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外文翻译--数字技术在***传感器中的应用
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中英文翻译英语原文Application of Digital Techniques in Ultrasonic Sensor1/ INTRODUCTIONIt is necessary for a number of applications to perform distance measurements/ Ultrasonic sensors are a state-of=the art choice to effectively solve this problem in different engineering fields/ such as medical imaging/ robot navigation/ flow velocity/ fluid level measurement and so on/ Although different kinds of measuring systems and sensors have been used for the specific applications respectively/ there are problems related to echo detection in every case/ attenuation and beam spreading/ presence of noise and interference/ sensitivity to temperature and humidity/ poor resolution/In many applications/ the time elapsed between the stimulus ultrasonic wave and its echo is taken as the basis of the measurement/ that is / the main operating principle is the estimation of the time of flight (ToF)/ the transmitting ultrasonic transducer transmits an ultrasonic pulse/ the pulse propagates through the transmission medium (air/ water/ etc) and is echoed by a suitable reflector/ The echo pulse is received by the receiving transducer/ which may be the same transmitting transducer/ So the distance from the transmitter to the reflector can be estimated indirectly by the formula/ (1)where v is the propagation velocity of the ultrasonic wave in the medium/Another principle is the phase shift method/ Here/ the transmitter generates a continuous wave/ who is reflected by an object/ and whose echo is detected by a separate receiver/ By computing the phase shift between the transmitted and the received continuous wave/ the distance is evaluated to within a wavelength/Pulse-echo and continuous wave techniques are widely known as the represents of the two measuring principles/ Continuous wave technique is more accurate/ but more expensive due to complex hardware used to measure the phase and due to the difficulty in determining the number of integer wavelengths/ As a result/ the pulse=echo technique is often used in commercial systems for industrial application/ Therefore/ this paper puts an emphasis on the pulse-echo technique/From the formula (1)/ we have concluded that those factors affecting v and Tf are the sources of the distance measurement uncertainty/ The variation of v doesnt only depend on the relative humidity and temperature/ but also on some chemical and physical parameters of the fluid/ For these effects/ different techniques have been developed successfully to compensate them satisfactorily/ so the critical point of the whole measurement procedure is the ToF estimation/ Many methods have been proposed to improve the ToF measurement accuracy/ Some require complicated/ not flexible and very expensive hardware to make the ToF measurement higher accuracy/ However/ others use sophisticated digital techniques/ that is/ digital signal processing software to do the same thing/ From the viewpoint of the engineering application/ it is not only possible/ but also feasible to improve ToF estimation using digital techniques/In this paper/ firstly/ the basic theories of these digital techniques are presented/ including some mathematical formula/ Then/ the applications of these digital techniques for the ultrasonic distance measurement is described/ Finally/ a objective assessment of the methods through analyzing both the systematic and random errors is given2/ SIGNAL MODEL AND ITS BUILDINGAs for the pulse -echo method / in the most engineering applications/ require only one transducer as both the transmitter and receiver/ That is it offers a simple and low cost solution/ But at the same time/ it may result in low accuracy owing to the error of the ToF estimation/ How to improve its accuracy but not use complex/ expensive additional hardware? In fact/ this problem can be solved by using cheap software signal processing/ Therefore/ the key of this problem is /of course/ the ToF estimation/To solve this problem/ it is necessary to set up a suitable mathematical model of the transmitted ultrasonic pulse/ (2)where As/ fs and s are the signal amplitude/ frequency and phase respectively/ while m and n are the parameters of the characters of ultrasonic transducer itself/ For the actual transducer/ both m 0 and u 0 is an absolute fact/At the same time / a suitable mathematical model of the reflected ultrasonic pulse must be considered to be written as follows/ E(t) = Ar(t-TfTe-(t-Ts)lu cos2xfs(t-Tf) + r (3)where Ar/ r are the amplitude and the phase of the reflected echo signal/ Tf is the ToF/To perform ToF measurement/ we must consider the model of the whole ultrasonic signal/ including both/the transmitted and the reflected pulse/ which can be represented by the equation/ (4)where 0 T and 0 F are the sampling periods for the time and frequency domain respectively/ and k n/ are integers/After STFT has mapped a one-dimensional signal of timex(t) / onto a two-dimensional function of time and frequency ) / ( f t X / what we do next is the envelope extraction/ The first step is to choose a suitable frequency s f ( when using the frequency s f / S/N is the maximum and the interference is the minimum )/ which always be the resonant frequency of the sensor/ The second step is to find out the magitude function of the STFT at the frequency s f of the signal x(t) / that is the envelope we need/3/ CORRELATION METHOD AND ToF ESTIMATIONAfter recovering the envelope from the distorted and noisy non-stationary signal/ The next work is to complete the ToF estimation/ Several techniques can be used to accomplish the task of the ToF estimation/ The traditional approach used in the most ultrasonic sensors is the threshold method/ A threshold level is settled/ and the ToF is considered to be measured when the threshold is first exceeded by the signal or its envelope/ Although it has proved to be simple and cheap/ this technique may suffer from poor resolution/ particularly the echo pulse has been greatly attenuated/The correlation technique is a kind of more sophisticated technique for applications requiring high accuracy/ which bases the ToF estimation on the search of the relative maximum in the cross-correlation function between the transmitted signal and the echo signal/ According to the index of the maximum value of the correlation function/ the time delay between the two signals is obtained/ The correlation function is defined as/ (5)when the value of ) (hT C is the maximum/ the ToF is hT / (6)Considering the procedure of the sampling data/ actually/ the f T estimation can be expressed in the form/ (7)where h is the integer part of ) 5 / 0 / ( + T Tf / and is a real number in the interval ) 5 / 0 / 5 / 0 ? / a suitable measurement algorithm must be used to evaluate exactly the real number / It is possible to estimation the fraction number through a suitable interpolation technique/ The second-order approximate interpolation determines the parameter as/ (8)the equation (1) can be expressed as/ (9)4/ SIMULATION AND ERROR ANALYSISIn order to validate the proposed method/ a realistic simulation must be setup to mirror the characters of an actual ultrasonic sensor/ assuming a sampling frequency M f = 8MHZ/ an ultrasonic sensor frequency fs =550KHZ /an ultrasonic wave speed in the medium s m v / 1390 = / the distance resolution is/ according to the equation (1)/ 0/087mm / The error analysis can be implemented on the computer simulations/4/1 Systematic component of errors in ToF estimationThe finite sampling frequency during the procedure of the A/D conversion make the ToF estimation inaccurate/that is/ the time resolution error of system is a error source for the ToF estimation/ This is a systematic error/which can be thought as a function of the time resolution/From the equation (5)/ this ideal resolution error can be written as/ (10)that corresponds to a maximum distance error equal to mm 043 / 0 / When the ToF is a multiple of the sampling period ( )/ the error will be zero/According to the equation (6)/ the result obtained by computer simulations confirm that the interpolation method make the time resolution error to a minimum value/ As a result/ the systematic error in distance measurement can be written as follows/ (11 ) 4/2 Random component of errors in ToF estimationIn the practical applications/ the existence of noise is a cause of ToF inaccuracy/ We can assume that the noise is a white noise/ From the viewpoint of energy/ low SNR leads to high noise intensity/ For the correlation method/ it is less sensitive to noise due to the inherent cancellation of zero-mean random effects itself/5/ CONCLUSIONSThe use of dedicated digital techniques proved to be essential for ultrasonic sensors/ A suitable measurement procedure have been set up allowing the performance of the proposed techniques/ With regard to envelope extraction/ the STFT is a good choice/ The STFT filter out the noise/ and recover the optimized envelope// the correlation method is better than the threshold method due to better performance both in terms of systematic error (time resolution) and in terms of random error (noise) for echo detection/ACKNOWLEDGMENTSThe authors would like to thank the reviewers for their suggestions that improved the readability of this paper/REFERENCES1 M/ Parrila/ J/J/ Anaya/ C/ Fritsch/ Digital signal processing techniques for high accuracy ultrasonic range measurements/ IEEE Trans/ Instr/ Meas/ IM-40 (4) (1991) 759/2 D/ Marioli/ C/ Narduzzi/ C/ Offelli/ D/ Petri/ A/ E Sardini/ Digital time-of-flight measurement of ultrasonic sensor/ IEEE Trans/ Instr/ Meas/ IM-41 (1) (1992) 93/3 M/ G/ Duncan/ Real-time analytic signal processor for ultrasonic non-destructive testing/ IEEE Trans/ Instr/ Meas/ IM-39 (6) (1990) 1024/4 G/ Betta/ P/ Daponte/ Detection of echoes in noisy environments for multiplayer structure characterization/ IEEE Trans/ Instr/ Meas/ IM-42 (4) (1993) 834/5 P/ Daponte/ G/ Fazio/ A/ Molinaro/ Detection of echoes using time-frequency analysis techniques/ IEEE Trans/ Instr/ Meas/ IM-45 (1) (1996) 30/6 L/ Cohen/ A time-frequency distributions-A review/ Proc/ IEEE IM-77 (1) (1989) 941/8-bit Microcontroller with 4K Bytes Flash AT89C51Features Compatible with MCS-51 Products 4K Bytes of In-System Reprogrammable Flash Memory Endurance/ 1/000 Write/Erase Cycles Fully Static Operation/ 0 Hz to 24 MHz Three-level Program Memory Lock 128 x 8-bit Internal RAM 32 Programmable I/O Lines Two 16-bit Timer/Counters Six Interrupt Sources Programmable Serial Channel Low-power Idle and Power-down ModesDescription:The AT89C51 is a low-power/ high-performance CMOS 8-bit microcomputer with 4K bytes of Flash programmable and erasable read only memory (PEROM)/ The device is manufactured using Atmels high-density nonvolatile memory technology and is compatible with the industry-standard MCS-51 instruction set and pinout/ The on-chipFlash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer/ By combining a versatile 8-bit CPU with Flash on a monolithic chip/ the Atmel AT89C51 is a powerful microcomputer which provides a highly-flexible and cost-effective solution to many embedded control applications/中文译文数字技术在***传感器中的应用1、 概述在完成测距的任务中有很多的方法可以应用,而运用***传感器便可以高效又巧妙的解决工程领域的此类问题,比如医学成像、航空(航海)遥控设备、流速测量、液位测量等等。虽然不同的测量系统和传感器有各自独特的应用,但是它们都是与***回波的探测相关的问题,即***的稀薄化和扩散、噪声和干扰的存在、对温度和湿度的敏感性以及稳定性。在众多的应用中,***发射和接受之间的时间差是测量的基础,也就是说,应用的基本工作原理是测量出时差,***发射传感器发射一个***脉冲,脉冲通过传播媒介(空气、液体等)到达适当的反射体而反射回来。回波脉冲又被接收传感器接收到,发射传感器和接收传感器可能是收发一体的。这样,***发射与反射之间的距离就可以有以下公式间接的计算出来: (1)这里v代表***在传播媒介中的传播速度。另一个测量原理是依据周期改变的方法。具体是,***发射器发出一列连续不断的波,这个波遇到障碍物就反射回来,反射波被另一个***检测到。通过计算连续波在发射与接收之间的周相移动就可以测出距离。回波法和连续脉冲技术被广泛认为是两种测量原理的体现。连续脉冲技术的精度更高一些,但是由于测量相位用到的复杂硬件和计算整数个波长的复杂性,这种方法就更昂贵一些。鉴于此,回波法在工业生产的商业系统中的应用更多一些。因此,本文重点介绍回波技术的应用。从公式(1)中我们可以看出与v和Tf相关的因素是引起测距不稳定的主要原因。V的变化不仅是与相对湿度和温度相关,而且与传播媒介的许多化学、自然参量相关。由于这些相关因素的存在,需要其他的一些技术来补偿这些影响以使得测量准确,因此,整个测量系统的核心是时间差的确定。许多方法被用来提高时间差的测量精度。有些方法使用昂贵的硬件可以提高测量的精度,但是复杂而且不灵活;而有些方法使用传统的数字技术,即利用数字信号处理软件完成测距的目的。从工程应用的角度来看,利用数字技术提高时间差的精度既是可能的也是可行的。本文中,首先提出了数字技术的理论,包括一些数学公式。接着描述了这些数字技术在***测距中的应用。最后,通过分析系统误差和随机误差给出了对这种方法的客观评价。2/模型及其组成就回波法来说,在大多数工程应用中,是采用收发一体的传感器。就是说它提供了一种低成本的方法。与此同时,由于它在时差计算中的错误使得测量精度下降。如何在不使用额外硬件的情况下能提高它的精度呢?事实上,这个问题可以通过使用低成本的信号处理软件。因此,这个问题的核心当然也是时差的计算。为了解决这个问题,建立***发射脉冲合适的数学模型是必要的。如下图所示: (2)As/ fs和s分别是脉冲振幅、频率和相位,m和n是***传感器的固有参数。对于实际的传感器,必须满足m 0和 u 0。同时,***接收脉冲也需要建立合适的数学模型,具体如下: (3)这里Ar/ r分别是反射波的振幅和频率。Tf是时差。为了测出时差,我们必须考虑整个***信号的模型,包括发射脉冲和接收脉冲。具体如下等式所示: (4)这里T0和F0分别是时间和频率的取样周期,k/n都是整数。在我们作出***发射接收关于时间的单独曲线X(t)基础上,作出他们关于时间和频率的二维函数X(t,f),接下来我们要做的是把他们结合起来。第一步是选择合适的频率fs (当使用频率fs时,S/N是最大量而干扰是
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