CN103940844B - The method that linear frequency modulation multi-beam laser heterodyne measures expansion coefficients of metal wire - Google Patents
The method that linear frequency modulation multi-beam laser heterodyne measures expansion coefficients of metal wire Download PDFInfo
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Abstract
The method that linear frequency modulation multi-beam laser heterodyne measures expansion coefficients of metal wire, belongs to the linear expansion coefficient fields of measurement of material.The present invention is that parameter measured directly is more, complex operation in order to solve to need in existing linear expansion coefficient measuring method, so that the problem of measurement error is bigger than normal.Linear frequency modulation multi-beam laser heterodyne of the present invention measures the device and method of expansion coefficients of metal wire, based on linear frequency modulation technology and laser heterodyne technique, parameter information to be measured is modulated in heterodyne signal difference on the frequency using linear frequency modulation technology, by the way that multiple parameters to be measured can be obtained simultaneously to the demodulation of heterodyne signal, weight averaged processing, and then obtain accurate parameter information to be measured.The present invention is applied to ultra precise measurement, detection, process equipment, laser radar system etc., and substantially, experimental data is reliable, especially suitable in the engineering design fields such as coherent laser windfinding radar for experimental phenomena of the present invention.
Description
Technical field
The invention belongs to the linear expansion coefficient fields of measurement of material.
Background technology
The hot expansion property of object reflects the attribute of material in itself, generally by solid it is heated after in one-dimensional square length
Change be referred to as line expansion.The linear expansion coefficient of material is measured, not only the development to new material is significant, and is also
One of important indicator of the selection of material.All must during manufacture, processing of material of Structural Design, machinery and instrument etc.
The thermal expansion character of material must be considered.Otherwise, by the stability and the precision of instrument that influence structure.It is improper to consider, or even can make
Into the damage of engineering, the failure of instrument, and the defect processed in welding and failure etc..At present, to expansion coefficients of metal wire
Measure have the measuring methods such as optical lever method, reading microscope method, electrothermal way and laser interferance method.
During being measured with these methods, due to needing parameter measured directly excessive, operation is more complicated, so that
The systematic error of experiment and accidental error are bigger than normal, for example, when surveying expansion coefficients of metal wire with optical lever method, due to approximate formula
Make its systematic error bigger than normal using with complicated operation, simultaneously as reading plotter is equipped with the accidental error of unreasonable introducing
It is larger, so that its relative error is up to 4.4%；Reading microscope method is due to accidental error caused by vision and the actual temperature of electrothermal way
Systematic error etc. all significantly limit its measurement accuracy caused by the delay of degree and sensor；Laser interferance method is due to the device
The sharp thin, high resolution of interference fringe, while experimental implementation is simple, so as to substantially reduce experimental error, realize metal wire
The accurate measurement of the coefficient of expansion, the relative error of measurement can be 2%, but this method exists when reading number of interference fringes and regarded
Accidental error caused by feeling, causes precision not improve again, can not meet the requirement of current superhigh precision measurement.
The content of the invention
The present invention is that parameter measured directly is more, it is multiple to operate in order to solve to need in existing linear expansion coefficient measuring method
It is miscellaneous, so that the problem of measurement error is bigger than normal, now provides linear frequency modulation multi-beam laser heterodyne measurement expansion coefficients of metal wire
Method.
Linear frequency modulation multi-beam laser heterodyne measures the device of expansion coefficients of metal wire, and it includes：Chirped laser device,
Thin glass plate, plane mirror, electrothermal furnace, temperature controller, convergent lens and photodetector；
The chirped laser of chirped laser device output incides the preceding surface of thin glass plate, and incidence angle θ0To be sharp
Angle, the laser beam splitter is reflected light and refraction light by thin glass plate, and thin glass plate is by a reflected light back to meeting
On poly- lens, thin glass plate is by the refraction anaclasis a to plane mirror, a plane mirror and thin glass plate
Rear surface No. two reflected lights of multi beam will be obtained after the refraction light multiple reflections, No. two reflected lights of the multi beam reflect through thin glass plate
To convergent lens, on the photosurface of the light collection that convergent lens is received to photodetector；
Electrothermal furnace is used to uniformly heat for metallic rod to be measured, and temperature controller is used for the temperature for controlling and detecting electrothermal furnace；
A number plane mirror is fixed on one end of metallic rod to be measured, and vertical with the axis of metallic rod to be measured, thin glass
Plate be arranged in parallel with a plane mirror, and the distance between thin glass plate and plane mirror 20mm to 30mm it
Between.
Linear frequency modulation multi-beam laser heterodyne based on said apparatus measures the method for expansion coefficients of metal wire, this method bag
Include following steps：
Step one：The chirped laser that opening chirped laser device sends chirped laser device incides thin glass
In glass plate, and ensure incidence angle θ0For acute angle；Electrothermal furnace and temperature controller are opened simultaneously, and the temperature of temperature controller control electrothermal furnace is simultaneously adopted
Collect the temperature of metallic rod to be measured；
Step 2：The photoelectric current I of photodetector output signal is gathered, and photoelectric current I DC terms are filtered
Except so as to obtain electric current of intermediate frequency IIF；
Step 3：The electric current of intermediate frequency I obtained to step 2IFAnalyzed, obtain the frequency f of interference signalp：
Wherein, p is nonnegative integer,For the rate of change of the modulating bandwidth of chirped laser device, T is frequency modulation week
Phase, △ F are modulating bandwidth, and n is the refractive index of medium between thin glass plate and a plane mirror, and d is thin glass plate and one
The distance between number plane mirror, θ is the refraction angle that incident light transmits thin glass plate, and c is the light velocity of incident light, KpRepresent
Proportionality coefficient between the frequency and refraction angle θ cosine of intermediate frequency heterodyne signal；
Step 4：Utilize the frequency f of interference signalpThe distance between thin glass plate and plane mirror d is obtained, is obtained
The distance between thin glass plate and plane mirror variable quantity △ d,
△ d=d0- d,
Wherein, d0Represent the initial distance between thin glass plate and a plane mirror；
Step 5：The linear expansion coefficient α of metallic rod to be measured is obtained using following formula,
Wherein, l0Represent the initial length of metallic rod to be measured, △ T=T1-T2The temperature variation of metallic rod to be measured is represented,
T1Represent the temperature of metallic rod to be measured at room temperature, T2It is to be measured when representing the distance between thin glass plate and a plane mirror for d
The temperature of metallic rod.
Linear frequency modulation multi-beam laser heterodyne of the present invention measures the device and method of expansion coefficients of metal wire, is based on
Parameter information to be measured, is modulated in heterodyne signal by linear frequency modulation technology and laser heterodyne technique using linear frequency modulation technology, is led to
Parameter information to be measured can accurately be obtained by crossing the demodulation to heterodyne, in the parameter information measurement process, and measuring speed is fast, line
Property degree is good, strong antijamming capability, dynamic response is fast, reproducible and measurement range is big；Apparatus structure of the present invention is simple,
It is small power consumption, easy to operate；The method of the invention experimental result error is small, precision is high；Tested by taking brass as an example, line expansion
The relative error of coefficient measurement is only 0.1%.The present invention is applied to ultra precise measurement, detection, process equipment, laser radar system
Deng, experimental phenomena of the present invention substantially, experimental data is reliable, especially suitable in engineering design fields such as coherent laser windfinding radars
In.
Brief description of the drawings
Fig. 1 is the dress of the linear frequency modulation multi-beam laser heterodyne measurement expansion coefficients of metal wire described in embodiment one
The structural representation put.
Fig. 2 is principle of interference signal of the linear frequency modulation multi-beam laser between thin glass plate and a plane mirror
Figure；Wherein E represents to incide the laser on thin glass plate, E1For the laser of thin glass plate front surface reflection, E2To EmRepresent thin glass
The laser of surface refraction after glass plate, d represents the distance between thin glass plate and plane mirror.
Fig. 3 is the dress of the linear frequency modulation multi-beam laser heterodyne measurement expansion coefficients of metal wire described in embodiment two
The structural representation put.
Fig. 4 is the dress of the linear frequency modulation multi-beam laser heterodyne measurement expansion coefficients of metal wire described in embodiment three
The structural representation put.
Fig. 5 is the dress of the linear frequency modulation multi-beam laser heterodyne measurement expansion coefficients of metal wire described in embodiment four
The structural representation put.
Fig. 6 be room temperature at 15 DEG C, the Fourier transformation spectrogram of linear frequency modulation multi-beam laser heterodyne signal.
Embodiment
Embodiment one：Present embodiment, the linear tune described in present embodiment are illustrated referring to Figures 1 and 2
Frequency multi-beam laser heterodyne measures the device of expansion coefficients of metal wire, and it includes：Chirped laser device 1, thin glass plate 2, one
Number plane mirror 3, electrothermal furnace 4, temperature controller 6, convergent lens 7 and photodetector 8；
The chirped laser that chirped laser device 1 is exported incides the preceding surface of thin glass plate 2, and incidence angle θ0For
Acute angle, the laser beam splitter is reflected light and refraction light by thin glass plate 2, and thin glass plate 2 is by a reflected light back
To convergent lens 7, thin glass plate 2 by the refraction anaclasis a to plane mirror 3, a plane mirror 3 with
The rear surface of thin glass plate 2 will obtain No. two reflected lights of multi beam after the refraction light multiple reflections, No. two reflected lights of the multi beam are through thin
Glass plate 2 is refracted on convergent lens 7, the photosurface of the light collection that convergent lens 7 is received to photodetector 8
On；
Electrothermal furnace 4 is used to uniformly heat for metallic rod 5 to be measured, and temperature controller 6 is used for the temperature for controlling and detecting electrothermal furnace 4；
A number plane mirror 3 is fixed on one end of metallic rod 5 to be measured, and vertical with the axis of metallic rod 5 to be measured, thin glass
Glass plate 2 be arranged in parallel with a plane mirror 3, and the distance between thin glass plate 2 and plane mirror 3 in 20mm extremely
Between 30mm.
Temperature controller 6 described in present embodiment is digital readout temperature controller, and the digital readout temperature controller is easy to reading, easy to operate, energy
Enough make measurement process easy.
Embodiment two：Reference picture 3 illustrates present embodiment, and present embodiment is to embodiment one
The device of described linear frequency modulation multi-beam laser heterodyne measurement expansion coefficients of metal wire is described further, present embodiment
In, it also includes：Data handling system 9；
The electrical signal of photodetector 8 connects the electric signal input end of data handling system 9；The data processing
The module of software realization is embedded with system 9, the module is included with lower unit：
Gather the signal gathering unit for the photoelectric current I that photodetector 8 is exported；
Photoelectric current I is filtered, so as to obtain electric current of intermediate frequency IIFFilter unit；
Utilize electric current of intermediate frequency IIFObtain the frequency f of interference signalpUnit；
Utilize the frequency f of interference signalpObtain the distance between thin glass plate 2 and plane mirror 3 d unit；
Thin glass plate 2 and a plane reflection are obtained according to the distance between thin glass plate 2 and plane mirror 3 d
The distance between mirror 3 variable quantity △ d unit；
The line for obtaining metallic rod 5 to be measured using distance change amount △ d between thin glass plate 2 and a plane mirror 3 is swollen
The unit of swollen factor alpha.
Embodiment three：Reference picture 4 illustrates present embodiment, and present embodiment is to embodiment one
The device of described linear frequency modulation multi-beam laser heterodyne measurement expansion coefficients of metal wire is described further, present embodiment
In, it also includes：Wave filter 9-1, amplifier 9-2, A/D converter 9-3 and DSP9-4；
The electrical signal connection wave filter 9-1 of photodetector 8 electric signal input end, wave filter 9-1 telecommunications
Number output end connection amplifier 9-2 electric signal input end, amplifier 9-2 electrical signal connection A/D converter 9-3's
Input end of analog signal, A/D converter 9-3 digital signal output end connects DSP9-4 digital signal input end；
The module of software realization is embedded with the DSP9-4, the module is included with lower unit：
Gather the electric current of intermediate frequency I of A/D converter 9-3 outputsIFSignal gathering unit；
Utilize electric current of intermediate frequency IIFObtain the frequency f of interference signalpUnit；
Utilize the frequency f of interference signalpObtain the distance between thin glass plate 2 and plane mirror 3 d unit；
Thin glass plate 2 and a plane reflection are obtained according to the distance between thin glass plate 2 and plane mirror 3 d
The distance between mirror 3 variable quantity △ d unit；
The line for obtaining metallic rod 5 to be measured using distance change amount △ d between thin glass plate 2 and a plane mirror 3 is swollen
The unit of swollen factor alpha.
The temperature probe of digital readout temperature controller obtains the signal for representing temperature by platinum resistance thermometer sensor,；And desired temperature is used
" setting knob " is adjusted, two chosen switches of signal and A/D converter, can be shown measurement temperature respectively on charactron and be set
Constant temperature degree.Electrothermal furnace heating uniform to testing sample disconnects heater circuit automatically close to design temperature by relay；In measurement
State, shows the temperature being currently detected.
Embodiment four：Reference picture 5 illustrates present embodiment, and present embodiment is to embodiment one
The device of described linear frequency modulation multi-beam laser heterodyne measurement expansion coefficients of metal wire is described further, present embodiment
In, it also includes：No. two plane mirrors 10；
The laser light incident that chirped laser device 1 is exported is on No. two plane mirrors 10, and No. two plane mirrors 10 will
The laser reflection is to the preceding surface of thin glass plate 2, and incidence angle θ0For acute angle.
Embodiment five：Present embodiment be to the linear frequency modulation multi-beam laser described in embodiment one outside
The device of difference measurements expansion coefficients of metal wire is described further, in present embodiment, the frequency modulation of the chirped laser device 1
Cycle is 1ms, and modulating bandwidth is 5GHz, and the wavelength of output laser is 1.55 μm.
Embodiment six：Present embodiment be to the linear frequency modulation multi-beam laser described in embodiment one outside
The device of difference measurements expansion coefficients of metal wire is described further, in present embodiment, incidence angle θ0For 15.26 °.
Embodiment seven：Present embodiment be to the linear frequency modulation multi-beam laser described in embodiment one outside
The device of difference measurements expansion coefficients of metal wire is described further, in present embodiment, and the thickness of the thin glass plate 2 is more than
0mm and less than 1mm.
Embodiment eight：Present embodiment be to the linear frequency modulation multi-beam laser described in embodiment one outside
The device of difference measurements expansion coefficients of metal wire is described further, in present embodiment, the frequency f of interference signalpFor：
Wherein, p is nonnegative integer,For the rate of change of the modulating bandwidth of chirped laser device 1, T is frequency modulation week
Phase, △ F be modulating bandwidth, n between thin glass plate 2 and a plane mirror 3 medium refractive index, d be thin glass plate 2 with
The distance between number plane mirror 3, θ is the refraction angle that incident light transmits thin glass plate 2, and c is the light velocity of incident light, Kp
Represent the proportionality coefficient between the frequency and refraction angle θ cosine of intermediate frequency heterodyne signal.
Embodiment nine：Present embodiment be to the linear frequency modulation multi-beam laser described in embodiment one outside
The device of difference measurements expansion coefficients of metal wire is described further, in present embodiment, and metallic rod 5 to be measured is obtained using following formula
Linear expansion coefficient α,
Wherein, l0Represent the initial length of metallic rod 5 to be measured, △ T=T1-T2Represent the temperature change of metallic rod 5 to be measured
Amount, T1Represent the temperature of metallic rod 5 to be measured at room temperature, T2Represent the distance between thin glass plate 2 and plane mirror 3 for d
When metallic rod 5 to be measured temperature.
Embodiment ten：Linear frequency modulation multi-beam laser heterodyne measurement metal wire based on embodiment one is swollen
In the method for swollen coefficient, present embodiment, this method comprises the following steps：
Step one：The chirped laser that opening chirped laser device 1 sends chirped laser device 1 incides thin
On glass plate 2, and ensure incidence angle θ0For acute angle；Electrothermal furnace 4 and temperature controller 6 are opened simultaneously, and temperature controller 6 gathers metallic rod to be measured
5 temperature；
Step 2：The signal for the photoelectric current I that photodetector 8 is exported is gathered, and photoelectric current I DC terms are filtered
Except so as to obtain electric current of intermediate frequency IIF；
Step 3：The electric current of intermediate frequency I obtained to step 2IFAnalyzed, obtain the frequency f of interference signalp：
Wherein, p is nonnegative integer,For the rate of change of the modulating bandwidth of chirped laser device 1, T is frequency modulation week
Phase, △ F be modulating bandwidth, n between thin glass plate 2 and a plane mirror 3 medium refractive index, d be thin glass plate 2 with
The distance between number plane mirror 3, θ is the refraction angle that incident light transmits thin glass plate 2, and c is the light velocity of incident light, Kp
Represent the proportionality coefficient between the frequency and refraction angle θ cosine of intermediate frequency heterodyne signal；
Step 4：Utilize the frequency f of interference signalpThe distance between thin glass plate 2 and plane mirror 3 d is obtained,
The distance between thin glass plate 2 and plane mirror 3 variable quantity △ d are obtained,
△ d=d0- d,
Wherein, d0Represent the initial distance between thin glass plate 2 and a plane mirror 3；
Step 5：The linear expansion coefficient α of metallic rod 5 to be measured is obtained using following formula,
Wherein, l0Represent the initial length of metallic rod 5 to be measured, △ T=T1-T2Represent the temperature change of metallic rod 5 to be measured
Amount, T1Represent the temperature of metallic rod 5 to be measured at room temperature, T2Represent the distance between thin glass plate 2 and plane mirror 3 for d
When metallic rod 5 to be measured temperature.
As shown in Fig. 2 because light beam constantly can reflect and reflect between thin glass plate and a plane mirror, and
This reflection and refraction are all contributed for the interference of reflected light and transmitted light at infinity or on lens focal plane, so
When interference is discussed, it is necessary to consider multiple reflections and refraction effect, i.e., it should discuss that multi-beam laser is interfered.
In the case where not considering thin glass plate its thickness, the laser after linear frequency modulation is with incidence angle θ0Oblique incidence
When, the mathematic(al) representation of incident field is：
E (t)=E0exp{i(ω0t+kt2)} (1)
Wherein,For the rate of change of the modulating bandwidth of chirped laser device, T is the frequency modulation cycle, and △ F are frequency modulation band
It is wide；E0For incident field amplitude, t is time, ω0For light field angular frequency.If the light path for reaching the preceding surface of thin glass plate is L,The reflection light field that moment reaches thin glass plate preceding surface is：
Wherein, α1=r, r are the reflectivity of thin glass plate.
And the light transmitted through thin glass plate by plane mirror multiple reflections and is not transmiting thin glass plate in the same time, its
The light field expression formula of transmitted light can be written respectively as following form：
Wherein, α2=β2R ' ..., αm=β2r′m-1rm-2, β is the transmissivity of thin glass plate, and r ' is the reflection of plane mirror
Rate, d is the distance between thin glass plate and plane mirror, and θ is that incident light transmits the refraction angle after thin glass plate, and n is thin
The refractive index of medium between glass plate and plane mirror, the value of subscript m is 2,3,4 ....Due to have ignored thin glass plate
Thickness, therefore do not consider the influence on surface after thin glass plate.
So, total light field that detector is received can be expressed as：
E ' (t)=E1(t)+E2(t)+…+Em(t)+… (4)
Then the photoelectric current of detector output can be expressed as：
Wherein, e is electron charge, and Z is the intrinsic impedance of detector surface medium, and η is quantum efficiency, and h is that Planck is normal
Number, ν is laser frequency, No. * expression complex conjugate.
Because heterodyne signal DC terms can be filtered out after low pass filter, therefore, exchange item is only considered here, this friendship
It is commonly referred to as electric current of intermediate frequency to flow item, and the electric current of intermediate frequency that arrangement can obtain chirped laser heterodyne signal is：
(2) formula and (3) formula are substituted into (6) formula, final result is：
Wherein, p and j are nonnegative integer.
It can see by (7) formula, an intermediate frequency that linear frequency modulation multiple beam heterodyne measurement method is obtained difference on the frequency and phase
There is the information apart from d between thin glass plate and plane mirror in difference.Analyzed mainly for difference on the frequency in intermediate frequency, because
To be easily achieved frequency measurement using Fourier transformation.Now, can be outside linear frequency modulation multi-beam laser according to (7) formula
The frequency of difference signal is designated as：
It should be noted that the photoelectric current expression formula that can be seen that detector output by (7) formula is fourier transformed it
Afterwards it can be seen that linear frequency modulation multi-beam laser heterodyne signal frequency crest, is believed by measuring multi-beam laser heterodyne on frequency spectrum
Number frequency, it is possible to the distance between thin glass plate and plane mirror d are measured, when d changes, it is possible to surveyed according to (8) formula
Go out correspondence d variable quantity △ d, it is known that △ d can just be calculated according to (9) formula and be obtained testing sample linear expansion coefficient.
Based on the measurement scheme of linear frequency modulation multi-beam laser heterodyne shown in Fig. 2, long 150mm, a diameter of Φ 18mm are measured
Brass wire bar material linear expansion coefficient, and verify the feasibility of multi-beam laser heterodyne measuring method.Configured in measurement
Temperature control instrument be XMT type digital displaying temperature adjusting apparatus；Chirped laser device wavelength is 1.55 μm, frequency modulation cycle T
=1ms, modulating bandwidth △ F=5GHz.
According to the emulation of (7) formula it can be seen that, when metal bar is in 15 DEG C of room temperature, the linear frequency modulation obtained through signal transacting
The Fourier transformation frequency spectrum of multi-beam laser heterodyne signal is as shown in fig. 6, wherein solid line is 15 DEG C of room temperature and laser oblique incidence feelings
Under condition, the Fourier transformation frequency spectrum of correspondence linear frequency modulation multi-beam laser heterodyne signal during measurement metal bar length change amount △ l；
In the case of dotted line is 15 DEG C of room temperature and laser normal incidence, correspondence linear frequency modulation multiple beam during measurement metal bar length change amount △ l
The Fourier transformation frequency spectrum of heterodyne signal.
It will be seen from figure 6 that the theoretical curve in the case of normal incidence is given in experiment, it is therefore an objective to：Linearly adjusting
In frequency multi-beam laser heterodyne signal spectrum figure, linear frequency modulation multi-beam laser heterodyne signal frequency during oblique incidence can be obtained simultaneously
The numerical value of the centre frequency of theoretical curve when the centre frequency and normal incidence of first main peak of spectrum, in this way it is easy to obtain two
The ratio of individual centre frequency：
ζ=cos θ (10)
In theoretical derivation, the thickness that have ignored thin glass plate does not consider the reflected light on surface after device to linear tune
The influence of frequency multi-beam laser heterodyne signal, but the thickness of actually thin glass plate is present generally less than 1mm, to overcome this
Influence is planted, the linear frequency modulation multiple beam heterodyne signal that the reflected light that can be seen that surface after thin glass plate according to (10) formula is produced
Frequency distribution near the zero-frequency of frequency spectrum, the dry of low frequency heterodyne signal can just be filtered out by experiment light path adding wave filter
Disturb.Using above-mentioned linear frequency modulation multi-beam laser heterodyne mensuration, continuously eight groups of data of measurement, have obtained laser light incident angle θ0=
At 15.26 °, the measurement result of metal bar length change amount to be measured in the case of different temperatures, as shown in table 1.
In the case of the different temperatures T of table 1, the measurement result of metal bar length change amount
It should be noted that：In table 1 15 DEG C be laboratory temperature.Meanwhile, the simulation experiment result in table 1 can be led
Go out each data of correlation：
(1) temperature T standard uncertainties σc(△T)
Duplicate measurementsThen, type A standard uncertaintyThe limit error Δ that temperature controller is introduced1=0.002 DEG C
Then, type B standard uncertaintyThen σc(△ T)=(0.0002+0.0012)1/2=0.001 DEG C.
(2) length l0Standard uncertainty σc(l0)
Use slide measure duplicate measurementsThen, type A standard uncertainty：
The limit error Δ that slide measure is introduced2=0.02mm then, type B standard uncertaintyThen σc(l0)=(0.0092+0.0122)1/2=0.015mm.
Using the experimental data of table 1, the average measurement value of the linear expansion coefficient of metal bar is
The standard uncertainty of linear expansion coefficient is
The measurement result of linear expansion coefficient can be expressed as：
And the theoretical value 2.06 × 10 of the linear expansion coefficient of metal bar-5/ DEG C, it so can be obtained by the phase of measurement result
It is to error：
By data processing as can be seen that measuring metal wire expansion with linear frequency modulation multi-beam laser heterodyne method measurement apparatus
The relative measurement error of coefficient is only 0.1%, compared with traditional measuring method, and the result measured by this method has more preferable
Precision.Meanwhile, analyze data can also be seen that in the case where sample is uniformly heated, and environmental error is to neglect in an experiment
Slightly.Error in experiment mostlys come from the precision after the limit error of measurement apparatus, and Fast Fourier Transform (FFT) (FFT)
Rounding error in error and calculating process, can reduce limit error by improving the measurement accuracy of measurement apparatus, pass through
Processing for Data Analysis in Physics is improved to miss to reduce the rounding-off in the trueness error and calculating process after Fast Fourier Transform (FFT) (FFT)
Difference, it is final further to improve measurement accuracy.
Claims (7)
1. the method that linear frequency modulation multi-beam laser heterodyne measures expansion coefficients of metal wire, it is swashed based on linear frequency modulation multiple beam
What the device of optical heterodyne expansion coefficients of metal wire was realized, described device includes：Chirped laser device (1), thin glass plate
(2), plane mirror (3), electrothermal furnace (4), temperature controller (6), convergent lens (7) and photodetector (8)；
The chirped laser of chirped laser device (1) output incides the preceding surface of thin glass plate (2), and incidence angle θ0For
The laser beam splitter is a reflected light and refraction light by acute angle, thin glass plate (2), and thin glass plate (2) is anti-by a reflected light
It is incident upon on convergent lens (7), thin glass plate (2) is by the refraction anaclasis a to plane mirror (3), and a plane is anti-
No. two reflected lights of multi beam, the multi beam two will be obtained by penetrating the rear surface of mirror (3) and thin glass plate (2) after the refraction light multiple reflections
Reflected light is refracted on convergent lens (7) through thin glass plate (2), the light collection that convergent lens (7) is received to photoelectricity
On the photosurface of detector (8)；
Electrothermal furnace (4) is used to uniformly heat for metallic rod to be measured (5), and temperature controller (6) is used for the temperature for controlling and detecting electrothermal furnace (4)
Degree；
A number plane mirror (3) is fixed on one end of metallic rod to be measured (5), and vertical with the axis of metallic rod to be measured (5), thin
Glass plate (2) be arranged in parallel with a plane mirror (3), and between thin glass plate (2) and a plane mirror (3) away from
From in 20mm between 30mm；
Characterized in that, the described method comprises the following steps：
Step one：The chirped laser that opening chirped laser device (1) sends chirped laser device (1) incides thin
On glass plate (2), and ensure incidence angle θ0For acute angle；Electrothermal furnace (4) and temperature controller (6) are opened simultaneously, and temperature controller (6) collection is treated
Survey the temperature of metallic rod (5)；
Step 2：The photoelectric current I of photodetector (8) output signal is gathered, and photoelectric current I DC terms are filtered out
So as to obtain electric current of intermediate frequency IIF；
Step 3：The electric current of intermediate frequency I obtained to step 2IFAnalyzed, obtain the frequency f of interference signalp：
<mrow>
<msub>
<mi>f</mi>
<mi>p</mi>
</msub>
<mo>=</mo>
<mfrac>
<mrow>
<mn>2</mn>
<mi>p</mi>
<mi>k</mi>
<mi>n</mi>
<mi>d</mi>
<mi> </mi>
<mi>c</mi>
<mi>o</mi>
<mi>s</mi>
<mi>&theta;</mi>
</mrow>
<mrow>
<mi>&pi;</mi>
<mi>c</mi>
</mrow>
</mfrac>
<mo>=</mo>
<msub>
<mi>K</mi>
<mi>p</mi>
</msub>
<mi>d</mi>
<mo>,</mo>
</mrow>
Wherein, p is nonnegative integer,For the rate of change of the modulating bandwidth of chirped laser device (1), T is the frequency modulation cycle,
△ F are modulating bandwidth, and n is the refractive index of medium between thin glass plate (2) and a plane mirror (3), and d is thin glass plate
(2) the distance between with plane mirror (3), θ is the refraction angle that incident light transmits thin glass plate (2), and c is incident light
The light velocity, KpRepresent the proportionality coefficient between the frequency and refraction angle θ cosine of intermediate frequency heterodyne signal；
Step 4：Utilize the frequency f of interference signalpThe distance between thin glass plate (2) and plane mirror (3) d is obtained,
The distance between thin glass plate (2) and plane mirror (3) variable quantity △ d are obtained,
△ d=d0- d,
Wherein, d0Represent the initial distance between thin glass plate (2) and a plane mirror (3)；
Step 5：The linear expansion coefficient α of metallic rod (5) to be measured is obtained using following formula,
<mrow>
<mi>&alpha;</mi>
<mo>=</mo>
<mfrac>
<mrow>
<mi>&Delta;</mi>
<mi>d</mi>
</mrow>
<mrow>
<msub>
<mi>l</mi>
<mn>0</mn>
</msub>
<mi>&Delta;</mi>
<mi>T</mi>
</mrow>
</mfrac>
<mo>,</mo>
</mrow>
Wherein, l0Represent the initial length of metallic rod to be measured (5), △ T=T1-T2Represent the temperature change of metallic rod to be measured (5)
Amount, T1Represent the temperature of metallic rod (5) to be measured at room temperature, T2Represent between thin glass plate (2) and a plane mirror (3)
The temperature of metallic rod (5) to be measured when distance is d.
2. the method that linear frequency modulation multi-beam laser heterodyne according to claim 1 measures expansion coefficients of metal wire, it is special
Levy and be, described device also includes：Data handling system (9)；
The electric signal input end of the electrical signal connection data handling system (9) of photodetector (8)；The data processing
The module of software realization is embedded with system (9), the module is included with lower unit：
Gather the photoelectric current I of photodetector (8) output signal gathering unit；
Photoelectric current I is filtered, so as to obtain electric current of intermediate frequency IIFFilter unit；
Utilize electric current of intermediate frequency IIFObtain the frequency f of interference signalpUnit；
Utilize the frequency f of interference signalpObtain the distance between thin glass plate (2) and plane mirror (3) d unit；
Thin glass plate (2) is obtained according to the distance between thin glass plate (2) and a plane mirror (3) d and a plane is anti-
Penetrate the distance between mirror (3) variable quantity △ d unit；
The line of metallic rod (5) to be measured is obtained using distance change amount △ d between thin glass plate (2) and a plane mirror (3)
Coefficient of expansion α unit.
3. the method that linear frequency modulation multi-beam laser heterodyne according to claim 1 measures expansion coefficients of metal wire, it is special
Levy and be, described device also includes：Wave filter (9-1), amplifier (9-2), A/D converter (9-3) and DSP (9-4)；
The electric signal input end of the electrical signal connection wave filter (9-1) of photodetector (8), the electricity of wave filter (9-1)
The electric signal input end of signal output part connection amplifier (9-2), the electrical signal connection A/D conversions of amplifier (9-2)
The input end of analog signal of device (9-3), the digital signal output end connection DSP (9-4) of A/D converter (9-3) data signal
Input；
The module of software realization is embedded with the DSP (9-4), the module is included with lower unit：
Gather the electric current of intermediate frequency I of A/D converter (9-3) outputIFSignal gathering unit；
Utilize electric current of intermediate frequency IIFObtain the frequency f of interference signalpUnit；
Utilize the frequency f of interference signalpObtain the distance between thin glass plate (2) and plane mirror (3) d unit；
Thin glass plate (2) is obtained according to the distance between thin glass plate (2) and a plane mirror (3) d and a plane is anti-
Penetrate the distance between mirror (3) variable quantity △ d unit；
The line of metallic rod (5) to be measured is obtained using distance change amount △ d between thin glass plate (2) and a plane mirror (3)
Coefficient of expansion α unit.
4. the method that the linear frequency modulation multi-beam laser heterodyne according to claim 1,2 or 3 measures expansion coefficients of metal wire,
Characterized in that, described device also includes：No. two plane mirrors (10)；
The laser light incident of chirped laser device (1) output is on No. two plane mirrors (10), No. two plane mirrors (10)
By the preceding surface of laser reflection to thin glass plate (2), and incidence angle θ0For acute angle.
5. the method that linear frequency modulation multi-beam laser heterodyne according to claim 4 measures expansion coefficients of metal wire, it is special
Levy and be, the frequency modulation cycle of the chirped laser device (1) is 1ms, and modulating bandwidth is 5GHz, the wavelength of output laser is
1.55μm。
6. the method that linear frequency modulation multi-beam laser heterodyne according to claim 5 measures expansion coefficients of metal wire, it is special
Levy and be, incidence angle θ0For 15.26 °.
7. the method that linear frequency modulation multi-beam laser heterodyne according to claim 6 measures expansion coefficients of metal wire, it is special
Levy and be, the thickness of the thin glass plate (2) is more than 0mm and less than 1mm.
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| JP2005083920A (en) * | 2003-09-09 | 2005-03-31 | Mitsutoyo Corp | Linear expansion coefficient measuring device |
| US7548317B2 (en) * | 2006-05-05 | 2009-06-16 | Agc Flat Glass North America, Inc. | Apparatus and method for angular colorimetry |
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| CN102253073A (en) * | 2011-05-31 | 2011-11-23 | 哈尔滨工业大学 | Device and method for measuring metal linear expansion coefficient by adopting Doppler galvanometer sine modulated multi-beam laser heterodyne |
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