CN113670466B - Temperature control method for alkali metal air chamber based on light absorption temperature measurement - Google Patents
Temperature control method for alkali metal air chamber based on light absorption temperature measurement Download PDFInfo
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C21/00—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00
- G01C21/10—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration
- G01C21/12—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning
- G01C21/16—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning by integrating acceleration or speed, i.e. inertial navigation
- G01C21/166—Mechanical, construction or arrangement details of inertial navigation systems
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
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- G05D23/19—Control of temperature characterised by the use of electric means
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Abstract
The invention discloses an alkali based on light absorption temperature measurementThe temperature control method of the metal air chamber comprises the following temperature control steps: firstly, will be charged with N 2 、 4 He and alkali metal atom R b The alkali metal gas chamber is heated to a certain temperature to be measured; measuring the linear absorption spectrum of rubidium atoms D1 in the heated alkali metal gas chamber; changing the heating temperature to obtain a plurality of groups of absorption curves and fitting to calculate a temperature value; and fitting a functional relation between the optical depth peak value and the temperature to realize the temperature sensitive temperature of the optical depth peak value, and realizing real-time temperature control based on the function relation, wherein in the optical depth acquisition process, a beam splitter prism with the beam splitting ratio of 50% is used for splitting incident light into two beams, one beam is incident into the air chamber and the other beam is used as reference light, and the emergent light intensity is divided by the reference light intensity to calculate the optical depth. The invention solves the problem that the traditional temperature control mode cannot control the temperature in the air chamber, avoids the influence of magnetic field interference on gyro signals caused by platinum resistor temperature measurement of the nuclear magnetic resonance inertial sensor, and has important significance for improving the index of the inertial sensor.
Description
Technical Field
The invention relates to a temperature control method for an alkali metal gas chamber based on light absorption temperature measurement, and belongs to the field of quantum sensing and precision instruments.
Background
The inertial sensor is a core device of an inertial navigation system, the nuclear magnetic resonance inertial sensor has a wide prospect as a new direction for the development of the inertial sensor, the alkali metal gas chamber is a sensitive core of the nuclear magnetic resonance inertial sensor, and the temperature in the gas chamber has direct influence on the polarizability of atoms and directly influences the output signal of the inertial sensor. Therefore, the precise temperature control inside the alkali metal gas chamber has important significance.
At present, the temperature control of an alkali metal gas chamber is based on platinum resistance to measure the single-point temperature of the outer wall of the gas chamber, the temperature control of the gas chamber is realized by adopting a platinum resistance four-wire system-based temperature measurement mode and a platinum resistance alternating current bridge temperature measurement mode respectively in the document [1] and the document [2], and the mk-level temperature control stability is realized by the platinum resistance temperature measurement-based temperature control mode, but the temperature measurement mode can only measure and control the single-point temperature of the outer wall of the alkali metal gas chamber, and cannot reflect the real temperature in the gas chamber. Document [3] discloses a method for measuring the temperature in an alkali metal air chamber based on a pressure broadening method, and the method is applied to the measurement of the temperature gradient in the alkali metal air chamber, and the method takes a long time and cannot realize the real-time control of the temperature based on the method. In addition, the conventional light absorption temperature measurement mode needs to scan the spectrum and then calculate the temperature, and the temperature cannot be controlled in real time.
[1] Hujepeng, Zhou bin of alkali metal air chamber non-magnetic electric heating technology research and system design [ J ] computer measurement and control, 2017,25(05):180-
[2] Wahlanhua-based experimental study on non-magnetic temperature measurement system based on alternating-current bridge temperature measurement [ D ]. Beijing, university of aerospace, 2020
[3] A method for accurately measuring atomic density based on mixed optical pumping [ P ]. Beijing: CN107167437B,2019-07-26.
Disclosure of Invention
The invention solves the problems that: the defects of the prior art are overcome, the temperature control method for the alkali metal gas chamber based on light absorption temperature measurement is provided, the problems that the temperature in the gas chamber cannot be measured by the traditional platinum resistor temperature measurement method and the temperature control cannot be realized by the conventional light absorption temperature measurement method are solved, and the real-time measurement and control of the temperature in the alkali metal gas chamber are realized.
The technical solution of the invention is as follows: a temperature control method of an alkali metal gas chamber based on light absorption temperature measurement is suitable for the alkali metal gas chamber of a nuclear magnetic resonance inertial sensor, and comprises the following steps:
firstly, measuring the temperature of the outer wall of a gas chamber based on a platinum resistance temperature sensor, and heating an alkali metal gas chamber of a nuclear magnetic resonance inertial sensor to a certain temperature point to be measured;
designing an optical path, selecting a DFB laser with a wavelength tuning range near a rubidium atom D1 line as a detection laser, and dividing incident light into two beams through a beam splitter prism with a splitting ratio of 50%, wherein one beam is light I 1 The light I is incident on the alkali metal gas chamber heated in the first step 2 Measuring transmitted light of different frequencies v as reference light
Light intensity and reference light I 2 The light intensity and the optical depth OD are calculated, resulting in an absorption curve with respect to the frequency v and the optical depth OD:
fitting an absorption curve about the optical depth OD and the incident light frequency v by using a Lorentz linear function, obtaining pressure broadening and calculating the atomic number density of the alkali metal through fitting, and then obtaining the temperature in the air chamber according to the relation between the atomic number density of the alkali metal and the temperature in the air chamber;
step four, changing the heating temperature, repeating the three steps to obtain not less than six absorption curves at different temperatures, calculating the temperature, and fitting the OD of the optical depth peak value max And temperature;
step five, optical depth peak value OD is used max The temperature is measured as a sensitive signal of the temperature in the gas chamber, and the temperature control of the alkali metal gas chamber based on light absorption temperature measurement is realized by combining PID control.
In the second step, the calculation formula of the optical depth OD is as follows:
where v is the frequency of the incident light,
to transmit light intensity, I 2 Is the reference light intensity.
In the third step, the lorentzian linear function can be expressed as:
where OD is the optical depth, v is the incident light frequency, v 0 Γ is the pressure broadening of the fitted curve, i.e. the full width at half maximum of the Lorentz curve, k, v, being the center frequency of the rubidium atom 0 And Γ are both parameters that need to be fitted.
In the third step, the formula for calculating the atomic number density of the alkali metal is as follows:
n is the atomic number density, OD of alkali metal at the temperature T in the air chamber max Is the peak of the optical depth of the absorption curve, c is the speed of light, r e Is the electron electromagnetic radius, f is the oscillator line strength, and the value is taken here
l is the optical path, Γ is the pressure spread resulting from the fitting, c, r e F, l are all constants;
the relationship between the number density of the alkali metal atoms (rubidium) and the temperature in the air chamber conforms to a saturated vapor pressure formula:
in step 2, the designed optical path is shown in fig. 2, and includes: DFB laser, beam splitter Prism (PBS), fiber coupler, wavelength meter, collimating lens, half-wave plate (HWP), alkali metal gas chamber, photodetector; laser emitted by the DFB laser is firstly split by a half-wave plate and a beam splitter prism, one part of the light beam enters a wavelength meter to detect wavelength through an optical fiber coupler, the other part of the light beam enters a main light path and enters an alkali metal air chamber through the half-wave plate and collimation, the splitting ratio can be adjusted by adjusting the half-wave plate, and light intensity is collected by a photoelectric detector.
The principle of the invention is as follows: the air chamber temperature is calculated according to a fitting absorption curve and a saturated vapor pressure formula, and the fitting function adopts a Lorentz line type because the pressure broadening of the general gas filled in the alkali metal air chamber is far larger than the natural broadening and the Doppler broadening. The alkali metal atomic number density and the temperature are obtained through fitting calculation, the temperature measuring process takes long time, so that the functional relation between the optical depth peak value and the temperature in the absorption curve is directly established by scanning the absorption curves with different temperatures, the temperature is sensitive by the optical depth peak value signal, the real-time measurement of the temperature can be realized, and the real-time control of the temperature can be realized on the basis of the real-time measurement.
Compared with the common temperature control method for the alkali metal air chamber, the invention has the advantages that: compared with the common platinum resistance measurement and control, the method has the advantages that the temperature inside the gas chamber is measured and controlled, the atom number density of the alkali metal in the gas chamber can be accurately reflected, and the high density and density stability of the alkali metal atoms are ensured.
Drawings
FIG. 1 is a flow chart of a temperature control method according to the present invention;
FIG. 2 is a block diagram of the temperature control system of the alkali metal gas chamber based on light absorption temperature measurement.
Detailed Description
The present invention will be described in detail below with reference to the drawings and examples.
As shown in fig. 1, the specific implementation steps of the present invention are as follows:
(1) firstly, the furnace is filled with N2, 4 He、 129 The alkali metal gas chamber of Xe and alkali metal atoms is heated to a certain temperature to be measured (N charged) 2 、 4 He is on the order of hundreds torr), the heating temperature is stabilized for at least 30 minutes.
(2) And a DFB laser with the wavelength tunable range near the rubidium atom D1 line is used for generating scanning laser with stable light intensity and wavelength, wherein the laser power is stabilized at +/-0.005 mw. The incident light is divided into two beams and one beam I by the half-wave plate HWP and the polarization beam splitter PBS1 0 The light enters an optical fiber coupler to be connected with a wavemeter to record wavelength information, the other path I is used as a main light path, is collimated and shaped and then enters a light splitting prism with the light splitting ratio of 1:1 to be split into two beams, wherein the light intensity of one beam entering an alkali metal gas chamber is marked as I 1 The intensity of light after passing through the air chamber is recorded as
Collected by a photodetector PD 1. The other beam is collected by PD2 after passing through the reference gas chamber and is marked as I 2 . No alkali metal atom exists in the reference gas chamber, and the incident light is not absorbed; signals collected by the photoelectric detector enter the DAQ data acquisition board card through the preamplifier and are processed by the upper computer. Heating circuit partial miningThe high-frequency electric heating mode is used, namely, the high-frequency current is used for exciting the heating wire of the heating film after power amplification. The alkali metal air chamber and the oven are arranged in a magnetic shielding barrel of the inertial sensor.
(3) Sweeping frequency near a rubidium atom D1 line, setting a step pitch of 0.002nm near a rubidium atom D1 line central frequency (794.98nm) and setting a step pitch of 0.005nm at other positions in order to ensure measurement accuracy; the wavelength is controlled by adjusting the current controller of the laser. Output signal of the photodetector
And I 2 And respectively entering an upper computer through a preamplification board card and a data acquisition board card to calculate the optical depth. The light depth calculation formula is as follows:
and fitting an absorption curve according to a Lorentz function, namely fitting the abscissa of a coordinate axis as laser frequency and the ordinate as optical depth, calculating the atomic number density of the alkali metal according to the pressure broadening obtained by fitting, and obtaining the temperature according to a relational formula of the atomic number density and the temperature. Wherein the Lorentzian fitting function may be expressed as:
the alkali metal atomic number density is calculated using the formula:
n is the density of alkali metal atoms at temperature T in the gas chamber, OD max Fitting the optical depth of the absorption peak in the third step, c is the speed of light, r e Is the electromagnetic radius of the electron, f is the oscillator line strength, and the value here is
l is the optical path.
The relationship between the number density of alkali metal atoms (rubidium) and the temperature in the air chamber conforms to the saturated vapor pressure formula:
n is the number density of alkali metal atoms (rubidium) at the temperature T in the gas chamber.
(4) Changing the heating temperature, repeating the three steps to obtain not less than six absorption curves at different temperatures, and calculating the temperature; fitting with respect to optical depth peak OD max And a function curve of the temperature, fitting the curve function as an exponential function;
(5) at the optical depth peak OD max The temperature is measured as a sensitive signal of the temperature in the gas chamber, and the temperature control of the alkali metal gas chamber based on light absorption temperature measurement is realized by combining PID control.
As shown in fig. 2, the temperature control system for the alkali metal gas chamber based on light absorption temperature measurement is composed of a DFB laser, a half-wave plate HWP, a polarization splitting prism PBS, an optical fiber coupler, a wavemeter, a collimating and shaping lens, a reflector, an alkali metal gas chamber and heating oven, a reference gas chamber, a magnetic shielding cylinder, a photodetector PD, a pre-amplification circuit, a DAQ acquisition board card, an upper computer, a heating circuit and the like. The DFB laser generates an incident light source signal with a center wavelength of 794.98nm, which can be adjusted by adjusting the laser drive current. The wavelength meter is used for monitoring the scanning wavelength of the light source, and the beam splitting ratio of the PBS can be changed by adjusting the half-wave plate HWP, so that the intensity of the incident light is adjusted. The alkali metal gas chamber is arranged in the heating oven, and a magnetic shielding barrel of the nuclear magnetic resonance inertial sensor is arranged outside the oven. The purpose of the reference gas cell is to suppress measurement inaccuracies due to light intensity fluctuations. The light intensity current signal is converted into a voltage signal through a preamplifier, the signals of PD1 and PD2 are collected by a data acquisition board card after passing through the preamplifier, temperature information is obtained through calculation after the calculation processing of an upper computer, PID control is realized by the upper computer, an alkali metal air chamber is heated through a heating circuit, and the heating circuit and a heating film adopt the existing high-frequency electric heating mode.
Details of the present invention not described in detail are well within the skill of those in the art.
The above examples are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the invention is defined by the appended claims. Various equivalent substitutions and modifications can be made without departing from the spirit and principles of the invention, and are intended to be within the scope of the invention.
Claims (5)
1. A temperature control method of an alkali metal air chamber based on light absorption temperature measurement is suitable for the alkali metal air chamber of a nuclear magnetic resonance inertial sensor, and is characterized in that: the method comprises the following steps:
firstly, measuring the temperature of the outer wall of an air chamber based on a platinum resistor temperature sensor, and heating an alkali metal air chamber of a nuclear magnetic resonance inertial sensor to a certain temperature point to be measured;
designing a light path, selecting a DFB laser with a wavelength tuning range near a rubidium atom D1 line as a detection laser, and dividing incident light into two beams through a beam splitter prism with a splitting ratio of 50%, wherein one beam of light I 1 The light I is incident to the alkali metal gas chamber heated in the first step and the other beam 2 Measuring transmitted light of different frequencies v as reference light
Light intensity and reference light I 2 The light intensity and the optical depth OD are calculated, resulting in an absorption curve with respect to the frequency v and the optical depth OD:
fitting an absorption curve about the optical depth OD and the incident light frequency v by using a Lorentz linear function, obtaining pressure broadening and calculating the atomic number density of the alkali metal through fitting, and then obtaining the temperature in the air chamber according to the relation between the atomic number density of the alkali metal and the temperature;
step four, changing the heating temperature, repeating the three steps, obtaining not less than six absorption curves at different temperatures, calculating the temperature, and fitting the OD of the optical depth peak max And temperature;
step five, using the optical depth peak value OD max As a sensitive signal of the temperature in the air chamber, the temperature is measuredAnd measuring, and combining PID control to realize temperature control of the alkali metal gas chamber based on light absorption temperature measurement.
2. The method for controlling the temperature of the alkali metal gas chamber based on the light absorption temperature measurement as claimed in claim 1, wherein: in the second step, the calculation formula of the optical depth OD is as follows:
wherein
To transmit the light intensity, I 2 Is the reference light intensity.
3. The method for controlling the temperature of the alkali metal gas chamber based on the light absorption temperature measurement as claimed in claim 1, wherein: in the third step, the lorentz linear function is expressed as:
where OD is the optical depth, v is the incident light frequency, v is 0 Γ is the pressure broadening of the fitted curve, i.e. the full width at half maximum of the Lorentz curve, k, v, being the center frequency of the rubidium atom 0 And Γ are both parameters that need to be fitted.
4. The method for controlling the temperature of the alkali metal gas chamber based on the light absorption temperature measurement as claimed in claim 1, wherein: in the third step, the formula for calculating the atomic number density of the alkali metal is as follows:
n is the atomic number density, OD of alkali metal at the temperature T in the air chamber max Is absorption curve opticsDepth peak, c is the speed of light, r e Is the electron electromagnetic radius, f is the oscillator line strength, and the value is taken here
l is the optical path, Γ is the pressure spread obtained by fitting, c, r e F, l are all constants;
the relationship between the atomic number density n of the alkali metal and the temperature T in the air chamber conforms to the saturated vapor pressure formula:
5. the method for controlling the temperature of the alkali metal gas chamber based on the light absorption temperature measurement as claimed in claim 1, wherein: in the second step, the designed optical path includes: the device comprises a DFB laser, a beam splitter prism, an optical fiber coupler, a wavemeter, a collimating lens, a half-wave plate, an alkali metal gas chamber and a photoelectric detector; laser emitted by the DFB laser is firstly split by a half-wave plate and a beam splitter prism, one part of the light beam enters a wavelength meter to detect wavelength through an optical fiber coupler, the other part of the light beam enters a main light path and enters an alkali metal air chamber through the half-wave plate and collimation, the splitting ratio can be adjusted by adjusting the half-wave plate, and light intensity is collected by a photoelectric detector.
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| CN103439218B (en) * | 2013-09-02 | 2015-06-17 | 北京航空航天大学 | Pressure-broadening-based alkali metal stream atomic density measuring method |
| CN105403322B (en) * | 2015-12-11 | 2018-02-02 | 东南大学 | The measurement apparatus and method of atom magnetometer alkali metal gas indoor temperature distribution |
| CN106248121B (en) * | 2016-08-11 | 2018-03-06 | 天津大学 | The fiber grating sensing demodulation device and demodulation method of suppression are fluctuated under environment alternating temperature |
| CN106768471A (en) * | 2016-12-05 | 2017-05-31 | 北京航空航天大学 | A kind of non-contact type temperature measurement method based on pressure broadening |
| CN106949985B (en) * | 2017-05-15 | 2019-04-30 | 北京航空航天大学 | A kind of precision measurement method of the alkali metal plenum interior temperature based on mixing optical pumping |
| CN107167437B (en) * | 2017-05-15 | 2019-07-26 | 北京航空航天大学 | A kind of atomic density accurate measurement method based on mixing optical pumping |
| CN109186578B (en) * | 2018-09-04 | 2021-11-05 | 北京航空航天大学 | Three-axis integrated SERF (spin exchange fiber) atomic spin gyroscope |
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