CN210269590U - Double-cell series photoacoustic spectroscopy gas detection device - Google Patents
Double-cell series photoacoustic spectroscopy gas detection device Download PDFInfo
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Abstract
The utility model provides a double-cell series photoacoustic spectrometry gas detection device, wherein a sample photoacoustic cell comprises a sample gas inlet, a sample gas outlet, a sample entrance window, a sample exit window and a sample detection device; the reference photoacoustic cell comprises a reference air inlet, a reference air outlet, a reference incident window, a reference exit window and a reference detection device; the sample exit window is connected with the reference entrance window in a sealing way through a window sheet with high infrared transmittance; the sample detection device comprises a first sound sensor, a first preamplifier, a first phase-locked amplifier and a collection unit; the reference detection device comprises a second sound sensor, a second preamplifier, a second lock-in amplifier and a measurement and control unit; the laser comprises a laser generating head, a laser main body, a temperature control unit and a frequency modulation unit, and a reference pool encapsulates high-concentration gas to be detected so as to help automatically lock the laser wavelength and the modulation frequency, so that the measured gas content value is credible and accurate, and the whole photoacoustic system always works in the best state.
Description
Technical Field
The utility model belongs to the technical field of gaseous detection, concretely relates to two ponds are established ties optoacoustic spectrum gas detection device.
Background
Trace gas in transformer oil is generated in the process of long-time operation of a transformer, the trace gas in the transformer oil reflects part of the operation state of the transformer, the possible operation risk of the transformer can be indicated through monitoring the trace gas in the transformer oil, and in recent years, the photoacoustic spectrum detection technology is gradually applied to detection of the trace gas in the transformer oil, particularly gases with low content such as C2H2 and the like. The photoacoustic spectroscopy technology is based on the photoacoustic effect of gas, gas molecules of a sample to be detected can absorb laser photon energy with specific wavelength, energy level transition occurs, a high-energy excited state is an unstable state, a large number of gas molecules release heat energy in the process of returning to the ground state, so that the gas expands when heated, the gas in the photoacoustic cell can synchronously expand and contract under the modulation of external signals by a laser source, if the expansion and contraction frequency of the gas is consistent with the characteristic frequency of the photoacoustic cell, resonance can occur, a microphone sensor is arranged on the photoacoustic cell, resonance signals can be detected, and the intensity of the resonance signals is positively correlated with the content of the gas to be detected.
The detection of trace gas in transformer oil based on photoacoustic spectroscopy technology is generally carried out by using a tunable semiconductor laser diode, and the output wavelength of the tunable semiconductor laser diode is single, but the defect is that the output wavelength is easy to drift. Because the gas molecules of the sample to be detected can only absorb photons with a specific wavelength, once the wavelength of the laser output shifts, the gas molecules of the sample to be detected generally do not have absorption characteristics for the wavelength, the photoacoustic effect cannot be generated, and microphone signals cannot be detected. To address this problem, there are patents that scan the laser output wavelength back and forth over a range to ensure that the desired characteristic absorption wavelength is passed. This has the disadvantage that the effective absorption time of the gas to be measured is short, the effective signal of the microphone is small in the photoacoustic detection, and the detection sensitivity is lowered. Besides the method of laser wavelength scanning, an infrared spectrometer can be added to monitor the laser wavelength, and the method is effectively controllable, and has the disadvantages that the cost is increased greatly, and the volume of a detector is increased. Therefore, how to find out the deviation of the output wavelength of the laser in time and correct the deviation in time is an important problem influencing the detection result.
In the photoacoustic spectrum detection, only if the expansion and contraction frequency of the gas to be detected is consistent with the characteristic frequency of the photoacoustic cell, resonance can occur, the microphone sensor can output a stronger signal, and otherwise, the microphone sensor signal is very weak and difficult to detect. However, in actual detection, the characteristic resonance frequency point may drift due to changes in conditions such as temperature, pressure, humidity, etc., once the characteristic resonance frequency point drifts, the photoacoustic resonance effect is significantly weakened, the output signal of the microphone sensor is reduced, and if the output signal of the microphone sensor is taken as a detection signal, the detection value is low and the error is large. Therefore, how to find the drift of the characteristic frequency point of the photoacoustic cell in time and adjust the external laser modulation frequency in time is also an important problem to improve the reliability and accuracy of the detection value.
SUMMERY OF THE UTILITY MODEL
The utility model aims at providing a two ponds establish ties optoacoustic spectrum gaseous detection device to in improving current optoacoustic spectrum and detecting, the credibility and the degree of accuracy of measured value.
The utility model provides a following technical scheme:
a double-cell series photoacoustic spectroscopy gas detection device comprises a sample photoacoustic cell, a reference photoacoustic cell and a laser which are arranged in series and have the same structure, wherein the sample photoacoustic cell comprises a sample gas inlet, a sample gas outlet, a sample entrance window, a sample exit window and a sample detection device; the reference photoacoustic cell comprises a reference air inlet, a reference air outlet, a reference incident window, a reference exit window and a reference detection device, wherein the reference air inlet is provided with a third valve, and the reference air outlet is provided with a fourth valve; the sample exit window is connected with the reference entrance window through glass sealing, and a light trap is arranged at the reference exit window; the sample detection device comprises a first sound sensor, a first preamplifier, a first phase-locked amplifier and a collection unit which are electrically connected in sequence; the reference detection device comprises a second sound sensor, a second preamplifier, a second lock-in amplifier and a measurement and control unit which are electrically connected in sequence; the laser instrument includes laser generator, laser instrument main part, control by temperature change unit and frequency modulation unit, the laser generator passes through optical fiber connection the sample incident window, the control by temperature change unit is located the laser instrument main part outside, the frequency modulation unit with laser instrument main part electric connection.
Furthermore, the sample photoacoustic cell and the reference photoacoustic cell are longitudinal resonance photoacoustic cells with consistent size, material, process and resonance frequency point parameters.
Further, the temperature control unit comprises a temperature control chip, an output voltage Vset and a current constant current source It, the model of the temperature control chip is WTC3243, a thermistor Rt and a semiconductor refrigerating sheet are connected to the temperature control chip, and the Vset is Rt It.
Furthermore, the measurement and control unit comprises an alarm device, and the alarm device is an audible and visual alarm.
Further, the measurement and control unit comprises a storage device.
Further, the first sound sensor and the second sound sensor are both a microphone, a piezoelectric ceramic microphone or an optical fiber sound sensor.
Further, the glass is a window piece with infrared transmittance.
The utility model has the advantages that:
the utility model relates to a two-cell series photoacoustic spectrometry gas detection device, which serially connects two photoacoustic cells with completely consistent size, material, process and other parameters, wherein the sample detection photoacoustic cell is in front of the reference photoacoustic cell, the two photoacoustic cells are in back of the reference photoacoustic cell, the gas path isolation is realized between the two photoacoustic cells by using a window material with high transmittance to specific wavelength laser, and the reference cell is filled with gas to be detected with higher concentration; and (3) outputting a signal of a reference photoacoustic cell to a measurement and control unit to obtain a concentration value of the reference standard gas, adjusting the working temperature of the laser according to the result, and changing the working temperature of the laser to change the output wavelength of the laser so that the output wavelength of the laser is consistent with the wavelength of an absorption peak of the sample gas. After the wavelength of the laser is adjusted, the monitoring control unit further calculates the output signal of the phase-locked amplifier, scans the external sine wave modulation frequency of the laser within a certain range, collects the output signal of the phase-locked amplifier in real time and finds out the optimal external modulation frequency. In order to ensure the reliability and accuracy of the detection value, the output wavelength and the modulation frequency of the laser diode are adjusted in real time according to the concentration value output of the second photoacoustic cell.
Firstly, because the tunable laser is influenced by the working temperature and the working current, the output wavelength of the tunable laser is easy to drift, once the output wavelength of the laser deviates, the photoacoustic effect can not be effectively generated, and if the output wavelength of the laser cannot be found and adjusted in time, the gas concentration in a sample photoacoustic cell can not be accurately detected; therefore, the laser output wavelength is firstly adjusted according to the phase-locked signal of the reference photoacoustic cell microphone. And secondly, due to the influence of the external environment, the resonance frequency of the reference photoacoustic cell can also shift, and if the preset laser modulation frequency is not adjusted in time, the gas resonance effect in the photoacoustic cell can be obviously weakened, so that the laser modulation frequency can be adjusted in real time according to the photoacoustic signal of the reference photoacoustic cell, and the optimal resonance frequency point can be obtained.
To sum up, the utility model discloses a monitor and regulate and control laser instrument wavelength and modulation frequency among the photoacoustic spectrometry detector to improve the credibility and the degree of accuracy of trace gas detection value in the transformer oil. The detection parameters (laser emission wavelength and modulation frequency) related to the photoacoustic spectrum are ensured to be in an effective and reasonable state in the whole detection process, so that the measured gas content value is credible and accurate, and the whole photoacoustic system always works in an optimal state.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a schematic structural view of the present invention;
fig. 2 is a schematic flow chart of the method of the present invention.
Labeled as: 1. the laser spectrometer comprises a sample photoacoustic cell, 101, a sample inlet, 102, a sample outlet, 103, a first valve, 104, a second valve, 105, a first sound sensor, 106, a sample entrance window, 107, a sample exit window, 108, glass, 2, a reference photoacoustic cell, 201, a reference inlet, 202, a reference outlet, 203, a third valve, 204, a fourth valve, 205, a second sound sensor, 206, a reference entrance window, 207, a reference exit window, 208, an optical trap, 3, a first preamplifier, 4, a first phase-locked amplifier, 5, a collection unit, 6, a second preamplifier, 7, a second phase-locked amplifier, 8, a measurement and control unit, 801, a storage device, 9, a temperature control unit, 10, a frequency modulation unit, 11, a laser body, 12, a temperature control chip, 13, a laser generation head, and 14, an optical fiber.
Detailed Description
As shown in fig. 1, a dual-cell serial photoacoustic spectroscopy gas detection apparatus includes a sample photoacoustic cell 1, a reference photoacoustic cell 2 and a laser, which are arranged in series and have the same structure, wherein the sample photoacoustic cell 1 and the reference photoacoustic cell 2 are longitudinal resonant photoacoustic cells with the same size, material, process and resonant frequency point parameters;
the sample photoacoustic cell 1 comprises a sample gas inlet 101, a sample gas outlet 102, a sample entrance window 106, a sample exit window 107 and a sample detection device, wherein the sample gas inlet 101 is provided with a first valve 103, and the sample gas inlet 101 is provided with a second valve 104; the reference photoacoustic cell 2 comprises a reference gas inlet 201, a reference gas outlet 202, a reference entrance window 206, a reference exit window 207 and a reference detection device, wherein the reference gas inlet 201 is provided with a third valve 203, and the reference gas outlet 202 is provided with a fourth valve 204; the sample exit window 107 and the reference entrance window 206 are hermetically connected through glass 108, the glass 108 is a window sheet with high infrared transmittance, and a light trap 208 is arranged at the reference exit window 207; the sample detection device comprises a first sound sensor 105, a first preamplifier 3, a first phase-locked amplifier 4 and a collection unit 5 which are electrically connected in sequence; the reference detection device 2 comprises a second sound sensor 205, a second preamplifier 6, a second lock-in amplifier 7 and a measurement and control unit 8 which are electrically connected in sequence, the measurement and control unit 8 comprises an alarm device, the alarm device is an audible and visual alarm, the measurement and control unit 8 comprises a storage device 801, and the first sound sensor 105 and the second sound sensor 205 are microphones, piezoelectric ceramic microphones or optical fiber sound sensors.
The laser comprises a laser generating head 13, a laser main body, a temperature control unit 9 and a frequency modulation unit 10, wherein the laser generating head 13 is connected with a sample entrance window 106 through an optical fiber 14, the temperature control unit 9 is arranged on the outer side of the laser main body 11, and the frequency modulation unit 10 is electrically connected with the laser main body 11; the temperature control unit 9 includes a temperature control chip, an output voltage Vset, and a current constant current source It, the model of the temperature control chip is WTC3243, a thermistor Rt and a semiconductor refrigerating chip are connected to the temperature control chip, and Vset is Rt.
As shown in FIG. 2, the operation of this embodiment includes the steps of:
s1, introducing gas: respectively introducing a sample gas to be detected and a reference standard gas into the sample photoacoustic cell 1 and the reference photoacoustic cell 2 through the sample gas inlet 101, the sample gas outlet 102, the reference gas inlet 201 and the reference gas outlet 202, and sequentially closing the second valve 104, the fourth valve 204, the first valve 103 and the third valve 203;
s2, laser incidence: opening a laser, wherein the laser emits laser, the laser is emitted 106 from a sample entrance window through an optical fiber 14, and the laser sequentially passes through a sample gas to be detected, a sample exit window 107, glass 108, a reference entrance window 206, a reference standard gas and a reference exit window 207 and finally enters a light trap 208;
s3, obtaining the gas concentration of the sample to be detected: after laser enters the gas of the sample to be detected, heat is released to enable the gas of the sample to be detected to be heated and expanded to generate vibration, a sound signal in the sample photoacoustic cell 1 is detected through the first sound sensor 105, the sound signal is amplified through the first preamplifier 3 and the first phase-locked amplifier 4, and the concentration VX of the gas of the sample to be detected is obtained through the collecting unit 5;
s4, acquiring the reference standard gas concentration: after laser enters the reference standard gas, heat is released to enable the reference standard gas to be heated and expanded to generate vibration, a sound signal in the reference photoacoustic cell 2 is detected through the second sound sensor 205, the sound signal is amplified through the second preamplifier 6 and the second lock-in amplifier 7, and the concentration V0 of the reference standard gas is obtained through the measurement and control unit 8;
s5, preliminary judgment: setting the pre-standard value of the concentration of the reference standard gas as V1, setting the error value of the reference standard gas as V2, judging whether | V0-V1| is larger than V2 through the measurement and control unit 8,
if yes, go to S6;
if not, ending and returning to S3, and outputting the concentration VX of the sample gas to be detected acquired by the acquisition unit 5 as an accurate value;
s6, temperature adjustment judgment: uniformly increasing the working temperature of the laser main body through the temperature control chip, simultaneously acquiring the concentration V0 'of the reference standard gas in real time through the measurement and control unit 8, judging whether | V0' -V1| is greater than V2 through the measurement and control unit 8, and if yes, entering S7;
if not, storing the working temperature modulated by the temperature control chip to the storage device 801, ending and returning to the step S3, and outputting the concentration VX of the sample gas to be detected acquired by the acquisition unit 5 as an accurate value;
s7, frequency adjustment judgment: the frequency modulation unit 10 uniformly increases the laser frequency generated by the laser generating head 13, meanwhile, the measurement and control unit 8 acquires the concentration V0 'of the reference standard gas in real time, the measurement and control unit 8 judges whether | V0' -V1| is larger than V2,
if so, judging the fault of the laser, alarming through an alarming device and stopping detection;
if not, the laser frequency modulated by the frequency modulation unit 10 at this time is stored in the storage device 801, and the process returns to S3, and the concentration VX of the sample gas to be measured acquired by the acquisition unit 5 is output as an accurate value.
The working mode of the specific embodiment is as follows:
the sample photoacoustic cell 1 is a longitudinal resonant photoacoustic cell and comprises a sample gas inlet 101, a sample gas outlet 102, a first valve 103, a second valve 104, a sample entrance window 106, a sample exit window 107 and a first sound sensor 105, wherein a signal of the first sound sensor 105 enters a first phase-locked amplifier 4 after passing through a first preamplifier 3, a signal of the first phase-locked amplifier 4 enters an acquisition unit 5, and the concentration of sample gas VX is obtained;
the size, material, process, resonance frequency point and other parameters of the reference photoacoustic cell 2 and the sample photoacoustic cell 1 are consistent, the reference entrance window 206 of the reference photoacoustic cell 2 is connected in series at the rear end of the sample exit window 107 of the sample photoacoustic cell 1, the two photoacoustic cells are hermetically connected by adopting glass 108, laser enters from the sample entrance window 106 of the sample photoacoustic cell 1, passes through the sample photoacoustic cell 1, enters from the sample exit window 107 into the reference entrance window 206 of the reference photoacoustic cell 2 through the glass 108, passes through the reference photoacoustic cell 2, and enters into the optical trap 208 from the reference exit window 207;
the signal of the second sound sensor 205 of the reference photoacoustic cell 2 enters the second preamplifier 6, enters the second lock-in amplifier 7 after being amplified, the output signal of the second lock-in amplifier 7 enters the measurement and control unit 8, the measurement and control unit 8 collects the signal of the second lock-in amplifier 7 to obtain the concentration V0 of the reference standard gas, the concentration V0 is compared with the concentration pre-standard value V1 of the reference standard gas,
if the absolute value of V0-V1 is smaller than the set value V2, the output wavelength of the laser does not need to be adjusted; if | V0-V1| is greater than the set value V2, the output wavelength of the laser generating head 13 needs to be adjusted. The output wavelength of the laser can be realized by adjusting the working current and the working temperature of the laser, and in this embodiment, the measurement and control unit 8 adjusts the working temperature of the laser by controlling the temperature control unit 9 to realize the adjustment of the output wavelength of the laser.
The working temperature of the laser is set in various ways, in this embodiment, the temperature control unit 9 is internally provided with a 16-bit precision D/a output circuit, the measurement and control unit 8 adjusts the output voltage value Vset of the D/a output circuit through a digital interface, the Vset is connected to the temperature control chip (WT3243), and each Vset corresponds to the unique working temperature T of the laser because the Vset is Rt/It, Rt is the resistance value of the thermistor, and It is a constant current source for the thermistor to work. The temperature control chip is connected to the semiconductor refrigeration chip and the thermistor;
the temperature-wavelength adjusting method is that the measurement and control unit 8 will scan in a fixed step between the low temperature value TL and the high temperature value TH, firstly, the laser working temperature T is set to the low value TL by the laser working temperature T, after the temperature is balanced, the output value V0 'of the second lock-in amplifier 7 is compared with the pre-stored standard value V1, then the laser working temperature T is increased by the fixed step, the V0' value is monitored cyclically until | V0 '-V1 | is smaller than the set value V2, Vset (i) is recorded, i ═ 1,2, 3., i represents that the Vset is used for sorting the set temperature value Vset meeting the conditions | V0' -V1| and smaller than the set value V2 until TH, the Vset (i) meeting the conditions is sorted according to the magnitudes of | V0 '-V1 | and the corresponding Vset (i) of | V0' -V1| minimum value is selected and the temperature set value is stored in the parameter storage device 801, for invocation during detection.
If the situation that | V0-V1| is smaller than the set value V2 does not occur during temperature scanning monitoring in the temperature range from TL to TH, the frequency of the laser can be adjusted through the frequency adjusting unit;
and after the output wavelength of the laser is adjusted, adjusting the external sine wave modulation frequency of the laser. The resonant frequency of the photoacoustic detection cell is influenced by external conditions and can shift, if the resonant frequency is not adjusted in time after shifting, the photoacoustic effect is reduced, the detection value is reduced, and the reliability and accuracy of the detection result are reduced. Therefore, by detecting the signal of the second sound sensor 205 of the reference photoacoustic cell 2, it can be found in time whether the resonance frequency of the photoacoustic detection cell is shifted, and if the shift occurs, the modulation frequency needs to be scanned and adjusted. The measurement and control unit 8 realizes frequency adjustment through an external frequency modulation unit 10.
The specific implementation is as follows, the measurement and control unit 8 collects the signal of the second lock-in amplifier 7 to obtain V0 ″, and compares the V0 ″, with the pre-stored standard value V1, if | V0 ″ -V1| is smaller than the set value V2, the external modulation frequency of the laser does not need to be adjusted; if | V0 "-V1 | is greater than the set value V2, then the laser external modulation frequency needs to be adjusted. The modulation frequency adjustment method is that the measurement and control unit 8 will scan between the low frequency value FL and the high frequency value FH in fixed steps, first set the output frequency F of the external frequency modulation unit 10 at the low value FL, after balancing, compare the output value V0 ″ of the second lock-in amplifier 7 with the pre-stored value V1, then increase the output frequency of the external frequency modulation unit 10 in fixed steps, cycle the output value V0 ″ of the second lock-in amplifier 7 until | V0 ″ -V1|, is less than the set value V2, record F (i), i ═ 1,2, 3.. said i represents the frequency value F for sorting the frequency values satisfying | V0 ″ -V1| less than the set value V2 until FH, sort the satisfying F (i) by the magnitude of | V0 ″ -V1|, select the minimum value of | V0 ″ -V1 |) (F i), the modulation frequency value is stored in the parameter storage unit 801 for being called during detection.
So far, the working wavelength of the laser is consistent with the absorption wavelength, the external modulation frequency of the laser is consistent with the modulation frequency of the photoacoustic cell, and the detection condition is met.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments described in the foregoing embodiments, or equivalents may be substituted for elements thereof. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A double-cell series photoacoustic spectrometry gas detection device is characterized by comprising a sample photoacoustic cell, a reference photoacoustic cell and a laser which are arranged in series and have the same structure,
the sample photoacoustic cell comprises a sample air inlet, a sample air outlet, a sample entrance window, a sample exit window and a sample detection device, wherein the sample air inlet is provided with a first valve, and the sample air inlet is provided with a second valve; the reference photoacoustic cell comprises a reference air inlet, a reference air outlet, a reference incident window, a reference exit window and a reference detection device, wherein the reference air inlet is provided with a third valve, and the reference air outlet is provided with a fourth valve; the sample exit window is connected with the reference entrance window through glass sealing, and a light trap is arranged at the reference exit window; the sample detection device comprises a first sound sensor, a first preamplifier, a first phase-locked amplifier and a collection unit which are electrically connected in sequence; the reference detection device comprises a second sound sensor, a second preamplifier, a second lock-in amplifier and a measurement and control unit which are electrically connected in sequence;
the laser instrument includes laser generator, laser instrument main part, control by temperature change unit and frequency modulation unit, the laser generator passes through optical fiber connection the sample incident window, the control by temperature change unit is located the laser instrument main part outside, the frequency modulation unit with laser instrument main part electric connection.
2. The gas detection apparatus with dual cell series photoacoustic spectroscopy of claim 1, wherein the sample photoacoustic cell and the reference photoacoustic cell are longitudinal resonant photoacoustic cells with consistent size, material, process, and resonant frequency point parameters.
3. The gas detection device with dual cells connected in series through photoacoustic spectroscopy of claim 1, wherein the temperature control unit comprises a temperature control chip, a type WTC3243, an output voltage Vset and a current constant current source It, a thermistor Rt and a semiconductor cooling chip are connected to the temperature control chip, and the Vset is Rt It.
4. The gas detection device with the double-cell series photoacoustic spectroscopy as claimed in claim 1, wherein the measurement and control unit comprises an alarm device, and the alarm device is an audible and visual alarm.
5. The gas detection apparatus according to claim 1, wherein the measurement and control unit comprises a storage device.
6. The gas detection apparatus according to claim 1, wherein the first acoustic sensor and the second acoustic sensor are both a microphone, a piezo-ceramic microphone or an optical fiber acoustic sensor.
7. The gas detection apparatus according to claim 1, wherein the glass is an infrared transmission window.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110186852A (en) * | 2019-06-26 | 2019-08-30 | 南京无书化工有限公司 | A kind of double ponds series connection optoacoustic spectroscopy gas-detecting device and method |
| CN112595687A (en) * | 2020-11-24 | 2021-04-02 | 南京工业大学 | Non-dispersive infrared gas concentration detection device and method with same optical axis |
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2019
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110186852A (en) * | 2019-06-26 | 2019-08-30 | 南京无书化工有限公司 | A kind of double ponds series connection optoacoustic spectroscopy gas-detecting device and method |
| CN110186852B (en) * | 2019-06-26 | 2023-12-01 | 南京无书化工有限公司 | Double-cell series photoacoustic spectrum gas detection device and method |
| CN112595687A (en) * | 2020-11-24 | 2021-04-02 | 南京工业大学 | Non-dispersive infrared gas concentration detection device and method with same optical axis |
| CN112595687B (en) * | 2020-11-24 | 2021-07-27 | 南京工业大学 | Non-dispersive infrared gas concentration detection device and method with same optical axis |
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