Editing Telemetry (section)

==History==

The beginning of industrial telemetry lies in the [[Steam power during the Industrial Revolution|steam age]], although the sensor was not called ''telemeter'' at that time.<ref name=Kopp>Brian Kopp, "Industrial telemetry", in ''Telemetry Systems Engineering'', pages 493-524, Artech House, 2002 {{ISBN|1580532578}}.</ref> Examples are [[James Watt]]'s (1736-1819) additions to his steam engines for monitoring from a (near) distance such as the [[mercury pressure gauge]] and the [[fly-ball governor]].<ref name=Kopp/>

Although the original telemeter referred to a ranging device (the [[rangefinding telemeter]]), by the late 19th century the same term had been in wide use by electrical engineers applying it refer to electrically operated devices measuring many other quantities besides distance (for instance, in the patent of an "Electric Telemeter Transmitter"<ref>{{cite patent| country = US| number = 490012| status = patent| title = Electric Telemeter Transmitter.| gdate = 1893-01-17| fdate = 1891-11-21| inventor = Fernando J. Dibble| url = https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=490012A&KC=A&FT=D&ND=&date=18930117&DB=&locale=#}} {{Webarchive|url=https://web.archive.org/web/20220125123531/https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=490012A&KC=A&FT=D&ND=&date=18930117&DB=&locale= |date=2022-01-25 }}</ref>). General telemeters 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 [[electrical resistance|resistance]]) and output devices such as [[Samuel Morse]]'s [[telegraph sounder]] and the [[relay]]. In 1889 this led an author in the [[Institution of Civil Engineers]] proceedings to suggest that the term for the rangefinder telemeter might be replaced with [[tacheometer]].<ref>"The term telemeter, which was introduced by surveyors, has been appropriated to so great an extent by electricians, that it is likely to be abandoned by the former for the term tacheometer." (p.207), {{cite journal|last1=Gribble|first1=T G|title=Preliminary Survey in New Countries, as Exemplified in the Survey of Windward Hawaii. (Includes Appendices)|journal=Minutes of the Proceedings of the Institution of Civil Engineers|volume=95|issue=1889|year=1889|pages=195–208|issn=1753-7843|doi=10.1680/imotp.1889.20841|url=https://zenodo.org/record/2331506|access-date=2021-05-19|archive-date=2022-01-25|archive-url=https://web.archive.org/web/20220125123634/https://zenodo.org/record/2331506|url-status=live}}</ref>

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.<ref>Kopp, page 497</ref>

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 crewed space missions it is used to monitor not only parameters of the vehicle, but also the health and life support of the astronauts.<ref>Sunny Tsiao, ''Read You Loud and Clear: The Story of NASA's Spaceflight Tracking and Data Network'', Government Printing Office, 2008 {{ISBN|0160801915}}.</ref> During the [[Cold War]] telemetry found uses in espionage. US intelligence found that they could monitor the telemetry from [[Soviet Union|Soviet]] missile tests by building a telemeter of their own to intercept the radio signals and hence learn a great deal about Soviet capabilities.<ref>MacKenzie, *Donald MacKenzie, "The Soviet Union and strategic missile guidance", in ''Soviet Military Policy: An International Security Reader'', MIT Press, 1989 {{ISBN|0262620669}}.</ref>

===Types of telemeter===
Telemeters are the physical devices used in telemetry.  It consists of a [[sensor]], a transmission path, and a display, recording, or control device.  Electronic devices are widely used in telemetry and can be [[wireless]] or hard-wired, [[analog signal|analog]] or [[Digital data|digital]]. Other technologies are also possible, such as mechanical, hydraulic and optical.<ref>K.A.Bakshi A.V.Bakshi U.A.Bakshi, ''Electronic Measurements'', Technical Publications, 2008 {{ISBN|8184313918}}.</ref>

Telemetering information over wire had its origins in the 19th century. One of the first data-transmission circuits was developed in 1845 between the [[Tsardom of Russia|Russian Tsar]]'s [[Winter Palace]] and army headquarters. In 1874, French engineers built a system of weather and snow-depth sensors on [[Mont Blanc]] that transmitted real-time information to [[Paris]]. In 1901 the American inventor C.&nbsp;Michalke patented the [[Synchro|selsyn]], a circuit for sending synchronized rotation information over a distance. In 1906 a set of seismic stations were built with telemetering to the Pulkovo Observatory in Russia.  In 1912, [[Commonwealth Edison]] developed a system of telemetry to monitor electrical loads on its power grid. The [[Panama Canal]] (completed 1913–1914) used extensive telemetry systems to monitor locks and water levels.<ref>Mayo-Wells, "The Origins of Space Telemetry", ''Technology and Culture'', 1963</ref>

Wireless telemetry made early appearances in the [[radiosonde]], developed concurrently in 1930 by Robert Bureau in France and [[Pavel Molchanov]] in [[Russia]].  Molchanov's system modulated temperature and pressure measurements by converting them to wireless [[Morse code]]. The German [[V-2]] rocket used a system of primitive multiplexed radio signals called "Messina" to report four rocket parameters, but it was so unreliable that [[Wernher von Braun]] once claimed it was more useful to watch the rocket through binoculars.

In the US and the USSR, the Messina system was quickly replaced with better systems; in both cases, based on [[pulse-position modulation]] (PPM).<ref>Joachim & Muehlner, "Trends in Missile and Space Radio Telemetry" declassified Lockheed report</ref>
Early Soviet missile and space telemetry systems which were developed in the late 1940s used either PPM (e.g., the Tral telemetry system developed by OKB-MEI) or [[pulse-duration modulation]] (e.g., the RTS-5 system developed by NII-885).  In the United States, early work employed similar systems, but were later replaced by [[pulse-code modulation]] (PCM) (for example, in the Mars probe [[Mariner&nbsp;4]]).  Later Soviet interplanetary probes used redundant radio systems, transmitting telemetry by PCM on a decimeter band and PPM on a centimeter band.<ref>Molotov, E. L., ''Nazemnye Radiotekhnicheskie Sistemy Upravleniya Kosmicheskiymi Apparatami''</ref>