CN109239011B - Optical fiber dew point humidity detection device, system and control method thereof - Google Patents
Optical fiber dew point humidity detection device, system and control method thereof Download PDFInfo
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- CN109239011B CN109239011B CN201810801296.5A CN201810801296A CN109239011B CN 109239011 B CN109239011 B CN 109239011B CN 201810801296 A CN201810801296 A CN 201810801296A CN 109239011 B CN109239011 B CN 109239011B
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Abstract
The invention relates to the technical field of sensor control, and particularly discloses an optical fiber dew point humidity detection device which comprises a first optical fiber, a humidity sensing layer, a second optical fiber, a first optical fiber coupler, a second optical fiber coupler, a third optical fiber coupler, a light source, a first optical power meter and a second optical power meter; the invention also discloses an optical fiber dew point humidity detection system which comprises the optical fiber dew point humidity detection device, a calculation controller, a data acquisition device, a temperature sensor, a refrigerator and an actuator. The invention also discloses a control method of the optical fiber dew point humidity detection system, which comprises the following steps: s1, cooling; s2, collecting real-time data; s3, transmitting the acquired data to a calculation controller; s4, processing to obtain a refractive index-time curve and a temperature-time curve; s5, judging a temperature value at which condensation occurs; s6, calculating the relative humidity. The invention has the advantages of high test precision, convenient operation, stable operation and high environment adaptability.
Description
Technical Field
The invention relates to the technical field of sensor control, in particular to an optical fiber dew point humidity detection device, an optical fiber dew point humidity detection system and a control method thereof.
Background
With the rapid development of industries such as industry, aquaculture, national defense, environmental detection, aerospace, food processing and the like, the requirements on the air water content in the manufacturing process are finer and finer, so that the measurement and control of the environmental humidity are also important. Correspondingly, higher standards are also put forward for important indexes such as sensitivity, response time, measurement range, repeatability, humidity stagnation, temperature characteristics and the like of the humidity sensor.
The traditional humidity measuring instrument comprises a dry-wet ball hygrometer, a mechanical hygrometer, an electronic humidity sensor and the like. The traditional humidity sensor is applied to certain measurement fields due to the advantages of simple structure, low technical threshold, low cost and the like. The electronic humidity sensor has wide application, very high market share and outstanding advantages in measurement sensitivity, measuring range and precision. However, the conventional sensor still has some drawbacks, such as poor interchangeability and long-term stability, difficult direct replacement, response to wet stagnation, drift, short service life, incapability of being used in severe environments (such as severe pollution, strong electromagnetic environments, inflammable and explosive environments, and the like), and the like, so that the sensor is limited in the fields of high-temperature high-pressure engineering, nuclear fuel, and the like, and is difficult to effectively measure humidity.
Disclosure of Invention
In view of the above, there is a need to provide an optical fiber dew point humidity detecting device, an optical fiber dew point humidity detecting system and a control method of the optical fiber dew point humidity detecting system based on a virtual instrument, so as to solve the above-mentioned drawbacks of the conventional humidity measuring instrument in the background art: poor interchangeability, poor long-term stability, short service life and low environmental adaptation.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
an optical fiber dew point humidity detection device includes: the first optical fiber, the humidity sensing layer, the second optical fiber, the first optical fiber coupler, the second optical fiber coupler, the third optical fiber coupler, the light source, the first optical power meter and the second optical power meter;
One end of the first optical fiber is coated with a humidity sensing layer and is arranged in an environment space for temperature regulation; the other end of the first optical fiber is in light guide connection with one end of the first optical fiber coupler; the other end of the first optical fiber coupler is in light guide connection with one end of the third optical fiber coupler;
One end of the second optical fiber is arranged in an environment space where the dew point of the air is not formed; the other end of the second optical fiber is in light guide connection with one end of the second optical fiber coupler; the other end of the second optical fiber coupler is in light guide connection with one end of the third optical fiber coupler;
The other end of the third optical fiber coupler is in light guide connection with the light source; the first optical power meter is in light guide connection with the first optical fiber coupler; the second optical power meter is in light guide connection with the second optical fiber coupler;
The first optical fiber is used for detecting the humidity of an experimental area where the air forms a dew point;
The humidity sensing layer is used for absorbing air moisture in the experimental area and changing the refractive index of the first optical fiber;
the second optical fiber is used for detecting the humidity of the environment in which the dew point of the air is not formed;
The first optical fiber coupler is used as an optical splitting connector of the first optical fiber and the first optical power meter; the second optical fiber coupler is used as an optical splitting connector of a second optical fiber and a second optical power meter; the third optical fiber coupler is used as a light splitting connector of the first optical fiber coupler, the second optical fiber coupler and the light source;
The light source is used for simultaneously providing light rays with the same light measurement to the first optical fiber and the second optical fiber;
The first optical power meter is used for collecting real-time data of the refractive index of the first optical fiber;
The second optical power meter is used for collecting real-time data of the refractive index of the second optical fiber.
Further, the humidity sensing layer is a lithium chloride-polyvinyl alcohol humidity sensitive film.
Further, the light source is a laser semiconductor light source.
Furthermore, the first optical power meter and the second optical power meter are both provided with a power digital display device.
Furthermore, the first optical power meter and the second optical power meter are both provided with an RS-232 interface.
An optical fiber dew point humidity detection system comprising: the optical fiber dew point and humidity detection device, the calculation controller, the data acquisition device, the temperature sensor, the refrigerator and the executor are described above; the calculation controller is respectively connected with the data acquisition device, the first optical power meter and the second optical power meter; the executor is electrically connected with the data collector and the refrigerator respectively; one end of the first optical fiber is arranged in a refrigerating space formed by the refrigerator;
The computing controller is used for reading, processing and analyzing the detection data and outputting corresponding control instructions;
The data acquisition device is used for reading detection data of the temperature sensor and controlling the actuator according to an instruction of the calculation controller;
The temperature sensor is used for detecting the ambient temperature of a refrigerating space formed by the refrigerator and transmitting detection data to the data collector;
The refrigerator is used for refrigerating and cooling the refrigerating space provided with the first optical fiber;
The actuator is used for controlling the start-stop and/or working power of the refrigerator.
Furthermore, the computing controller is connected with the first optical power meter and the second optical power meter respectively through an RS-232 communication protocol.
Further, the computation controller is provided with a computation control module; the calculation control module comprises an optical power meter setting module, a handshake communication module, a temperature acquisition module, a dew point judging module, a refractive index calculation module, a data storage template and a virtual display module;
The optical power meter setting module is used for sending parameter setting commands and/or reading commands to the first optical power meter and/or the second optical power meter and reading response connection signals of the first optical power meter and/or the second optical power meter;
the handshake communication module is used for detecting the connection state of the first optical power meter and/or the second optical power meter;
the temperature acquisition module is used for acquiring real-time temperature data of the temperature sensor;
the dew point judging module is used for calculating and judging the dew point forming time and the temperature value of the refrigerating space formed by the refrigerator according to the real-time temperature data of the temperature acquisition module;
The refractive index calculation module is used for calculating the refractive index of the humidity sensing layer according to the power value of the first optical power meter, the power value of the second optical power meter, the refractive index of air and the refractive index of the optical fiber core;
the data storage template is used for storing the data of the temperature acquisition module and the refractive index calculation module;
the virtual display module is used for virtually displaying the control process, the data change process and the parameter setting process of the computing controller.
Furthermore, the computing controller is also provided with a LabVIEW software system.
The control method of the optical fiber dew point humidity detection system is applied to the optical fiber dew point humidity detection system, and comprises the following steps:
S1, a computing controller cools a refrigerating space provided with a first optical fiber by controlling a refrigerator;
s2, acquiring real-time data of the refractive index of a first optical fiber by a first optical power meter; the second optical power meter collects real-time data of the refractive index of the second optical fiber; the temperature sensor collects real-time data of temperature;
S3, the first optical power meter, the second optical power meter and the temperature sensor transmit acquired data to a calculation controller;
S4, the computing controller controls the temperature of the refrigerator, and a refractive index-time curve and a temperature-time curve are obtained through processing of a LabVIEW software system installed in the computing controller;
S5, the computing controller judges a temperature value of the condensation in the refrigerating space provided with the first optical fiber by analyzing a curve inflection point of the refractive index-time curve;
S6, the calculation controller processes the data of the temperature acquisition module, so that the data are converted into corresponding temperature refractive index values, and the corresponding relative humidity at room temperature is obtained through calculation.
The beneficial effects of the invention are as follows:
The invention has the characteristics of friendly man-machine interaction interface, real-time detection, flexible storage and alarm, flexible parameter setting and the like; experiments prove that the system has stable operation, easy operation, high precision, low cost and strong anti-interference capability, and can be applied to a plurality of humidity detection fields. The invention has the advantages of small volume, light weight, electromagnetic interference resistance, large response variation, good electrical insulation performance, corrosion resistance, wide measurement bandwidth, suitability for flammable and explosive dangerous environments, convenient realization of distributed multi-point measurement and the like, and is widely applied to the fields of modern industry, agriculture and science and technology. The invention adopts the LABVIEW software system, collects data through communication with the optical fiber sensor, displays the data on the virtual oscilloscope interface, can dynamically observe the experimental data display process in real time, and can complete the whole test work of collecting, analyzing, processing, displaying, storing and the like of measured data through a computer displayed by a friendly graphical operation interface, and realize remote monitoring and data sharing through a network. The invention can accurately measure the humidity of the gas in the environment, has low requirement on the environment, good repeatability and small error, and can be widely applied to measurement and monitoring of the humidity in various fields.
Drawings
FIG. 1 is a schematic diagram of a device for detecting dew point and humidity of an optical fiber according to the present invention;
FIG. 2 is a schematic diagram of a system for detecting dew point and humidity of an optical fiber according to the present invention;
FIG. 3 is a schematic diagram of a computing control module according to the present invention;
FIG. 4 is a flow chart of a control method of an optical fiber dew point humidity detection system according to the present invention;
FIG. 5 is a flow chart of the LABVIEW software system for dew point determination in S5 according to the present invention;
FIG. 6 is a flow diagram of a LABVIEW software system for refractive index calculation in S4 of the present invention;
FIG. 7 is a flow diagram of a LABVIEW-based software system for data preservation of a data preservation template of the present invention;
FIG. 8 is a diagram of a virtual display interface of a virtual display module of the present invention with a temperature inflection point;
FIG. 9 is a virtual display interface of the virtual display module of the present invention for performing a repeatability experiment;
FIG. 10 is a schematic diagram illustrating the operation of an optical fiber dew point humidity detecting device according to the present invention;
FIG. 11 is a schematic diagram illustrating a calculation process of a control method of an optical fiber dew point humidity detection system according to the present invention;
FIG. 12 is a program form diagram of a control method of an optical fiber dew point humidity detection system according to the present invention;
Reference numerals illustrate:
A first optical fiber 1; a moisture sensitive layer 2; a second optical fiber 3; a first optical fiber coupler 4; a second optical fiber coupler 5; a third fiber coupler 6; a light source 7; a first optical power meter 8; a second optical power meter 9; a calculation controller 10; a data collector 11; a temperature sensor 12; a refrigerator 13; an actuator 14; an optical power meter setting module 15; a handshake communication module 16; a temperature acquisition module 17; a dew point determination module 18; a refractive index calculation module 19; a data-saving template 20; a virtual display module 21.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be further clearly and completely described in the following in conjunction with the embodiments of the present invention. It should be noted that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It is to be understood that the terms "upper," "lower," "front," "rear," "left," "right," and the like indicate an orientation or positional relationship based on that shown in the drawings, and are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the apparatus or element in question must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
The terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a definition of "a first", "a second", "a third" feature may include one or more of the features, either explicitly or implicitly.
Examples
As shown in fig. 1, an optical fiber dew point humidity detection apparatus includes: a first optical fiber 1, a humidity sensing layer 2, a second optical fiber 3, a first optical fiber coupler 4, a second optical fiber coupler 5, a third optical fiber coupler 6, a light source 7, a first optical power meter 8 and a second optical power meter 9;
one end of the first optical fiber 1 is coated with a humidity sensing layer 2 and is arranged in an environment space for temperature regulation; the other end of the first optical fiber 1 is in light guide connection with one end of a first optical fiber coupler 4; the other end of the first optical fiber coupler 4 is in light guide connection with one end of the third optical fiber coupler 6;
One end of the second optical fiber 3 is arranged in an environment space where the dew point of the air is not formed; the other end of the second optical fiber 3 is in light guide connection with one end of a second optical fiber coupler 5; the other end of the second optical fiber coupler 5 is in light guide connection with one end of the third optical fiber coupler 6;
the other end of the third optical fiber coupler 6 is in light guide connection with a light source 7; the first optical power meter 8 is in light guide connection with the first optical fiber coupler 4; the second optical power meter 9 is in light guide connection with the second optical fiber coupler 5;
The first optical fiber 1 is used for detecting the humidity of an experimental area where the air forms a dew point;
the humidity sensing layer 2 is used for absorbing air moisture in the experimental area and changing the refractive index of the first optical fiber 1;
The second optical fiber 3 is used for detecting the humidity of the environment where the dew point of the air is not formed;
the first optical fiber coupler 4 is used as an optical splitting connector of the first optical fiber 1 and the first optical power meter 8; the second optical fiber coupler 5 is used as an optical splitting connector of the second optical fiber 3 and the second optical power meter 9; the third optical fiber coupler 6 is used as a light splitting connector of the first optical fiber coupler 4, the second optical fiber coupler 5 and the light source 7;
the light source 7 is used for providing light rays with the same light measurement to the first optical fiber 1 and the second optical fiber 3 at the same time;
the first optical power meter 8 is used for collecting real-time data of the refractive index of the first optical fiber 1;
the second optical power meter 9 is used for collecting real-time data of the refractive index of the second optical fiber 3.
Specifically, the power adopted by the first optical power meter 1 and the second optical power meter 3 is an RS-232 interface, the basic command mode of data transmission is a master-slave mode, namely, the computing controller is a main body for sending commands, various parameter setting commands or reading commands are sent to each power meter, the power meter receives the commands and responds, the response contact signal is requested by the RTS/CTS in the RS-232 interface, the power meter is used for switching between a sending mode and a receiving mode in a half-duplex MODEM system, the switching between the sending mode and the receiving mode is carried out in a full-duplex system, and finally, the power meter returns corresponding response signals or data to the computing controller (which can be a PC); the serial port parameters are set as follows: baud rate-57600 b/s; no verification is performed; 8 data bits; 1 stop bit; before data acquisition, the wavelength of each optical power meter is set to be 1550nm, and the resource names of VISA are corresponding.
Specifically, the humidity sensing layer 2 is obtained by the following method:
The manufacturing steps of the humidity sensing layer 2 are as follows:
(1) Wet feeling liquid: at 20 ℃,10ml of deionized water is used for dissolving lithium chloride to prepare a saturated solution; then, fully mixing 1g of polyvinyl alcohol, 12ml of deionized water, 16ml of ethanol and 0.18ml of lithium chloride saturated solution to obtain a humidity sensing liquid;
(2) Cleaning the optical fiber: sterilizing and drying the optical fiber; because the optical fiber probe cannot be processed at high temperature, the optical fiber is processed for 10 minutes at 50 ℃ and low humidity, and then the end face of the optical fiber is cleaned by deionized water and absolute ethyl alcohol;
(3) Coating: placing the cleaned optical fiber head into the humidity sensing liquid to make a round trip Tu La, and ensuring that the humidity sensing liquid is uniformly attached to the optical fiber head as much as possible;
(4) And (3) drying: and (3) placing the soaked optical fiber into a 50-DEG incubator, heating for 24 hours to obtain a coated optical fiber probe, and placing the coated optical fiber probe in a sealed and dry environment.
Further, the humidity sensing layer 2 is a lithium chloride-polyvinyl alcohol humidity sensitive film.
Further, the light source 7 is a laser semiconductor light source.
Further, the first optical power meter 8 and the second optical power meter 9 are both provided with a power digital display device.
Further, the first optical power meter 8 and the second optical power meter 9 are both provided with an RS-232 interface.
As shown in fig. 2, an optical fiber dew point humidity detection system includes: the optical fiber dew point humidity detection device, the calculation controller 10, the data collector 11, the temperature sensor 12, the refrigerator 13 and the actuator 14 as described above; the calculation controller 10 is respectively connected with the data collector 11, the first optical power meter 8 and the second optical power meter 9; the actuator 14 is electrically connected with the data collector 11 and the refrigerator 13 respectively; one end of the first optical fiber 1 is arranged in a refrigerating space formed by the refrigerator 13;
The computing controller 10 is used for reading, processing and analyzing the detection data and outputting corresponding control instructions;
The data collector 11 is used for reading detection data of the temperature sensor 12 and controlling the executor 14 according to instructions of the calculation controller 10;
The temperature sensor 12 is used for detecting the ambient temperature of the refrigerating space formed by the refrigerator 13 and transmitting detection data to the data collector 11;
The refrigerator 13 is used for refrigerating and cooling the refrigerating space provided with the first optical fiber 1;
The actuator 14 is used for controlling the start-stop and/or the operating power of the refrigerator 13.
Specifically, the temperature sensor 12 is a MCT80S small temperature transmitter, which is powered by 24VCD, and has the advantages of 4-20 mA output by PT100 input, 0-30 ℃ range, less than plus or minus 0.025% temperature drift, high precision, interference resistance, good stability and the like;
principle of operation of the temperature sensor 12: the temperature is affected to generate resistance or potential effect, and a voltage signal is generated through conversion, and the signal is amplified by an operational amplifier and then sent out to be a 4-20mA current signal or a 0-5V and 0-10V voltage signal corresponding to the measuring range.
Specifically, the refrigerator 13 is an XH-X266 semiconductor refrigeration module, and is connected with a 1-path 5v relay module through a data acquisition device for controlling heating and cooling; the semiconductor refrigeration module does not need a special working environment, has no pollution to the environment, can randomly adjust refrigeration parameters, and can change the running state of the refrigerator 13 by changing the direction of current.
Specifically, the actuator adopts a 1-path 5v relay module, and is connected with the actuator through the data collector 11, so that the operation and suspension of the refrigerator 13 can be directly controlled at any time on software, and the operation and suspension are convenient and safe; the interface mode of the module is as follows: DC+ is connected with the positive electrode of the power supply, DC-is connected with the negative electrode of the power supply, and IN can control the relay to be attracted by high or low level; the output end is: NO is a normally open interface of the relay, the relay is suspended before being attracted, and the relay is short-circuited with COM after being attracted; COM is the common interface of the relay; NC is a normally closed interface of the relay, and is in short circuit with COM before the relay is attracted and is suspended after the relay is attracted.
Specifically, the data collector 11 adopts a PCI-6221 data collection card, mainly uses AI and AO channels in experiments, and the VI program realizes the analog signal collection and output functions of the virtual instrument through the PCI-6221 data collection card; the PCI-6221 data acquisition card is a high-performance and multifunctional data acquisition card based on a PCI bus; the basic specification is as follows: 16 analog inputs, 16 bit resolution; a sampling rate of 250 kS/s; 8 differential inputs, 1 successive approximation ADC of 16 bits, 2 DACs of 16 bits output with voltages; 24-way digital I/O; AI. The maximum voltage sustainable by the AO channel is + -10 v; the temperature sensor 12 converts the temperature into an electrical signal, and the electrical signal is transmitted into the computing controller 10 through the PCI-6221 data acquisition card and processed into required data by the LabVIEW software system.
Further, the computing controller 10 is connected to the first optical power meter 8 and the second optical power meter 9 through RS-232 communication protocol, respectively.
As shown in fig. 2 and 3, the computation controller 10 is provided with a computation control module; the calculation control module comprises an optical power meter setting module 15, a handshake communication module 16, a temperature acquisition module 17, a dew point judging module 18, a refractive index calculation module 19, a data storage template 20 and a virtual display module 21;
the optical power meter setting module 15 is configured to send a parameter setting command and/or a reading command to the first optical power meter 8 and/or the second optical power meter 9, and read a response connection signal of the first optical power meter 8 and/or the second optical power meter 9;
the handshake communication module 16 is configured to detect a connection state of the first optical power meter 8 and/or the second optical power meter 9;
The temperature acquisition module 17 is used for acquiring real-time temperature data of the temperature sensor 12;
the dew point judging module 18 is used for calculating and judging the dew point forming time and the temperature value of the refrigerating space formed by the refrigerator 13 according to the real-time temperature data of the temperature collecting module 17;
the refractive index calculation module 19 is configured to calculate the refractive index of the humidity sensing layer 2 according to the power value of the first optical power meter 8, the power value of the second optical power meter 9, the refractive index of air and the refractive index of the fiber core;
The data storage template 20 is used for storing the data of the temperature acquisition module 17 and the refractive index calculation module 19;
the virtual display module 21 is configured to virtually display a control process, a data change process, and a parameter setting process of the computing controller 10.
Specifically, the workflow of handshake communication module 16 is when computing controller 10 sends "? "at the time, if the handshake is successful, the first optical power meter 8 and/or the second optical power meter 9 should respond". But when the CPU has task processing (this is the case only at the time of zeroing operation, and no command is responded to), then "B" will be responded to. If the response is not a case of both signals or a delay (response time in the order of ms), this indicates that the connection or the optical power meter is problematic (connection error or system paralysis).
Specifically, the temperature acquisition program of the temperature acquisition module 12 includes a temperature change operator vi, a temperature upper and lower limit setting, a thermometer, a humidity operator vi, and dew point temperature and humidity display; the upper and lower limits of the temperature are set to 0-30 ℃, and an alarm can be displayed when the temperature exceeds the range; the thermometer dynamically displays the temperature change condition, the minimum scale is 0.1 ℃, and the thermometer can be used for reading the approximate real-time temperature; the temperature value read after the program starts to run (refrigeration is not started) for 2s is taken as room temperature, then refrigeration is started to perform experiments, when an obvious inflection point (from rising abrupt change to falling) appears in the refractive index curve, the actuator 14 controls the refrigerator to stop cooling, and the real-time temperature value read by the temperature acquisition module 17 is the dew point temperature; the values of the room temperature and the dew point temperature can be subjected to a humidity calculation algorithm vi to obtain corresponding humidity values.
Specifically, as shown in fig. 3 and 5, the specific working process of the dew point judging module 18 is a dew point judging sub vi under the automatic control condition, the program divides each 3 of the read refractive index values into a group and calculates the average value thereof, then compares the adjacent 3 average values to judge whether the rising trend or the falling trend is carried out, when the maximum value in the 3 numbers is in the middle (i.e. the index is 1), the situation that the mutation exists is illustrated, when the three numbers are increased first and then reduced, the refractive index can be judged to reach the maximum value, and at the moment, the program controls the refrigerator 13 to adopt the refrigeration stopping mode through the actuator 14; when the three numbers are firstly reduced and then increased, the refractive index can be judged to reach the minimum value, and the system can correspondingly start refrigeration; when the refractive index shows periodic response in the experimental process (as shown in fig. 9), the system will periodically cool-warm, and the corresponding temperature curve will also change periodically.
Specifically, as shown in fig. 3 and 6, the refractive index calculation module 19 specifically works by obtaining a required C value by a correction procedure, and then combining two power values, the refractive index of air and the refractive index of the fiber core to calculate the refractive index to be measured; the flow chart of fig. 6 is obtained by the fresnel reflection principle of the two channels, deduced by the theoretical formula, and then subjected to deformation replacement writing procedure; the method greatly reduces the calculation difficulty and has high running speed.
Specifically, as shown in fig. 3 and 7, the data storage template 20 executes a program as shown in fig. 7, and the program is used for writing the acquired refractive index and temperature data into a document through a file IO, so as to facilitate further analysis and processing, wherein the refractive index sets the data precision to five bits after decimal point.
Specifically, as shown in fig. 3 and 8, the interface virtually displayed by the virtual display module 21 comprises two parts, namely a refractive index acquisition system and a temperature acquisition system, wherein the refractive index acquisition system comprises a channel data display column, a correction operation column, a program control column, a data storage column and the like; the laboratory ensures that serial ports of two channels are correctly arranged, and the serial ports are specifically required to be connected according to equipment in the laboratory, wherein the first channel is an optical power meter connected with a probe arranged in air, and the second channel is an optical power meter connected with a measuring probe; before the experiment, the first optical fiber 1 and the second optical fiber 3 are both placed in the air, and then a correction button is clicked to correct the constant C; in addition, a path for storing experimental data is required to be set so as to prevent data loss; the temperature acquisition system of the interface mainly comprises a physical channel, a real-time temperature, a room temperature, a dew point temperature, a humidity and other data display control, a thermometer, a refrigeration control button and an alarm display.
Further, as shown in fig. 2, the computing controller 10 is further installed with a LabVIEW software system.
Specifically, the LabVIEW software system is developed by using LabVIEW 8.6; the design idea of the system software is that the data is read from the channel appointed by the data collector, is stored and displayed on the panel after corresponding processing, and meanwhile, a control signal is generated and sent to the output channel.
As shown in fig. 4, a control method of an optical fiber dew point humidity detecting system is applied to the optical fiber dew point humidity detecting system as described above, and includes the steps of:
S1, a computing controller 10 cools a refrigerating space provided with a first optical fiber 1 by controlling a refrigerator 13;
s2, acquiring real-time data of the refractive index of the first optical fiber 1 by the first optical power meter 8; the second optical power meter 9 collects real-time data of the refractive index of the second optical fiber 3; the temperature sensor 12 collects real-time data of temperature;
S3, the first optical power meter 8, the second optical power meter 9 and the temperature sensor 12 transmit acquired data to the calculation controller 10;
S4, the computing controller 10 controls the temperature of the refrigerator 13, and the refractive index-time curve and the temperature-time curve are obtained through the LabVIEW software system installed in the computing controller 10;
s5, the computing controller 10 judges the temperature value of the condensation of the refrigerating space provided with the first optical fiber 1 by analyzing the curve inflection point of the refractive index-time curve;
s6, the calculation controller 10 processes the data of the temperature acquisition module 17, so that the data are converted into corresponding temperature refractive index values, and the corresponding relative humidity at room temperature is calculated.
Specifically, in S6, as the temperature decreases, the refractive index of the humidity sensing layer 2 is continuously increased; when the temperature is reduced to a certain value, the inflection point appears on the refractive index-time curve, and at the moment, the temperature of the condensation of water molecules in the environment can be considered to be reached, and the moisture-sensitive film is formed and dissolved by dew, so that the refractive index is reduced; when the inflection point is reached, the system automatically obtains the temperature at the moment and stops refrigerating, and the temperature gradually rises, so that the highest point of the refractive index-time curve corresponds to the lowest point of the temperature-time curve, and the system can automatically read the inflection point temperature and convert the inflection point temperature into relative humidity for display; three different humidity environments are selected for collection, and the results shown in the following table 1 are obtained; as can be seen from table 1, the measured humidity data and the hygrometer data are better matched, which proves the reliability of the method; the error is mainly derived from the judgment error of the dew point temperature, and the response error of the refractive index curve to the dew point;
table 1 shows the humidity measured by the system versus the hygrometer:
| Room temperature | Dew point temperature | Humidity measured herein | Humidity measured by hygrometer | |
| 1 | 29.8℃ | 6.0℃ | 22.6％ | 23％ |
| 2 | 24.5℃ | 11.2℃ | 43.7％ | 43％ |
| 3 | 27.4℃ | 24.2℃ | 83.6％ | 84％ |
TABLE 1
Specifically, as shown in fig. 9, in S6, a method of repeatability test is adopted to perform accurate correction;
The influence of periodic temperature rise and drop on the measurement result is tested, and the result is shown in fig. 9; as the moisture absorption and release effects of the polyvinyl alcohol-lithium chloride are good, when the temperature is periodically changed, the refractive index is correspondingly and periodically changed, and experiments prove that the film has good moisture sensitivity effect and the system has the advantage of repeated measurement. The humidity measuring device can continuously collect for many times during actual measurement and then take an average value, so that the humidity result finally measured is more accurate.
The working principle of the invention is further explained by combining a calculation formula (the operation evolution process is shown in fig. 10, 11 and 12):
Wherein nx is the refractive index to be measured, nc is the refractive index of the fiber core, n0 is the refractive index of air, R is the light intensity ratio of the fiber head 1 to the fiber head 2 (the fiber head 1 is placed in the environment to be measured, and 2 is placed in air); k is the light intensity ratio of the optical fiber heads 1 and 2 when the two optical fiber heads are both placed in the air;
Definition of relative humidity (RH%): the percentage of the actual water vapor pressure (denoted Pn) and saturated water vapor pressure (denoted Pw) per unit volume of air at the same temperature. The expression is:
the simplified saturated water vapor pressure equation is as follows:
wherein t is the ambient temperature, temperature range: -45 to +60 ℃;
where td is the dew point temperature, temperature range: -65 ℃ to +0.01 ℃;
the simultaneous calculation formula of the relative humidity is that
The program form of this formula is shown in fig. 12.
The working principle of the invention is as follows:
The hardware system of the invention can be understood as consisting of a refrigerating system, a signal acquisition system, an optical fiber sensing system, a temperature sensing system and an upper computer system, wherein the optical fiber sensing system is used for monitoring the refractive index change in the cooling process, and the temperature sensing system is used for monitoring the temperature change. When the temperature drops to the dew point, the refractive index-time curve shows an inflection point, and the temperature of the point can be obtained from the temperature-time curve, so that the ambient humidity can be obtained. The software system adopts a LABVIEW software platform, acquires data through communication with the optical fiber sensing system, and displays the data on a virtual oscilloscope interface, so that the experimental data display process can be dynamically observed in real time. The virtual instrument uses a novel functional module combining system monitoring and control equipment with hardware, a user can complete the whole testing work of acquisition, analysis, processing, display, storage and the like of measurement data through a computer displayed by a friendly graphical operation interface, remote monitoring and data sharing are realized through a network, and the humidity of gas in the environment can be accurately measured by using optical fiber refractive index sensing.
The invention combines the LabVIEW software platform and the corresponding hardware to realize the measurement, display and control of the temperature refractive index and the humidity; when the system is used for measuring, a first optical fiber head coated with the lithium chloride-polyvinyl alcohol humidity-sensitive film and a temperature sensor probe are close to a refrigerating surface of the refrigerator, the refrigerator is started to start cooling, refractive index-time data and temperature-time data of the humidity-sensitive film are collected, signals are sent to a calculation controller (which can be an upper computer) through a serial port and a data collection card, and a refractive index-time curve and a temperature-time curve are obtained after the signals are processed by a LabVIEW software platform and displayed on a virtual panel. When the temperature is reduced to the dew point, the refractive index-time curve presents an inflection point, the software automatically judges the temperature at the inflection point (the temperature can be considered as the dew point temperature), and the program calculates and displays the corresponding relative humidity at the room temperature; the hardware part converts the temperature refractive index signal into an electric signal, carries out conditioning conversion, transmits the data to the calculation controller, and simultaneously controls the temperature according to the instruction of the functional software; the software part is responsible for processing the data input from the data collector, converting the data into corresponding temperature refractive index values, calculating the relative humidity at the corresponding room temperature, displaying corresponding graphs and data on a display corresponding to the virtual display module, storing the graphs and the data in a hard disk, receiving temperature set values input by a user, and generating control signals; all measurement processes of the system are performed under the control of a mouse or a keyboard on a virtual panel of the computing controller. The structure not only simplifies the hardware design and reduces the cost, but also provides favorable conditions for the later improvement of the test system, and the operation of the instrument by the user becomes simpler and faster.
The functions of the system can be divided into:
(1) And measuring and displaying the temperature. The environmental temperature is converted into continuous voltage signals through the temperature sensor, the continuous voltage signals are subjected to A/D conversion through the data acquisition device after being conditioned, the data are sent into the computer, and the data are processed and displayed through instrument function software.
(2) Refractive index measurement and display.
(3) A refrigeration system. The operation and suspension of the refrigerator can be directly controlled at any time on software, and the refrigerator is convenient and safe.
(4) And calculating and displaying the humidity. Based on the relationship between the dew point temperature and the relative humidity, the relative humidity at room temperature is obtained from the dew point temperature by program calculation and displayed on the virtual panel.
(5) And (5) data storage. And storing the temperature and humidity data processed by the software into a designated electronic table file for later analysis and remote sharing.
The foregoing examples illustrate only a few embodiments of the invention and are described in detail herein without thereby limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.
Claims (7)
1. The humidity detection system based on the optical fiber dew point measurement is characterized by comprising a humidity detection device based on the optical fiber dew point measurement, a calculation controller (10), a data acquisition device (11), a temperature sensor (12), a refrigerator (13) and an actuator (14);
The humidity detection device based on the optical fiber dew point measurement comprises: the device comprises a first optical fiber (1), a humidity sensing layer (2), a second optical fiber (3), a first optical fiber coupler (4), a second optical fiber coupler (5), a third optical fiber coupler (6), a light source (7), a first optical power meter (8) and a second optical power meter (9);
One end of the first optical fiber (1) is coated with a humidity sensing layer (2) and is arranged in an environment space for temperature regulation; the other end of the first optical fiber (1) is in light guide connection with one end of the first optical fiber coupler (4); the other end of the first optical fiber coupler (4) is in light guide connection with one end of the third optical fiber coupler (6);
One end of the second optical fiber (3) is arranged in an environment space where the dew point of the air is not formed; the other end of the second optical fiber (3) is in light guide connection with one end of a second optical fiber coupler (5); the other end of the second optical fiber coupler (5) is in light guide connection with one end of the third optical fiber coupler (6);
The other end of the third optical fiber coupler (6) is in light guide connection with a light source (7); the first optical power meter (8) is in light guide connection with the first optical fiber coupler (4); the second optical power meter (9) is in light guide connection with the second optical fiber coupler (5);
The first optical fiber (1) is used for detecting the refractive index of an experimental area where the air forms a dew point;
the humidity sensing layer (2) is used for absorbing air moisture in the experimental area and changing the refractive index of the first optical fiber (1);
the second optical fiber (3) is used for detecting the refractive index of the environment where the dew point of the air is not formed;
The first optical fiber coupler (4) is used as an optical splitting connector of the first optical fiber (1) and the first optical power meter (8); the second optical fiber coupler (5) is used as an optical splitting connector of the second optical fiber (3) and the second optical power meter (9); the third optical fiber coupler (6) is used as a light splitting connector of the first optical fiber coupler (4), the second optical fiber coupler (5) and the light source (7);
The light source (7) is used for simultaneously providing the light rays with the same light measurement to the first optical fiber (1) and the second optical fiber (3);
the first optical power meter (8) is used for collecting real-time data of the reflected light intensity of the first optical fiber (1);
the second optical power meter (9) is used for collecting real-time data of the reflected light intensity of the second optical fiber (3);
the calculation controller (10) is respectively connected with the data acquisition device (11), the first optical power meter (8) and the second optical power meter (9); the actuator (14) is respectively and electrically connected with the data acquisition device (11) and the refrigerator (13); one end of the first optical fiber (1) is arranged in a refrigerating space formed by the refrigerator (13);
The computing controller (10) is used for reading, processing and analyzing the detection data and outputting corresponding control instructions;
the data acquisition device (11) is used for reading detection data of the temperature sensor (12) and controlling the executor (14) according to an instruction of the calculation controller (10);
the temperature sensor (12) is used for detecting the ambient temperature of a refrigerating space formed by the refrigerator (13) and transmitting detection data to the data collector (11);
The refrigerator (13) is used for refrigerating and cooling a refrigerating space provided with the first optical fiber (1);
The actuator (14) is used for controlling the start-stop and working power of the refrigerator (13);
the computing controller (10) is provided with a computing control module; the calculation control module comprises an optical power meter setting module (15), a handshake communication module (16), a temperature acquisition module (17), a dew point judging module (18), a refractive index calculating module (19), a data storage template (20) and a virtual display module (21);
The optical power meter setting module (15) is used for sending parameter setting commands and reading commands to the first optical power meter (8) and the second optical power meter (9) and reading response connection signals of the first optical power meter (8) and the second optical power meter (9);
the handshake communication module (16) is used for detecting the connection state of the first optical power meter (8) and the second optical power meter (9);
the temperature acquisition module (17) is used for acquiring real-time temperature data of the temperature sensor (12);
the dew point judging module (18) is used for calculating and judging the dew point forming time and the temperature value of the refrigerating space formed by the refrigerator (13) according to the real-time temperature data of the temperature collecting module (17);
The refractive index calculation module (19) is used for calculating the refractive index of the humidity sensing layer (2) according to the power value of the first optical power meter (8), the power value of the second optical power meter (9), the refractive index of air and the refractive index of the fiber core;
The data storage template (20) is used for storing data of the temperature acquisition module (17) and the refractive index calculation module (19);
the virtual display module (21) is used for virtually displaying a control process, a data change process and a parameter setting process of the computing controller (10);
the computing controller (10) controls the temperature of the refrigerator (13) and obtains a refractive index-time curve and a temperature-time curve of the humidity sensing layer through a LabVIEW software system installed in the computing controller (10);
The computing controller (10) judges a temperature value of condensation in the refrigerating space provided with the first optical fiber (1) by analyzing a curve inflection point of a refractive index-time curve of the humidity sensing layer and a temperature-time curve, wherein the highest point of the refractive index-time curve corresponds to the lowest point of the temperature-time curve;
The calculation controller (10) calculates the dew point temperature to obtain the corresponding relative humidity at the room temperature, and the calculation formula is as follows: where td is the dew point temperature and t is the temperature of the ambient space where the air does not form the dew point, i.e. the corresponding room temperature.
2. The optical fiber dew point based humidity detection system according to claim 1, wherein the humidity sensing layer (2) is a lithium chloride-polyvinyl alcohol humidity sensitive film.
3. The optical fiber dew point based humidity detection system according to claim 1, wherein the light source (7) is a laser semiconductor light source.
4. The system for detecting the humidity based on the optical fiber dew point according to claim 1, wherein the first optical power meter (8) and the second optical power meter (9) are provided with power digital display devices.
5. The system for detecting humidity based on optical fiber dew point determination according to claim 1, wherein the first optical power meter (8) and the second optical power meter (9) are provided with RS-232 interfaces.
6. The optical fiber dew point measurement based humidity detection system according to claim 1, wherein the calculation controller (10) is connected to the first optical power meter (8) and the second optical power meter (9) through RS-232 communication protocol, respectively.
7. A control method of a humidity detection system based on optical fiber dew point measurement, characterized in that the control method is applied to the humidity detection system based on optical fiber dew point measurement according to any one of claims 1 to 6, the control method comprising the steps of:
s1, a computing controller (10) cools a refrigerating space provided with a first optical fiber (1) by controlling a refrigerator (13);
s2, collecting real-time data of the reflected light intensity of the first optical fiber (1) by the first optical power meter (8); the second optical power meter (9) collects real-time data of the reflected light intensity of the second optical fiber (3); the temperature sensor (12) collects real-time data of temperature;
S3, transmitting acquired data to a calculation controller (10) by a first optical power meter (8), a second optical power meter (9) and a temperature sensor (12);
S4, the computing controller (10) controls the temperature of the refrigerator (13), and a refractive index-time curve and a temperature-time curve of the humidity sensing layer are obtained through processing of a LabVIEW software system installed in the computing controller (10);
S5, the computing controller (10) judges the temperature value of the condensation of the refrigerating space provided with the first optical fiber (1) through analyzing the curve inflection point of the refractive index-time curve of the humidity sensing layer and the temperature-time curve, namely the dew point temperature;
S6, the calculation controller (10) processes the data of the temperature acquisition module (17) and calculates the relative humidity at the corresponding room temperature.
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