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The original meaning of telemeter, and still one of the main uses of the word, was a device used to measure distances to remote objects, that is, a rangefinder. Originally optical devices used in surveying, they soon found military applications in rangefinding, especially naval gunnery. More generally, a telemeter is a device used to remotely measure any quantity. It consists of a sensor, a transmission path, and a display, recording, or control device. Telemeters are the physical devices used in telemetry. Electronic devices are widely used in telemetry and can be wireless or hard-wired, analog or digital. Other technologies are also possible, such as mechanical, hydraulic and optical.〔Bakshi ''et al.'', pages 8.1-8.3〕 ==History== The first rangefinder telemeter was invented by James Watt in 1769 and put to use in 1771 in surveying canals. Watt called his instrument a ''micrometer'', a term now used with a different meaning in engineering. It consisted of two parallel hairs in the focal plane of a telescope eyepiece crossing an upright hair. At the point to be measured, two sliding targets on a surveyor's rod were adjusted to align with the hairs in the telescope. The distance to the rod could then be determined from the distance between the targets on the rod by trigonometry.〔Dickinson, pages 56, 75-76〕 Several others have been credited with the invention of the rangefinder telemeter at one time or another. The Royal Society of Arts gave an award to W. Green for its invention in 1778, even though they were made aware of Watt's priority.〔Dickinson, pages 76-77〕 Alexander Selligue is often mistakenly credited with the invention. Selligue did invent a telemeter in 1821 and is responsible for coining the term.〔Johann Gottfried Dingler, (''Polytechnisches Journal'' ), volume 8, page 121, Stuttgart: Cotta 1822 (in German)〕 In 1781 Georg Friedrich Brander invented the coincidence telemeter. Two mirrors set a distance apart horizontally and forming two images in the same eyepiece. This rangefinder does not require a measuring rod at the target and could perhaps be considered the first true telemeter. In 1790 Jesse Ramsden invented a half-image range finder. In 1899 Carl Pulfrich at Carl Zeiss AG invented the stereo telemeter.〔Deumlich, page 15〕 Many authors place the beginning of telemeters (in the general sense) in the steam age, although they were not called such at the time. Examples of these are James Watt's (1736-1819) additions to his steam engines of the mercury pressure gauge and the fly-ball governor.〔Kopp, page 494 Kirby, pages 167-169〕 By the late 19th century the term had been thoroughly hijacked by electrical engineers applying it to electrically operated devices measuring many other quantities besides distance. These included such sensors as the thermocouple (from the work of Thomas Johann Seebeck), the resistance thermometer (by William Siemens based on the work of Humphry Davy), and the electrical strain gauge (based on Lord Kelvin's discovery that conductors under mechanical strain change their resistance) and output devices such as Samuel Morse's telegraph sounder and the relay. In 1889 this led the Institution of Civil Engineers to suggest that the term for a rangefinder be replaced with tachometer.〔''Minutes of Proceedings of the Institution of Civil Engineers'', volume 95, part 1, page 207, Institution of Civil Engineers (Great Britain) 1889.〕 In the 1930s use of electrical telemeters grew rapidly. The electrical strain gauge was widely used in rocket and aviation research and the radiosonde was invented for meteorological measurements. The advent of World War II gave an impetus to industrial development and henceforth many of these telemeters became commercially viable.〔Kopp, page 497〕 Carrying on from rocket research, radio telemetry was used routinely as space exploration got underway. Spacecraft are in a place where a physical connection is not possible, leaving radio or other electromagnetic waves (such as infrared lasers) as the only viable option for telemetry. During manned space missions it is used to monitor not only parameters of the vehicle, but also the health and life support of the astronauts.〔Tsiao, pages xxxii-xxxiii〕 During the Cold War telemetry found uses in espionage. US intelligence found that they could monitor the telemetry from Soviet missile tests by building a telemeter of their own to intercept the radio signals and hence learn a great deal about Soviet capabilities.〔MacKenzie, page 235〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「telemeter」の詳細全文を読む スポンサード リンク
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