Telemetry

Telemetry covers the range of techniques for converting observations, made by sensors remote from the data collection and analysis facility, to a form that can be transmitted by an appropriate electromagnetic transmission facility. Early telemetry from, for example, guided missiles used various modulation techniques to put a continuously varying instrument reading onto a radio frequency received by an earth station. Extremely complex analog tape recorders, with a precise timing track, captured the information.

Later, as digital electronics became increasingly common, the telemetry carried information from multiple sensors, sampled repeatedly, and sent as bit streams. To receive signals from transmitters deep in space, fully steerable parabolic antennas, 34 meters in diameter, were common.

When the telemetry is on a moving vehicle, it is often necessary to have steerable directional antennas, sometimes very large, to stay focused on the vehicle's transmitter.

Especially when the sensors can be connected to terrestrial transmission facilities, they are often encapsulated in Internet Protocol packets and transferred via the public Internet or a virtual private network. Telemetry need not be for exotic applications such as "rocket science", but simply sending back the water level in a river or lake, or the position of an animal being tracked. System Control And Data Acquisition (SCADA) combines remote sensing and remote control.