CHAPTER 12ELECTRONIC SURVEYING EQUIPMENTChapter 12 of the EA3 TRAMAN introduced youto electronic surveying equipment, specificallyelectronic distance-measuring equipment. This chapteris intended to supplement what you learned in the EA3TRAMAN discussion, and, in addition, introduces youto the basic principles and uses of other types ofelectronic surveying equipment.As a rule, the EA seldom has the need or opportunityto use any of the equipment discussed in this chapter;however, when the need and occasion arise, the EAshould have at least a basic familiarity with the differentelectronic equipment used in surveying. This chapterprovides that familiarization.ELECTRONICDISTANCE-MEASURING (EDM)EQUIPMENTWhen electronically determining the straight-linedistance (horizontal or slope) between two points orstations, you use equipment that (1) sends an electronicimpulse of known velocity or rate of speed and (2)measures the time it takes for the impulse to travel thelength of the interval between the points. Then, by usingthe well-known equation of distance = rate x time, thelength of the interval is determined.Two types of electronic distance meters (simplyreferred to as EDMs) are commonly used. They are theelectromagnetic (microwave) instruments and theelectro-optical (light wave) instruments. In this section,we will briefly discuss both types of instruments;however, since there are many different makes andmodels of EDMs on the market and since you shouldalways study the manufacturer’s operating instructionsbefore you try to use the equipment, only the basicprinciples of the operation and use of EDM equipmentis covered. For in-depth discussions of EDM principles,you should read publications, such as Surveying Theoryand Practice, by Davis, Foote, Anderson, and Mikhail.ELECTROMAGNETIC (MICROWAVE)EDM INSTRUMENTSElectromagnetic EDMs, first1950s, use high-frequency radiodeveloped in thewaves. The firstgeneration of this equipment was very precise formeasuring long distances; however, it was too bulky andheavy for the practicing surveyor’s needs. Over theyears, the equipment has undergone rapid improvementto the extent that modern electromagnetic EDMs aresmaller, more portable, and are being equipped withdirect readout capability.When used, two identical and interchangeableinstruments, such as shown in figure 12-1, are setup atboth ends of the line that you are measuring. This linemust be unobstructed, but intervisibility is not required;so, you can make observations in fog or during otherunfavorable weather conditions. As illustrated in figure12-2, the sending (master) instrument transmits a seriesof modulated radio waves to the receiving (remote)instrument. The remote instrument interprets thesesignals and sends them back to the master unit thatmeasures the time required for the radio waves to makethe round trip. The distance is computed based on thevelocity of the radio waves. Because this velocity isaffected by atmospheric conditions, corrections fortemperature and barometric pressure are appliedaccording to the operating instructions provided withthe equipment.ELECTRO-OPTICAL (LIGHT WAVE)EDM INSTRUMENTSElectro-optical EDMs use the velocity of lightwaves to determine the distance between two points.The earliest of these instruments, typified by theGeodimeter, was developed during the same decade asthe electromagnetic EDMs. Figure 12-3 shows anexample of a Geodimeter. Like the electromagneticinstruments, the first generation of electro-opticalinstruments were heavy, bulky, and not well suited to theneeds of the practicing surveyor; however, through laterdevelopment, modern electro-optical EDMs aresmaller, lighter, easier to use, and require less power.Modern short-range instruments have ranges from 0.3miles to 3 miles. Longer range instruments, usingcoherent laser light, have ranges from 50 feet to 36miles.To use an electro-optical EDM, you set up theinstrument at one end of the line being measured and a12-1
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