【正文】 可以增加DS18B20測量環(huán)境溫度模塊，如果想要增強(qiáng)系統(tǒng)的可靠性，可在軟硬件上采用抗干擾措施。溫度(℃)3020100102030100聲速（m/s）313319325323338344349386濕度對(duì)超聲波衰減程度的影響聲波傳播過程中，聲壓的幅度由于媒質(zhì)中聲吸收而衰減，聲強(qiáng)隨頻高衰減增加，進(jìn)而濕度對(duì)超聲波衰減程度有一定的影響。需要進(jìn)行硬件調(diào)試才會(huì)有所改善，但是不可能完全消除[1 16]。超聲波測距由于其能進(jìn)行非接觸測量和相對(duì)較高的精度，越來越被人們所重視。本文以檢測距離為目標(biāo)，對(duì)超聲波的工作原理、超聲波測距主要誤差來源作了相應(yīng)的分析。圍繞如何開發(fā)基于單片機(jī)的超聲波測距系統(tǒng)進(jìn)行了如下的工作：(1)探討了超聲波測量技術(shù)，分析了超聲波測距的誤差來源，提出了系統(tǒng)的總體設(shè)計(jì)思想。(3)在系統(tǒng)硬件設(shè)計(jì)的基礎(chǔ)上，對(duì)系統(tǒng)的軟件需要實(shí)現(xiàn)的功能進(jìn)行了分析，設(shè)計(jì)了系統(tǒng)的主程序流程，分析各個(gè)中斷程序和主程序之間的關(guān)系，用匯編語言和C語言逐個(gè)實(shí)現(xiàn)了各自的功能模塊。如果需要擴(kuò)大測距范圍，可以根據(jù)實(shí)際情況添加更合適的溫度傳感器。(3)超聲波探頭相對(duì)安裝位置的影響，渡越時(shí)間延遲造成的誤差及其他誤差源的存在，從軟件角度，使用一些數(shù)據(jù)處理算法，消除誤差干擾，提高測量精度。值此畢業(yè)論文完成之際，我謹(jǐn)向所有關(guān)心、愛護(hù)、幫助我的人們表示最誠摯的感謝與最美好的祝愿。論文的字里行問都傾注了導(dǎo)師的關(guān)懷和心血。此謹(jǐn)向老師致以誠摯的謝意和崇高的敬意。由于本人知識(shí)水平有限，文中難免有錯(cuò)誤和不完善之處，謹(jǐn)請(qǐng)讀者提出批評(píng)和指正。參考文獻(xiàn)[1] [D].華北電力大學(xué)碩士學(xué)位論文,2006:18頁 [2] 童峰，[J].廈門大學(xué)學(xué)報(bào)（自然科學(xué)版）.1998,34（4）：507512頁[3] [M].科學(xué)出版社,2003:612頁[4] [J].,(1)：1115頁[5] 常靜，[M].棉花加工技術(shù),2005:2223頁[6] 江 [M].清華大學(xué)出版社,2006 ：21150頁[7] 房小翠,王金鳳編著 .單片機(jī)實(shí)用系統(tǒng)設(shè)計(jì)技術(shù)[M]. 國防工業(yè)出社,1996:105110頁[8] [M].高等技術(shù)出版社,1998：492541頁[9] 陳 杰,黃 [M].高等教育出版社,2002。s characteristic. Practically all acoustic arrangements presently known for checking distances use a method of measuring the propagation time for certain information samples from the radiator to the reflecting member and back.The unmodulated acoustic(ultrasonic)vibrations radiated by a transducer are not in themselves a source of order to transmit some informational munication that can then be selected at the receiving end after reflection from the test member,the radiated vibrations must be this case the ultrasonic vibrations are the carrier of the information which lies in the modulation signal,.,they are the means for establishing the spatial contact between the measuring instrument and the object being measured.This conclusion,however,does not mean that the analysis and selection of parameters for the carrier vibrations is of minor the contrary,the frequency of the carrier vibrations is linked in a very close manner with the coding method for the informational munication,with the passband of the receiving and radiating elements in the apparatus,with the spatial characteristics of the ultrasonic munication channel,and with the measuring accuracy.Let us dwell on the questions of general importance for ultrasonic ranging in air,namely:on the choice of a carrier frequency and the amount of acoustic power received.An analysis shows that with conical directivity diagrams for the radiator and receiver,and assuming that the distance between radiator and receiver is substantially smaller than the distance to the obstacle,the amount of acoustic power arriving at the receiving area Pr for the case of reflection from an ideal plane surface located at right angles to the acoustic axis of the transducer es to （1）where Prad is the amount of acoustic power radiated,B is the absorption coefficient for a plane wave in the medium,L is the distance between the electroacoustic transducer and the test me mber,d is the diameter of the radiator(receiver),assuming they are equal,and c~is the angle of the directivity diagram for the electroacoustic transducer in the radiator. Both in Eq.(1)and below,the absorption coefficient is dependent on the amplitude and not on the intensity as in some works[1],and therefore we think it necessary to stress this difference.In the various problems of sound ranging on the test members of machines and structures,the relationship between the signal attenuations due to the absorption of a planewave and due to the geometrical properties of the sound beam are,as a rule,quite must be pointed out that the choice of the geometrical parameters for the beam in specific practical cases is dictated by the shape of the reflecting surface and its spatial distortion relative to some average position.Let us consider in more detail the relationship betweenthe geometric and the power parameters of acoustic beams for the most mon cases of ranging on plane and cylindrical structural members.It is well known that the directional characteristic W of a circular piston vibrating in an infinite baffle is a function of the ratio of the piston39。s directivity diagram.The directivity diagrm needed for a radiator is dictated by the maximum distance to be measured and by the spatial disposition of the test member relative to the other structural order to avoid the incidence of signals reflected from adjacent members onto the acoustic receiver,it is necessary to provide a small angle of divergence for the sound beam and,as far as possible,a smalldiameter two requirements are mutually inconsistent since for a given radiation frequency a reduction of the beam39。s axis is given by （6）where L is the least distance to the test surface.The specified value of Dmin corresponds to a radiator with a diameter （7）As seen from Eqs.(,6)and(7),the minimum diameter of thesonieatedspot at the maximum required distancecannot be less than two radiator ,with shorter distances to the obstacle the size of thesonicated surface is less. Let us consider the case of sound ranging on a cylindrically shaped object of radius problem is to measure the distance from the electroacoustic transducer to the side surface of the cylinder with its various possible displacements along the X and Y necessary angleαof the radiator39。s center from the acoustic axis,and Lmin is the minimum distance from the center of the electroacoustic transducer to the reflecting surface measured along the straight line connecting the center of the m e m b e r with the center of the transducer.It is clear that when measuring distance,therunningtime of the information signal is controlled by the length of the path in a direction normal to the cylinder3