CN101738375A - Data signal processing-based laser frequency modulation polarimeter and measurement method thereof - Google Patents

Abstract

Translated fromChinese

本发明涉及一种基于数据信号处理的激光调频旋光仪及其测量方法，包括光路部分和电路部分，利用DSP产生信号驱动步进电机带动检偏器旋转一周，再由DSP对所记录下来的信号进行数据处理，采用曲线拟合的方法得到一条关于光强与步进电机转动角度的曲线，然后直接利用该曲线，从曲线上计算出物质的旋光度。利用本发明计算旋光角，相比传统技术，可消除电机回程误差等影响，精确的找出光学零点，大大提高旋光仪的精度，并且具有体积小，成本低，功耗低的特点。

The invention relates to a laser FM polarimeter based on data signal processing and its measurement method, which includes an optical path part and a circuit part, uses a DSP to generate a signal to drive a stepper motor to drive a polarizer to rotate for a circle, and then uses the DSP to record the signal Carry out data processing, adopt the method of curve fitting to obtain a curve about the light intensity and the rotation angle of the stepping motor, and then directly use the curve to calculate the optical rotation of the substance from the curve. Using the invention to calculate the optical rotation angle, compared with the traditional technology, can eliminate the influence of the motor return error, accurately find the optical zero point, greatly improve the precision of the polarimeter, and has the characteristics of small size, low cost, and low power consumption.

Description

Translated fromChinese

基于数据信号处理的激光调频旋光仪及其测量方法Laser Frequency Modulation Polarimeter Based on Data Signal Processing and Its Measurement Method

技术领域technical field

本发明涉及一种检测技术，特别涉及一种使用DSP进行数据处理以及调频激光的测量旋光质旋转角的旋光仪及其测量方法的技术。The invention relates to a detection technology, in particular to a technology of a polarimeter using DSP for data processing and a frequency-modulated laser to measure the rotation angle of an optical rotator and its measuring method.

背景技术Background technique

旋光分析法(简称旋光法)是利用线偏振光通过含有化学活性物质的溶液或液体时引起旋光现象，使通过的偏振光平面向左或向右旋转。因此，在一定的条件下，检测线偏振光旋转的方向和度数，可以分析某些化合物的旋光性，或检测化合物的杂质、纯度和含量。用于测量旋光度的仪器，被称为旋光仪。旋光法多用于糖类的含量测定，近年来，制药、食品加工、化工和生化分析等领域也都涉及到这一方法。Optical rotation analysis (abbreviated as optical rotation method) is to use linearly polarized light to cause optical rotation when it passes through a solution or liquid containing chemically active substances, so that the plane of the polarized light passing through it is rotated to the left or right. Therefore, under certain conditions, detecting the direction and degree of rotation of linearly polarized light can analyze the optical activity of certain compounds, or detect the impurities, purity and content of compounds. Instruments used to measure optical rotation are called polarimeters. Optical polarimetry is mostly used for the determination of sugar content. In recent years, this method has also been involved in the fields of pharmacy, food processing, chemical industry and biochemical analysis.

物质的旋光度的大小与下列因素有关：一是与物质的温度有关。有的物质随温度的升高而增加，如石英等。有的物质随温度的而减小，如蔗糖等。二是与线偏振光的波长有关，波长不同，旋光度也不同。The optical rotation of a substance is related to the following factors: First, it is related to the temperature of the substance. Some substances increase with the increase of temperature, such as quartz and so on. Some substances decrease with temperature, such as sucrose. The second is related to the wavelength of linearly polarized light. Different wavelengths have different optical rotations.

旋光质的旋光度a(线偏振光经旋光物质后振动面转过的角度)与旋光物质溶液体积百分比浓度c及偏振光所通过的溶液厚度1成正比，a＝kcl(1)，其中c为g/100ml，1为mm。The optical rotation a of the optically active substance (the angle at which the vibration plane of the linearly polarized light passes through the optically active substance) is proportional to the volume percentage concentration c of the optically active substance solution and the thickness 1 of the solution through which the polarized light passes, a=kcl(1), where c It is g/100ml, and 1 is mm.

传统的旋光仪采用钠光灯用光源，由小孔光栅和物镜组成一个简单的点光源平行光管如图1所示，平行光经偏振镜(I)变为平面偏振光，其振动平面为00如图2a，当偏振光经过有法拉弟效应的磁旋线圈时，其振动平面产生50Hz的β角往复摆动如图2b，光线经过偏振镜(II)投射到光电倍增管上，产生交变的电信号，通过样品后的偏振光振动面旋转α1度如图2c，仪器示数平衡后偏振镜反向转过α1度补偿了样品的旋光度，如图2d。The traditional polarimeter adopts the light source of sodium lamp, a simple point light source collimator composed of a small hole grating and an objective lens, as shown in Figure 1, the parallel light is changed into plane polarized light by the polarizer (I), and its vibration plane is 00 As shown in Figure 2a, when the polarized light passes through the magnetic gyro coil with Faraday effect, its vibration plane produces a 50Hz β angle reciprocating swing, as shown in Figure 2b, the light is projected onto the photomultiplier tube through the polarizer (II), resulting in alternating After the electrical signal passes through the sample, the vibration plane of the polarized light rotates α1 degree as shown in Figure 2c. After the instrument reads and balances, the polarizer reverses and rotates α1 degree to compensate the optical rotation of the sample, as shown in Figure 2d.

仪器以两偏振镜光轴正交时(即OO⊥PP)作为光学零点，此时，α＝0°如图3。磁旋圈产生的β角摆动，在光学零点时得到100Hz的光电信号(曲线C′)，在有α1°或α2°的试样时得到50Hz的信号，但它们的相位正好相反(曲线B′、D′)。因此，能使工作频率为50Hz的伺服电机转动。伺服电机通过蜗轮，蜗杆将偏振镜转过α°(α＝α1或α＝α2)，仪器回到光学零点，伺服电机在100Hz信号的控制下，重新出现平衡指示。The instrument takes the time when the optical axes of the two polarizers are perpendicular (ie OO⊥PP) as the optical zero point, at this time, α=0° as shown in Figure 3. The β-angle swing generated by the magnetic gyro produces a 100Hz photoelectric signal (curve C') at the optical zero point, and a 50Hz signal when there is an α1° or α2° sample, but their phases are just opposite (curve B' , D'). Therefore, a servo motor whose operating frequency is 50 Hz can be rotated. The servo motor passes through the worm gear, and the worm rotates the polarizer through α° (α=α1 or α=α2), and the instrument returns to the optical zero point. Under the control of the 100Hz signal, the servo motor reappears the balance indication.

就上述技术而言，这个测旋转角的方法采用法拉第线圈调制光信号，其电压高，功耗大，体积大，其调制频率为50HZ，频率低，易受干扰，严重影响测量精度。另外该方法中采用钠光灯作为光源，功耗较大，易老化，方向性差，需要后续光路进行聚焦准直形成平行光。针对这些缺点，在此之前我们所申请的专利中提出了采用频率可调的激光源来代替以往的法拉第线圈调制部分和钠灯光源。调制频率为f的激光经过起偏器，待测物和检偏器后的频率不变。检偏器和起偏器正交时，通过检偏器的光强频率虽然为f，可是光强很弱不足以带动后续电路。检偏器和起偏器不正交时，光强频率为f被选频放大带动伺服电机转动。As far as the above technology is concerned, this method of measuring the rotation angle uses a Faraday coil to modulate the optical signal, which has high voltage, high power consumption, and large volume. The modulation frequency is 50HZ, and the frequency is low. It is susceptible to interference and seriously affects the measurement accuracy. In addition, this method uses a sodium lamp as the light source, which consumes a lot of power, is prone to aging, and has poor directivity. It requires subsequent optical paths to be focused and collimated to form parallel light. In response to these shortcomings, we proposed to use a frequency-tunable laser source to replace the previous Faraday coil modulation part and sodium lamp light source in our previous patent application. The laser with the modulation frequency f passes through the polarizer, and the frequency after the object under test and the polarizer remains unchanged. When the polarizer and the polarizer are orthogonal, although the frequency of the light intensity passing through the polarizer is f, the light intensity is too weak to drive the subsequent circuit. When the polarizer and the polarizer are not orthogonal, the light intensity frequency is f, which is amplified by frequency selection to drive the servo motor to rotate.

发明内容Contents of the invention

本发明是针对现有技术的不足问题，提出了一种基于数据信号处理的激光调频旋光仪及其测量方法，与传统旋光仪所完成相同的功能，但为全自动数字化控制，进一步减小误差，提高了精度。The present invention aims at the deficiencies of the prior art, and proposes a laser FM polarimeter based on data signal processing and its measurement method, which has the same function as the traditional polarimeter, but is fully automatic digital control, further reducing the error , which improves the accuracy.

本发明的技术方案为：一种基于数据信号处理的激光调频旋光仪，包括光路部分和电路部分，光路部分依次连接包括可调频半导体激光器作为光源、起偏器、旋光管、检偏器和光电池；电路部分包括依次连接的光电池、前置放大单元、二级放大单元、选频放大单元、限幅钳位电路、DSP数据信号处理单元、步进电机、数字显示单元；DSP数据信号处理单元包括DSP模数转换单元、DSP信号发生单元、DSP数字存储单元、DSP数据处理单元；DSP数据信号处理单元中的DSP信号发生单元产生的高频信号加载到可调频半导体激光器上，同时发出信号驱动步进电机，步进电机带动检偏器转动；限幅钳位电路输出信号接DSP数据信号处理单元中的DSP模数转换单元，DSP模数转换单元将模拟信号转换为数字信号后，输出到DSP数字存储单元储存信号，DSP数据处理单元对DSP数字存储单元储存的信号进行处理后输出到数字显示单元显示数据。The technical solution of the present invention is: a laser frequency modulation polarimeter based on data signal processing, including an optical path part and a circuit part, and the optical path part is sequentially connected to include a frequency-tunable semiconductor laser as a light source, a polarizer, a polarizer, an analyzer and a photocell ; The circuit part includes a photocell, a preamplifier unit, a secondary amplifier unit, a frequency selective amplifier unit, a limiter clamp circuit, a DSP data signal processing unit, a stepping motor, and a digital display unit connected in sequence; the DSP data signal processing unit includes DSP analog-to-digital conversion unit, DSP signal generation unit, DSP digital storage unit, DSP data processing unit; the high-frequency signal generated by the DSP signal generation unit in the DSP data signal processing unit is loaded onto the frequency-tunable semiconductor laser, and at the same time sends out a signal to drive the step Into the motor, the stepper motor drives the polarizer to rotate; the output signal of the limiter clamp circuit is connected to the DSP analog-to-digital conversion unit in the DSP data signal processing unit, and the DSP analog-to-digital conversion unit converts the analog signal into a digital signal and outputs it to the DSP The digital storage unit stores the signal, and the DSP data processing unit processes the signal stored in the DSP digital storage unit and outputs it to the digital display unit to display the data.

一种基于数据信号处理的激光调频旋光仪的测量方法，包括基于数据信号处理的激光调频旋光仪，测量方法具体包括如下步骤：A method for measuring a laser frequency modulation polarimeter based on data signal processing, including a laser frequency modulation polarimeter based on data signal processing, the measurement method specifically includes the following steps:

1)在未加待测物质时调整起偏器和检偏器正交并固定；1) When no substance to be tested is added, the polarizer and analyzer are adjusted to be orthogonal and fixed;

2)在试管加入旋光物质后，DSP信号发生单元产生高频f的方波信号，加载到可调频半导体激光器，调制频率为f的激光经过起偏器变为线偏光、线偏光经过旋光管中的旋光物质后旋转再经过检偏器，照在光电池上，光电池将频率为f的光信号转变为频率为f交流电信号；2) After the optically active substance is added to the test tube, the DSP signal generating unit generates a square wave signal of high frequency f, which is loaded into the frequency-tunable semiconductor laser, and the laser with a modulation frequency of f passes through the polarizer to become linearly polarized light, and the linearly polarized light passes through the optical rotator The optically active substance rotates and then passes through the analyzer, and shines on the photocell, and the photocell converts the optical signal with frequency f into an alternating current signal with frequency f;

3)频率为f交流电信号依次经前置放大单元、二级放大单元的放大、选频放大单元的选频、限幅和钳位电路的输入保护后进入模数转换单元转换为数字信号输入到DSP数据存储单元；3) The AC signal with a frequency of f passes through the preamplifier unit, the amplification of the secondary amplifier unit, the frequency selection of the frequency selection amplifier unit, the limiter and the input protection of the clamping circuit, and then enters the analog-to-digital conversion unit to be converted into a digital signal input to the DSP data storage unit;

4)DSP信号发生单元发出信号驱动步进电机带动检偏器转动，交流信号强度发生变化，重复步骤3，DSP数据存储单元记录储存每个信号；4) The DSP signal generation unit sends a signal to drive the stepping motor to drive the polarizer to rotate, the AC signal strength changes, repeat step 3, and the DSP data storage unit records and stores each signal;

5)DSP数据处理单元对DSP数字存储单元储存的信号进行处理，通过FFT快速傅里叶分解，然后再数字滤波，最后通过包络检波的方法得到一条频率为f信号的幅值和步进电机转动角度的曲线，对实际曲线进行拟合，最终计算出旋光角进而得知溶液浓度。5) The DSP data processing unit processes the signal stored in the DSP digital storage unit, decomposes it through FFT fast Fourier, then digitally filters it, and finally obtains the amplitude of a signal with a frequency of f and the stepper motor through the method of envelope detection The curve of the rotation angle is fitted to the actual curve, and finally the optical rotation angle is calculated to obtain the solution concentration.

本发明的有益效果在于：本发明基于数据信号处理的激光调频旋光仪及其测量方法，具有体积小，成本低，功耗低，全自动数字化的，测量精度高的特点。The beneficial effect of the present invention is that the laser FM polarimeter and its measurement method based on data signal processing have the characteristics of small size, low cost, low power consumption, fully automatic digitalization, and high measurement accuracy.

附图说明Description of drawings

图1为现有技术旋光仪的结构原理示意图；Fig. 1 is the structural principle schematic diagram of prior art polarimeter;

图2为现有技术偏振光的振动情况示意图；Fig. 2 is a schematic diagram of the vibration of polarized light in the prior art;

图3为现有技术中法拉第线圈工作原理的曲线示意图；FIG. 3 is a schematic diagram of a curve showing the working principle of a Faraday coil in the prior art;

图4为马吕斯定律曲线示意图；Fig. 4 is the schematic diagram of Marius' law curve;

图5是本发明基于数据信号处理的激光调频旋光仪的原理框图。Fig. 5 is a functional block diagram of the laser frequency modulation polarimeter based on data signal processing in the present invention.

具体实施方式Detailed ways

如图5所示，基于DSP的激光调频旋光仪结构原理示意图，包括光路部分和电路部分，光路部分依次包括可调频半导体激光器1作为光源、起偏器2、旋光管3、检偏器4和光电池5。电路部分包括依次连接的光电池5、前置放大单元6、二级放大7、选频放大单元8、限幅钳位电路9、DSP数据信号处理单元10、步进电机11、数字显示单元12。DSP数据信号处理单元10包括DSP模数转换单元、DSP信号发生单元、DSP数字存储单元、DSP数据处理单元。As shown in Figure 5, the schematic diagram of the structure and principle of the laser frequency modulation polarimeter based on DSP includes the optical path part and the circuit part. Photocell 5. The circuit part includes a photocell 5, a preamplifier unit 6, asecondary amplifier 7, a frequencyselective amplifier unit 8, alimiter clamp circuit 9, a DSP datasignal processing unit 10, astepping motor 11, and adigital display unit 12 connected in sequence. The DSP datasignal processing unit 10 includes a DSP analog-to-digital conversion unit, a DSP signal generation unit, a DSP digital storage unit, and a DSP data processing unit.

选用可调频激光光源替代钠灯光，DSP信号发生单元产生高频f的方波信号，加载到可调频激光器，激光器输出频率f为可调节。调制频率为f的激光经过起偏器变为线偏光、线偏光经过旋光管中的旋光物质后旋转，这束光再经过检偏器，照在光电池上，频率为f的激光经过起偏器、待测物和检偏器后的频率不变，光电池将频率为f的光信号转变为频率为f电信号，并输入前置放大单元，前置放大单元用于放大从光电池发来的电信号，放大此信号以驱动选频放大单元，选频放大单元用于选择激光源频率f的信号而滤除其它频率的信号。信号通过限幅和钳位电路的输入保护单元，DSP模数转换单元用于将选频放大单元出来的模拟信号转换为数字信号，并由DSP数字存储单元记录下该信号。然后DSP信号发生单元发出信号驱动步进电机转动，并带动检偏器转动。步进电机每转动一步，调制频率为f的激光信号偏振角度与检偏器的角度便发生变化，导致经过检偏器的激光信号的幅值大小发生变化，经过光电转换、前置放大、选频放大、模数转换后，由DSP数据存储单元记录下最新的信号。当步进电机转过一圈后，由DSP对每个记录下的信号进行数据处理，首先进行FFT(快速傅里叶分解)，然后再数字滤波，最后通过包络检波的方法得到一条关于频率为f信号的幅值和步进电机转动角度的曲线。根据马吕斯定律I＝I0cos2α，如图4该曲线理论上应为一条如图所示的曲线。运用DSP进行数据处理，将实际得到的曲线与已知理论曲线进行对比，对实际曲线进行拟合，并计算出拟合曲线上的最初时刻到最近零点之间的角度。该角度便是物质的旋光角。再通过数据处理单元将该角度与已知国际标准比对，查找出该溶液浓度。最后通过数字显示单元输出结果。采用DSP产生信号对激光信号进行调制，可以得到频率很高的调制信号，避免了50HZ工频干扰。在传统的旋光仪中，采用伺服电机带动检偏器自动旋转到光学零位原理，而在本技术中，DSP产生信号驱动步进电机带动检偏器旋转一周，再由DSP对所记录下来的信号进行数据处理，采用曲线拟合的方法得到一条关于光强与步进电机转动角度的曲线，然后直接利用该曲线，从曲线上计算出物质的旋光度。利用本技术计算旋光角，相比传统技术，可消除电机回程误差等影响，精确的找出光学零点，大大提高旋光仪的精度。The frequency-tunable laser light source is selected to replace the sodium light source, and the DSP signal generation unit generates a square wave signal of high frequency f, which is loaded to the frequency-tunable laser, and the output frequency f of the laser is adjustable. The laser with the modulation frequency f passes through the polarizer to become linearly polarized light, and the linearly polarized light passes through the optically active material in the optical rotation tube and then rotates. This beam of light then passes through the analyzer and shines on the photocell. , the frequency of the object under test and the polarizer remains unchanged, the photocell converts the optical signal of frequency f into an electrical signal of frequency f, and inputs it into the preamplifier unit, which is used to amplify the electricity sent from the photocell signal, and amplify the signal to drive the frequency-selective amplifying unit, which is used to select the signal of laser source frequency f and filter out signals of other frequencies. The signal passes through the input protection unit of the limiting and clamping circuit, and the DSP analog-to-digital conversion unit is used to convert the analog signal from the frequency selection amplifying unit into a digital signal, and the DSP digital storage unit records the signal. Then the DSP signal generating unit sends out a signal to drive the stepper motor to rotate, and drives the polarizer to rotate. Every time the stepper motor rotates one step, the polarization angle of the laser signal with a modulation frequency of f and the angle of the analyzer will change, resulting in a change in the amplitude of the laser signal passing through the analyzer. After photoelectric conversion, preamplification, and selection After frequency amplification and analog-to-digital conversion, the latest signal is recorded by the DSP data storage unit. When the stepper motor rotates a circle, the DSP will process the data of each recorded signal, first perform FFT (Fast Fourier Decomposition), then digital filter, and finally obtain a signal about the frequency through the method of envelope detection. It is the curve of the amplitude of the f signal and the rotation angle of the stepper motor. According to Marius' law I=I0cos2α, as shown in Figure 4, the curve should theoretically be a curve as shown in the figure. Use DSP for data processing, compare the actual curve with the known theoretical curve, fit the actual curve, and calculate the angle between the initial moment and the nearest zero point on the fitted curve. This angle is the optical rotation angle of the substance. Then compare the angle with the known international standard through the data processing unit to find out the concentration of the solution. Finally, the result is output through the digital display unit. The signal generated by DSP is used to modulate the laser signal, and a modulated signal with a high frequency can be obtained, which avoids 50HZ power frequency interference. In the traditional polarimeter, the servo motor is used to drive the polarizer to automatically rotate to the optical zero position principle, but in this technology, the DSP generates a signal to drive the stepping motor to drive the polarizer to rotate for a circle, and then the DSP records the polarizer. The signal is processed for data, and the curve fitting method is used to obtain a curve about the light intensity and the rotation angle of the stepping motor, and then directly use the curve to calculate the optical rotation of the substance from the curve. Using this technology to calculate the optical rotation angle, compared with the traditional technology, can eliminate the influence of the motor return error, accurately find the optical zero point, and greatly improve the accuracy of the polarimeter.

测量旋光物质旋光角的测量方法，其步骤如下：1)在未加待测物质时调整起偏器和检偏器正交并固定；2)在试管加入旋光物质后，光通过所述光路部分到达光电池，从光电池输出的是一个高频交流信号；3)该交流信号经前置放大单元的放大、选频放大单元的选频、模数转换单元的模数转换后输入DSP数据存储单元。4)步进电机带动检偏器转动，交流信号强度发生变化，DSP记录下每个信号。通过FFT以及包络检波得到一条曲线，并进行拟合。最终计算出旋光角进而得知溶液浓度。The measurement method for measuring the optical rotation angle of an optically active substance, the steps are as follows: 1) When no substance to be measured is added, the polarizer and the analyzer are adjusted to be orthogonal and fixed; 2) After the test tube is added with an optically active substance, the light passes through the optical path part When it reaches the photocell, a high-frequency AC signal is output from the photocell; 3) The AC signal is input to the DSP data storage unit after being amplified by the pre-amplifier unit, frequency-selected by the frequency-selective amplifying unit, and converted by the analog-to-digital conversion unit. 4) The stepper motor drives the polarizer to rotate, the strength of the AC signal changes, and the DSP records each signal. A curve is obtained by FFT and envelope detection and fitted. Finally, the optical rotation angle is calculated to obtain the solution concentration.

Claims (2)

1. a laser frequency modulation polarimeter of handling based on data-signal is characterized in that comprise light path part and circuit part, light path part connects successively and comprises that the Frequency Adjustable semiconductor laser is as light source, the polarizer, polarization tube, analyzer and photoelectric cell; Circuit part comprises photoelectric cell, pre-amplifier unit, secondary amplifying unit, frequency-selecting amplifying unit, amplitude limit clamping circuit, DSP data signal processing unit, stepper motor, the digital display unit that connects successively; The DSP data signal processing unit comprises DSP AD conversion unit, DSP signal generating unit, DSP digital storage unit, DSP data processing unit; The high-frequency signal that DSP signal generating unit in the DSP data signal processing unit produces is loaded on the Frequency Adjustable semiconductor laser, sends the signal drive stepping motor simultaneously, and stepper motor drives analyzer and rotates; Amplitude limit clamping circuit output signal connects the DSP AD conversion unit in the DSP data signal processing unit, after the DSP AD conversion unit is digital signal with analog signal conversion, output to DSP digital storage unit storage assembly, output to the digital display unit video data after the signal that the DSP data processing unit stores the DSP digital storage unit is handled.

2. the measuring method based on the laser frequency modulation polarimeter of data-signal processing comprises the laser frequency modulation polarimeter of handling based on data-signal, it is characterized in that measuring method specifically comprises the steps:

1) when not adding test substance, adjusts the polarizer and analyzer quadrature and fixing;

2) after test tube adds optical active substance, the DSP signal generating unit produces the square-wave signal of high frequency f, be loaded into the Frequency Adjustable semiconductor laser, modulating frequency be f laser through the polarizer become line polarisation, line polarisation through the optical active substance in the polarization tube after rotation pass through analyzer again, impinge upon on the photoelectric cell, photoelectric cell is that to change frequency into be the f ac signal for the light signal of f with frequency;

3) frequency is that the f ac signal enters AD conversion unit successively and is converted to digital signal and is input to the DSP data storage cell after the input protection of frequency-selecting, amplitude limit and the clamping circuit of the amplification of pre-amplifier unit, secondary amplifying unit, frequency-selecting amplifying unit;

4) the DSP signal generating unit sends the signal drive stepping motor and drives the analyzer rotation, and AC signal intensity changes, repeating step 3, and DSP data storage cell record stores each signal;

5) the DSP data processing unit is handled the signal that the DSP digital storage unit stores, decompose by the FFT fast Fourier, and then digital filtering, method by the envelope detection amplitude that to obtain a frequency be the f signal and the curve of stepper motor rotational angle at last, actual curve is carried out match, finally calculate angle of rotation and then learn solution concentration.

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