CN102495009A - Wireless sensing method for gas detection and device thereof - Google Patents

Abstract

A wireless sensing method and device for gas detection. The device includes a sensing unit, a processor unit, a wireless transceiver unit and a battery unit; wherein the sensing unit includes a laser current and temperature controller, an adjustable laser diode module, an air chamber, a photodiode and an analog-to-digital converter; the laser current and The temperature controller drives the adjustable laser diode module to output a constant power laser, and the wavelength of the laser scans within the absorption spectrum of the gas to be measured. The laser passes through the gas chamber and is converted into an electrical signal by the photodiode, and then converted by analog to digital. The measured digital signal is collected by the detector and delivered to the processor unit. The processor unit reconstructs the measured digital signal into the measured gas absorption spectrum according to the synchronous signal fed back from the laser current and temperature controller, and according to the calibrated standard gas absorption The spectrum calculates the concentration of the measured gas, and the result of the gas concentration is transmitted by the wireless transceiver unit. The device is small in size, simple in structure, stable in work and flexible in networking.

Description

A wireless sensing method and device for gas detection

technical field

The invention relates to a gas detection wireless sensing method and device.

Background technique

Optical fiber sensing technology was developed rapidly with the development of optical fiber communication technology in the 1970s. It uses light waves as the carrier and optical fiber as the medium to perceive and transmit external measured signals. Fiber-based optical detection systems have many advantages over traditional optical sensing systems. The most important point is that a stable passive probe can be designed to work in a harsh environment, far away from the monitoring station, which is a very advantageous factor in harsh environment applications. Secondly, a multiplexing network system can be developed. Through the preset propagation medium in the optical cable, a single demodulation unit can monitor multiple low-cost passive sensing heads. However, there is a problem with the conventional silicon optical fiber, that is, the transmission spectrum is limited only from visible light to near-infrared region (600nm～2000nm). Generally speaking, the absorption of gas in the mid-infrared and far-infrared regions is stronger than that in the near-infrared region, so working in the near-infrared region will affect the measurement accuracy of gases. Many literatures use long gas chambers of tens of meters or even hundreds of meters to increase the intensity of the absorption signal; or control the pressure of the measured gas to reduce the pressure to make the absorption line narrow and the signal clear. The above methods can reduce the difficulty of signal processing and improve the accuracy of measurement, but these methods make the detection system bulky and complex, which limits the practicability of the method.

In addition, with the development of MEMS, wireless communication and digital electronic technology, it becomes possible to develop sensing nodes with small size and short-distance wireless communication. The wireless sensor node has the characteristics of low cost, low power consumption and multi-function, and generally consists of sensing, data processing and communication parts. A large number of wireless sensor nodes distributed in the sensing area form a wireless sensor network, and they can be relatively independent individuals or form a cooperative network. On the one hand, wireless sensing points have their own processors that perform calculations locally and transmit only measurements, not raw data. On the other hand, sensor nodes must cooperate with each other to establish data routing and transmit measurement results to sink nodes and end users.

Contents of the invention

Technical problem to be solved: Combining optical fiber sensing gas detection technology with wireless sensing technology, inventing a new type of wireless sensing method and device for gas detection, solving the problem of bulky, complex structure and assembly problems of the original optical fiber sensing gas detection technology The problem of network inflexibility.

The technical solution adopted by the present invention to solve its technical problems is:

A wireless sensing device for gas detection, which includes a sensing unit, a processor unit, a wireless transceiver unit and a battery unit; wherein the sensing unit includes a laser current and temperature controller, an adjustable laser diode module, a gas chamber, a photodiode and Analog-to-digital converter; the laser current and temperature controllers are connected to the adjustable laser diode module circuit, the photodiode is connected to the analog-to-digital converter circuit, the gas chamber is located between the adjustable laser diode module and the photodiode, and the processor unit is connected to the The analog-to-digital converter circuit is connected, one side is connected with the laser current and temperature controller circuit, and the battery unit is respectively connected with the sensor unit, the processor unit and the wireless transceiver unit circuit and supplies power.

In the gas detection wireless sensor device of the present invention, the adjustable laser diode module is a distributed feedback laser module, which includes a thermoelectric cooler inside.

The working method of the gas detection wireless sensor device of the present invention is: the laser current and temperature controller drive the adjustable laser diode module to output a constant power laser, and the wavelength of the laser scans within the range of the absorption spectrum of the gas to be measured, and the laser passes through The gas chamber is received by the photodiode and converted into an electrical signal, and then collected by the analog-to-digital converter as a digital signal to be measured and delivered to the processor unit. The processor unit converts the digital signal to be measured according to the synchronous signal fed back from the laser current and temperature controller. The measured gas absorption spectrum is reconstructed, and the measured gas concentration is calculated according to the calibrated standard gas absorption spectrum, and the result of the gas concentration is transmitted by the wireless transceiver unit.

In the gas detection wireless sensor device of the present invention, the data processing method of the processor unit includes a correlation translation algorithm and a least square method to solve redundant linear equations, firstly calculate the correlation coefficient between the measured gas absorption spectrum and the standard gas absorption spectrum, and Move the position of the measured gas absorption spectrum until the correlation coefficient is maximum, and then use the least square method to find the difference between the measured gas absorption spectrum R(λ ₁ ) and the standard gas absorption spectrum R ₀ (λ ₁ ) according to the following formula The linear coefficient ρ, which is the measured gas concentration.

$\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ \mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>\end{array}\right]<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>\end{array}\right]<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; A</span>}$

The tunable laser diode module is a distributed feedback laser module, which includes a thermoelectric cooler to control the wavelength output by modulating the temperature of the distributed feedback laser. The battery unit supplies power to the sensor unit, processor unit and wireless transceiver unit. The sensor unit, processor unit and wireless transceiver unit are in the standby state when they are idle, and are activated to enter the working state when receiving a wireless signal command, and return to the standby state after the work is completed.

The beneficial effects of the present invention are: the gas detection wireless sensing method and structure can work independently, and can be activated according to the wireless signal command to complete the gas detection task; the networking is flexible, and the limitation of power connection and communication connection is avoided; the structure is simple, and the work Stable, improved hardware and data processing methods.

Description of drawings

Figure 1 is a gas detection wireless sensor structure diagram

In the figure: 1. Sensing unit, 2. Processor unit, 3. Wireless transceiver unit, 4. Battery unit, 5. Laser current and temperature controller, 6. Adjustable laser diode module, 7. Air chamber, 8. Photodiode, 9. Analog-to-digital converter, 10. Thermoelectric cooler.

Figure 2 is the measured gas absorption spectrum

Detailed ways

The gas detection wireless sensing structure of the present invention, as shown in Figure 1, includes a sensing unit 1, a processor unit 2, a wireless transceiver unit 3 and a battery unit 4, wherein the sensing unit 1 includes a laser current and temperature controller 5, Adjustable laser diode module 6, gas chamber 7, photodiode 8 and analog-to-digital converter 9; its laser current and temperature controller 5 is connected to the adjustable laser diode module 6 circuit, and the photodiode 8 is connected to the analog-to-digital converter 9 circuit , the gas chamber 7 is located between the adjustable laser diode module 6 and the photodiode 8, the processor unit 2 is connected to the circuit of the analog-to-digital converter 9, and the circuit of the laser current and temperature controller 5 is connected to the other side, and the battery unit 4 is respectively connected to the transmission circuit The sensing unit 1, the processor unit 2 and the wireless transceiver unit 3 are electrically connected and supplied with power. Its laser current and temperature controller 5 drives the adjustable laser diode module 6 to output a constant power laser, and the wavelength of the laser scans within the absorption line range of the gas to be measured. The laser passes through the gas chamber 7 and is received by the photodiode 8 and converted into The electrical signal is then collected by the analog-to-digital converter 9 as a measured digital signal and delivered to the processor unit 2, and the processor unit 2 reconstructs the measured digital signal into the measured digital signal according to the synchronous signal fed back from the laser current and temperature controller 5 Measure the gas absorption spectrum, and calculate the measured gas concentration according to the calibrated standard gas absorption spectrum, and the result of the gas concentration is transmitted by the wireless transceiver unit 9.

The data processing method of the processor unit includes a correlation translation algorithm and a least square method for solving redundant linear equations. Due to the hysteresis between temperature modulation and wavelength output, and the degree of hysteresis is related to the ambient temperature, there is a difference between the reconstructed gas absorption spectrum and the calibrated standard gas absorption spectrum position, which causes the error of concentration measurement. Therefore, first calculate the correlation coefficient between the measured gas absorption spectrum and the standard gas absorption spectrum, and move the position of the measured gas absorption spectrum until the correlation coefficient is maximum, and translate the measured gas absorption spectrum to the position of the standard gas absorption spectrum. This method is called Related translation algorithms. Then calculate the linear coefficient ρ between the shifted measured gas absorption spectrum R(λ ₁ ) and the standard gas absorption spectrum R ₀ (λ ₁ ) by the least square method according to the following formula, and this coefficient is the measured gas concentration.

$\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\\ \mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ \mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>\end{array}\right]<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&rho;</span>}\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>\end{array}\right]<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; A</span>}$

In this embodiment, carbon dioxide is used as the measured gas for testing, and the absorption line of carbon dioxide at 1572 nm in the near-infrared region is selected for measurement. The absorption intensity of carbon dioxide in this area is low, which is 1/400 of that of methane, which can verify the measurement accuracy of the present invention. The absorption spectra of different concentrations of carbon dioxide obtained from the test are shown in FIG. 2 . This embodiment can measure carbon dioxide gas with a concentration range of 0-100%, and the measurement accuracy can reach 0.3%.

The tunable laser diode module 6 is a distributed feedback laser module LECENT D2526, which includes a thermoelectric cooler 10 to control the wavelength output by modulating the temperature of the distributed feedback laser. The battery unit 4 supplies power to the sensor unit 1, the processor unit 2 and the wireless transceiver unit 3, and the power consumption for completing a gas detection task is 1.26mAh. The sensor unit 1, the processor unit 2 and the wireless transceiver unit 3 are in the standby state when idle, and are activated to enter the working state when receiving a wireless signal command, and return to the standby state after the work is completed. The processor unit 2 used in the present invention is a 16-bit reduced instruction set computer MSP430F2274 specially developed by TI for wireless sensor networks, with an instruction cycle time of 62.5ns, 32kB flash memory and 1kB random access memory. The wireless transceiver unit 3 is a low-cost, low-power RF transceiver CC2500 working in the frequency band of 2400-2483MHz.

Claims (8)

1. gas detection wireless sensing device, it is characterized in that: it comprises sensing unit (1), processor unit (2), wireless transmit/receive units (3) and battery unit (4); Wherein sensing unit (1) comprises laser diode current and temperature controller (5), tunable laser diode module (6), air chamber (7), photodiode (8) and analog to digital converter (9); Its laser diode current links to each other with tunable laser diode module (6) circuit with temperature controller (5); Photodiode (8) links to each other with analog to digital converter (9) circuit; Air chamber (7) is positioned between tunable laser diode module (6) and the photodiode (8); Processor unit (2) links to each other with analog to digital converter (9) circuit on one side; Link to each other with temperature controller (5) circuit with laser diode current on one side, battery unit (4) links to each other with sensing unit (1), processor unit (2) and wireless transmit/receive units (3) circuit respectively and gives power supply.

2. gas detection wireless sensing device according to claim 1 is characterized in that: tunable laser diode module (6) is distributed feedback laser module LECENT D2526, and inside comprises a thermoelectric (al) cooler (10).

3. gas detection wireless sensing device according to claim 1; It is characterized in that: that processor unit (2) is that TI aims at radio sensing network exploitation is 16 Reduced Instruction Set Computer MSP430F2274; Instruction cycletime is 62.5ns, has flash memory and the 1kB RAS of 32kB.

4. gas detection wireless sensing device according to claim 1 is characterized in that: wireless transmit/receive units (3) is operated in the RF transceiver CC2500 of 2400～2483MHz frequency range.

5. each described gas detection wireless sensing device method of work of claim 1-4; It is characterized in that: laser diode current and temperature controller (5) drive the laser of tunable laser diode module (6) output firm power; And this Wavelength of Laser is in the interscan of tested gas absorption spectrum line scope; This laser is received by photodiode (8) through air chamber (7) and is converted into electric signal; Gather to the measured number signal by analog to digital converter (9) then and give processor unit (2); Processor unit (2) is tested gas absorption spectrum according to the synchronizing signal from laser diode current and temperature controller (5) feedback with the measured number signal reconstruction, and calculates tested gas concentration according to the calibrating gas absorption spectra of demarcating, and the result of gas concentration is transmitted by wireless transmit/receive units (9).

6. gas detection wireless sensing device method of work according to claim 5; It is characterized in that: the data processing method of processor unit (2) comprises associated shift algorithm and the redundant linear equation of least square solution; At first calculate the related coefficient of tested gas absorption spectrum and calibrating gas absorption spectra; And the position of moving tested gas absorption spectrum is maximum up to related coefficient; Ask tested gas absorption spectrum and the linear coefficient between the calibrating gas absorption spectra after being moved with least square method then, this linear coefficient is exactly tested gas concentration.

7. gas detection wireless sensing device method of work according to claim 5 is characterized in that: tunable laser diode module (6) is through the output of the temperature control wavelength of modulation profile formula feedback laser.

8. gas detection wireless sensing device method of work according to claim 5; It is characterized in that: sensing unit (1), processor unit (2) and wireless transmit/receive units (3) are in holding state when idle; When receiving the wireless signal order entering duty that the time is activated, work is returned holding state after accomplishing.

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