Telemetry

Telemetry, in engineering, the use of electrical or electronic equipment for detecting, collecting, and processing physical data of one form or another at a given site, and then relaying this data to a receiving station at another site where the data can be recorded and analysed. One obvious use of telemetry, for example, is in the measuring, relaying, and recording of physical conditions encountered or produced by high-speed aircraft, rockets, and spacecraft. Such data might include air temperatures, wind speeds, or radiation intensities in outer space.

The matter of distance in telemetry is relative, however, because such systems may also be employed for obtaining data from sites that are near to the receiving instruments but that are difficult, impossible, or dangerous for human observers to encounter. For example, biological sensors of various kinds may be used within the human body to transmit information on medical conditions to detectors placed outside the body. Other examples include the use of telemetry for running tests of engines, for detecting flaws or changing conditions in industrial systems, or for obtaining data from dangerously radioactive sites. Meteorologists make use of a wide range of telemetric devices to obtain information from the upper atmosphere for use in making their weather forecasts. Such meteorological uses were, in fact, the first to which the techniques of radio telemetry were applied.

In any telemetric system, the equipment used must be able to make a measurement of a physical quantity, produce a signal that can be modified in some way to carry the measured data, and relay this encoded signal over some form of transmission link. The receiving equipment must then be able to decode the signal and to display it in some format for analysis and, probably, for recording. Usually more than one signal must be sent over the transmission link at any one time, in which case some form of multiplexing must be used. This can be done by employing different frequency bands for the measurement of different quantities or by splitting up the signal into discrete time intervals to which the quantities to be measured are assigned. The coding techniques used are commonly digital; the use of pulse-code modulation, by which continuous waves are transformed into a binary-code signal, has been enhanced in recent decades by the advances made in the digital computer field and in microelectronics.