the operational amplifier U401A is connected to the output of the DC blocking first-stage amplification and integration circuit to receive the distorted pulse signal from the DC blocking first-stage amplification and integration circuit. A resistor R410 and a capacitor C408 are connected in series between pin 6 of the operational amplifier U401A and the DC blocking first-stage amplification and integration circuit. A resistor R411 is connected in series between the resistor R410 and the capacitor C408, and one end of the resistor R411 is connected to AGND. Pin 5 of operational amplifier U401A is directly connected to AGND, and a capacitor C407 is connected in parallel between pins 5 and 6 of operational amplifier U401A; a resistor R412 is connected in parallel between pins 6 and 7 of operational amplifier U401A; a capacitor C409 is connected in parallel between pin 7 of operational amplifier U401A and capacitor C408; pin 7 of operational amplifier U401A is connected to the pure AC sine wave signal to DC signal conversion circuit MZ1, which uses operational amplifier U401A to convert the input deformed pulse into a pure AC sine wave signal with a zero crossing point of 0V.

[0020] Preferably, the pure AC sine wave signal to DC signal conversion circuit MZ1 includes an operational amplifier U402, and pin 8 of operational amplifier U402 is connected to pin 7 of operational amplifier U401A to receive the pure AC sine wave signal from the two-stage amplification bandpass filter circuit M1; a resistor R413 is connected in series between pin 8 of operational amplifier U402 and pin 7 of operational amplifier U401A; pin 2 of operational amplifier U402 is connected to GND, and pin 1 is connected in series with a resistor R414, one end of which is connected to AGND; a capacitor C413 is connected in parallel between pin 1 and pin 4 of operational amplifier U402; pin 4 of operational amplifier U402 is connected in series with... A resistor R418 is connected in parallel with a resistor R416 between the other end of R418 and pin 1 of operational amplifier U402. A capacitor C415 is connected in series between R418 and R416, with one end of C415 connected to AGND. A capacitor C412 is connected in parallel between pins 8 and 5 of operational amplifier U402. A resistor R417 is connected in series with pin 5 of operational amplifier U402, and a resistor R415 is connected in parallel between the other end of R417 and pin 8 of operational amplifier U402. A capacitor C414 is connected in series between R417 and R415, with one end of C414 connected to AGND. Operational amplifier U40... Pin 3 of operational amplifier U402 is connected to a +5V power supply. The other end of the +5V power supply is connected to a capacitor C410, with one end of C410 connected to AGND. Pin 6 of operational amplifier U402 is connected to a -5V power supply. The other end of the -5V power supply is connected to a capacitor C411, with one end of C411 connected to AGND. A dual diode D401 is installed between resistors R417 and R418. Resistor R417 is connected to pin 1 of diode D401, and resistor R418 is connected to pin 2 of diode D401. A capacitor C416 is connected in parallel between pins 1 and 2 of diode D401. A capacitor C416 is connected to pin 3 of diode D401. Operational amplifier U403A is connected in series with resistors R420 and R421 between pin 3 of operational amplifier U403A and pin 3 of dual diode D401. Pin 3 of dual diode D401 is connected in series with resistor R420 with resistor R419 and capacitor C416 respectively. Resistor R419 is placed close to pin 3 of dual diode D401, and capacitor C416 is placed close to resistor R420. A capacitor C417 is connected in series between resistor R420 and resistor R421. A capacitor C418 is connected in series between resistor R421 and pin 3 of operational amplifier U403A. Resistors R419, capacitors C416, C417 and C418 are all connected to AGND.Pins 2 and 1 of operational amplifier U403A are directly connected. Operational amplifier U402 outputs two sinusoidal signals with opposite phases. These two sinusoidal signals are rectified by dual diodes D401 into pulsating DC signals. These signals are then filtered by a double π-type filter composed of resistors R419, R420, R421, and capacitors C416, C417, and C418, resulting in a smooth DC signal. This smoothed DC signal is then sent to operational amplifier U403A for impedance transformation to output the Ush DC signal.

[0021] Preferably, the temperature-compensated DC signal generation circuit MZ2 includes an operational amplifier U401B. Pin 5 of the operational amplifier U401B is connected to the data processor, and a resistor R422 is connected in series between pin 5 of the operational amplifier U401B and the data processor. A capacitor C421 is connected in series between the resistor R422 and pin 5 of the operational amplifier U401B, and one end of the capacitor C421 is connected to AGND. Pins 6 and 7 of the operational amplifier U401B are directly connected. Pin 8 of the operational amplifier U401B is connected to a +5V power supply, and the other end of the +5V power supply is connected to a capacitor C419, one end of which is connected to AGND. Pin 6 of the operational amplifier U401B is connected to a -5V power supply, and the other end of the -5V power supply is connected to a capacitor C420, one end of which is connected to AGND. The operational amplifier U401B performs impedance transformation on the signal from the data processor and outputs a DC signal Uz.

[0022] Preferably, the differential amplifier circuit MZ3 includes operational amplifier U403B, pin 5 of which is connected to pin 7 of operational amplifier U401B for receiving the Ush DC signal, and a resistor R423 is connected in series between pin 5 of operational amplifier U403B and pin 7 of operational amplifier U401B; pin 6 of operational amplifier U403B is connected to pin 1 of operational amplifier U403A for receiving the Uz DC signal, and a resistor R424 is connected in series between pin 6 of operational amplifier U403B and pin 1 of operational amplifier U403A; a resistor R425 is connected in series between pin 5 of operational amplifier U403B and resistor R423, and one end of resistor R425 is connected to AGND. A capacitor C421 is connected in parallel between the two ends of pin 5; a resistor R426 is connected in parallel between pins 6 and 7 of operational amplifier U403B, and a capacitor C422 is connected in parallel across the two ends of resistor R426; a +5V power supply is connected to pin 8 of operational amplifier U403B, and a capacitor C419 is connected to the other end of the +5V power supply, with one end of capacitor C419 connected to AGND; a -5V power supply is connected to pin 6 of operational amplifier U403B, and a capacitor C420 is connected to the other end of the -5V power supply, with one end of capacitor C420 connected to AGND. Operational amplifier U403B is used to perform a difference operation on the input Uz DC signal and Ush DC signal, and then amplifies and converts the difference signal into a Uco2 DC signal.

[0023] Preferably, the fully differential output amplifier circuit MZ4 includes an operational amplifier U405. Pin 1 of operational amplifier U405 is connected to pin 7 of operational amplifier U403B to receive the amplified DC signal. A resistor R428 is connected in series between pin 1 of operational amplifier U405 and pin 7 of operational amplifier U403B. A capacitor C426 is connected in parallel between pin 1 and pin 4 of operational amplifier U405. A resistor R432 is connected in series with pin 4 of operational amplifier U405, and the resistor R432 is positioned away from the capacitor C426. A resistor R430 is connected in parallel between the end of the resistor R432 away from pin 4 of operational amplifier U405 and pin 1 of operational amplifier U405. A capacitor C428 is connected in series between resistor R430 and resistor R432, and one end of the capacitor C428 is connected to AGND. An output bias circuit is connected to pin 2 of operational amplifier U405. A resistor R43 is connected in series with pin 5 of operational amplifier U405. 1. A resistor R427 is connected in series with pin 8 of operational amplifier U405, and one end of resistor R427 is connected to AGND; a capacitor C425 is connected in parallel between pins 5 and 8 of operational amplifier U405; a resistor R429 is connected in parallel between pin 8 of operational amplifier U405 and the end of resistor R431 furthest from operational amplifier U405; a capacitor C427 is connected in series between resistors R429 and R431; and the capacitor C427 is connected in parallel with operational amplifier U405. The capacitor C427 is connected to AGND. A capacitor C429 is connected in parallel between the ends of resistors R431 and R432 that are furthest from operational amplifier U405. The ends of resistors R431 and R432 that are furthest from operational amplifier U405 are connected to the differential input 24-bit A / D sampling circuit M2. Operational amplifier U405 converts the input Uco2 DC signal into a fully differential signal, and outputs AIN+ and AIN- signals through resistors R431 and R432 respectively.

[0024] Preferably, the output bias circuit includes an operational amplifier U404A. Pin 1 of operational amplifier U404A is connected to pin 2 of operational amplifier U405 to adjust the output AIN+ and AIN- signals of operational amplifier U405 to above 0V. A capacitor C430 is connected in series between pin 1 of operational amplifier U404A and pin 2 of operational amplifier U405, with one end of capacitor C430 connected to AGND. Pins 1 and 2 of operational amplifier U404A are directly connected. A capacitor C429 is connected in series between pin 3 of operational amplifier U404A, with one end of capacitor C429 grounded. The capacitor C429 is connected to the operational amplifier U404A. Resistors R433 and R434 are connected in series between pins 3 and 4 of operational amplifier A. One end of resistor R434 is connected to AGND, and one end of resistor R433 is connected to the differential input 24-bit A / D sampling circuit M2. Pin 3 of operational amplifier U405 and pin 8 of operational amplifier U404A are each connected to a +5V power supply, and the other end of the +5V power supply is connected to a capacitor C423, one end of which is connected to AGND. Pin 6 of operational amplifier U405 and pin 4 of operational amplifier U404A are both connected to a -5V power supply, the other end of which is connected to a capacitor C424, one end of which is connected to AGND.

[0025] Preferably, the differential input 24-bit A / D sampling circuit M2 includes a 24-bit A / D sampler U406. Pin 3 of the 24-bit A / D sampler U406 is connected to the end of resistor R431 away from operational amplifier U405, and is used to receive the AIN+ signal generated by operational amplifier U405. Pin 4 of the 24-bit A / D sampler U406 is connected to the end of resistor R432 away from operational amplifier U405, and is used to receive the AIN- signal generated by operational amplifier U405. Pin 5 of the 24-bit A / D sampler U406 is connected to the end of resistor R433 away from operational amplifier U404A. The 24-bit A / D sampler U406 converts the input AIN+ and AIN- signals into digital signals, and transmits them to the data processor through the SPI1 port.

[0026] Preferably, the data processor includes an MCU chip, which receives the digital signal from the 24-bit A / D sampling circuit, performs calculations according to the Beer-Lambert theorem, and converts it into a digital quantity that completely corresponds to the concentration of the carbon dioxide sensor. The digital quantity is then transmitted to the host computer through the communication port. The MCU chip also sends a DAC signal to the temperature-compensated DC signal generation circuit MZ2 and a VREF signal to the output bias circuit.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1) This invention doubles the output range of a sine wave by improving the two-stage amplification bandpass filter circuit;

[0029] 2) This invention improves the utilization rate of power supply space by adding a pure AC sine wave signal to DC signal circuit, a DC signal generation circuit with temperature compensation, a differential amplifier circuit, and a fully differential output amplifier circuit to form an "cancellation" circuit.

[0030] 3) By changing the 16-bit single-ended input to a differential input 24-bit A / D sampling circuit, this invention can suppress common-mode interference and further improve the resolution of the sensor;

[0031] Combining the above three points can improve the resolution of single-wavelength, single-beam DNIR carbon dioxide sensors by one to two orders of magnitude.

[0032] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A schematic block diagram illustrating the basic principle of existing single-wavelength, single-beam DNIR carbon dioxide sensors;

[0035] Figure 2 This document presents a block diagram and partial circuit diagram of the signal processing section of an existing single-wavelength, single-beam DNIR carbon dioxide sensor.

[0036] Figure 3 This is a block diagram and partial circuit diagram of the signal processing part of the improved single-wavelength, single-beam DNIR carbon dioxide sensor of the present invention;

[0037] Figure 4 This is a schematic diagram of the full-function block diagram of the improved single-wavelength, single-beam DNIR carbon dioxide sensor of the present invention.

[0038] Figure 5 This is a partial schematic diagram of the improved single-wavelength, single-beam DNIR carbon dioxide sensor of the present invention.

[0039] Figure 6 This is a schematic diagram of the specific circuit of the two-stage amplification bandpass filter circuit M1 of the present invention;

[0040] Figure 7 This is a schematic diagram of the MZ1 circuit for converting a pure AC sine wave signal to a DC signal, as described in this invention.

[0041] Figure 8 The schematic diagram of the temperature-compensated DC signal generation circuit MZ2 of this invention is shown below.

[0042] Figure 9 This is a schematic diagram of the differential amplifier circuit MZ3 of the present invention.

[0043] Figure 10 This is a schematic diagram of the MZ4 fully differential output amplifier circuit of the present invention.

[0044] Figure 11 This is a schematic diagram of the specific circuit of the differential input 24-bit A / D sampling circuit M2 of the present invention;

[0045] Figure 12 This is a schematic diagram of the data processor of the present invention. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] like Figure 2 The diagram shows the working principle circuit of an existing single-wavelength, single-beam DNIR carbon dioxide sensor, including a pyroelectric sensor, a DC blocking first-stage amplification and integration circuit, a second-stage amplification and bandpass filter circuit, a single-ended input 16-bit A / D sampling circuit, and a data processor and output circuit. This is to address the shortcomings of existing single-wavelength, single-beam DNIR carbon dioxide sensors in terms of low resolution and accuracy in detecting carbon dioxide concentration.

[0048] See Figure 2-3This invention provides a technical solution: a high-precision and high-resolution DNIR carbon dioxide sensor, comprising a pyroelectric sensor, a DC-blocking first-stage amplification and integration circuit, a second-stage amplification and bandpass filter circuit M1, a differential input 24-bit A / D sampling circuit M2, a data processor, and a host computer. The pyroelectric sensor collects the carbon dioxide concentration voltage signal and inputs the collected signal to the DC-blocking first-stage amplification and integration circuit. The DC-blocking first-stage amplification and integration circuit outputs a distorted pulse signal, which is then input to the second-stage amplification and bandpass filter circuit M1 (the circuit of the second-stage amplification and bandpass filter circuit M1 is the same as the existing second-stage amplification and bandpass filter circuit, except that the connection of pin 3 to the 2.048V reference voltage is modified to a direct connection to AGND). Figure 2 and Figure 3As can be seen from the comparison of the dashed boxes, the sine wave output range has been improved from approximately 0 to 3.5V (the linear region of the 5V power supply op-amp is <3.5V) to -3.5V to +3.5V. The gain can be increased to twice the previous value. Simultaneously, the secondary amplification bandpass filter circuit M1 converts the distorted pulse signal into a pure AC sine wave signal. Four new functional modules are added between the secondary amplification bandpass filter circuit M1 and the differential input 24-bit A / D sampling circuit M2: a pure AC sine wave signal to DC signal conversion circuit MZ1, a temperature-compensated DC signal generation circuit MZ2, a differential amplifier circuit MZ3, and a fully differential output amplifier circuit MZ4. Specifically, the pure AC sine wave signal to DC signal conversion circuit MZ1 receives the pure AC sine wave signal output from the secondary amplification bandpass filter circuit M1 and converts it into a DC signal, which is input to the -IN terminal of the differential amplifier circuit MZ3. The temperature-compensated DC signal generation circuit MZ2 generates a DC signal, which is also input to the +IN terminal of the differential amplifier circuit MZ3. The differential amplifier circuit MZ3 differentially amplifies the two received DC signals and inputs the amplified DC signal to the -I terminal of the fully differential output amplifier circuit MZ4. The MZ4 converts the received DC signal into two DC signals with opposite phases. The in-phase signal is input to the -AIN terminal of the differential input 24-bit A / D sampling circuit M2, and the inverted signal is input to the +AIN terminal of the differential input 24-bit A / D sampling circuit M2. The differential input 24-bit A / D sampling circuit M2 is a modification of the existing single-ended input 16-bit A / D sampling circuit. The differential input of the A / D sampling can suppress common-mode interference generated by the power supply. Furthermore, by using a 24-bit A / D sampling circuit, combined with improvements to the power supply circuit and reference voltage, the sampling resolution can be improved by at least one order of magnitude. This can improve the resolution of the single-wavelength, single-beam DNIR carbon dioxide sensor by one to two orders of magnitude. The differential input 24-bit A / D sampling circuit M2 converts the received signal into a digital signal and transmits the converted digital signal to the data processor through the SPI1 port. After the data processor performs calculations according to the Beer-Lambert theorem, it converts the signal into a digital quantity that corresponds exactly to the carbon dioxide concentration and transmits it to the host computer through the communication port.

[0049] Figure 4 and Figure 5 The figures show the full-function block diagram and partial schematic diagram of the improved DNIR carbon dioxide single-wavelength, single-beam sensor, respectively. Figure 4 and Figure 5 The portion within the dashed box is relevant to this invention. Since this invention only relates to improving the resolution and accuracy of carbon dioxide sensors, Figure 4 and Figure 5Only the relevant circuitry related to this invention is disclosed. Other parts are represented by block diagrams in the accompanying drawings for easier overall understanding of the carbon dioxide sensor's principle. Please refer to the attached diagram for details. Figure 4 and Figure 5 Amplification of the overall circuit and local circuits Figure 2 The circuit consists of a multi-stage amplifier bandpass filter circuit M1, a differential input 24-bit A / D sampling circuit M2, a pure AC sine wave signal to DC signal conversion circuit MZ1, a DC signal generation circuit with temperature compensation MZ2, a differential amplifier circuit MZ3, and a fully differential output amplifier circuit MZ4.

[0050] The basic principle of a carbon dioxide sensor has been briefly explained in the background section (see [link to background section]). Figure 1 The details will not be elaborated here. However, it must be emphasized that the improved circuitry of this invention can only function properly after these auxiliary circuits (such as the temperature control system, light source driver, etc.) are powered on and reach the set stable state. Otherwise, correct results will not be obtained.

[0051] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The ultimate goal of the present invention is to achieve a more refined measurement of target values ​​than in the prior art, utilizing limited power supply space. The following embodiments are illustrative of the invention, and the invention is by no means limited to these embodiments.

[0052] See Figures 4 to 10 The main body of this invention consists of two parts: a newly added circuit and an improved circuit. The newly added circuit includes: a pure AC sine wave signal to DC signal conversion circuit MZ1, a DC signal generation circuit with temperature compensation MZ2, a differential amplifier circuit MZ3, and a fully differential output amplifier circuit MZ4. The improved part includes: a two-stage amplification bandpass filter circuit M1 and a differential input 24-bit A / D sampling circuit M2.

[0053] like Figure 6The diagram shows the schematic of the two-stage bandpass filter circuit M1, including operational amplifier U401A. Pin 2 of operational amplifier U401A is connected to the output of the DC blocking first-stage amplifier-integrator circuit to receive the distorted pulse signal from this circuit. A 7.5K resistor R410 and a 100nF / 16V high-voltage ceramic capacitor C408 are connected in series between them. The common terminal of resistor R410 and capacitor C408 is connected to one end of a 27K resistor R411, and the other end of R411 is connected to AGND. Pin 3 of operational amplifier U401A is directly connected to AGND (improving the sine wave output range from approximately 0 to 3.5V (the linear region of a 5V powered op-amp is <3.5V) to -3.5V to +3.5V). A 100nF / 16V capacitor C407 is connected in parallel between pins 1 and 3. A 390K resistor R412 is connected in parallel between pins 2 and 2 of operational amplifier U401A. A 100nF / 16V high-voltage ceramic capacitor C409 is connected in parallel between pin 1 of operational amplifier U401A and capacitor C408. Pin 1 of operational amplifier U401A is connected to the pure AC sine wave signal to DC signal conversion circuit MZ1. When the distorted pulse signal from the DC blocking first-stage amplification and integration circuit is input to the second-stage amplification bandpass filter circuit M1, operational amplifier U401A is converted into a pure AC sine wave signal with a zero-crossing point of 0V. The amplitude of this sine wave signal reflects the voltage signal corresponding to the remaining light flux after part of the infrared light flux is absorbed by carbon dioxide. This signal is then sent to the "+" input terminal of the pure AC sine wave signal to DC signal conversion circuit.

[0054] like Figure 7The diagram shows the circuit schematic of the pure AC sine wave signal to DC signal conversion circuit MZ1. It includes operational amplifier U402. Pin 8 of operational amplifier U402 is connected to pin 1 of operational amplifier U401A in the two-stage amplification and bandpass filter circuit M1 via a 1K resistor R413. This connection is used to receive the pure AC sine wave signal from the two-stage amplification and bandpass filter circuit M1. Pin 2 of operational amplifier U402 is connected to GND, and pin 1 is connected to AGND via a 1K resistor R414. A 5.6nF / 16V capacitor C413 is connected between pins 1 and 4 of operational amplifier U402. A capacitor is connected in series with pin 4 of operational amplifier U402. Connect a resistor R418 in series, and connect a 2K resistor R416 in parallel between the other end of R418 and pin 1 of operational amplifier U402. Connect a 1nF / 16V capacitor C415 in series between R418 and R416, with one end of C415 connected to AGND. Connect a 5.6nF / 16V capacitor C412 in parallel between pins 8 and 5 of operational amplifier U402. Connect a resistor R417 in series with pin 5 of operational amplifier U402, and connect a 2K resistor R415 in parallel between the other end of R417 and pin 8 of operational amplifier U402. Connect a 1nF / 16V capacitor C41 in series between R417 and R415. 4. One end of capacitor C414 is connected to AGND. A +5V power supply is connected to pin 3 of operational amplifier U402, and the other end of the +5V power supply is connected to a 10uF / 16V capacitor C410. One end of capacitor C410 is connected to AGND. A -5V power supply is connected to pin 6 of operational amplifier U402, and the other end of the -5V power supply is connected to a 10uF / 16V capacitor C411. One end of capacitor C411 is connected to AGND. A dual diode D401 is installed between resistors R417 and R418. Resistor R417 is connected to pin 1 of the dual diode D401, and resistor R418 is connected to pin 2 of the dual diode D401. A 1nF / 16V capacitor C416 is connected in parallel between pins 1 and 2 of diode D401. An operational amplifier U403A is connected to pin 3 of the dual diode D401. Resistors R420 and R421, both 200K resistors, are connected in series between pin 3 of the operational amplifier U403A and pin 3 of the dual diode D401. A 100K resistor R419 and a 1uF / 16V capacitor C416 are connected in series between pin 3 of the dual diode D401 and resistor R420, with resistor R419 positioned close to pin 3 of the dual diode D401 and capacitor C416 positioned close to resistor R420. One end of resistor R416...One end of capacitor C415, one end of capacitor C416, and pin 2 of dual diode D401 share the same network node. One end of resistor R415, one end of resistor R417, and one end of capacitor C414 share the same network node. A 1uF / 16V capacitor C417 is connected in series between resistors R420 and R421. A 1uF / 16V capacitor C418 is connected in series between resistor R421 and pin 3 of operational amplifier U403A. Resistors R419, capacitors C416, C417, and C418 are all connected to AGND. Pins 2 and 1 of operational amplifier U403A are directly connected. The signal input to the bandpass filter circuit M1 is processed by operational amplifier U402, which outputs two sinusoidal signals with opposite phases. These two sinusoidal signals are rectified by dual diodes D401 into pulsating DC signals. After being filtered by a dual "π"-type filter composed of resistors (R419-R421) and capacitors (C416-C418), they become smooth DC signals. This DC signal is then sent to operational amplifier U403A for impedance transformation, outputting a Ush DC signal. This Ush DC signal is then input to differential amplifier circuit MZ3. This signal reflects the electrical signal quantity corresponding to the luminous flux remaining after the infrared radiation from the light source is absorbed by the carbon dioxide sensor.

[0055] like Figure 8 The diagram shown is a schematic of the temperature-compensated DC signal generation circuit MZ2, including operational amplifier U401B. Pin 5 of operational amplifier U401B is connected to the DAC signal terminal from the MCU (the MCU is located in the data processor, such as...). Figure 11 (As shown), a 10K resistor R422 is connected in series between the two. A 100nF / 16V capacitor C421 is connected in series between resistor R422 and pin 5 of operational amplifier U401B, with one end of capacitor C421 connected to AGND. Pins 6 and 7 of operational amplifier U401B are directly connected. A +5V power supply is connected to pin 8 of operational amplifier U401B, with the other end of the +5V power supply connected to a 10uF / 16V capacitor C419. One end of capacitor C419 is connected to AGND. A -5V power supply is connected to pin 6 of the operational amplifier U401B, and a 10uF / 16V capacitor C420 is connected to the other end of the -5V power supply. One end of capacitor C420 is connected to AGND. The temperature-compensated DAC signal from the MCU is impedance-transformed by the operational amplifier U401B to output a DC signal Uz. The output DC signal Uz is then input into the differential amplifier circuit MZ3. The maximum output value Ush = Uz is reached when the carbon dioxide concentration is zero (after being cleaned by nitrogen, i.e., not absorbed at all).

[0056] like Figure 9 The diagram shows the specific circuit schematic of the differential amplifier circuit MZ3, including operational amplifier U403B. Pin 5 of operational amplifier U403B is connected to pin 7 of operational amplifier U401B in the temperature-compensated DC signal generation circuit MZ2 to receive the Uz DC signal. A 10K resistor R423 is connected in series between them. Pin 6 of operational amplifier U403B is connected to pin 1 of operational amplifier U403A in the pure AC sine wave signal to DC signal conversion circuit MZ1 to receive the Ush DC signal. A 10K resistor R424 is connected in series between them. A 30K resistor R425 is connected in series between pin 5 of the 03B and resistor R423, with one end of resistor R425 connected to AGND. A 10nF / 16V capacitor C421 is connected in parallel between the two ends of resistor R425. A 30K resistor R426 is connected in parallel between pins 6 and 7 of the operational amplifier U403B, with a 10nF / 16V capacitor C422 connected in parallel between the two ends of resistor R426. Pin 8 of the U403B is connected to one end of a 10uF / 16V capacitor C423, and both are connected to the +5V power supply. The other end of capacitor C423 is connected to AGND. Pin 4 of the U403B is connected in parallel with a 10uF / 16V capacitor C424 and both are connected to the -5V power supply. The other end of capacitor C424 is connected to AGND. The operational amplifier U403B converts the input DC signals Uz and Ush into a DC signal Uco2. The output voltage amplitude is a DC signal with the formula Uco2 = K*(Uz - Ush), where K is the gain of the differential amplifier circuit (the value of K can be modified according to the range). This further amplifies the signal by a factor of K (K≥3). This Uco2 DC signal is the electrical signal corresponding to the luminous flux of infrared light absorbed by carbon dioxide. This signal is a single-ended signal and cannot be directly sent to the input of the differential input A / D converter. Therefore, this signal must be sent to the fully differential output amplifier circuit MZ4 to be converted into a fully differential signal.

[0057] like Figure 10The diagram shows the schematic of the fully differential output amplifier circuit MZ4, including operational amplifier U405. Pin 1 of operational amplifier U405 is connected to pin 7 of operational amplifier U403B in differential amplifier circuit MZ3 to receive the DC signal Uco2. A 1K resistor R428 is connected in series between them. A 5.6nF / 16V capacitor C426 is connected in parallel between pins 1 and 4 of operational amplifier U405. A resistor R43 is connected in series with pin 4 of operational amplifier U405. 2. Resistor R432 is positioned away from capacitor C426. A 1K resistor R430 is connected in parallel between the end of resistor R432 away from pin 4 of operational amplifier U405 and pin 1 of operational amplifier U405. A 1nF / 16V capacitor C428 is connected in series between resistors R430 and R432, with one end of capacitor C428 connected to AGND. An output bias circuit is connected to pin 2 of operational amplifier U405. A resistor R431 is connected in series to pin 5 of operational amplifier U405. A 1K resistor R427 is connected in series with pin 8 of operational amplifier U405, with one end of R427 connected to AGND. A 5.6nF / 16V capacitor C425 is connected in parallel between pins 5 and 8 of operational amplifier U405. A 1K resistor R429 is connected in parallel between pin 8 of operational amplifier U405 and the end of resistor R431 furthest from operational amplifier U405. A 1nF / 16V capacitor C427 is connected in series between resistors R429 and R431. Capacitor C427 is connected to the operational amplifier... U405 is connected in parallel, and one end of capacitor C427 is connected to AGND. A 1nF / 16V capacitor C429 is connected in parallel between the ends of resistors R431 and R432 that are furthest from operational amplifier U405. The ends of resistors R431 and R432 that are furthest from operational amplifier U405 are respectively connected to the differential input 24-bit A / D sampling circuit M2. The fully differential operational amplifier U405 converts the input Uco2 DC signal into two differential signals with opposite phases and sends them to the signal input terminals of the next stage AIN+ and AIN-.

[0058] The output bias circuit includes operational amplifier U404A. Pin 1 of operational amplifier U404A is connected to pin 2 of operational amplifier U405, with a 100nF / 16V capacitor C430 connected in series between them. One end of capacitor C430 is connected to AGND. Pins 1 and 2 of operational amplifier U404A are directly connected. A 100nF / 16V capacitor C429 is connected in series with pin 3 of operational amplifier U404A, with one end of capacitor C429 grounded. A 51K resistor R433 and a 100K resistor R434 are connected in series between capacitor C429 and pin 3 of operational amplifier U404A. One end of resistor R433 and one end of resistor R434 share the same network node, and the other end of resistor R434 is connected to AGND. One end of resistor R433 is connected to the differential input 24-bit A / D sampling circuit. Connect M2. A +5V power supply is connected to pin 3 of operational amplifier U405 and pin 8 of operational amplifier U404A. A 10uF / 16V capacitor C423 is connected to the other end of the +5V power supply, with one end of C423 connected to AGND. A -5V power supply is connected to pin 6 of operational amplifier U405 and pin 4 of operational amplifier U404A. A 10uF / 16V capacitor C424 is connected to the other end of the -5V power supply, with one end of C424 connected to AGND. This is used to adjust the bias voltage of the two differential signals output by operational amplifier U405, ensuring that the absolute voltage values ​​of both signals are above 100mV (because the minimum absolute voltage of the A / D analog input is Vmin = GND + 100mV), so that the subsequent 24-bit A / D sampling circuit can obtain the correct results.

[0059] like Figure 11 The diagram shows the specific circuit schematic of the differential input 24-bit A / D sampling circuit M2, including a 24-bit A / D sampler U406. Pin 3 of the 24-bit A / D sampler U406 is connected to the end of resistor R431 furthest from operational amplifier U405. Pin 4 of the 24-bit A / D sampler U406 is connected to the end of resistor R432 furthest from operational amplifier U405. Pin 5 of the 24-bit A / D sampler U406 is connected to the end of resistor R433 furthest from operational amplifier U404A. The 24-bit A / D sampler U406 transmits data to the data processor via SPI1. The digital-to-analog conversion function of the differential input 24-bit A / D sampling circuit converts the input AIN+ and AIN- signals into digital signals. The differential input of the 24-bit A / D sampling circuit can suppress common-mode interference generated by the power supply. With improvements to the power supply circuit and reference voltage, the sampling resolution can be increased by at least one order of magnitude.

[0060] like Figure 12The diagram shows a specific schematic of the data processor, including an MCU chip. The MCU chip receives the digital signal from the 24-bit A / D sampling circuit, performs calculations according to the Beer-Lambert theorem, and converts it into a digital quantity that corresponds exactly to the carbon dioxide concentration. This digital quantity is then transmitted to the host computer through the communication port. The MCU chip also supplies DAC signals to the temperature-compensated DC signal generation circuit MZ2 and VREF signals to the output bias circuit.

[0061] In summary, improvements to the two-stage amplification bandpass filter circuit M1 can double the output range of the sine wave, extending it from 0 to 3.5V to -3.5V to +3.5V. The addition of a pure AC sine wave to DC signal conversion circuit MZ1, a temperature-compensated DC signal generation circuit MZ2, a differential amplifier circuit MZ3, and a fully differential output amplifier circuit MZ4 amplifies the output Uco2 DC signal voltage by a factor of K (K≥3). Improvements to the differential input 24-bit A / D sampling circuit M2 suppress common-mode interference from the power supply. Combined with improvements to the power supply circuit and reference voltage, the sampling resolution can be increased by at least one order of magnitude. Therefore, by combining these three points, the resolution of the single-wavelength, single-beam DNIR carbon dioxide sensor can be improved by one to two orders of magnitude.

[0062] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0063] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high-precision and high-resolution DNIR carbon dioxide sensor, comprising a pyroelectric sensor, a DC blocking first-stage amplification and integration circuit, a second-stage amplification and bandpass filter circuit M1, a differential input 24-bit A / D sampling circuit M2, a data processor, and a host computer, characterized in that: The secondary amplification bandpass filter circuit M1 includes an operational amplifier U401A. Pin 6 of the operational amplifier U401A is connected to the output of the DC blocking primary amplification and integration circuit to receive the distorted pulse signal from the DC blocking primary amplification and integration circuit. A resistor R410 and a capacitor C408 are connected in series between pin 6 of the operational amplifier U401A and the DC blocking primary amplification and integration circuit. A resistor R411 is connected in series between resistor R410 and capacitor C408, and one end of resistor R411 is connected to AGND. The operational amplifier U401A... Pin 5 of the operational amplifier U401A is directly connected to AGND, and a capacitor C407 is connected in parallel between pins 5 and 6 of the operational amplifier U401A; a resistor R412 is connected in parallel between pins 6 and 7 of the operational amplifier U401A; a capacitor C409 is connected in parallel between pin 7 of the operational amplifier U401A and capacitor C408; pin 7 of the operational amplifier U401A is connected to the pure AC sine wave signal to DC signal conversion circuit MZ1, which uses the operational amplifier U401A to convert the input deformed pulse into a pure AC sine wave signal with a zero crossing point of 0V. Between the secondary amplification bandpass filter circuit M1 and the differential input 24-bit A / D sampling circuit M2, there are respectively a pure AC sine wave signal to DC signal conversion circuit MZ1, a temperature-compensated DC signal generation circuit MZ2, a differential amplifier circuit MZ3, and a fully differential output amplifier circuit MZ4. The pure AC sine wave signal to DC signal conversion circuit MZ1 includes an operational amplifier U402, and pin 8 of operational amplifier U402 is connected to pin 7 of operational amplifier U401A to receive the pure AC sine wave signal from the secondary amplification bandpass filter circuit M1; a resistor R413 is connected in series between pin 8 of operational amplifier U402 and pin 7 of operational amplifier U401A; pin 2 of operational amplifier U402 is connected to GND, and pin 1 is connected in series with a resistor R414, one end of which is connected to AGND; a capacitor C413 is connected in parallel between pin 1 and pin 4 of operational amplifier U402; a capacitor C413 is connected in series between pin 4 of operational amplifier U402. A resistor R418 is connected in parallel with pin 1 of operational amplifier U402, and a resistor R416 is connected in parallel between the other end of resistor R418 and pin 1. A capacitor C415 is connected in series between resistors R418 and R416, with one end of capacitor C415 connected to AGND. A capacitor C412 is connected in parallel between pins 8 and 5 of operational amplifier U402. A resistor R417 is connected in series with pin 5 of operational amplifier U402, and a resistor R415 is connected in parallel between the other end of resistor R417 and pin 8 of operational amplifier U402. A capacitor C414 is connected in series between resistors R417 and R415, with one end of capacitor C414 connected to AGND. Operational amplifier U402... Pin 3 of the amplifier is connected to a +5V power supply. The other end of the +5V power supply is connected to a capacitor C410, one end of which is connected to AGND. Pin 6 of the operational amplifier U402 is connected to a -5V power supply. The other end of the -5V power supply is connected to a capacitor C411, one end of which is connected to AGND. A dual diode D401 is installed between resistors R417 and R418. Resistor R417 is connected to pin 1 of the dual diode D401, and resistor R418 is connected to pin 2 of the dual diode D401. A capacitor C416 is connected in parallel between pins 1 and 2 of the dual diode D401. A capacitor C416 is connected to pin 3 of the dual diode D401. Operational amplifier U403A is connected in series with resistors R420 and R421 between pin 3 of operational amplifier U403A and pin 3 of dual diode D401. Pin 3 of dual diode D401 is connected in series with resistor R420 with resistor R419 and capacitor C416 respectively. Resistor R419 is placed close to pin 3 of dual diode D401, and capacitor C416 is placed close to resistor R420. A capacitor C417 is connected in series between resistor R420 and resistor R421. A capacitor C418 is connected in series between resistor R421 and pin 3 of operational amplifier U403A. Resistors R419, capacitors C416, C417 and C418 are all connected to AGND.Pin 2 of operational amplifier U403A is directly connected to pin 1. Operational amplifier U402 outputs two sinusoidal signals with opposite phases. These two sinusoidal signals are rectified by dual diodes D401 into pulsating DC signals. After being filtered by a double π-type filter composed of resistors R419, R420, R421 and capacitors C416, C417, and C418, they become smooth DC signals. The smooth DC signals are then sent to operational amplifier U403A for impedance transformation to output the Ush DC signal. The pyroelectric sensor is used to collect carbon dioxide concentration voltage signals and input the collected carbon dioxide concentration voltage signals into a DC blocking first-stage amplification and integration circuit. The DC blocking first-stage amplifier and integrator circuit converts the received carbon dioxide concentration voltage signal into a deformed pulse signal, and inputs the deformed pulse signal into the second-stage amplifier and bandpass filter circuit M1. The secondary amplification bandpass filter circuit M1 converts the deformed pulse signal into a pure AC sine wave signal, and inputs the pure AC sine wave signal into the -IN terminal of the differential amplifier circuit MZ3. The temperature-compensated DC signal generation circuit MZ2 uses the control of the data processor to output a DC signal, and inputs the DC signal to the +IN terminal of the differential amplifier circuit MZ3. The differential amplifier circuit MZ3 differentially amplifies the two received DC signals and inputs the amplified DC signals to the -I terminal of the fully differential output amplifier circuit MZ4. The fully differential output amplifier circuit MZ4 converts the received amplified DC signal into two DC signals with opposite phases. The in-phase signal is input to the -AIN terminal of the differential input 24-bit A / D sampling circuit M2, and the inverted signal is input to the +AIN terminal of the differential input 24-bit A / D sampling circuit M2. The differential input 24-bit A / D sampling circuit M2 converts the received signal into a digital signal and communicates the digital signal with the data processor through the SPI1 port. The data processor performs calculations according to the Beer-Lambert theorem and converts the signal into a digital quantity that corresponds exactly to the concentration of the carbon dioxide sensor, which is then transmitted to the host computer through the communication port.

2. The high-precision and high-resolution DNIR carbon dioxide sensor according to claim 1, characterized in that: The temperature-compensated DC signal generation circuit MZ2 includes an operational amplifier U401B. Pin 5 of the operational amplifier U401B is connected to the data processor, and a resistor R422 is connected in series between pin 5 of the operational amplifier U401B and the data processor. A capacitor C421 is connected in series between the resistor R422 and pin 5 of the operational amplifier U401B, with one end of the capacitor C421 connected to AGND. Pins 6 and 7 of the operational amplifier U401B are directly connected. Pin 8 of the operational amplifier U401B is connected to a +5V power supply, and the other end of the +5V power supply is connected to a capacitor C419, with one end of the capacitor C419 connected to AGND. Pin 6 of the operational amplifier U401B is connected to a -5V power supply, and the other end of the -5V power supply is connected to a capacitor C420, with one end of the capacitor C420 connected to AGND. The operational amplifier U401B performs impedance transformation on the signal from the data processor to output a DC signal Uz.

3. The high-precision and high-resolution DNIR carbon dioxide sensor according to claim 1, characterized in that: The differential amplifier circuit MZ3 includes operational amplifier U403B. Pin 5 of operational amplifier U403B is connected to pin 7 of operational amplifier U401B to receive the Ush DC signal. A resistor R423 is connected in series between pin 5 of operational amplifier U403B and pin 7 of operational amplifier U401B. Pin 6 of operational amplifier U403B is connected to pin 1 of operational amplifier U403A to receive the Uz DC signal. A resistor R424 is connected in series between pin 6 of operational amplifier U403B and pin 1 of operational amplifier U403A. A resistor R425 is connected in series between pin 5 of operational amplifier U403B and resistor R423. One end of resistor R425 is connected to AGND. A capacitor C421 is connected in parallel between the two ends of the operational amplifier U403B; a resistor R426 is connected in parallel between pins 6 and 7 of the operational amplifier U403B, and a capacitor C422 is connected in parallel across the two ends of the resistor R426; a +5V power supply is connected to pin 8 of the operational amplifier U403B, and a capacitor C419 is connected to the other end of the +5V power supply, with one end of the capacitor C419 connected to AGND; a -5V power supply is connected to pin 6 of the operational amplifier U403B, and a capacitor C420 is connected to the other end of the -5V power supply, with one end of the capacitor C420 connected to AGND. The operational amplifier U403B performs a difference operation on the input Uz DC signal and the Ush DC signal, and then amplifies and converts the difference signal into a Uco2 DC signal.

4. A high-precision and high-resolution DNIR carbon dioxide sensor according to claim 3, characterized in that: The fully differential output amplifier circuit MZ4 includes an operational amplifier U405. Pin 1 of operational amplifier U405 is connected to pin 7 of operational amplifier U403B to receive the amplified DC signal. A resistor R428 is connected in series between pin 1 of operational amplifier U405 and pin 7 of operational amplifier U403B. A capacitor C426 is connected in parallel between pin 1 and pin 4 of operational amplifier U405. A resistor R432 is connected in series between pin 4 of operational amplifier U405, with the resistor R432 positioned away from capacitor C426. A resistor R430 is connected in parallel between the end of resistor R432 away from pin 4 of operational amplifier U405 and pin 1 of operational amplifier U405. A capacitor C428 is connected in series between resistor R430 and resistor R432, with one end of capacitor C428 connected to AGND. An output bias circuit is connected to pin 2 of operational amplifier U405. A resistor R431 is connected in series between pin 5 of operational amplifier U405. A resistor R427 is connected in series with pin 8 of operational amplifier U405, and one end of resistor R427 is connected to AGND. A capacitor C425 is connected in parallel between pins 5 and 8 of operational amplifier U405. A resistor R429 is connected in parallel between pin 8 of operational amplifier U405 and the end of resistor R431 furthest from operational amplifier U405. A capacitor C427 is connected in series between resistors R429 and R431. The capacitor C427 is connected in parallel with operational amplifier U405. The capacitor C427 is connected to AGND. A capacitor C429 is connected in parallel between the ends of resistors R431 and R432 that are furthest from operational amplifier U405. The ends of resistors R431 and R432 that are furthest from operational amplifier U405 are connected to the differential input 24-bit A / D sampling circuit M2. Operational amplifier U405 converts the input Uco2 DC signal into a fully differential signal, and outputs AIN+ and AIN- signals through resistors R431 and R432 respectively.

5. A high-precision and high-resolution DNIR carbon dioxide sensor according to claim 4, characterized in that: The output bias circuit includes an operational amplifier U404A. Pin 1 of operational amplifier U404A is connected to pin 2 of operational amplifier U405 to adjust the output AIN+ and AIN- signals of operational amplifier U405 to above 0V. A capacitor C430 is connected in series between pin 1 of operational amplifier U404A and pin 2 of operational amplifier U405, with one end of capacitor C430 connected to AGND. Pins 1 and 2 of operational amplifier U404A are directly connected. A capacitor C429 is connected in series between pin 3 of operational amplifier U404A, with one end of capacitor C429 grounded. The capacitor C429 is connected to the operational amplifier U404A. Resistors R433 and R434 are connected in series between pins 3 and 4, respectively. One end of resistor R434 is connected to AGND, and one end of resistor R433 is connected to the differential input 24-bit A / D sampling circuit M2. Pin 3 of operational amplifier U405 and pin 8 of operational amplifier U404A are each connected to a +5V power supply, and the other end of the +5V power supply is connected to a capacitor C423, one end of which is connected to AGND. Pin 6 of operational amplifier U405 and pin 4 of operational amplifier U404A are both connected to a -5V power supply, the other end of which is connected to a capacitor C424, one end of which is connected to AGND.

6. A high-precision and high-resolution DNIR carbon dioxide sensor according to claim 5, characterized in that: The differential input 24-bit A / D sampling circuit M2 includes a 24-bit A / D sampler U406. Pin 3 of the 24-bit A / D sampler U406 is connected to the end of resistor R431 away from operational amplifier U405, and is used to receive the AIN+ signal generated by operational amplifier U405. Pin 4 of the 24-bit A / D sampler U406 is connected to the end of resistor R432 away from operational amplifier U405, and is used to receive the AIN- signal generated by operational amplifier U405. Pin 5 of the 24-bit A / D sampler U406 is connected to the end of resistor R433 away from operational amplifier U404A. The 24-bit A / D sampler U406 converts the input AIN+ and AIN- signals into digital signals, and sends them to the data processor through the SPI1 port.

7. A high-precision and high-resolution DNIR carbon dioxide sensor according to claim 6, characterized in that: The data processor includes an MCU chip, which receives the digital signal from the 24-bit A / D sampling circuit, performs calculations according to the Beer-Lambert theorem, and converts it into a digital quantity that completely corresponds to the concentration of the carbon dioxide sensor. The digital quantity is then transmitted to the host computer through the communication port. The MCU chip also sends a DAC signal to the temperature-compensated DC signal generation circuit MZ2 and a VREF signal to the output bias circuit.

Images