測繪工程畢業(yè)設計外文翻譯---水準尺和水準儀(存儲版)
【正文】 lectromagic energy upon which a reference frequency has been superimposed or modulated. The signal is returned from staion B to the revevier, so its trvel path is double the slope distance AB. In ,the modulated electromagic energy is represented by a series of sine waves having wavelength λ. Any position along a givenj wave can be specified by its phase angle, which is 0176。讀數(shù)在 713 英尺之間時，后面部分不必延伸出來；讀數(shù)在 713 英尺之間，則要延伸水準尺。戰(zhàn)標是附加在標尺上很小的、紅白相間的金屬卡。給儀器提供一些特殊的支持如林莊或平臺是必要的。這個過程要小心的重復幾次，直到望遠鏡轉到任意一對腳螺旋的方向氣泡都對中。在晚 上，儀器傳送可見，并且可精確 40km的距離。它是相當主觀的 ，但通常兩種方法都適用這種系統(tǒng)：短波和長波。 電磁能通過大氣依下列方式傳播： v=fλ（ 1）其中 v 是電磁波的速度，單位是 m/s ,f是電磁波的頻率，單位是赫茲； λ是波長，單位是米。 EDM 裝置在測量中，是通過測量相位變化來工作的，在這個過程中，反射波經(jīng)歷了一個 360o 的相變。調(diào)制電磁波是通過一系列的不確定波長的波來表示的。他們主要被用在海洋或水路測 量中，以及導航中大體上， EDM 測量距離是通過比較一條未知長度的邊到一條已知邊，調(diào)制電磁波波長實現(xiàn)的。 微波儀器，它傳送微波的頻率為 300035000HZ，相當于 到 長。 電子測距儀 近年來，測量中的主要進步是電子測距儀的發(fā)展，當已知波長的電波能從一條邊的一端傳播一另一端并返回時就發(fā)生了相變，這些裝置就是根據(jù)這些來測定長度的。通過向相反方向轉動兩個腳螺旋，水準氣泡粗略對中，氣泡將向左手大拇指方向移動。換句話說，他應該考慮到如何安置三角架的腿，以便他能舒服的站在腿的中間，測他所想的工作。一但工作完成，帶尺便可以重新移動或若卷起，而木條則可以扔掉。 在使用的幾種水準尺中有費拉德爾菲亞水準尺，芝加哥水準尺和佛羅里達水準尺，費拉德爾菲亞水準尺由兩部分組成，是最普通的一種。 however, the precision of thework should not be adversely affected if the bubble is centered each time a rod reading is taken. The first step in leveling a threescrew instrument is to turn the telescope untill the bubble tube is parallel to two of the screws. The bubble is centered by turning these two screws in opposite directions. Next, the telescope is turned so that the bubble tube is perpendicular to a line through screws. The bubble is centered by turning screw . These steps are repeated untill the bubble stays centered when the telescope is turned back and forth. Electronic Distance Measurements A major advance in surveying in recent years has been the development of electronic distancemeasuring instruments (EDMIs). These devices determine lengths based on phase changes that occur as eletromagic energy of known wavelength travels from one end of a line to the other and returns. The first EDM instrument was intronduced in 1948 by Swedish physicist Erik Bergstrand. His device, called the geodimeter(an acronym for geodetic distance meter), resulted from attempts to improve methods for measuring the velocity of light. The instrument transmetted visible light and was capable of accurately measuring distances up to about 25 mi (40km) at night. In 1957 a second EDM apparatus. the tellurometer. Designed by and introduced in South Africa, transmitted invisible microwaves and was capable of measuring distances up to 50 mi (80km) or or night. The potential value of these early EDM models to the Surveying profession was immediately recognized: houever, they were expensive and not readily portable for field oper
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