Editing Telemetry (section)

===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>