CN101933810A - Method and system for detecting blood oxygen saturation - Google Patents

Abstract

The invention discloses a system and a method for detecting blood oxygen saturation. The system for detecting the blood oxygen saturation comprises a signal acquisition device, an adaptive normalization device, a FFT (Fast Fourier Transform) device, an R value calculation device and a blood oxygen saturation calculation device, wherein the FFT device is used for transforming detection data from a time domain into a frequency domain by FFT. The method for detecting the blood oxygen saturation comprises the following steps of: acquiring a signal first and then performing pre-processing and adaptive normalization processing; performing FFT processing and transforming the detection data from the time domain into the frequency domain; and finally calculating the R value and calculating the blood oxygen saturation according to the R value. In a system for detecting the blood oxygen saturation by using the method for detecting the blood oxygen saturation of the technical scheme of the invention, the calculation is simpler because the blood oxygen saturation is calculated from the frequency domain, and the random interference can be reduced and therefore the detection precision is higher.

Description

A kind of method for detecting blood oxygen saturation and system

Technical field

The present invention relates to technical field of medical instruments, be specifically related to the blood oxygen saturation detection technique, particularly a kind of method for detecting blood oxygen saturation and system.

Background technology

The detection of noinvasive blood oxygen saturation is based on arterial blood the absorbtivity of light is moved the principle that changes with arteriogram.During the transmission-type blood oxygen saturation detects, when the transmission region arteries is beaten, arterial blood will change the absorbtivity of light thereupon, be called flutter component or of ac (AC); And its hetero-organizations such as skin, muscle, skeleton and venous blood are invariable to the absorption of light, are called DC quantity (DC).If ignore because the decay that factors such as scattering, reflection cause.(Beer-Lambert Law) can know according to Beer-Lambert law,

$I_{\mathrm{out}}=I_{\mathrm{in}}{e}^{-\mathrm{CL}[S{\mathrm{\β}}_0+[1-S\left]{\mathrm{\β}}_r\right]}$

Wherein, I _OutBe the output current of photodetector, I _InBe the input current (corresponding different HONGGUANG and infrared lights) of diode, C is the concentration of blood, and L is the distance between two LED and the detector, and S is a saturation, β _oAnd β _rRepresent material coefficient respectively.

Usually first calculating ratio value R (Ratio of Ratios) during blood oxygen saturation is calculated calculates blood oxygen saturation according to R again, and the key of oxygen saturation measurement also just is the calculating of R value.If the computational accuracy of R value is improved, the certainty of measurement of blood oxygen saturation is just corresponding so improves.

At present, widely used to the calculating of R value is the peak-to-peak value method.The waveform of red light has a maximum and minima between each sphygmic period, is respectively R _H, R _LWherein, R _LCorresponding when being heart contraction, the value when promptly arterial blood volume is maximum; R _HCorresponding when being diastole, i.e. arterial blood volume value hour.Consider that light passes through the time-delay coefficient of uniform dielectric, can be expressed as:

$R_L=I_o{e}^{-[\mathrm{\α}\left({\mathrm{\λ}}_R\right)d+\mathrm{\αA}\left({\mathrm{\λ}}_R\right)\mathrm{\Δd}]}$

Wherein, I _oThe expression incident intensity, α represents to organize absorptance, α _AExpression arterial blood absorptance, λ _RThe expression specific absorbance, d represents penetration range, Δ d represents the variable quantity that heart contraction and diastole cause.

Similarly,

$R_H=I_o{e}^{-{\mathrm{\α}}_A{\mathrm{\λ}}_{R}d}$

Above two equatioies are made a ratio, obtain

$\frac{R_L}{R_H}=e^{-{\mathrm{\α}}_A{\mathrm{\λ}}_R\mathrm{\Δd}}$

Taking the logarithm in both sides, obtains

$\ln \frac{R_L}{R_H}=-{\mathrm{\α}}_A{\mathrm{\λ}}_R\mathrm{\Δd}$

Similarly, infrared light can obtain

$\ln \frac{{\mathrm{IR}}_L}{{\mathrm{IR}}_H}={-\mathrm{\α}}_A{\mathrm{\λ}}_{\mathrm{IR}}\mathrm{\Δd}$

Wherein, IR _LExpression infrared light minima; IR _HExpression infrared light maximum.

By above formula, can obtain

$R=\frac{{-\mathrm{\α}}_A{\mathrm{\λ}}_R\mathrm{\Δd}}{{-\mathrm{\α}}_A{\mathrm{\λ}}_{\mathrm{IR}}\mathrm{\Δd}}=\frac{\ln \frac{R_L}{R_H}}{\ln \frac{{\mathrm{IR}}_L}{{\mathrm{IR}}_H}}$

From above formula is described as can be seen, adopt rate value that the peak-to-peak value method calculates only with the peak point and the valley point signal correction of pulse signal, therefore the signal to noise ratio of this algorithm is not high, be interfered the easily influence of signal of rate value.

In order to improve signal to noise ratio, a kind of method that is called differentiation has appearred again recently, different with the peak-to-peak value method is, differentiation does not select peak point and valley point to calculate, carry out differential calculation but between peak value and valley, choose one section sample point, promptly calculate the difference of red light of ac between adjacent 2 and the ratio of its D. C. value respectively, two ratios are asked ratio again.At last, all ratios value that obtains is obtained the average ratio value of this segment data after average.The differentiation computing formula is as follows:

$\frac{{\mathrm{dI}}_{\mathrm{out}}}{\mathrm{dt}}=I_{\mathrm{in}}{e}^{-\mathrm{CL}[S{\mathrm{\β}}_0+[1-S\left]{\mathrm{\β}}_r\right]}(-\mathrm{CL}(\mathrm{dL}/\mathrm{dt})[S{\mathrm{\β}}_0+[1-S]{\mathrm{\β}}_r\left]\right)$

Wherein, I _OutBe the output current of photodetector, I _InBe the input current (corresponding different HONGGUANG and infrared lights) of diode, C is a haemoconcentration, and L is the distance between LED lamp and the detector, and S is a saturation, β ₀And β _rRepresent material coefficient respectively.

Again by

$I_{\mathrm{out}}=I_{\mathrm{in}}{e}^{-\mathrm{CL}[S{\mathrm{\β}}_0+[1-S\left]{\mathrm{\β}}_r\right]}$

Obtain

$\frac{{\mathrm{dI}}_{\mathrm{out}}/\mathrm{dt}}{I_{\mathrm{out}}}=-\mathrm{CL}(\mathrm{dL}/\mathrm{dt})[{\mathrm{S\β}}_0+[1-S\left]{\mathrm{\β}}_r\right]$

Two waveforms are divided by, can obtain ratio

$R=\frac{{[S{\mathrm{\β}}_0+(1-S{\mathrm{\β}}_r)]}_{{\mathrm{\λ}}_2}}{{[{\mathrm{S\β}}_0+(1-S{\mathrm{\β}}_r)]}_{{\mathrm{\λ}}_1}}=\frac{\frac{{\mathrm{dI}}_{{\mathrm{out}}_{{\mathrm{\λ}}_2}}}{\mathrm{dt}}*I_{{\mathrm{out}}_{{\mathrm{\λ}}_1}}}{\frac{{\mathrm{dI}}_{{\mathrm{out}}_{{\mathrm{\λ}}_1}}}{\mathrm{dt}}*I_{{\mathrm{out}}_{{\mathrm{\λ}}_2}}}$

Promptly

$R^{`}=\frac{\frac{{{\mathrm{dI}}_{\mathrm{out}}}_{{\mathrm{\λ}}_2}}{\mathrm{dt}}*I_{{\mathrm{out}}_{{\mathrm{\λ}}_1}}}{\frac{{\mathrm{dI}}_{{\mathrm{out}}_{{\mathrm{\λ}}_1}}}{\mathrm{dt}}*I_{{\mathrm{out}}_{{\mathrm{\λ}}_2}}}$

Obtain after asking on average

$\stackrel{\‾}{R}=\frac{1}{N-1}\underset{i=2}{\overset{N}{\mathrm{\Σ}}}\frac{\frac{{\mathrm{dI}}_{{\mathrm{out}}_{{\mathrm{\λ}}_2}}^i}{\mathrm{dt}}*I_{{\mathrm{out}}_{{\mathrm{\λ}}_1}}^{i-1}}{\frac{{\mathrm{dI}}_{{\mathrm{out}}_{{\mathrm{\λ}}_1}}^i}{\mathrm{dt}}*I_{{\mathrm{out}}_{{\mathrm{\λ}}_2}}^{i-1}}=\frac{1}{N-1}\underset{i=2}{\overset{N}{\mathrm{\Σ}}}\frac{(I_{{\mathrm{out}}_{{\mathrm{\λ}}_2}}^i-I_{{\mathrm{out}}_{{\mathrm{\λ}}_2}}^{i-1})*I_{{\mathrm{out}}_{{\mathrm{\λ}}_1}}^{i-1}}{(I_{{\mathrm{out}}_{{\mathrm{\λ}}_1}}^i-I_{{\mathrm{out}}_{{\mathrm{\λ}}_1}}^{i-1})*I_{{\mathrm{out}}_{{\mathrm{\λ}}_2}}^{i-1}}$

From can know the computing formula of codifferentiation, the rate value account form is relevant with the of ac of each sample point of choosing, promptly by increasing the mode of sample point, has improved the signal to noise ratio of algorithm.But because differentiation is to choose in the pulse wave one piece of data arbitrarily, such mode is not considered each section of pulse wave shared weight when calculating blood oxygen saturation, has reduced the precision that blood oxygen saturation is calculated.

In addition, the pulse signal that collects from human body is when analog channel enters processor, just be accompanied by various noises and interference, as power frequency interference, baseline drift, motion artifacts, low perfusion etc., these all can have influence on the R value, finally influence the accuracy of oxygen saturation measurement.

In sum, at present in order to improve the precision of oxygen saturation measurement, mainly adopted peak-to-peak value method and differentiation to come the calculating ratio value.For the peak-to-peak value method, when the human body blood oxygen saturation was lower than 80%, the blood oxygen saturation peak of curve that the peak-to-peak value method obtains can not be represented blood oxygen saturation exactly, therefore can not solve the problem of low saturation well.For differentiation, owing to try to achieve the rate value of this section sample point by calculating rate value between every adjacent 2, though can reduce the influence of noise to signal, but because its rate value is relevant with the rate value of whenever adjacent sample point, when one of appearance or one group of noise signal, will be subjected to very big influence by the average ratio value that calculates at last.

Also there is so not attractive problem in prior art in fact, that be exactly prior art generally all be to calculate the R value from time domain, just calculate blood oxygen saturation then according to the R value.This just causes computational process comparatively complicated, and can not give full play to the advantage of time domain and frequency domain, finally causes the result of calculation of R value accurate inadequately.So all there is the not high problem of accuracy of detection in the existing method that detects blood oxygen saturation, need to improve.

Summary of the invention

One of technical problem to be solved by this invention provides a kind of blood oxygen saturation detection system, solves blood oxygen saturation detection technique complexity and the not high enough problem of precision in the prior art.

For solving the problems of the technologies described above, the present invention adopts following technical scheme:

A kind of blood oxygen saturation detection system, comprise and being linked in sequence: signal pickup assembly, pre-procesor, self adaptation normalization device, R value calculation apparatus and blood oxygen saturation are calculated device, comprise also being used for the detection data of self adaptation normalization device output are transformed from the time domain to the FFT device of frequency domain by fast Fourier transform that described FFT device is arranged between self adaptation normalization device and the R value calculation apparatus.

In the optimized technical scheme, described pre-procesor comprises wave trap and low pass filter, and described wave trap and low pass filter are arranged between signal pickup assembly and the self adaptation normalization device.

Further in the optimized technical scheme, described low pass filter be 15HZ by frequency domain.

In the optimized technical scheme, described blood oxygen saturation detection system also comprises the Kalman filtering device, and described Kalman filtering device is arranged on the R value calculation apparatus and blood oxygen saturation is calculated between the device.

Two of technical problem to be solved by this invention provides a kind of method for detecting blood oxygen saturation, solves blood oxygen saturation detection technique complexity and the not high enough problem of precision in the prior art.

For solving the problems of the technologies described above, the present invention adopts following technical scheme:

A kind of method for detecting blood oxygen saturation comprises the steps:

S1), signals collecting, carry the HONGGUANG detection signal Red and the infrared light detection signal Ir of blood oxygen signal by signal pickup assembly collection;

S2), pretreatment, promptly remove surround lighting and High-frequency Interference among HONGGUANG detection signal Red and the infrared light detection signal Ir by pretreatment unit;

S3), the self adaptation normalized, mainly be to utilize self adaptation normalized device, pretreated detection data are carried out normalized;

S4), FFT handles, data V1 and the V2 after with normalization adopts fast Fourier transform by the FFT device, transforms from the time domain to frequency domain;

S5), the R value calculates, the data after the frequency domain normalization that obtains after handling according to FFT calculate the R value;

S6), blood oxygen saturation calculates, and utilizes the curve of R value, obtains the oximetry value of correspondence according to look-up table.

In the optimized technical scheme, step S2) pretreatment described in comprises: adopt wave trap can remove the interference of surround lighting in the detection signal, adopt low pass filter to remove High-frequency Interference in the detection signal.

Further in the optimized technical scheme, described low pass filter be 15HZ by frequency domain.

In the optimized technical scheme, described step S5) and step S6) between also comprise the step of Kalman filtering.

Further in the optimized technical scheme, during described Kalman filtering, need judge whether to proceed Kalman filtering according to the residual sum signal quality index; If residual error is too big or signal quality index is too small, then abandon Kalman filtering, directly allow present R value be the preceding R value of once calculating; Wherein the computing formula of signal quality index FSQI is as follows:

$\mathrm{FSQI}=\sqrt{\frac{S^2}{{N1}^2+{N2}^2+...+{N512}^2}}$ (formula 3)

Wherein, S is the amplitude of V2 at frequency domain pulse frequency place, and N1, N2...N512 are the amplitude of V2 at the non-direct current of frequency domain.

During normalized in the optimized technical scheme, step S3), calculate the AC compounent R of HONGGUANG respectively _AcWith DC component R _DcAC compounent IR with infrared light _AcWith DC component IR _Dc, obtain value V1 and V2 after the normalization by following formula then

$V1=\frac{R_{\mathrm{ac}}*{\mathrm{IR}}_{\mathrm{dc}}}{R_{\mathrm{dc}}}$ V2＝IR _ac

The invention has the beneficial effects as follows:

Adopted a kind of blood oxygen saturation detection system of a kind of method for detecting blood oxygen saturation of technical solution of the present invention, owing to from the frequency domain of HONGGUANG and infrared light, calculate blood oxygen saturation, it is simpler to calculate blood oxygen with respect to prior art from time domain, and can reduce random disturbances, thereby accuracy of detection is higher.Experiment showed, and adopt the blood oxygen estimation technique the present invention is based on frequency domain, can calculate and pour into intensity is 0.3% pulse signal, and oximetry value 70%-100% can obtain precision 1% with interior oximetry value.

Description of drawings

Fig. 1 is the theory of constitution schematic block diagram of blood oxygen saturation detection system in the specific embodiment of the invention.

Fig. 2 is the flow chart of method for detecting blood oxygen saturation in the specific embodiment of the invention.

Fig. 3 is the amplitude spectrum of detection signal behind FFT in the specific embodiment of the invention.

The invention will be further described below in conjunction with accompanying drawing.

The specific embodiment

As shown in Figure 1, a kind of blood oxygen saturation detection system that this specific embodiment provides, comprise and being linked in sequence: signal pickup assembly, wave trap, low pass filter, self adaptation normalization device, FFT (Fast Fourier Transform, fast Fourier transform) device, R value calculation apparatus, Kalman filtering device and blood oxygen saturation are calculated device; Wherein wave trap, low pass filter can be collectively referred to as pre-procesor.

As shown in Figure 2, a kind of method for detecting blood oxygen saturation that this specific embodiment provides comprises the steps:

1, signals collecting is carried the HONGGUANG detection signal Red and the infrared light detection signal Ir of blood oxygen signal by signal pickup assembly collection.

2, pretreatment promptly by wave trap and low pass filter, is carried out pretreatment to HONGGUANG detection signal Red and infrared light detection signal Ir, mainly removes surround lighting and High-frequency Interference.

Wave trap can remove the interference of surround lighting in the detection signal, and low pass filter can remove the High-frequency Interference in the detection signal.As shown in Figure 1, Red1 is through the filtered HONGGUANG of wave trap; Ir1 is through the filtered infrared light of wave trap; Red ' is through the HONGGUANG behind the low pass filter; Ir ' is through the infrared light behind the low pass filter.

Need to prove, owing to generally only consider first-harmonic, second harmonic and the triple-frequency harmonics of pulse signal,, generally uses and end frequency domain and can reach promising result as the low pass filter of 15HZ so be the pulse signal of 0.5HZ-5HZ for bandwidth.Certainly, can also determine the exponent number of wave filter in case of necessity as required.

3, self adaptation normalized mainly is to utilize self adaptation normalized device, pretreated detection data is carried out normalized obtain V1 and V2;

$V1=\frac{R_{\mathrm{ac}}*{\mathrm{IR}}_{\mathrm{dc}}}{R_{\mathrm{dc}}}$ (formula 1)

V2=IR _Ac(formula 2)

In the formula, R _AcIt is the AC compounent of HONGGUANG; R _DcIt is the DC component of HONGGUANG; IR _AcIt is the AC compounent of infrared light; IR _DcIt is the DC component of infrared light.

4, FFT handles, and data V1 and the V2 after with normalization adopts fast Fourier transform by the FFT device, transforms from the time domain to frequency domain.

FFT part is by carrying out the FFT conversion to V1 and V2, obtains as shown in Figure 3 V1 and V2 at the amplitude spectrum of frequency domain.

V1 and V2 can carry out windowing process before the FFT conversion, as add rectangular window or Blackman window etc., and the length of FFT conversion can be 1024,2048,4096 etc., and these parameters are decided as required.

V1 wherein and V2 are exactly the variable of following two expression formula correspondences, in theory directly with following ratio formula Ask the R value, promptly respectively to R _Ac/ R _DcAnd IR _Ac/ IR _DcCarry out the FFT conversion, obtain the R value according to their ratio then, but a lot of processor can only be handled integer, just is not suitable for (because R with this formula at pulse first-harmonic place _Ac/ R _Dc＜1, IR _Ac/ IR _Dc＜1), just formula can be become

The problem that runs in such cases is R _Ac* IR _DcThe very big or IR of product _Ac* R _DcProduct very big, cause processor to overflow, and the best approach that solves them is with right respectively

With IR _AcCarry out the FFT conversion, the frequency domain at them obtains R ratio again, and this method can realize on more processor.

5, the R value is calculated, and the frequency domain detection data that obtain after handling according to FFT calculate the R value.The R value is calculated and is belonged to prior art, and this paper no longer describes in detail this.This concrete enforcement particularly, can select 20 maximum peak values separately at the frequency domain of FV1 and FV2 (signal after FV1 and FV2 are V1 and V2 process FFT conversion respectively) earlier, whether the first-harmonic of request signal and the FV1/FV2 of harmonic wave place be in certain very little scope in these peak values, if in certain very little scope then first-harmonic herein is a pulse frequency, and FV1/FV2 herein is exactly the R value.

6, Kalman filtering can prevent the interference that random noise causes, anti-stop signal is undergone mutation, and promptly the R value is played level and smooth effect.

It is emphasized that, when the R value is carried out Kalman filtering, need judge whether to proceed Kalman filtering according to residual sum signal quality index FSQI, if residual error is too big or signal quality index is little then abandon Kalman filtering, wherein signal quality index is determined at the amplitude spectrum of frequency domain according to V2, and concrete computing formula is as follows:

$\mathrm{FSQI}=\sqrt{\frac{S^2}{{N1}^2+{N2}^2+...+{N512}^2}}$ (formula 3)

Wherein, S is the amplitude of V2 at frequency domain pulse frequency place, and N1, N2...N512 are the amplitude of V2 at the non-direct current of frequency domain.

7, blood oxygen saturation is calculated, and utilizes the curve of R value, obtains corresponding oximetry value according to look-up table, and this part belongs to prior art, and this paper no longer describes in detail.

The blood oxygen saturation of this specific embodiment is calculated system, adopt the method for detecting blood oxygen saturation of this specific embodiment, from HONGGUANG and and the frequency domain of infrared light calculate blood oxygen saturation, simpler with prior art relatively, and can reduce random disturbances from time domain calculating blood oxygen.Experiment showed, and adopt the blood oxygen estimation technique the present invention is based on frequency domain, can calculate and pour into intensity is 0.3% pulse signal, and oximetry value 70%-100% can obtain precision 1% with interior oximetry value.

Above content be in conjunction with concrete preferred implementation to further describing that the present invention did, can not assert that concrete enforcement of the present invention is confined to these explanations.For the general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, can also make some simple deduction or replace, all should be considered as belonging to protection scope of the present invention.

Claims (10)

1. blood oxygen saturation detection system, comprise and being linked in sequence: signal pickup assembly, self adaptation normalization device, R value calculation apparatus and blood oxygen saturation are calculated device, it is characterized in that, described blood oxygen saturation detection system comprises also and is used for the detection data of self adaptation normalization device output are transformed from the time domain to the FFT device of frequency domain by fast Fourier transform that described FFT device is arranged between self adaptation normalization device and the R value calculation apparatus.

2. a kind of blood oxygen saturation detection system as claimed in claim 1 is characterized in that described blood oxygen saturation detection system also comprises pre-procesor, and described pre-procesor is arranged between signal pickup assembly and the self adaptation normalization device.

3. a kind of blood oxygen saturation detection system as claimed in claim 2 is characterized in that described pre-procesor comprises wave trap and low pass filter, and described wave trap and low pass filter are arranged between signal pickup assembly and the self adaptation normalization device; Described low pass filter by frequency domain be 15HZ.

4. as any described a kind of blood oxygen saturation detection system in the claim 1 to 3, it is characterized in that, described blood oxygen saturation detection system also comprises the Kalman filtering device, and described Kalman filtering device is arranged on the R value calculation apparatus and blood oxygen saturation is calculated between the device.

5. a method for detecting blood oxygen saturation comprises the steps:

S1), signals collecting, carry the HONGGUANG detection signal Red and the infrared light detection signal Ir of blood oxygen signal by signal pickup assembly collection;

S2), the self adaptation normalized, utilize self adaptation normalized device, pretreated detection data are carried out normalized;

S3), FFT handles, and by the The data fast Fourier transform of FFT device after with normalized, transforms from the time domain to frequency domain;

S4), the R value calculates, the data after the frequency domain normalization that obtains after handling according to FFT calculate the R value;

S5), blood oxygen saturation calculates, and utilizes the R value that is calculated, and obtains the oximetry value of correspondence according to look-up table.

6. a kind of method for detecting blood oxygen saturation as claimed in claim 5, it is characterized in that, described method for detecting blood oxygen saturation also comprise be arranged on step S1) and S2) between pre-treatment step, remove surround lighting and High-frequency Interference among HONGGUANG detection signal Red and the infrared light detection signal Ir by pretreatment unit.

7. a kind of method for detecting blood oxygen saturation as claimed in claim 6 is characterized in that, described pretreatment comprises: adopt wave trap can remove the interference of surround lighting in the detection signal, the employing low pass filter removes the High-frequency Interference in the detection signal; Described low pass filter by frequency domain be 15HZ.

8. a kind of method for detecting blood oxygen saturation as claimed in claim 5 is characterized in that, described step S4) and step S5) between also comprise the step of Kalman filtering.

9. a kind of method for detecting blood oxygen saturation as claimed in claim 8 is characterized in that, during described Kalman filtering, need judge whether to proceed Kalman filtering according to the residual sum signal quality index; If residual error is too big or signal quality index is too small, then abandon kalman filtering, directly allow present R value be the preceding R value of once calculating; Wherein the computing formula of signal quality index FSQI is as follows:

$\mathrm{FSQI}=\sqrt{\frac{S^2}{{N1}^2+{N2}^2+...+{N512}^2}}$

Wherein, S is the amplitude of V2 at frequency domain pulse frequency place, and N1, N2...N512 are the amplitude of V2 at the non-direct current of frequency domain.

10. as any described a kind of method for detecting blood oxygen saturation in the claim 5 to 9, it is characterized in that step S2) in normalized be to calculate the AC compounent R of HONGGUANG respectively _AcWith DC component R _DcAC compounent IR with infrared light _AcWith DC component IR _Dc, obtain value V1 and V2 after the normalization by following formula then

$V1=\frac{R_{\mathrm{ac}}*{\mathrm{IR}}_{\mathrm{dc}}}{R_{\mathrm{dc}}}$ V2＝IR _ac

In the formula, R _AcIt is the AC compounent of HONGGUANG; R _AcIt is the DC component of HONGGUANG; IR _AcIt is the AC compounent of infrared light; IR _DcIt is the DC component of infrared light.

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