Telemetry is the automatic measurement and wireless transmission of data from remote sources. In general, telemetry works in the following way: Sensors at the source measure either electrical data (such as voltage or current) or physical data (such as temperature or pressure). These measurements are converted to specific electrical voltages. A multiplexer combines the voltages, along with timing data, into a single data stream for transmission to a remote receiver. Upon reception, the data stream is separated into its original components and the data is displayed and processed according to user specifications.
In 1912, the first telemetrics application in Chicago used telephone lines to transmit operational data from a power plant to a central office. Because telemetry was originally used in projects like this, the first telemetry systems were called supervisory systems. In 1960, the interrogation-reply principle was developed, which allowed a more selective transmission of data upon request. At that time, a telemetry transmitter consisted of a set of measuring instruments, an encoder that translated instrument readings into analog or digital signals, a modulator, and a wireless transmitter with an antenna. The receiver consisted of an antenna, a set of radio-frequency (RF) amplifiers, a demodulator and recording devices. Mainframe computers were used to process and store the received information.
Today, telemetry applications include measuring and transmitting data from sensors located in automobiles, smart meters, power sources, robots and even wildlife in what is commonly called the Internet of Things (IoT).