An optical multi-channel gas sensor based on the principle of NDIR

Abstract

The utility model discloses a kind of optical multi-channel gas sensors based on NDIR principle, it is related to infrared gas sensor technical field;By infrared light source, air chamber, four-channel thermoelectric detector composition infrared absorption light system, light source voltage stabilizing modulation circuit, thermoelectric weak signal conditioning circuit, high-precision analog-digital conversion circuit, single-chip microcomputer control and communication circuit system composition, the utility model realizes compact structure, the function of the real-time measurement of multiple gas;Realize low-noise zero drift self-stable signal processing circuit, design low-power 24-bit sampling circuit, accurate real-time digital signal can be obtained without complex data processing algorithm, the utility model design has the characteristics such as wide range, high precision, good stability, long life, miniaturization, simultaneously replace sensor end can measure multiple types of gas, solve the problem that traditional infrared optical gas sensor is high in cost, bulky inconvenient to carry, detection result is time-consuming long precision is susceptible to environmental interference.

Description

TECHNICAL FIELD

[0001] The utility model relates to infrared gas sensor technical field, concretely is a kind of optical multi-channel gas sensor based on NDIR principle. BACKGROUND

[0002] Mine gas is the gas that is generated in the process of coal generation and metamorphism of coal, mainly CH4.In addition, underground blasting, ore oxidation and spontaneous combustion, pitwood decay, etc., can produce toxic and harmful gases, which mainly include CO2 and CO.Currently, coal mine multi-gas detection mainly uses non-dispersive infrared spectroscopy (NDIR) and tunable diode laser absorption spectroscopy (TDLAS) and other spectral analysis technologies.

[0003] Tunable diode laser absorption spectroscopy (TDLAS) technology mainly uses the selective absorption characteristics of gas molecules to laser, uses laser as light source by modulating semiconductor laser, analyzes the near-infrared region laser spectrum after gas to calculate the gas concentration.NDIR uses the characteristic that gas has selective absorption to mid-infrared band light, calculates the concentration value of the measured gas according to the change of incident light and outgoing light wavelength intensity, has the advantages of simple system structure, stable performance, wide detection range, long time work without maintenance and correction, etc., and has been widely used in multi-gas detection.Both TDLAS and NDIR have many research methods to detect mixed gas, but the detection system with high precision is often large in size, and the cost of using multiple sensors to detect multiple gases is also expensive, and it is difficult to balance the precision, detection range and cost in overall design, and only one of them can be selected.

[0004] The utility model aims at providing a kind of multi-channel gas detection sensor design method based on NDIR principle, by combining advanced signal processing, data acquisition technology and multi-channel design, realize the goal of compact structure, low cost, multi-channel gas real-time detection, to solve the above technical problems. SUMMARY

[0005] The utility model provides a kind of optical multi-channel gas sensor based on NDIR principle, for CH4, CO2 and CO gas in the process of coal mining, improves modulating device, light source and embedded soft and hard system, solves the problems of existing gas detection equipment, such as large size, high error and high cost.

[0006] In order to achieve the above object, the utility model provides the following technical scheme: a kind of optical multi-channel gas sensor based on NDIR principle, including circuit module, the circuit module includes power supply circuit, light source driving circuit, infrared light source, gas sample unit, thermoelectric pile sensor, optical gas chamber, temperature compensation circuit, signal processing circuit, ADC acquisition circuit and MCU minimum system unit;The utility model mainly includes infrared absorption light system by infrared light source, gas chamber, four-channel thermoelectric pile detector, light source voltage stabilizing modulation circuit, thermoelectric pile weak signal conditioning circuit, high-precision analog-digital conversion circuit, single-chip microcomputer control and communication circuit system composition;

[0007] Infrared light is emitted by infrared light source, and the heat change formed after the gas absorption of gas sample unit is detected by thermoelectric pile sensor, and then converted into voltage signal, which is processed by signal processing circuit, and finally the concentration of each gas is read and calculated by MCU.

[0008] Further, the power supply circuit is used to provide voltage for each module circuit.

[0009] The light source driving circuit is used to drive the infrared light source.

[0010] The infrared light source is used to provide infrared light source for the detector.

[0011] The gas sample unit is arranged on the infrared light beam path in the optical gas chamber.

[0012] Further, the thermoelectric pile sensor is used to measure the heat change after the infrared light absorption of gas molecules.

[0013] The optical gas chamber is used to provide isolated and sealed space for the measured gas sample, and fix the light source and the detector.

[0014] The temperature compensation circuit is used to compensate the environmental temperature error caused by the heating of infrared light source.

[0015] The signal processing circuit is composed of filter circuit, bias voltage circuit and single power supply operational amplifier, and is used to process the small voltage signal output by thermoelectric pile.

[0016] Further, the ADC acquisition circuit is used to acquire the amplified analog voltage signal, and convert it into digital signal after second-stage amplification and filtering processing, and transmit it to MCU.

[0017] The MCU minimum system unit is used to drive light source, read ADC signal and process and transmit gas concentration signal to host computer.

[0018] The host computer is used to display and analyze smoke concentration information.

[0019] Further, the MCU drives the infrared light source in a PWM mode to emit infrared light pulses, the light reaches the thermoelectric detector HTS-Q21 after being reflected by the air chamber, and the detector signal is amplified and filtered by a signal conditioning circuit, the amplified analog signal is sampled by an ADC chip to convert it into a digital signal which is transmitted to the host MCU through the SPI protocol, and the MCU outputs the collected data to the host computer through the serial port after processing.

[0020] Further, the infrared air chamber, infrared light source, thermoelectric sensor and part of the drive circuit are placed on the front of the circuit board, and the MCU minimum system circuit, ADC acquisition circuit and signal processing circuit are arranged on the back of the circuit board.

[0021] Further, the infrared light source is a wide-spectrum infrared light source with a concave light reflector around the bulb, with a wavelength band of 0-5um and a glass transmittance about twice that of a normal light source.

[0022] Further, the infrared detection sensor is a four-channel thermoelectric sensor, each channel filter has a peak wavelength of 3.91um for the reference channel, 4.64um for the CO channel, 3.40um for the CH4 channel, and 4.43um for the CO2 channel, and the noise voltage is 37nV / √Hz.

[0023] Further, the ADC circuit is designed based on an 8-channel low-noise 24-bit sigma-delta type ADC chip AD7124-8 with integrated PGA and reference voltage source, uses differential signal input, internal reference voltage is 2.5V, sets gain PGA to 32, filter register is set to use sinc4+sinc1 to quickly establish a filter, and full power working mode FS=20.

[0024] Compared with the prior art, the optical multi-channel gas sensor based on the NDIR principle has the following beneficial effects:

[0025] The optical multi-channel gas sensor based on the NDIR principle has the functions of compact structure and real-time measurement of multiple gases, uses a high-performance operational amplifier chip to realize a low-noise zero-drift self-stable signal processing circuit, and designs a low-power 24-bit Sampling circuit, without complex data processing algorithm, accurate real-time digital signal can be obtained, the design has the characteristics of wide range, high precision, good stability, long service life, miniaturization, etc., and multiple types of gases can be measured by replacing the sensor end. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical scheme of the embodiments of the present application, the drawings needed to be used in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the premise of not deviating from the concept of the present application.

[0027] Figure 1 The system circuit block diagram of the optical multi-channel gas sensor based on the NDIR principle is provided by the present application.

[0028] Figure 2 The program design flow chart of the optical multi-channel gas sensor based on the NDIR principle is provided by the present application.

[0029] Figure 3 The bias circuit design diagram of the optical multi-channel gas sensor based on the NDIR principle is provided by the present application.

[0030] Figure 4 The low-pass filtering and operational amplification circuit design diagram of the optical multi-channel gas sensor based on the NDIR principle is provided by the present application.

[0031] Figure 5 The ADC acquisition circuit design diagram of the optical multi-channel gas sensor based on the NDIR principle is provided by the present application. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned purpose, features and advantages of the present application more apparent and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings of the specification.

[0033] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be practiced in other ways different from the description, and those skilled in the art can make similar generalizations without deviating from the concept of the present application, therefore the present application is not limited by the specific embodiments disclosed below.

[0034] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. In this specification, "in one embodiment" does not mean the same embodiment, nor is it an embodiment that is separate from or mutually exclusive of other embodiments.

[0035] Please refer to Figures 1-5The utility model discloses a kind of optical multi-channel gas sensors based on NDIR principle, including circuit module and program module, the circuit module includes power supply circuit, light source driving circuit, infrared light source, gas sample unit, thermoelectric pile sensor, optical gas chamber, temperature compensation circuit, signal processing circuit, ADC acquisition circuit and MCU minimum system unit;The program module includes light source driving program, AD7124 driving program, concentration data acquisition processing and transmission program, infrared light is emitted using infrared light source, the heat change formed after the gas absorption of gas sample unit is detected by thermoelectric pile sensor, and then converted into voltage signal, signal processing circuit processes it, and finally the concentration of each gas is read and calculated by MCU;Including the following steps:

[0036] S1, infrared light source emits infrared light beam;

[0037] S2, infrared light beam passes through gas sample unit;

[0038] S3, gas molecule absorbs infrared light beam;

[0039] S4, thermoelectric pile sensor measures the intensity change of infrared light beam after gas sample unit;

[0040] S5, signal processing circuit amplifies and filters the sampled signal;

[0041] S6, ADC chip converts the amplified analog signal into digital signal;

[0042] S7, program converts digital signal into gas concentration value according to NDIR principle;

[0043] S8, host computer displays and transmits gas concentration value.

[0044] The power supply circuit is used for providing each module circuit voltage.

[0045] The light source driving circuit is used for driving infrared light source.

[0046] The infrared light source is used for providing infrared light source for detector.

[0047] The gas sample unit is arranged on the infrared light beam path in the optical gas chamber.

[0048] The thermoelectric pile sensor is used for measuring the heat change of infrared light absorbed by gas molecule.

[0049] The optical gas chamber is used for providing isolated and sealed space for measured gas sample, and fixing light source and detector.

[0050] The temperature compensation circuit is used for compensating environmental temperature error caused by infrared light source heating.

[0051] The signal processing circuit is composed of a filter circuit, a bias voltage circuit and a single power supply operational amplifier, and is used for processing the tiny voltage signal output by the thermoelectric pile.

[0052] The ADC acquisition circuit is used for acquiring the amplified analog voltage signal, converting the signal into a digital signal after second-stage amplification and filtering, and transmitting the digital signal to the MCU.

[0053] The MCU minimum system unit is used for driving the light source, reading the ADC signal and processing and transmitting the gas concentration signal to the host computer.

[0054] The host computer is used for displaying and analyzing the flue gas concentration information.

[0055] In the application, a high-performance infrared light source IR715EN-PR is selected, which has high radiation efficiency, low power consumption and good temperature stability. A high-performance thermoelectric pile sensor HTS-Q21 is used, which has low noise, high sensitivity and fast response characteristics. A low-noise signal processing circuit is designed, which effectively reduces the noise level and improves the signal quality by using a double-channel operational amplifier AD8629 and a filter circuit. A high-precision ADC chip AD7124-8 is selected, which is an 8-channel low-noise 24-bit sigma-delta type ADC chip with high-precision sampling capability and can accurately measure the gas concentration. An algorithm is designed based on the NDIR principle, which is derived from the NDIR principle, combined with the sensor calibration experimental data, and obtained by data fitting method.

[0056] Specifically, STM32F103RCT6 is taken as the core, and when working normally, the STM32 outputs a 0.5Hz square wave to drive the infrared light source IR715EN-PR to emit infrared light. The light is reflected by the gas chamber and reaches the thermoelectric pile detector HTS-Q21. The detector signal is amplified and filtered by the signal conditioning circuit. The amplified analog signal is sampled by the ADC chip and converted into a digital signal, which is transmitted to the host microcontroller through the SPI protocol. The microcontroller sorts the collected data and outputs them to the host computer through the serial port.

[0057] Specifically, the infrared gas chamber, infrared light source, thermoelectric pile sensor and part of the driving circuit are placed on the front surface of the circuit board, and the MCU minimum system circuit, ADC acquisition circuit and signal processing circuit are placed on the back surface of the circuit board.

[0058] Specifically, the infrared light source is an enhanced type, and the wide-spectrum infrared light source has a concave light reflector around the bulb. The waveband is 0-5um, and the glass transmittance is about twice that of the ordinary light source.

[0059] Further, the light source is selected as IR715EN-PR enhanced infrared light source, which has better radiation light intensity in 3-5um, and the bulb is provided with a concave light reflector on the periphery, so that the infrared light radiation is maximized, and the glass transmittance is about twice that of the ordinary light source. The steady-state working current of IR715EN-PR is 115mA, and the transient conduction has a surge current of about 150mA. The heat generated by the bulb during operation keeps the temperature of the reflector above the ambient temperature, which helps to prevent the interference of condensed water vapor in the humid environment.

[0060] The light source drive is powered by an independent power supply, which effectively avoids the pulse surge current of the light source from introducing noise interference to the subsequent circuit. The light source drive circuit is designed as a low dropout programmable regulator ADP7105-5 to provide 5V power supply for the light source. The ADP7105-5 can buffer the transient current during low-frequency square wave modulation by externally connecting a 10nF soft start capacitor to the SS pin, and the current loop is independently wired and laid out without flowing through the subsequent circuit.

[0061] Specifically, the infrared detection sensor is a four-channel thermoelectric pile sensor, and the peak wavelengths of the filters of the respective channels are 3.91um for the reference channel, 4.64um for the CO channel, 3.40um for the CH4 channel, and 4.43um for the CO2 channel. The noise voltage is 37nV / √Hz.

[0062] Further, the infrared detector is selected as a four-channel thermoelectric pile detector HTS-Q21, and the peak wavelengths of the filters of the respective channels are 3.91um for the reference channel, 4.64um for the CO channel, 3.40um for the CH4 channel, and 4.43um for the CO2 channel. The noise voltage is 37nV / √Hz. The temperature compensation circuit is designed to be powered by 3.3V, and 510kΩ and 130kΩ are connected in series. The thermoelectric pile thermistor signal pin is connected in parallel with the 130kΩ circuit. When collecting the gas channel signal, the thermistor signal is also collected to calculate the real-time environmental temperature.

[0063] Specifically, the operational amplifier chip is selected as a dual-channel operational amplifier AD8629 supporting rail-to-rail input / output, zero drift and single power supply. The AD4528 follower circuit provides bias voltage for the single power supply amplification circuit. The signal conditioning circuit is designed as a first-order low-pass filter negative feedback in-phase amplification circuit. The first-stage low-pass RC filter circuit is built by combining the single-channel internal resistance 84kΩ of the thermoelectric pile sensor. The -3dB cutoff frequency is 126.4HZ. The second-stage RC low-pass filter circuit is built by using the negative feedback resistance of the amplification circuit, and the -3dB cutoff frequency is 72.1Hz. The gain of the negative feedback amplification circuit is 213.7.

[0064] Specifically, the ADC circuit is designed based on an 8-channel low-noise 24-bit sigma-delta ADC chip AD7124-8 integrated with a PGA and a reference voltage source. The chip has a full-power mode gain of 128, and the root mean square noise is only 23 nV rms. The maximum output data rate is 19200 SPS, and the chip supports 50Hz / 60Hz suppression. The SPI communication protocol is selected, the differential signal input is used, the internal reference voltage is 2.5V, the gain PGA is set to 32, the filter register is set to use the sinc4+sinc1 fast filter, and the full-power mode FS=20.

[0065] Specifically, the light source driving program generates a PWM light source modulation signal with a duty cycle of 50% for the timer to control the infrared light source to turn on and off at a frequency of 0.5Hz.

[0066] The AD7124 driving program is used to read and write and configure the AD7124 register driving using the SPI protocol communication. The register configuration of the AD7124 is mainly written into the operation and operation object to be performed through the 8-bit write-only communication register. When the operation is completed, the interface returns to the execution write operation state of the communication register. After the AD7124 is powered on, the main configuration is divided into four steps: channel configuration, setting, diagnosis, and ADC control.

[0067] First, the channel configuration is performed, and the channel register is used to select the required analog input channel and analog input pair AINP and AINN. Here, to reduce the error, the AD8629 is configured to amplify the difference between the output of the four channels of the thermoelectric pile and the common-mode voltage. In the second step, the configuration register is set to single polarity input, the internal 2.5V reference voltage source is used, the PGA gain is 32, the filter register is set to use the sinc4+sinc1 fast filter, the full-power mode FS=20, and the data output rate is 50.5SPS. The establishment time of the sinc4+sinc1 fast filter is close to the inverse of the first filter notch frequency. Therefore, at an output data rate close to 1 / 50Hz or 1 / 60Hz, the user can achieve 50Hz and / or 60Hz suppression performance. The establishment time is approximately equal to the inverse of the output data rate. Therefore, the conversion time is almost constant on a single channel or on multiple channels. The offset register and the gain register are kept at the default settings and are not changed. In the third step, the diagnosis enable register is configured, and the default settings are kept. In the fourth step, the ADC control register is configured, the power mode is full power, the continuous conversion mode is used, the internal clock source and the reference voltage source are used.

[0068] The concentration data acquisition processing and transmission program is derived from a formula based on the NDIR principle, and combined with sensor calibration experimental data, an actual each channel gas concentration calculation formula based on the sensor is obtained by using data fitting, and the collected voltage value is calculated as a gas concentration value according to the formula and output to the upper computer.

[0069] The utility model provides a kind of optical multi-channel gas sensor based on NDIR principle, realize compact structure, the function of real-time measurement of multiple gas.It is Beer-Lambert reference detection as basic principle, using high-performance operational amplifier chip realizes low-noise zero-drift self-stable signal processing circuit, 24 bits Sampling circuit with low power consumption is designed, accurate real-time digital signal can be obtained without complex data processing algorithm.Experimental results show that the combustible gas concentration sensor designed by the utility model can detect CH4 gas concentration in the range of 0-2.5%vol and CO2 gas concentration in the range of 0-3%vol.It has the characteristics of wide range, high precision, good stability, long service life, miniaturization, etc., and can measure multiple types of gas by replacing sensor end, providing a low-cost solution for combustible gas concentration detection in coal mining.

[0070] The multi-channel gas detection sensor designed by the utility model realizes multifunctional, high-precision and stable gas detection function, and has the following technical effects:

[0071] Multi-channel detection: multiple gases such as CH4 and CO2 can be detected simultaneously.

[0072] High precision: gas concentration can be accurately measured to meet high-precision detection requirements.

[0073] Good stability: temperature compensation circuit effectively compensates for the influence of environmental temperature on detection results, improving sensor stability.

[0074] Long service life: using high-quality components improves sensor service life.

[0075] Miniaturization: compact structure, small size, easy to install and use.

[0076] Low cost: mature and reliable circuit design and manufacturing process are adopted to reduce cost.

[0077] Through the ingenious design and combination of the above technical solutions, the multi-channel gas detection sensor achieves high precision, stability, miniaturization and low cost, providing an efficient and convenient safety gas detection solution for coal mining and other occasions

[0078] In use: The infrared light emitted by the light source is absorbed by the gas sample in the chamber and then received by the thermoelectric detector; the detector generates a voltage signal corresponding to the light intensity, which is amplified and filtered by the signal conditioning circuit, and then converted into a digital signal by the ADC for single-chip microcomputer processing.

[0079] Motion process: The light source emits infrared light, which is accurately irradiated onto the sample in the gas chamber through the reflector, and carbon dioxide, methane and other gas components selectively absorb infrared light of specific wavelengths. After that, these lights return to the thermoelectric sensor through the reflector, and the sensor outputs a small voltage signal, which is amplified and filtered by a high-performance amplifier, and then converted into a digital signal with higher precision using the AD7124-8 ADC chip. These signals are sorted by the MCU and transmitted to the host computer through the serial interface for analysis.

[0080] Reference Figure 3 The circuit diagram shows a simple signal amplification circuit using ADA4528-1ARMZ operational amplifier. ADA4528-1ARMZ is a low-power, low-noise operational amplifier. The circuit is as follows:

[0081] Main components and functions:

[0082] ADA4528-1ARMZ operational amplifier: single operational amplifier with low offset voltage, low noise and high input impedance. The pins of the operational amplifier include: positive power supply (+Vs), negative power supply (-Vs), inverting input (-), non-inverting input (+), output (Out) and compensation pin (Comp).

[0083] Resistor and capacitor network: resistors R5 (5.1kΩ) and R10 (330Ω) form a feedback network that determines the gain of the amplifier. Capacitor C15 (1μF) is used for input filtering to reduce high-frequency noise in the input signal. Capacitor C12 (1μF) is used for power decoupling to stabilize the power supply voltage and reduce the impact of power supply noise on the performance of the operational amplifier.

[0084] Power supply: The operational amplifier is powered by dual power supply, the positive power supply pin (+Vs) is connected to A3.3, and the negative power supply pin (-Vs) is connected to AGND.

[0085] Signal input and output: The input signal enters the non-inverting input terminal (+) of the operational amplifier through resistor R10. The amplified signal is output from the output terminal (Out) of the operational amplifier and connected to the ADC5 port for subsequent use by the analog-to-digital converter.

[0086] Circuit Working Principle: The input signal enters the non-inverting input terminal (+) of the operational amplifier through resistor R10; the operational amplifier amplifies the input signal according to the configuration of the feedback network; the amplified signal is output through the output terminal, and after further filtering and protection processing, it is transmitted to the ADC for analog-to-digital conversion.

[0087] The entire circuit design aims to provide high-precision signal amplification while maintaining low noise and high stability

[0088] Reference Figure 4 The circuit diagram shows a differential amplification circuit using AD8629ARMZ operational amplifiers for signal conditioning. The circuit mainly consists of two identical amplifier modules, each containing an AD8629ARMZ operational amplifier to amplify the input differential signal to a level suitable for analog-to-digital converter (ADC) processing. Here is a detailed introduction to the circuit:

[0089] Main components and functions:

[0090] AD8629ARMZ Operational Amplifier: This is a low-power, high-precision operational amplifier suitable for applications requiring high input impedance and low offset voltage. Each operational amplifier has two input terminals (+IN / A and -IN / A or +IN / B and -IN / B) and an output terminal (OUT / A or OUT / B).

[0091] Resistor and capacitor network: Resistors (such as R4, R7, R8, R9, etc.) and capacitors (such as C11, C14, C16, C17, etc.) form the feedback network, determining the gain and frequency response of the amplifier. The selection of resistor values (such as 47kΩ and 221Ω) and capacitor values (such as 15nF and 8.2nF) is to optimize the performance of the circuit, such as gain-bandwidth product, stability, and noise performance.

[0092] Power supply filtering: Capacitors (such as C11, C17, C20, C23) are used for power decoupling to reduce the impact of power supply noise on the performance of the operational amplifier. These capacitors help stabilize the power supply voltage, ensuring that the operational amplifier works stably under various load conditions.

[0093] Signal input and output: Input signals enter the circuit through ports ADC2, ADC4, ADC5, etc., which may be differential signals from sensors or other analog sources. The amplified signal is output through OUT / A or OUT / B and then connected to ports ADC1, ADC3, ADC5, etc. for subsequent analog-to-digital conversion.

[0094] Protection elements: Diodes (such as F1, F2, F3, F4) are used to protect the circuit from voltage spikes or reverse voltage, ensuring the safe operation of the operational amplifier.

[0095] Circuit Operation: The input differential signal passes through a resistor network to the differential input of the operational amplifier; the operational amplifier amplifies the input signal according to the configuration of the feedback network; the amplified signal is output through the output terminal, and after further filtering and protection processing, it is transmitted to the ADC for analog-to-digital conversion.

[0096] The entire circuit design aims to provide high-precision signal amplification while maintaining low noise and high stability.

[0097] Reference Figure 5 As shown: This circuit diagram shows an analog-to-digital converter (ADC) application circuit using the AD7124-8BCPZ 8-channel, 16-bit precision ADC chip. This circuit design is used to convert analog signals to digital signals, suitable for occasions requiring high-precision data acquisition. The following is a detailed introduction to the circuit:

[0098] Main components and functions:

[0099] AD7124-8BCPZ ADC Chip: This chip provides 8 analog input channels (AIN0 to AIN7) that can be sampled individually or simultaneously. It supports multiple input ranges, including ±10V, ±5V, ±2.5V, etc.; it has high precision and low noise characteristics, suitable for precision measurement applications.

[0100] Power Management: The circuit includes multiple power supply pins, such as D5V, AGND, DGND-A, etc., for powering the ADC and other components. Capacitors (such as C28, C31, C4, etc.) are used for power decoupling to reduce power noise and ensure stable operation of the circuit.

[0101] Signal Conditioning: Resistor networks (such as R1 to R16) are used for signal conditioning, including current limiting and voltage division, to meet the input requirements of the ADC; capacitors (such as C1 to C16) are used for signal filtering to reduce high-frequency noise affecting measurement results.

[0102] Clock and Synchronization: The CLK pin is used to provide a clock signal to control the sampling rate of the ADC; the SYNC_N pin is used to synchronize multiple ADCs to ensure consistency in data acquisition.

[0103] Communication Interface: The CS_N, SCLK, SDIN, SDO, etc. pins are used for communication with microcontrollers or other digital devices, supporting SPI interface; the DOUT / RDY# pin is used to indicate that the data output is ready.

[0104] Reference Voltage: The REFIN+ and REFIN- pins are used to provide a reference voltage to ensure the accuracy of ADC conversion; the circuit may contain a precision resistor and capacitor network to stabilize the reference voltage.

[0105] Circuit working principle: analog signals are input to the ADC through AIN0 to AIN7; the ADC samples according to the clock signal (CLK) to convert the analog signal into a digital signal; the digital signal is transmitted to the microcontroller or other digital devices through the SPI interface (CS_N, SCLK, SDIN, SDO); the reference voltage (REFIN+ and REFIN-) ensures the accuracy and consistency of the ADC conversion.

[0106] The power decoupling and signal filtering circuit reduces power noise and signal interference, and improves measurement accuracy. Specific embodiments

[0107] Please refer to Figures 1 to 5 The utility model provides a kind of optical multi-channel gas sensor based on NDIR principle, comprising:

[0108] Single-chip microcomputer drives infrared light source to emit infrared light by light source drive circuit, light reaches thermopile detector after being reflected by gas chamber, and thermopile detector outputs voltage signal after detecting heat change, the voltage signal includes gas channel signal and thermistor temperature signal, the tiny analog voltage signal is amplified and filtered by signal conditioning circuit for first stage, and the amplified analog signal is sampled by ADC chip and converted into digital signal, which is transmitted to host single-chip microcomputer by SPI protocol, and the collected data is arranged by single-chip microcomputer and output to host computer by serial port.

[0109] In order to further illustrate the technical scheme involved in the utility model, the following will be illustrated by taking CO2 concentration detection as an example. Of course, it is not limited to CO2 concentration detection, and the gas sensing device involved in the utility model can also detect the concentration of CH4 and CO at the same time.

[0110] In the embodiment, 6-20V DC power supply is used for power supply, the light source chopping frequency is 0.5Hz, and the ADC sampling frequency is set to 50.53Hz. The experimental conditions are room temperature (25±2℃) and standard atmospheric pressure, the gas flow is controlled by mass flow controller (MFC) to be 200sccm, and the experiment is carried out as follows: the gas chamber is filled with pure nitrogen gas (99.99%) for 5 minutes. Then CO2 gas is injected into the gas chamber, and the sensor output data is measured after 2 minutes. MCU will obtain mathematical model according to pre-calibration experiment and data fitting, and the specific formula is as follows:

[0111]

[0112] The above formula is used to calculate the gas concentration of CO2.

[0113] The application provides a multi-channel gas detection sensor design method based on the NDIR principle, which mainly comprises an infrared light source, a gas chamber, a four-channel thermoelectric detector, a light source voltage stabilizing and modulating circuit, a thermoelectric weak signal conditioning circuit, a high-precision analog-to-digital conversion circuit and a single-chip microcomputer control and communication circuit system and the like. The light source driving circuit is improved to reduce the interference of the load on the subsequent circuit, a high-performance circuit is designed to reduce noise and drift, the detection accuracy is ensured, a low-power 24-bit sigma-delta type ADC circuit is used to improve the sensitivity and stability of the sensor. These improvements enable the designed gas detection sensor to perform accurate and real-time multi-gas concentration detection in a small volume, the light source driving circuit ensures the stability of the signal, the high-performance circuit design reduces noise and drift, improves the accuracy of signal processing, the low-power 24-bit sigma-delta type ADC circuit provides high-precision data acquisition and enhances the stability of the sensor, and the single-chip microcomputer control and communication circuit system realizes real-time analysis and transmission of the measurement results, ensuring the overall performance of the system.

[0114] In summary, the optical multi-channel gas sensor based on the NDIR principle, the utility model puts forward a kind of optical multi-channel gas sensor based on the NDIR principle, realizes the function of compact structure, real-time measurement of multiple gases. With Beer-Lambert reference detection as the basic principle, a low-noise zero-drift self-stable signal processing circuit is realized using a high-performance operational amplifier chip, a low-power 24-bit Sampling circuit is designed, accurate real-time digital signals can be obtained without complex data processing algorithms, the utility model design has the characteristics of wide range, high precision, good stability, long service life, miniaturization, etc., and multiple types of gases can be measured by replacing the sensor end.

[0115] It should be noted that the above embodiments are only used to illustrate the technical solutions of the utility model and not to limit, although the utility model is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the utility model can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the utility model, which should be covered in the scope of the claims of the utility model.

Claims

1. An optical multi-channel gas sensor based on the NDIR principle, comprising a circuit module, characterized in that: The circuit module comprises a power supply circuit, a light source driving circuit, an infrared light source, a gas sample unit, a thermoelectric pile sensor, an optical gas chamber, a temperature compensation circuit, a signal processing circuit, an ADC acquisition circuit and an MCU minimum system unit. The infrared light source emits infrared light, the heat change formed after the infrared light is absorbed by the gas sample unit is detected by the thermoelectric pile sensor, and then converted into a voltage signal, which is processed by the signal processing circuit, and finally read and calculated by the MCU to obtain the concentration of each gas.

2. The optical multi-channel gas sensor based on the NDIR principle according to claim 1, characterized in that: The power supply circuit is used for providing voltage for each module circuit. The light source driving circuit is used for driving the infrared light source. The infrared light source is used for providing infrared light source for the detector. The gas sample unit is arranged on the infrared light beam path in the optical gas chamber.

3. The optical multi-channel gas sensor based on the NDIR principle according to claim 1, characterized in that: The thermoelectric pile sensor is used for measuring the heat change after the infrared light is absorbed by the gas molecules. The optical gas chamber is used for providing an isolated and sealed space for the measured gas sample, and fixing the light source and the detector. The temperature compensation circuit is used for compensating the environmental temperature error caused by the heat of the infrared light source. The signal processing circuit is composed of a filter circuit, a bias voltage circuit and a single power supply operational amplifier, and is used for processing the small voltage signal output by the thermoelectric pile.

4. The optical multi-channel gas sensor based on the NDIR principle according to claim 1, characterized in that: The ADC acquisition circuit is used for acquiring the amplified analog voltage signal, and converting the signal into a digital signal after second-stage amplification and filtering, and transmitting the digital signal to the MCU. The MCU minimum system unit is used for driving the light source, reading the ADC signal and processing and transmitting the gas concentration signal to the upper computer. The upper computer is used for displaying and analyzing the flue gas concentration information.

5. The optical multi-channel gas sensor based on the NDIR principle according to claim 1, characterized in that: The MCU drives the infrared light source in a PWM mode, emits infrared light pulses, and the light rays are reflected by the gas chamber and reach the thermoelectric pile detector HTS-Q21. The detector signal is amplified and filtered by the signal conditioning circuit, the amplified analog signal is sampled by the ADC chip, converted into a digital signal, transmitted to the master chip microcontroller through the SPI protocol, and the collected data is arranged and output to the upper computer through the serial port.

6. The optical multi-channel gas sensor based on the NDIR principle according to claim 1, characterized in that: The infrared gas chamber, infrared light source, thermoelectric pile sensor and part of the driving circuit are arranged on the front surface of the circuit board, and the MCU minimum system circuit, ADC acquisition circuit and signal processing circuit are arranged on the back surface of the circuit board.

7. The optical multi-channel gas sensor based on the NDIR principle according to claim 1, characterized in that: The infrared light source is an enhanced wide-spectrum infrared light source with a concave light reflector around the bulb, with a wavelength band of 0-5 μm and a glass transmittance about twice that of a common light source.

8. The optical multi-channel gas sensor based on the NDIR principle according to claim 1, characterized in that: The infrared detection sensor is a four-channel thermoelectric pile sensor, and the peak wavelengths of the channels are 3.91 μm for the reference channel, 4.64 μm for the CO channel, 3.40 μm for the CH4 channel and 4.43 μm for the CO2 channel; the noise voltage is 37 nV / √Hz.

9. The optical multi-channel gas sensor based on the NDIR principle according to claim 1, characterized in that: The ADC circuit is designed based on the 8-channel low-noise 24-bit sigma-delta type ADC chip AD7124-8 integrated with PGA and reference voltage source, uses differential signal input, the internal reference voltage is 2.5 V, the gain PGA is set to 32, the filter register is set to use sinc4+sinc1 to quickly establish the filter, and the full power working mode FS=20.

Images