CN105115900A - Atmospheric trace gas detecting device - Google Patents

Abstract

The invention discloses an atmospheric trace gas detection device, which comprises a sinusoidal signal generating circuit, a modulation current source, a light-emitting diode light source, a band-pass interference filter, a lens, an aperture, a high reflectivity lens, a gas pool, and a photomultiplier tube , broadband amplifier and sinusoidal signal phase difference detection circuit. The sinusoidal modulation current source drives the light-emitting diode to emit sinusoidal modulation light to excite the optical resonant cavity composed of two high-reflectivity lenses. Detection sensitivity. The photomultiplier tube is used to detect the optical signal of the sinusoidal modulated light passing through the optical resonant cavity, and the measured atmospheric trace gas is obtained by measuring the phase difference change of the sinusoidal optical signal when the gas cell is filled with background gas and the measured atmospheric trace gas. concentration.

Description

An Atmospheric Trace Gas Detection Device

technical field

The invention relates to the field of gas concentration detection devices, in particular to an atmospheric trace gas detection device.

Background technique

The concentration of trace gases in the atmosphere is extremely low, and their volume mixing ratio in the atmosphere is on the order of 10 ^-12 to 10 ^-7 . The detection of trace gases in the atmosphere requires detection instruments with very high detection sensitivity. The use of spectral absorption technology to detect atmospheric trace gases usually achieves the purpose of high detection sensitivity by increasing the absorption path length. An optical resonant cavity composed of two high-reflectivity lenses, when the light emitted by the light source is incident from one end of the cavity, the incident light can be reflected back and forth in the cavity multiple times before exiting from the other end, thus achieving increased light absorption purpose of the program. At present, the technologies that use this optical resonant cavity to detect the concentration of atmospheric trace gases are mainly cavity ring-down spectroscopy (CRDS) and incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS). Among them, CRDS technology uses a laser light source to excite the optical resonant cavity. It uses a photomultiplier tube and is equipped with a high-speed data acquisition card to obtain the ring-down signal of the laser after passing through the resonator, and then obtains the ring-down signal of the laser in the cavity from the ring-down signal. Time finally determines the concentration of the gas to be measured; IBBCEAS technology uses broadband light sources, such as xenon arc lamps, light-emitting diodes, etc., to excite the optical resonant cavity. (such as CCD or PDA) to detect, and then determine the concentration of the gas to be measured through the analytical method of spectral fitting. High-speed data acquisition card and laser light source are expensive, and the life of the laser light source is limited. At the same time, a dedicated drive device is required, which is not conducive to the use of CRDS technology for long-term field measurements. The IBBCEAS technology is a broadband spectral measurement technology. Usually, it is necessary to obtain the absorption information of the measured gas in the tens of nanometers band to invert the concentration of the measured gas. Spectrometers and multi-channel optical detectors are essential for measurement. The spectrometer is greatly affected by temperature, especially in the field measurement, where the temperature difference between day and night is large, and the wavelength drift of the measurement spectrum is inevitable, thus affecting the measurement results. In addition, the measurement results of IBBCEAS technology are directly related to the light intensity of the light source. This measurement technique has high requirements on the stability of the light source, and usually requires measures to stabilize the light output of the light source, which undoubtedly increases the complexity of the measurement device.

Contents of the invention

The purpose of the present invention is to provide an atmospheric trace gas detection device to solve the problem of using an optical resonant cavity to measure the existence of atmospheric trace gases in the prior art.

In order to achieve the above object, the technical scheme adopted in the present invention is:

An atmospheric trace gas detection device is characterized in that it includes a sinusoidal signal generating circuit, a modulation current source, a broadband amplifier, a sinusoidal signal phase difference detection circuit, a light source, a photomultiplier tube, and a gas cell, and the gas cell is cylindrical , one end of the gas pool is provided with a light inlet, the other end of the gas pool is provided with a light outlet, one end of the side wall of the gas pool is provided with an air inlet, and the other end of the side wall of the gas pool is provided with a gas outlet, and The light inlet and the light outlet are respectively located at both ends of the central axis of the gas pool. A first high-reflectivity mirror is arranged in the gas pool near the light inlet, and a second high-reflectivity mirror is arranged in the gas pool near the light outlet. The first, The reflective surfaces of the second high-reflectivity lens are opposite to each other, the light source is arranged outside the end where the light entrance of the gas pool is located and aligned with the light entrance, and a band-pass interference filter is sequentially arranged between the light source and the light entrance of the gas pool , the first lens, the first diaphragm, the photomultiplier tube is arranged outside the end where the light outlet of the gas cell is located, the receiving window of the photomultiplier tube is aligned with the light outlet, and the light outlet of the gas cell and the photomultiplier tube are arranged in turn The second diaphragm and the second lens, the output end of the sinusoidal signal generating circuit is connected to the input end of the modulation current source, the output end of the modulation current source is connected to the driving end of the light source, and the output end of the photomultiplier tube is connected to the input end of the broadband amplifier , the sinusoidal signal phase difference detection circuit has two input terminals, one of the input terminals of the sinusoidal signal phase difference detection circuit is connected to the output terminal of the broadband amplifier, and the other input terminal of the sinusoidal signal phase difference detection circuit is connected to the output terminal of the sinusoidal signal generation circuit ;

The sinusoidal voltage signal output by the sinusoidal signal generation circuit controls the modulation current source, so that the modulation current source outputs a sinusoidal modulation current, and then drives the light source to emit sinusoidal modulation light. The sinusoidal modulation light is first filtered by a band-pass interference filter, and then passes through the first lens Converge the sinusoidal modulated light at the center of the gas cell, the first diaphragm is used to limit the diameter of the incident light spot, the sinusoidal modulated light after entering the gas cell returns more often between the first high reflectivity lens and the second high reflectivity lens The secondary reflection increases the absorption optical path. The sinusoidal modulated light transmitted from the second high-reflectivity lens passes through the second diaphragm to limit the spot diameter, and is collected by the second lens and converged to the receiving window of the photomultiplier tube. The transmitted sinusoidal light The signal is converted into a sinusoidal voltage signal by a photomultiplier tube. After being amplified by a broadband amplifier, the sinusoidal voltage signal is input to one input terminal of the sinusoidal signal phase difference detection circuit, and the signal at the other input terminal of the sinusoidal signal phase difference detection circuit is generated by a sinusoidal signal. The sinusoidal voltage signal output by the circuit, and the phase difference output by the sinusoidal signal phase difference detection circuit are related to the concentration of the gas to be measured.

The aforementioned atmospheric trace gas detection device is characterized in that: the light source is a high-brightness light-emitting diode, and the center wavelength of the band-pass interference filter is the same as that of the light source.

The atmospheric trace gas detection device is characterized in that: the gas pool is made of polytetrafluoroethylene material, and the two ends of the gas pool are respectively sealed with the first high-reflectivity lens and the second high-reflectivity lens. connected together.

The described atmospheric trace gas detection device is characterized in that: the sinusoidal signal generating circuit includes a single-chip microcomputer U21 whose model is AT89C51, a direct digital frequency synthesis chip U22 whose model is AD9834, a passive crystal oscillator X21, an active Crystal oscillator X22, OP07 operational amplifier U23, DIP switch SW21 and two-pin output terminal J21, the XTAL1 and XTAL2 pins of the single-chip microcomputer U21 are respectively connected to the two ends of the passive crystal oscillator X21 one by one There are capacitors C21 and C22 in series at both ends of the passive crystal oscillator X21, and the capacitors C21 and C22 are grounded through wires. The clock circuit is composed of the passive crystal oscillator X21, capacitors C21 and C22, and the RESET pin of the microcontroller U21 passes through Capacitor C23 is connected to +5V voltage, and the RESET pin of the single-chip microcomputer U21 is also grounded through the resistor R21. The reset circuit is composed of the capacitor C23 and the resistor R21. The P2.0-P2.7 pin of the single-chip microcomputer U21 is connected with the end of the dial switch SW21 connection, the other end of the DIP switch SW21 is grounded, the DIP switch SW21 constitutes the DIP switch input circuit, and the MCU U21 The pin is connected to the +5V voltage through the resistor R23, and the P1.0-P1.3 pin of the single-chip microcomputer U21 is connected with the SCLK pin, SDATA pin, FSYNC pin, and RESET pin of the direct digital frequency synthesis chip U22 one by one Corresponding to the connection, the VCC pin of the single-chip microcomputer U21 is connected to +5V voltage, the VCC pin of the single-chip microcomputer U21 is also connected to the ground with its own GND pin through the capacitor C24, and the MCLK pin of the direct digital frequency synthesis chip U22 is connected to the ground through the resistor R22. One end of the active crystal oscillator X22 is connected, the other end of the active crystal oscillator X22 is connected to the GND pin of the microcontroller U21, the power supply end of the active crystal oscillator X22 is connected to +5V voltage, and the CAP pin of the direct digital frequency synthesis chip U22 Pin is connected to its own DGND pin through capacitor C25, DGND of direct digital frequency synthesis chip U22 is grounded, DGND pin of direct digital frequency synthesis chip U22 is also connected to +5V voltage through capacitor C27 and its own DVDD pin, directly The AGND pin of the digital frequency synthesis chip U22 is connected to its own DGND pin, the AGND pin of the direct digital frequency synthesis chip U22 is also connected to its own AVDD pin through the capacitor C26, and the AVDD pin of the direct digital frequency synthesis chip U22 is connected to its own DVDD pin. Pin connection, the COMP pin of the direct digital frequency synthesis chip U22 is connected to +5V voltage through the capacitor C29, the REFOUT pin of the direct digital frequency synthesis chip U22 is connected to the ground with its own SLEEP pin through the capacitor C210, and the direct digital frequency synthesis chip The FSADJ pin of U22 is grounded through the resistor R24, the IOUT pin of the direct digital frequency synthesis chip U22 is connected to its own VIN pin through the resistor R25, the VIN pin of the direct digital frequency synthesis chip U22 is grounded through the capacitor C211, and the direct digital frequency synthesis chip The IOUTB pin of U22 is grounded through the capacitor C28 and resistor R27 connected in parallel with each other. The non-inverting input terminal of the operational amplifier U23 is connected to the IOUT pin of the direct digital frequency synthesis chip U22 through the resistor R29 and the resistor R28 in turn, and the resistor R28 is directly connected to the IOUTB pin of the direct digital frequency synthesis chip U22. The IOUT pins of the digital frequency synthesis chip U22 are also grounded through the capacitor C212 and the resistor R26 connected in parallel, the non-inverting input terminal of the operational amplifier U23 is also grounded through the capacitor C213, and the inverting input terminal of the operational amplifier U23 is grounded through the resistor R210. The inverting input terminal of the amplifier U23 is also connected to its own output terminal through the resistor R211, the output terminal of the operational amplifier U23 is connected between the resistor R28 and the resistor R29 through the capacitor C214, and the output terminal of the operational amplifier U23 is also connected to the pin of the output terminal J21 1 connection, pin 2 of the output terminal J21 is grounded, and an active low-pass filter circuit is formed by the operational amplifier U23, resistors R28-R211, capacitors C213 and C214, and the output terminal J21.

The described atmospheric trace gas detection device is characterized in that: the modulation current source includes operational amplifiers U1A and U1B, MOS tube Q31, two-pin output terminal J32 whose models are respectively TL064, and the inverting phase of the operational amplifier U1A The input terminal is connected to the pin 1 of the output terminal J21 in the sinusoidal signal generating circuit, the non-inverting input terminal of the operational amplifier U1A is connected to the output terminal of the operational amplifier U1B, and the positive and negative power supply terminals of the operational amplifier U1A are respectively connected to +12V voltage, - 12V voltage, and the positive power supply terminal of the operational amplifier U1A is also grounded through the capacitor C31, the negative power supply terminal of the operational amplifier U1A is also grounded through the capacitor C32, the output terminal of the operational amplifier U1A is connected to the gate of the MOS transistor Q31 through the resistor R31, and the MOS transistor The source of Q31 is connected to +12V voltage, the source of MOS transistor Q31 is also connected to its own gate through the parallel capacitor C33 and resistor R32, the drain of MOS transistor Q31 is connected to pin 1 of output terminal J32, and the output terminal The pin 2 of J32 is grounded through the resistor R33, the non-inverting input terminal of the operational amplifier U1B is grounded through the parallel capacitors C34 and C35, and the non-inverting input terminal of the operational amplifier U1B is also connected between the pin 2 of the output terminal J32 and the resistor R33 , the inverting input terminal of the operational amplifier U1B is grounded through the parallel capacitor C36 and the resistor R34, the inverting input terminal of the operational amplifier U1B is also connected to its own output terminal through the resistor R35, and the pin 1 and pin 2 of the output terminal J32 Connect to the positive and negative poles of the light source respectively.

Said a kind of atmospheric trace gas detection device is characterized in that: said sinusoidal signal phase difference detection circuit includes a phase difference detection integrated chip U41 whose model is AD8302, a single chip microcomputer U42 whose model is Atmega8, input terminals J41 and J42, a dial The code switch SW41, the INPA pin of the phase difference detection integrated chip U41 is connected to its own OFSA pin through the capacitor C41, the resistor R41, and the capacitor C42 in turn, and wires are respectively drawn between the capacitor C41 and the resistor R41, and between the capacitor C42 and the resistor R41 Connect to the input terminal J41, the input terminal J41 is connected to the pin 1 of the output terminal J21 in the sinusoidal signal generating circuit, the capacitor C42 and the resistor R41 are connected to the ground through a wire, and the INPB pin of the phase difference detection integrated chip U41 is passed through the capacitor C43, resistor R42, and capacitor C44 are connected to their own OFSB pins. Wires are drawn between capacitor C43 and resistor R42, and between capacitor C44 and resistor R42 to connect to input terminal J42. Input terminal J42 is connected to the output end of the broadband amplifier. Capacitor The connection between C44 and the resistor R42 is also grounded through a wire, the VCC pin of the phase difference detection integrated chip U41 is connected to +5V voltage, and the VCC pin of the phase difference detection integrated chip U41 is also connected to the ground with its own GND pin through the capacitor C45. The PSET pin and VPHS pin of the phase difference detection integrated chip U41 are connected together and connected to the ADC0 pin of the single chip microcomputer U42, and the MFLT pin of the phase difference detection integrated chip U41 is connected with its own PFLT pin through the capacitor C46 through the capacitor C47. Grounding, a passive crystal oscillator X41 is connected between the XTAL1 pin and the XTAL2 pin of the single-chip microcomputer U42, and a capacitor C48 and a capacitor C49 are connected in series between the two ends of the passive crystal oscillator X41, and the capacitor C48 and the capacitor C49 pass through The wire is grounded, the VCC pin and AVCC pin of the single-chip microcomputer U42 are connected together and connected to +5V voltage, the VCC pin of the single-chip microcomputer U42 is also connected to its own AREF pin through the resistor R43, and the AREF pin of the single-chip microcomputer U42 is connected to a. It is the cathode of the 2.5V reference voltage chip Q41 of LM336-2.5, the anode of the 2.5V reference voltage chip Q41 is connected to the GND pin of the single-chip microcomputer U42, and the ground of the single-chip microcomputer U42 The pin is connected to +5V voltage through the pull-up resistor R44, and the MCU U42 The pin is also grounded through the capacitor C410, the PC3 pin of the single-chip microcomputer U42 is connected to +5V voltage through the pull-up resistor R45, the PC3 pin of the single-chip microcomputer U42 is also connected to one end of the dial switch SW41, and the other end of the dial switch SW41 is grounded.

Compared with the prior art, the present invention has the advantages of:

(1) The present invention utilizes the light-emitting diode after the sinusoidal modulation to excite the optical resonant cavity, and obtains the concentration of the measured atmospheric trace gas by detecting the phase change of the sinusoidal light signal after passing through the resonant cavity instead of the light intensity change, avoiding the light source light The impact of strong fluctuations on the measurement results improves the accuracy of the measurement results.

(2) The present invention does not use a laser, but uses a light-emitting diode as a light source to excite the optical resonant cavity. The light-emitting diode has the advantages of small size, long service life, energy saving and environmental protection, and can work continuously and safely for a long time. Long-term observations of gases provide a guarantee.

(3) The present invention obtains the concentration of the atmospheric trace gas to be measured by detecting the phase change of the sinusoidal light signal after passing through the resonant cavity. The detection of the sinusoidal light signal only requires an ordinary photomultiplier tube, and does not need to use an expensive spectrometer, multi-channel The optical detector and the high-speed data acquisition card avoid the impact of the wavelength drift of the spectrometer on the measurement results, and also reduce the cost of the measurement device.

Description of drawings

Fig. 1 is a composition block diagram of an atmospheric trace gas detection device according to the present invention.

Fig. 2 is a schematic circuit diagram of a sinusoidal signal generating circuit in an atmospheric trace gas detection device of the present invention.

Fig. 3 is a schematic circuit diagram of a modulation current source in an atmospheric trace gas detection device according to the present invention.

Fig. 4 is a schematic circuit diagram of a sinusoidal signal phase difference detection circuit in an atmospheric trace gas detection device according to the present invention.

Detailed ways

As shown in Figure 1, an atmospheric trace gas detection device includes a sinusoidal signal generating circuit 1, a modulation current source 2, a broadband amplifier 13, a sinusoidal signal phase difference detection circuit 14, a light source 3, a photomultiplier tube 12, and a gas cell 8 , the gas pool 8 is cylindrical, the gas pool 8 is provided with a light inlet at one end of the circular surface, the other end of the gas pool 8 is provided with a light outlet, and one end of the side wall of the gas pool 8 is provided with an air inlet. The other end of the 8 side wall is provided with an air outlet, and the light entrance and the light exit are respectively located at both ends of the central axis of the gas pool 8, and the first high reflectivity lens 7 is arranged in the gas pool 8 near the light entrance, and the gas pool 8 A second high-reflectivity mirror 9 is provided near the light outlet, and the reflection surfaces of the first and second high-reflectance mirrors 7 and 9 are opposite to each other. A light port, and a bandpass interference filter 4, a first lens 5, and a first diaphragm 6 are sequentially arranged between the light source 3 and the light entrance of the gas cell 8, and the photomultiplier tube 12 is arranged at the end where the light exit of the gas cell 8 is located In addition, the receiving window of the photomultiplier tube 12 is aligned with the light outlet, and a second aperture 10 and a second lens 11 are arranged in sequence between the light outlet of the gas cell 8 and the photomultiplier tube 12, and the output terminal of the sinusoidal signal generation circuit 1 is connected to the modulation The input end of the current source 2 is connected, the output end of the modulation current source 2 is connected to the driving end of the light source 3, the output end of the photomultiplier tube 12 is connected to the input end of the broadband amplifier 13, the sinusoidal signal phase difference detection circuit 14 has two input ends, and the sinusoidal signal One of the input terminals of the phase difference detection circuit 14 is connected to the output terminal of the broadband amplifier 13, and the other input terminal of the sinusoidal signal phase difference detection circuit 14 is connected to the output terminal of the sinusoidal signal generation circuit 1;

The sinusoidal voltage signal output by the sinusoidal signal generating circuit 1 controls the modulation current source 2, so that the modulation current source 2 outputs a sinusoidally modulated current, and then drives the light source 3 to emit sinusoidal modulation light. The sinusoidal modulation light is first filtered by a band-pass interference filter 4, The sinusoidally modulated light is converged at the center of the gas pool 8 through the first lens 5, and the first diaphragm 6 is used to limit the diameter of the incident light spot. Multiple reflections between the second high-reflectivity mirrors 9 increase the absorption optical path, and the sinusoidally modulated light transmitted from the second high-reflectance mirror 9 is collected by the second lens 11 after passing through the second aperture 10 to limit the spot diameter. Converging to the receiving window of the photomultiplier tube 12, the transmitted sinusoidal light signal is converted into a sinusoidal voltage signal by the photomultiplier tube 12, and the sinusoidal voltage signal is amplified by the broadband amplifier 13 and input to one of the sinusoidal signal phase difference detection circuits 14. end, the signal at the other input end of the sinusoidal signal phase difference detection circuit 14 is the sinusoidal voltage signal output by the sinusoidal signal generation circuit 1, because the sinusoidal modulation light after entering the gas cell 8 is transmitted after a certain absorption optical path transmission, so the transmission The outgoing sinusoidal light signal must lag behind the sinusoidal modulation light emitted by the light source 3 in phase. The higher the concentration of the gas to be measured in the gas cell 8, the shorter the absorption path and the smaller the phase lag. Therefore, the magnitude of the phase difference output by the sinusoidal signal phase difference detection circuit 14 is related to the measured gas concentration.

The light source 3 is a high-brightness light-emitting diode, and the center wavelength of the bandpass interference filter 4 is the same as that of the light source 3 .

The gas pool 8 is made of polytetrafluoroethylene, and the two ends of the gas pool 8 are sealed and connected with the first high-reflectivity lens 7 and the second high-reflectivity lens 9 respectively.

As shown in Figure 2, the sinusoidal signal generating circuit includes a microcontroller U21 model AT89C51, a direct digital frequency synthesis chip U22 model AD9834, a passive crystal oscillator X21, an active crystal oscillator X22, and an operational amplifier U23 model OP07 , DIP switch SW21 and two-pin output terminal J21, the XTAL1 pin and XTAL2 pin of the single-chip microcomputer U21 are respectively connected to the two ends of the passive crystal oscillator X21 in one-to-one correspondence, and the two ends of the passive crystal oscillator X21 are connected in series Capacitors C21, C22, capacitors C21, C22 are grounded through wires, a clock circuit is composed of a passive crystal oscillator X21, capacitors C21 and C22, the RESET pin of the single-chip microcomputer U21 is connected to +5V voltage through the capacitor C23, and the RESET of the single-chip microcomputer U21 The pin is also grounded through the resistor R21, and the reset circuit is composed of the capacitor C23 and the resistor R21. The P2.0 pin-P2.7 pin of the microcontroller U21 is connected to one end of the dial switch SW21, and the other end of the dial switch SW21 is grounded. The code switch SW21 constitutes the input circuit of the dial switch, and the single-chip microcomputer U21 The pin is connected to the +5V voltage through the resistor R23, and the P1.0-P1.3 pin of the single-chip microcomputer U21 is connected with the SCLK pin, SDATA pin, FSYNC pin, and RESET pin of the direct digital frequency synthesis chip U22 one by one Corresponding to the connection, the VCC pin of the single-chip microcomputer U21 is connected to +5V voltage, the VCC pin of the single-chip microcomputer U21 is also connected to the ground with its own GND pin through the capacitor C24, and the MCLK pin of the direct digital frequency synthesis chip U22 is connected to the ground through the resistor R22. One end of the active crystal oscillator X22 is connected, the other end of the active crystal oscillator X22 is connected to the GND pin of the microcontroller U21, the power supply end of the active crystal oscillator X22 is connected to +5V voltage, and the CAP pin of the direct digital frequency synthesis chip U22 Pin is connected to its own DGND pin through capacitor C25, DGND of direct digital frequency synthesis chip U22 is grounded, DGND pin of direct digital frequency synthesis chip U22 is also connected to +5V voltage through capacitor C27 and its own DVDD pin, directly The AGND pin of the digital frequency synthesis chip U22 is connected to its own DGND pin, the AGND pin of the direct digital frequency synthesis chip U22 is also connected to its own AVDD pin through the capacitor C26, and the AVDD pin of the direct digital frequency synthesis chip U22 is connected to its own DVDD pin. Pin connection, the COMP pin of the direct digital frequency synthesis chip U22 is connected to +5V voltage through the capacitor C29, the REFOUT pin of the direct digital frequency synthesis chip U22 is connected to the ground with its own SLEEP pin through the capacitor C210, and the direct digital frequency synthesis chip The FSADJ pin of U22 is grounded through the resistor R24, the IOUT pin of the direct digital frequency synthesis chip U22 is connected to its own VIN pin through the resistor R25, the VIN pin of the direct digital frequency synthesis chip U22 is grounded through the capacitor C211, and the direct digital frequency synthesis chip The IOUTB pin of U22 is grounded through the capacitor C28 and resistor R27 connected in parallel with each other. The non-inverting input terminal of the operational amplifier U23 is connected to the IOUT pin of the direct digital frequency synthesis chip U22 through the resistor R29 and the resistor R28 in turn, and the resistor R28 is directly connected to the IOUTB pin of the direct digital frequency synthesis chip U22. The IOUT pins of the digital frequency synthesis chip U22 are also grounded through the capacitor C212 and the resistor R26 connected in parallel, the non-inverting input terminal of the operational amplifier U23 is also grounded through the capacitor C213, and the inverting input terminal of the operational amplifier U23 is grounded through the resistor R210. The inverting input terminal of the amplifier U23 is also connected to its own output terminal through the resistor R211, the output terminal of the operational amplifier U23 is connected between the resistor R28 and the resistor R29 through the capacitor C214, and the output terminal of the operational amplifier U23 is also connected to the pin of the output terminal J21 1 connection, pin 2 of the output terminal J21 is grounded, and an active low-pass filter circuit is formed by the operational amplifier U23, resistors R28-R211, capacitors C213 and C214, and the output terminal J21.

The sinusoidal signal generating circuit 1 is composed of a single-chip microcomputer control system and a direct digital frequency synthesis circuit, specifically, the single-chip microcomputer U21 of the model AT89C51, the direct digital frequency synthesis chip U22 of the model AD9834, resistors R21~R211, capacitors C21~C214, passive crystal Oscillator X21, active crystal oscillator X22, OP07 operational amplifier U23, dial switch SW21 and output terminal J21. The single-chip microcomputer control system is composed of a clock circuit composed of a single-chip microcomputer U21, capacitors C21-C22 and crystal oscillator X21, a reset circuit composed of a resistor R21 and a capacitor C23, and a dial switch input circuit composed of a dial switch SW21; the direct digital frequency synthesis circuit consists of The direct digital frequency synthesis chip U22 is composed of an active low-pass filter circuit, and the active crystal oscillator X22 outputs a 50MHz square wave signal as a reference clock for U22. The active low-pass filter circuit is composed of resistors R28-R211, capacitors C213, C214, operational amplifier U23 and output terminal J21. The I/O ports P1.0~P1.3 of the single-chip microcomputer U21 are respectively connected to the SCLK, SDATA, FSYNC and RESET pins of the direct digital frequency synthesis chip U22, that is, the single-chip microcomputer U21 communicates with the direct The digital frequency synthesis chip U22 is programmed to control the direct digital frequency synthesis circuit to output a sinusoidal voltage signal with a set frequency. The specific control process is: MCU U21 first reads the state of the DIP switch SW21 in the DIP switch input circuit to its P2. Data size Program the corresponding frequency control command word for the direct digital frequency synthesis chip U22, so that the 19 pin of U22 outputs a sinusoidal current signal with a set frequency. The sinusoidal current signal is converted into a sinusoidal voltage signal by resistor R26, and then passed through The low-pass filter circuit is connected to the output terminal J21 after filtering the high-order harmonics, and the sinusoidal voltage signal of the set frequency can be obtained on the output terminal J21.

As shown in Figure 3, the modulating current source includes operational amplifiers U1A and U1B of the model TL064, MOS transistor Q31, two-pin output terminal J32, the inverting input terminal of the operational amplifier U1A and the output terminal J21 of the sinusoidal signal generating circuit. Pin 1 is connected, the non-inverting input terminal of operational amplifier U1A is connected with the output terminal of operational amplifier U1B, the positive and negative power supply terminals of operational amplifier U1A are respectively connected to +12V voltage and -12V voltage, and the positive power supply terminal of operational amplifier U1A is also connected to Grounded through capacitor C31, the negative power supply terminal of operational amplifier U1A is also grounded through capacitor C32, the output terminal of operational amplifier U1A is connected to the gate of MOS transistor Q31 through resistor R31, the source of MOS transistor Q31 is connected to +12V voltage, and the MOS transistor The source of Q31 is also connected to its own gate through the parallel capacitor C33 and resistor R32, the drain of the MOS transistor Q31 is connected to the pin 1 of the output terminal J32, and the pin 2 of the output terminal J32 is grounded through the resistor R33. The non-inverting input terminal of U1B is grounded through the capacitors C34 and C35 connected in parallel. The non-inverting input terminal of the operational amplifier U1B is also connected between the pin 2 of the output terminal J32 and the resistor R33. The capacitor C36 and the resistor R34 are grounded, the inverting input terminal of the operational amplifier U1B is also connected to its own output terminal through the resistor R35, and the pin 1 and pin 2 of the output terminal J32 are respectively connected to the positive pole and the negative pole of the light source.

Modulating current source 2 is composed of operational amplifiers U1A, U1B of model TL064, resistors R31-R35, capacitors C31-C36, MOS transistor Q31 of model IR9540 and output terminal J32. Among them, the operational amplifier U1A, Q31, current sampling resistor R33 and operational amplifier U1B form a current negative feedback circuit, the output of the modulation current source 2 is drawn from the terminal J32, and the current direction is from pin 1 to pin 2 of J32, and the magnitude of the output current is determined by The 2-pin control of U1A is controlled by the 1-pin signal of the input terminal J21. The input is connected to the output of the sinusoidal signal generating circuit 1 (that is, the output terminal J21 in FIG. 2 ), and the output of the sinusoidal signal generating circuit 1 is a sinusoidal voltage signal, so the sinusoidal current drawn from the output terminal J32 is used to drive the light source 3. When connecting, connect pin 1 of the output terminal J32 to the positive pole of the light source 3, and pin 2 of the output terminal J32 to the negative pole of the light source 3, so that the light source 3 can emit sinusoidal modulated light.

As shown in Figure 4, the sinusoidal signal phase difference detection circuit includes a phase difference detection integrated chip U41 whose model is AD8302, a single-chip microcomputer U42 whose model is Atmega8, input terminals J41 and J42, a dial switch SW41, and the INPA of the phase difference detection integrated chip U41. The pins are connected to their own OFSA pins in turn through capacitor C41, resistor R41, and capacitor C42. There are wires drawn between capacitor C41 and resistor R41, and between capacitor C42 and resistor R41 to connect to input terminal J41. Input terminal J41 is connected to the sinusoidal signal The pin 1 of the output terminal J21 in the generating circuit is connected, the capacitor C42 and the resistor R41 are connected to the ground through a wire, and the INPB pin of the phase difference detection integrated chip U41 passes through the capacitor C43, the resistor R42, the capacitor C44 and its own OFSB pin in turn. connection, between the capacitor C43 and the resistor R42, and between the capacitor C44 and the resistor R42, wires are respectively drawn to connect to the input terminal J42, and the input terminal J42 is connected to the output end of the broadband amplifier, and the wires between the capacitor C44 and the resistor R42 are also grounded, and the phase The VCC pin of the difference detection integrated chip U41 is connected to +5V voltage, the VCC pin of the phase difference detection integrated chip U41 is also connected to the ground with its own GND pin through the capacitor C45, the PSET pin of the phase difference detection integrated chip U41, VPHS After the pins are connected together, they are connected to the ADC0 pin of the single-chip microcomputer U42. The MFLT pin of the phase difference detection integrated chip U41 is connected to its own PFLT pin through the capacitor C46 and then grounded. The XTAL1 pin of the single-chip microcomputer U42 is connected to the XTAL2 pin. There is a passive crystal oscillator X41 connected between them, and a capacitor C48 and a capacitor C49 are connected in series between the two ends of the passive crystal oscillator X41. The capacitor C48 and the capacitor C49 are grounded through a wire. The pins are connected to +5V voltage. The VCC pin of the single-chip microcomputer U42 is also connected to its own AREF pin through the resistor R43. The AREF pin of the single-chip microcomputer U42 is connected to a 2.5V reference voltage chip Q41 whose model is LM336-2.5 Cathode, the anode of the 2.5V reference voltage chip Q41 is connected to the GND pin of the single-chip microcomputer U42, and the ground of the single-chip microcomputer U42 The pin is connected to +5V voltage through the pull-up resistor R44, and the MCU U42 The pin is also grounded through the capacitor C410, the PC3 pin of the single-chip microcomputer U42 is connected to +5V voltage through the pull-up resistor R45, the PC3 pin of the single-chip microcomputer U42 is also connected to one end of the dial switch SW41, and the other end of the dial switch SW41 is grounded.

The sinusoidal signal phase difference detection circuit 14 is composed of a phase difference detection integrated chip circuit and a single-chip microcomputer system. The phase difference detection integrated chip circuit is composed of the phase difference detection integrated chip U41 of model AD8302, capacitors C41~C47 and input terminals J41 and J42; Source crystal oscillator X41), reset circuit (composed of capacitor C410 and resistor R44), A/D sampling reference voltage circuit (composed of resistor R43 and 2.5V reference voltage chip Q41 of model LM336-2.5) and single-way dial Code switch circuit (composed of dial switch SW41 and resistor R45). The phase difference detection integrated chip circuit has two signal inputs, which are respectively introduced from the input terminals J41 and J42. The input from the input terminal J41 is the sinusoidal voltage signal generated by the sinusoidal signal generation circuit 1, that is, the input terminal J41 and the output in Figure 2 The terminals J21 are connected; the input from the J42 terminal is the sinusoidal voltage signal output by the broadband amplifier 13 . The phase difference detection integrated chip U41 converts the phase difference of the two sinusoidal voltage signals input into the sinusoidal signal phase difference detection circuit into a corresponding voltage signal, and the voltage signal is input to the ADC0 channel in the single-chip microcomputer U42, and is sampled by the single-chip microcomputer U42 Convert it into a digital signal for analysis and processing to get the size of the phase difference. The single-chip microcomputer U42 obtains the concentration of trace gas in the measured atmosphere by sampling the magnitude of the phase difference of the two sinusoidal voltage signals. For the first time, the gas cell is filled with background gas, which can be nitrogen or zero air, to obtain the phase difference φ ₁ ; for the second time, the gas cell is filled with the measured atmospheric trace gas to obtain the phase difference φ ₂ . Molecular concentration of the measured gas c is the speed of light, f is the frequency of the sinusoidal voltage signal, and σ is the absorption cross section of the measured gas.

The invention includes a sinusoidal signal generating circuit, a modulation current source, a light source, a band-pass interference filter, a first lens, a first aperture, a first high-reflectivity lens, a gas pool, a second high-reflectivity lens, and a second light Diaphragm, second lens, photomultiplier tube, broadband amplifier and sinusoidal signal phase difference detection circuit. Among them, the light source adopts a high-brightness light-emitting diode; the center wavelength of the band-pass interference filter is the same as that of the light source light-emitting diode, and the passband bandwidth is less than 10nm; the gas pool is a cylinder made of polytetrafluoroethylene, and the two end faces of the cylinder are A small hole is respectively opened in the vicinity, which is respectively an air inlet and an air outlet. The two ends of the cylinder are straight through, and are sealed and connected with the first high-reflectivity lens and the second high-reflectivity lens respectively. The sinusoidal voltage signal output by the sinusoidal signal generation circuit controls the modulation current source, so that the modulation current source outputs a sinusoidal modulation current, and then drives the light source to emit sinusoidal modulation light. The sinusoidal modulation light is first filtered by a band-pass interference filter, and then passes through the first lens Converge the sinusoidally modulated light at the center of the gas cell, and the first diaphragm is used to limit the diameter of the incident light spot. After entering the gas cell, the sinusoidally modulated light returns between the first high-reflectivity lens and the second high-reflectivity lens to reflect multiple times to increase the absorption optical path, and the sinusoidally modulated light transmitted from the second high-reflectivity lens passes through the second light After the diameter of the light spot is limited by the diaphragm, it is collected by the second lens and converged to the receiving window of the photomultiplier tube. The transmitted sinusoidal light signal is converted into a sinusoidal voltage signal by the photomultiplier tube. The sinusoidal voltage signal is amplified by a broadband amplifier and input to the sinusoidal signal. One input terminal of the phase difference detection circuit, the signal of the other input terminal of the sinusoidal signal phase difference detection circuit is the sinusoidal voltage signal output by the sinusoidal signal generation circuit. Since the sinusoidal modulated light entering the gas cell is transmitted after a certain absorption optical path, the transmitted sinusoidal light signal must lag behind the sinusoidal modulated light emitted by the light source 3 in phase. The higher the concentration of the gas to be measured in the gas cell, the shorter the absorption path and the smaller the phase lag. Therefore, the magnitude of the phase difference output by the sinusoidal signal phase difference detection circuit is related to the measured gas concentration.

The sinusoidal signal generating circuit is composed of a single-chip microcomputer control system and a direct digital frequency synthesis circuit. The single-chip microcomputer control system includes a single-chip microcomputer U21, a clock circuit, a reset circuit and a dial switch input circuit. The direct digital frequency synthesis circuit includes a direct digital frequency synthesis chip U22 and an active low-pass filter circuit. The single-chip microcomputer U21 programs the direct digital frequency synthesis chip U22 through its I/O port, so that the direct digital frequency synthesis circuit outputs a sinusoidal voltage signal with a set frequency, and the frequency setting is completed by the dial input switch circuit.

The modulation current source is composed of a current negative feedback circuit, and the magnitude of the output current is controlled by the sinusoidal voltage signal input by the modulation current source.

The sinusoidal signal phase difference detection circuit is composed of a phase difference detection integrated chip U41 circuit and a single chip microcomputer U42. The phase difference detection integrated chip U41 converts the phase difference of the two sinusoidal voltage signals input into the sinusoidal signal phase difference detection circuit into a corresponding voltage signal, which is sampled by the single-chip microcomputer U42 and converted into a digital signal for analysis and processing. The magnitude of the phase difference. The single-chip microcomputer U42 obtains the concentration of trace gas in the measured atmosphere by sampling the magnitude of the phase difference of the two sinusoidal voltage signals. For the first time, the gas cell is filled with background gas, which can be nitrogen or zero air, to obtain the phase difference φ ₁ ; for the second time, the gas cell is filled with the measured atmospheric trace gas to obtain the phase difference φ ₂ . Molecular concentration of the measured gas c is the speed of light, f is the frequency of the sinusoidal voltage signal, σ is the absorption cross section of the measured gas, and π is the circumference ratio.

Claims (6)

1. an atmospheric trace gas sniffer, it is characterized in that: comprise sinusoidal signal and produce circuit, modulation current source, broad band amplifier, sinusoidal signal phase difference detecting circuit, light source, photomultiplier, gas cell, described gas cell is cylindrical shape, gas cell one end disc end is provided with light inlet, gas cell other end disc end is provided with light-emitting window, on gas cell sidewall, one end is provided with air intake opening, on gas cell sidewall, the other end is provided with gas outlet, and light inlet, light-emitting window lays respectively at gas cell central axis two ends, in gas cell, light inlet position is provided with the first high reflectance eyeglass, in gas cell, light-emitting window position is provided with the second high reflectance eyeglass, and first, second high reflectance eyeglass reflecting surface toward each other, it is at one end outer and aim at light inlet that described light source is arranged on gas cell light inlet institute, and be disposed with bandpass interference filter between light source and gas cell light inlet, first lens, first diaphragm, described photomultiplier be arranged on gas cell light-emitting window institute at one end outside, light-emitting window aimed at by the receive window of photomultiplier, and be disposed with the second diaphragm between gas cell light-emitting window and photomultiplier, second lens, described sinusoidal signal produces circuit output end and is connected with modulation current source input end, modulating current source output terminal is connected with the drive end of light source, described photomultiplier output terminal is connected with broad band amplifier input end, described sinusoidal signal phase difference detecting circuit has two input ends, one of them input end of sinusoidal signal phase difference detecting circuit is connected with broad band amplifier output terminal, another input end of sinusoidal signal phase difference detecting circuit and sinusoidal signal produce circuit output end and are connected,

Sinusoidal signal produces the sine voltage signal control modulation current source that circuit exports, the electric current rear drive light source making modulation current source export Sine Modulated sends electroencephalogram, first electroencephalogram filters through bandpass interference filter, by the first lens, electroencephalogram is converged in the center of gas cell again, first diaphragm is used for limiting the diameter of launching spot, enter the electroencephalogram after gas cell return between the first high reflectance eyeglass and the second high reflectance eyeglass multiple reflections increase absorb light path, the electroencephalogram transmitted from the second high reflectance eyeglass is after the second diaphragm limited spot diameter, collected by the second lens and converge to the receive window of photomultiplier, the sinusoidal light signal transmitted is converted into sine voltage signal by photomultiplier, sine voltage signal is after broad band amplifier amplifies, be input to one of them input end of sinusoidal signal phase difference detecting circuit, the signal of another input end of sinusoidal signal phase difference detecting circuit is the sine voltage signal that sinusoidal signal produces circuit output, association is there is in the phase differential size that sinusoidal signal phase difference detecting circuit exports with tested gas concentration.

2. a kind of atmospheric trace gas sniffer according to claim 1, is characterized in that: described light source is high brightness LED, and the centre wavelength of described bandpass interference filter is identical with the centre wavelength of light source.

3. a kind of atmospheric trace gas sniffer according to claim 1, is characterized in that: described gas cell is made up of polytetrafluoroethylmaterial material, and gas cell two ends are corresponding to be respectively sealed connected together with the first high reflectance eyeglass and the second high reflectance eyeglass.

4. a kind of atmospheric trace gas sniffer according to claim 1, it is characterized in that: described sinusoidal signal produces circuit and comprises the single-chip microcomputer U21 that model is AT89C51, model is the direct digital synthesis technique chip U22 of AD9834, passive crystal oscillator X21, active crystal oscillator X22, model is the operational amplifier U23 of OP07, the lead-out terminal J21 of toggle switch SW21 and bipod is formed, the XTAL1 pin of single-chip microcomputer U21, XTAL2 pin connects one to one with passive crystal oscillator X21 two ends respectively, passive crystal oscillator X21 two ends are also in series with electric capacity C21, C22, electric capacity C21, wired earth is passed through between C22, by passive crystal oscillator X21, electric capacity C21 and C22 forms clock circuit, the RESET pin of single-chip microcomputer U21 accesses+5V voltage by electric capacity C23, the RESET pin of single-chip microcomputer U21 is also by resistance R21 ground connection, reset circuit is formed by electric capacity C23 and resistance R21, P2.0 pin-P2.7 the pin of single-chip microcomputer U21 is connected with toggle switch SW21 one end, toggle switch SW21 other end ground connection, toggle switch input circuit is formed by toggle switch SW21, single-chip microcomputer U21's pin accesses+5V voltage by resistance R23, P1.0 pin-P1.3 the pin of single-chip microcomputer U21 and the SCLK pin of direct digital synthesis technique chip U22, SDATA pin, FSYNC pin, RESET pin connects one to one, the VCC pin access+5V voltage of single-chip microcomputer U21, the VCC pin of single-chip microcomputer U21 is also by electric capacity C24 and self GND pin ground connection altogether, the MCLK pin of described direct digital synthesis technique chip U22 is connected with active crystal oscillator X22 one end by resistance R22, the active crystal oscillator X22 other end is connected with the GND pin of single-chip microcomputer U21, power end access+5V the voltage of active crystal oscillator X22, the CAP pin of direct digital synthesis technique chip U22 is connected with the DGND pin of self by electric capacity C25, the DGND ground connection of direct digital synthesis technique chip U22, the DGND pin of direct digital synthesis technique chip U22 also accesses+5V voltage altogether by electric capacity C27 and self DVDD pin, the AGND pin of direct digital synthesis technique chip U22 is connected with self DGND pin, the AGND pin of direct digital synthesis technique chip U22 is also connected with self AVDD pin by electric capacity C26, the AVDD pin of direct digital synthesis technique chip U22 is connected with self DVDD pin, the COMP pin of direct digital synthesis technique chip U22 accesses+5V voltage by electric capacity C29, the REFOUT pin of direct digital synthesis technique chip U22 is by electric capacity C210 and self SLEEP pin ground connection altogether, the FSADJ pin of direct digital synthesis technique chip U22 is by resistance R24 ground connection, the IOUT pin of direct digital synthesis technique chip U22 is connected with self VIN pin by resistance R25, the VIN pin of direct digital synthesis technique chip U22 is by electric capacity C211 ground connection, the IOUTB pin of direct digital synthesis technique chip U22 is by electric capacity C28 parallel with one another, resistance R27 ground connection, the in-phase input end of described operational amplifier U23 is successively by resistance R29, resistance R28 is connected with the IOUT pin of direct digital synthesis technique chip U22, and also by electric capacity C212 parallel with one another between the IOUT pin of resistance R28 and direct digital synthesis technique chip U22, resistance R26 ground connection, the in-phase input end of operational amplifier U23 is also by electric capacity C213 ground connection, the inverting input of operational amplifier U23 is by resistance R210 ground connection, the inverting input of operational amplifier U23 is also connected with self output terminal by resistance R211, the output terminal of operational amplifier U23 accesses resistance R28 by electric capacity C214, between resistance R29, the output terminal of operational amplifier U23 is also connected with the pin 1 of lead-out terminal J21, pin 2 ground connection of lead-out terminal J21, by operational amplifier U23, resistance R28-R211, electric capacity C213 and C214, lead-out terminal J21 forms active low-pass filter circuit.

5. a kind of atmospheric trace gas sniffer according to claim 1, it is characterized in that: described modulation current source comprises operational amplifier U1A and U1B that model is respectively TL064, metal-oxide-semiconductor Q31, the lead-out terminal J32 of bipod, the pin 1 that inverting input and the sinusoidal signal of operational amplifier U1A produce lead-out terminal J21 in circuit is connected, the in-phase input end of operational amplifier U1A is connected with the output terminal of operational amplifier U1B, operational amplifier U1A just, negative power end is corresponding access+12V voltage respectively,-12V voltage, and the positive power source terminal of operational amplifier U1A is also by electric capacity C31 ground connection, the negative power end of operational amplifier U1A is also by electric capacity C32 ground connection, the output terminal of operational amplifier U1A is connected with the grid of metal-oxide-semiconductor Q31 by resistance R31, source electrode access+12V the voltage of metal-oxide-semiconductor Q31, the source electrode of metal-oxide-semiconductor Q31 is also by electric capacity C33 parallel with one another, resistance R32 is connected with self grid, the drain electrode of metal-oxide-semiconductor Q31 is connected with the pin 1 of lead-out terminal J32, the pin 2 of lead-out terminal J32 is by resistance R33 ground connection, the in-phase input end of operational amplifier U1B is by electric capacity C34 parallel with one another, electric capacity C35 ground connection, the in-phase input end of operational amplifier U1B also accesses between the pin 2 of lead-out terminal J32 and resistance R33, operational amplifier U1B inverting input is by electric capacity C36 parallel with one another, resistance R34 ground connection, operational amplifier U1B inverting input is also connected with the output terminal of self by resistance R35, the pin 1 of described lead-out terminal J32, pin 2 respectively with light source just, negative pole connects.

6. a kind of atmospheric trace gas sniffer according to claim 1, it is characterized in that: described sinusoidal signal phase difference detecting circuit comprises the phase difference detection integrated chip U41 that model is AD8302, model is the single-chip microcomputer U42 of Atmega8, input terminal J41 and J42, toggle switch SW41, the INPA pin of phase difference detection integrated chip U41 is successively by electric capacity C41, resistance R41, electric capacity C42 is connected with self OFSA pin, between electric capacity C41 and resistance R41, lead to wire between electric capacity C42 and resistance R41 respectively and be connected to input terminal J41, the pin 1 of the lead-out terminal J21 that input terminal J41 and sinusoidal signal produce in circuit is connected, also wired earth is passed through between electric capacity C42 and resistance R41, the INPB pin of phase difference detection integrated chip U41 is successively by electric capacity C43, resistance R42, electric capacity C44 is connected with self OFSB pin, between electric capacity C43 and resistance R42, lead to wire between electric capacity C44 and resistance R42 respectively and be connected to input terminal J42, input terminal J42 is connected with broad band amplifier output terminal, also wired earth is passed through between electric capacity C44 and resistance R42, the VCC pin access+5V voltage of phase difference detection integrated chip U41, the VCC pin of phase difference detection integrated chip U41 is also by electric capacity C45 and self GND pin ground connection altogether, the PSET pin of phase difference detection integrated chip U41, be connected with the ADC0 pin of single-chip microcomputer U42 after VPHS pin connects altogether, the MFLT pin of phase difference detection integrated chip U41 connects rear ground connection by electric capacity C47 and self PFLT pin altogether by electric capacity C46, passive crystal oscillator X41 is connected with between the XTAL1 pin of single-chip microcomputer U42 and XTAL2 pin, electric capacity C48 is also in series with between passive crystal oscillator X41 two ends, electric capacity C49, wired earth is passed through between electric capacity C48 and electric capacity C49, the VCC pin of single-chip microcomputer U42, AVCC pin connects rear access+5V voltage altogether, the VCC pin of single-chip microcomputer U42 is also connected with self AREF pin by resistance R43, the AREF pin of single-chip microcomputer U42 is connected to one. and model is the negative electrode of the 2.5V reference voltage chip Q41 of LM336-2.5, the anode of 2.5V reference voltage chip Q41 and the GND pin ground connection altogether of single-chip microcomputer U42, single-chip microcomputer U42's pin accesses+5V voltage by pull-up resistor R44, single-chip microcomputer U42's pin is also by electric capacity C410 ground connection, and the PC3 pin of single-chip microcomputer U42 accesses+5V voltage by pull-up resistor R45, and the PC3 pin of single-chip microcomputer U42 is also connected with one end of toggle switch SW41, the other end ground connection of toggle switch SW41.