CN114526831A - Dew point frost point temperature sensor and measuring method thereof - Google Patents
Dew point frost point temperature sensor and measuring method thereof Download PDFInfo
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Abstract
The invention discloses a dew point frost point temperature sensor and a measuring method thereof, wherein the method comprises the steps of optimizing a gas absorption spectrum line selection strategy and selecting an absorption line suitable for a measuring object; the spectral model fitting is combined with the background absorption correction, and accurate integral absorbance and spectrum Lorentz broadening are extracted; calculating the gas temperature by adopting a double-line ratio method; calculating to obtain the total pressure of the gas according to the relationship between the spectrum Lorentz broadening and the total pressure of the gas; and calculating the water vapor partial pressure according to the integral absorbance, correcting the non-ideal gas, and then obtaining the water vapor atmospheric pressure dew point/frost point temperature according to the relation between the dew point/frost point temperature and the water vapor partial pressure and by combining the pressure and temperature calculation result. The invention simultaneously carries out calibration-free measurement of the water vapor temperature, the pressure and the dew point/frost point temperature by a laser spectrum method, does not need an external temperature and pressure sensor, not only can effectively improve the precision of the dew point/frost point temperature measurement, but also can effectively reduce the complexity and the cost of a dew point/frost point temperature measurement system.
Description
Technical Field
The invention relates to the field of laser spectrum gas sensing, in particular to a dew point frost point temperature sensor and a measuring method thereof.
Background
The dew point temperature is the temperature at which the gas is cooled under isobaric conditions, and the temperature of the gas when water vapor in the gas condenses to liquid water/ice is the dew point temperature of the water vapor. The dew point/frost point temperature is an important gas state parameter and is mainly used for representing the humidity of gas. In general, a condensation temperature point at zero or higher is called a dew point, and a condensation temperature point at zero or lower is called a frost point.
High-precision monitoring of water vapor dew point/frost point temperature plays a very important role in the fields of meteorology, atmospheric research, industrial process control, agriculture, medical treatment, aerospace and the like. The traditional dew point temperature measuring method mainly comprises a hair hygrometer method, a dry-wet ball method, a resistance-capacitance method, an electronic hygrometer, a gravimetric method, a material humidity sensor, a cold mirror type dew point meter and the like. The traditional dew point measuring methods can meet the requirements of specific use scenes, such as a hair hygrometer, a dry-wet bulb, a resistance-capacitance method, a gravimetric method and an electronic hygrometer, can be used in a common atmospheric environment, and have low requirements on precision; the material humidity-sensitive sensor is widely applied to industrial processes, has the advantage of wide detection range, but cannot be used in environments with extremely low temperature, extremely high temperature, corrosion and the like, and in addition, the material humidity-sensitive sensor needs to be calibrated and replaced regularly; the cold mirror type dew point instrument is a standard instrument for tracing the source of the current humidity, has the highest precision, but can only adopt a mode of air suction, and a measurement result is easily influenced by a sampling pipeline.
The optical-based method has the advantages of non-invasion, high response speed, wide measurement range, high precision and the like. The device for measuring the dew point/frost point temperature by adopting the technology based on the tunable diode laser line absorption spectrum (TDLAS) also has the advantages of simple structure, miniaturization and the like. The dew point detection system of the prior art principle comprises a two-stage gas pressure reducing valve, a gas flow meter, a pipeline filter and a detection device. The TDLAS detection device extracts gas to be detected from the pipeline to the gas chamber and then detects the gas, and the adsorption and desorption of water vapor by the pipeline can generate negative influence on a dew point measurement result; in addition, although the system is provided with the pressure adjusting device, the measurement result does not take the influence of the temperature and the pressure into consideration, so that the accuracy of the measurement result is not high. Under the condition of large temperature and pressure wave bands, measurement even has errors.
Disclosure of Invention
In order to solve at least one technical problem existing in the prior art to a certain extent, the invention aims to provide a dew point frost point temperature sensor and a measuring method thereof.
The technical scheme adopted by the invention is as follows:
a dew point frost point temperature sensor, comprising:
the tunable laser is used for tuning and outputting laser within a preset wavelength range and scanning two complete water vapor absorption spectrums;
the optical path module comprises an optical fiber beam splitter, a first collimator, a second collimator, a first photoelectric detector and a second photoelectric detector, wherein the optical fiber beam splitter is used for splitting the tunable laser into a first laser and a second laser; the first laser light passes through the first collimator and reaches the first photodetector; the second laser passes through the second collimator and penetrates through the environment to be detected, and then reaches the second photoelectric detector;
and the data acquisition system is used for receiving the first photoelectric detector and the signals acquired by the first photoelectric detector and acquiring a dew point/frost point temperature result according to the acquired signals and the spectrum model.
Further, the dew point/frost point temperature sensor further comprises a driving system for driving the tunable laser, wherein the driving system comprises a signal generator, a temperature control module and a current control module;
the signal generator is used for outputting a sawtooth wave signal;
the temperature control module is used for controlling the temperature of the tunable laser to be kept constant;
the current control module is used for tuning the working current of the tunable laser according to the sawtooth wave signal so as to tune the laser wavelength output by the tunable laser.
Furthermore, the tunable laser is a tunable diode laser, the central wavelength of the laser output by the tunable laser is determined according to the actual gas concentration range to be measured, two gas absorption lines are arranged near the central wavelength, the wavelength interval meets the requirement of being capable of being scanned simultaneously, and in addition, the energy level difference of the two absorption lines can ensure that the temperature measurement sensitivity is enough.
Further, the optical path of the second laser penetrating through the environment to be measured is adjusted according to the concentration range of the gas to be measured in the actual measurement environment;
the adjusting method comprises the following steps: calculating an absorption spectrum according to the Lambert-beer absorption law, firstly ensuring that the absorption spectrum is not absorbed and saturated, and secondly keeping the signal-to-noise ratio as high as possible; the optical path of the reference spectrum, which is the optical path between the first collimator and the first photodetector, is kept as 0 as possible.
The other technical scheme adopted by the invention is as follows:
a measuring method of a dew point frost point temperature sensor comprises the following steps:
fixing the driving temperature of the tunable laser, and adjusting the driving current to enable the laser to scan two complete water vapor absorption lines;
measuring the current tuning characteristic of the tunable laser, establishing a cubic multi-project model for converting a time domain into a frequency domain, and acquiring model parameters;
setting a reference light path and a measuring light path, wherein laser of the measuring light path penetrates through an environment to be measured, and a collimator in the reference light path is in direct contact with a photoelectric detector;
dividing laser output by the tunable laser into two beams of laser by adopting a beam splitter, respectively transmitting the two beams of laser to a measuring light path and a reference light path, and respectively measuring absorption signals in the measuring light path and the reference light path;
performing online fitting on the measured double spectral lines by using a spectral model to obtain the Lorentz broadening of the spectrum and the integral absorbance;
correcting the spectrum Lorentz broadening and the integral absorbance on the measuring optical path based on the absorption spectrum of the reference optical path;
calculating the gas temperature according to the corrected integral absorbance;
calculating partial pressure of the gas to be detected according to the gas temperature and the known effective optical path length, and calculating total pressure of the gas;
and calculating to obtain the atmospheric pressure dew point/frost point temperature according to the relationship between the partial pressure of the gas and the dew point temperature and the total pressure of the gas.
Further, the spectrum model is a partial correlation quadratic velocity dependence hard collision spectrum model, and a fitting algorithm adopted in online fitting of the measured double spectral lines by the spectrum model is an L-M algorithm.
Further, the integrated absorbance is corrected by:
and subtracting the absorbance of the reference light path from the absorbance of the measuring light path to obtain the absorbance of the actual gas absorption.
Further, the calculating the gas temperature according to the corrected integrated absorbance includes:
and calculating the gas temperature by adopting a two-line ratio method according to the corrected integral absorbance.
Further, the calculating a total pressure of the gas comprises:
and calculating the pressure value of the gas according to the relationship between the Lorentz broadening and the total pressure of the gas to be used as the total pressure of the gas.
Further, the calculating to obtain the atmospheric pressure dew point/frost point temperature according to the relationship between the partial pressure of the gas and the dew point temperature and the total pressure of the gas comprises:
acquiring gas partial pressure according to the spectrum and correcting the non-ideal gas effect of the gas partial pressure;
and calculating the dew point/frost point temperature by adopting an interpolation method according to the relation between the gas partial pressure and the dew point/frost point temperature and the total gas pressure.
The invention has the beneficial effects that: the invention can realize the synchronous detection of multiple parameters of temperature, pressure and dew point/frost point temperature by only using one laser, can carry out accurate dew point/frost point temperature measurement without additional temperature and pressure sensors, and can reduce the cost of the sensors.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description is made on the drawings of the embodiments of the present invention or the related technical solutions in the prior art, and it should be understood that the drawings in the following description are only for convenience and clarity of describing some embodiments in the technical solutions of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a dew point frost point temperature sensor according to an embodiment of the present invention;
FIG. 2 is a flow chart of an inversion of dew point/frost point temperature in an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention. For the step numbers in the following embodiments, they are set for convenience of illustration only, the order between the steps is not limited at all, and the execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.
In the description of the present invention, it should be understood that the orientation or positional relationship referred to in the description of the orientation, such as the upper, lower, front, rear, left, right, etc., is based on the orientation or positional relationship shown in the drawings, and is only for convenience of description and simplification of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.
In the description of the present invention, the meaning of a plurality of means is one or more, the meaning of a plurality of means is two or more, and larger, smaller, larger, etc. are understood as excluding the number, and larger, smaller, inner, etc. are understood as including the number. If the first and second are described for the purpose of distinguishing technical features, they are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.
In the description of the present invention, unless otherwise explicitly limited, terms such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific contents of the technical solutions.
In the present invention, the meaning of "dew point/frost point" appearing throughout includes that the dew point, or the frost point, or both the dew point and the frost point satisfy three parallel schemes. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.
Fig. 1 shows a schematic structural diagram of a full-laser dew point/frost point temperature sensor according to an embodiment of the present invention, the sensor includes three parts:
(1) laser and drive. Comprises a signal generator, a temperature and current control module and a tunable diode laser 1. The signal generator generates a sawtooth wave signal, the temperature controller controls the temperature of the laser to keep constant, and the current controller tunes the working current of the laser according to the sawtooth wave current signal, so that the wavelength output of the laser is tuned.
(2) And the optical path comprises a reference optical path and a measuring optical path. The diode laser is transmitted to an optical fiber beam splitter 3 through an optical fiber 2, the laser is divided into two beams, and the two beams are respectively transmitted to two collimators 4 through the optical fiber 2, wherein one beam of light is directly received by a detector 6 after passing through the collimator 4, the beam of light is used as a reference light path, the other beam of light is received by the detector 6 after passing through an environment to be measured 5 after passing through the collimator 4, and the beam of light is used as a measurement light path.
(3) And (5) data acquisition and processing. Transconductance amplifier circuit and data collection station. After the signals of the detector are converted and amplified by the transconductance amplifying circuit, the signals are collected by the data collector and processed on line to obtain a dew point/frost point temperature result.
Fig. 2 shows the flow of data inversion based on the dew point/frost point temperature of the full laser. The method comprises the following specific steps:
1) respectively obtaining the absorbance alpha of the measured absorption spectrum according to the measured signals of the measuring light path and the reference light path detector and the tuning characteristic of the laser1And alpha2；
2) Background absorption, alpha, is subtracted by subtracting the absorbance of the measurement and reference pathseffective＝α1-α2Obtaining an effective absorption spectrum;
3) performing multi-line online fitting on the measured effective spectrum by adopting a partially correlated secondary velocity dependent hard collision spectrum model, and acquiring integral absorbance and Lorentz broadening of the spectrum by adopting an L-M algorithm in the fitting;
4) and calculating and acquiring the temperature by integrating the absorbance and adopting a two-line ratio method:
5) after the gas temperature is obtained, the water vapor partial pressure can be obtained according to the Lambor-beer law:
and then calculating to obtain the total gas pressure according to the relationship between the Lorentz broadening and the pressure:
the spectral parameters can be referred to a spectral database HITRAN;
6) and (3) after acquiring the water vapor partial pressure, calculating the water vapor partial pressure under the atmospheric pressure according to the measured total gas pressure:
and then correcting the water vapor partial pressure by adopting a Goff and Gratch method:
wherein α, β are constants;
7) and after the corrected water vapor partial pressure is obtained, calculating the dew point/frost point temperature according to a Murphy-Koop formula:
lneS(Td)＝-6763.22/Td-4.210ln(Td)+0.000367Td+tanh{0.0415(Td-218.8)}×...×(53.878-1331.22/Td-9.44523ln(Td)+0.014025Td)+54.842663
wherein es(Td) (Pa) is the saturated water vapor partial pressure below the level of pure water, Td(K) Is the dew point temperature.
lnes(Tf)＝9.550426-5723.265/Tf+3.53068ln(Tf)-0.00728332Tf
Wherein es(Tf) (Pa) is the partial pressure of saturated water vapor under a pure level ice surface, Tf(K) The frost point temperature.
The embodiment also provides a method for sensing the dew point/frost point temperature based on the full laser, which is characterized in that a single DFB laser is adopted, and additional temperature and pressure sensors are not required to be arranged. The method comprises the following steps:
setting the temperature and current of a laser, and enabling the central wavelength output by the laser to scan two complete water vapor absorption lines;
step two, measuring the dynamic tuning characteristic of the laser by adopting the etalon to obtain the time-frequency conversion relation of the measurement signal, and specifically comprising the following steps:
1) controlling the laser output laser adjusted in the step 1 to vertically penetrate through the quartz etalon to acquire an interference signal in a time domain;
2) based on the peak position of the interference peak in the interference signal and the time between sampling pointsCorresponding relation, establishing cubic polynomial model v ═ a. Sample3+b·Sample2+ c, Sample + d describes a time-frequency relation, and parameters a, b, c and d are obtained by fitting measured data;
and step three, dividing laser emitted by the tunable diode laser into two beams by the beam splitter, wherein one beam penetrates through a gas area to be detected and is detected and received by the photoelectric detector (measuring part), and the emitting end of the other beam is directly contacted by the receiving end of the photoelectric detector (reference part). And calculating to obtain the water vapor absorption spectrum according to the Lambert-beer absorption law and the time-frequency conversion relation of the laser in the second step. Correcting the measurement spectrum in a mode of subtracting the absorption spectrum of the reference part from the absorption spectrum of the measurement part;
performing multi-line fitting on the corrected absorption spectrum line by adopting a part of related secondary velocity dependence hard collision spectrum model to obtain accurate integral absorbance and Lorentz broadening;
step five, calculating the gas temperature according to a two-line ratio method;
calculating according to the relationship between the Lorentz broadening and the pressure to obtain the gas pressure;
step seven, calculating the water vapor partial pressure according to the relation between the integral absorbance and the concentration;
and step eight, correcting the non-ideal gas effect of the water vapor partial pressure, and calculating to obtain the dew point/frost point temperature according to the relation between the water vapor partial pressure and the dew point/frost point temperature.
To sum up, compared with the prior art, the sensor of the embodiment has the following beneficial effects:
(1) compared with the traditional laser dew point measurement method, the method can accurately measure the dew point/frost point temperature without additional temperature and pressure sensors, can reduce the cost of the sensor, and has the advantages of high response speed up to ms magnitude, large measurement range, strong environmental adaptability and calibration-free measurement result.
(2) In the embodiment, the synchronous detection of multiple parameters of temperature, pressure and dew point/frost point temperature can be realized by only using one laser, and the detection capability is stronger.
(3) The embodiment adopts the synchronous measurement mode of temperature, pressure and dew point/frost point temperature of full laser, can effectively overcome the influence of temperature and pressure fluctuation to dew point/frost point temperature measurement, and the measuring result is more reliable, and in addition, measuring device structure is simpler, and is more miniaturized.
(4) The method and the device have the advantages of simplicity in operation, good robustness and the like, and are suitable for in-situ calibration-free measurement of the water vapor dew point/frost point temperature in the common environment and the extreme environment.
In the foregoing description of the specification, reference to the description of "one embodiment/example," "another embodiment/example," or "certain embodiments/examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A dew point frost point temperature sensor, comprising:
the tunable laser is used for tuning and outputting laser within a preset wavelength range and scanning two complete water vapor absorption spectrums;
the optical path module comprises an optical fiber beam splitter, a first collimator, a second collimator, a first photoelectric detector and a second photoelectric detector, wherein the optical fiber beam splitter is used for splitting the tunable laser into a first laser and a second laser; the first laser light passes through the first collimator and reaches the first photodetector; the second laser passes through the second collimator and penetrates through the environment to be detected, and then reaches the second photoelectric detector;
and the data acquisition system is used for receiving the first photoelectric detector and the signals acquired by the first photoelectric detector and acquiring a dew point/frost point temperature result according to the acquired signals and the spectrum model.
2. A dew point frost point temperature sensor according to claim 1, further comprising a drive system for driving the tunable laser, the drive system comprising a signal generator, a temperature control module and a current control module;
the signal generator is used for outputting a sawtooth wave signal;
the temperature control module is used for controlling the temperature of the tunable laser to be kept constant;
the current control module is used for tuning the working current of the tunable laser according to the sawtooth wave signal so as to tune the laser wavelength output by the tunable laser.
3. The dew point frost point temperature sensor of claim 1, wherein said tunable laser is a tunable diode laser, the central wavelength of the output laser of said tunable laser is determined according to the actual gas concentration range to be measured, there are two gas absorption lines near said central wavelength, and the wavelength interval satisfies the requirement of being able to be scanned simultaneously, and in addition, the energy level difference of these two absorption lines can ensure sufficient temperature measurement sensitivity.
4. The dew point frost point temperature sensor according to claim 1, wherein the optical path of the second laser through the environment to be measured is adjusted according to the concentration range of the gas to be measured in the actual measurement environment;
the adjusting method comprises the following steps: calculating an absorption spectrum according to the Lambert-beer absorption law, firstly ensuring that the absorption spectrum is not absorbed and saturated, and secondly keeping the signal-to-noise ratio as high as possible; the optical path of the reference spectrum, which is the optical path between the first collimator and the first photodetector, is kept as 0 as possible.
5. A method for measuring a dew point frost point temperature sensor according to any of claims 1-4, characterized in that it comprises the following steps:
fixing the driving temperature of the tunable laser, and adjusting the driving current to enable the laser to scan two complete water vapor absorption lines;
measuring the current tuning characteristic of the tunable laser, establishing a cubic multi-project model for converting a time domain into a frequency domain, and acquiring model parameters;
setting a reference light path and a measuring light path, wherein laser of the measuring light path penetrates through an environment to be measured, and a collimator in the reference light path is in direct contact with a photoelectric detector;
dividing laser output by the tunable laser into two beams of laser by adopting a beam splitter, respectively transmitting the two beams of laser to a measuring light path and a reference light path, and respectively measuring absorption signals in the measuring light path and the reference light path;
performing online fitting on the measured double spectral lines by using a spectral model to obtain the Lorentz broadening of the spectrum and the integral absorbance;
correcting the spectrum Lorentz broadening and the integral absorbance on the measuring optical path based on the absorption spectrum of the reference optical path;
calculating the gas temperature according to the corrected integral absorbance;
calculating partial pressure of the gas to be detected according to the gas temperature and the known effective optical path length, and calculating total pressure of the gas;
and calculating to obtain the atmospheric pressure dew point/frost point temperature according to the relationship between the partial pressure of the gas and the dew point temperature and the total pressure of the gas.
6. The measurement method according to claim 5, wherein the spectral model is a partially correlated quadratic velocity dependent hard collision spectral model, and the fitting algorithm used in the online fitting of the measured bispectrum lines using the spectral model is an L-M algorithm.
7. The measurement method according to claim 5, characterized in that the integrated absorbance is corrected by:
and subtracting the absorbance of the reference light path from the absorbance of the measuring light path to obtain the absorbance of the actual gas absorption.
8. The method of claim 5, wherein calculating the gas temperature from the corrected integrated absorbance comprises:
and calculating the gas temperature by adopting a two-line ratio method according to the corrected integral absorbance.
9. The method of measurement according to claim 5, wherein the calculating a total pressure of the body of gas comprises:
and calculating the pressure value of the gas according to the relationship between the Lorentz broadening and the total pressure of the gas to be used as the total pressure of the gas.
10. The method of measurement according to claim 5, wherein the calculating of the atmospheric dew point/frost point temperature from the relationship between the partial pressure of the gas and the dew point temperature and the total pressure of the gas comprises:
acquiring gas partial pressure according to the spectrum and correcting the non-ideal gas effect of the gas partial pressure;
and calculating the dew point/frost point temperature by adopting an interpolation method according to the relation between the gas partial pressure and the dew point/frost point temperature and the total gas pressure.
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