Telemetry

Telemetry is the science of gathering information at some remote location and transmitting the data to a convenient location to be examined and recorded. Telemetry can be done by different methods: optical, mechanical, hydraulic, electric, etc. The mechanical methods, either pneumatic or hydraulic, have acceptable results for short distances and are used in environments that have a high level of electromagnetic interference and in those situations where, for security reasons, it is not possible to use electrical signals, for example, in explosive environments. More recently, use of optical fiber systems allows the measurement of broad bandwidth and high immunity tonoise and interference. Other proposed telemetry systems are based on ultrasound, capacitive or magnetic coupling, and infrared radiation, although these methods are not routinely used. The discussion in this chapter will be limited to the most-used systems: telemetry based on electric signals. The main advantage of electric over mechanical methods is that electrically based telemetry does not have practical limits regarding the distance between the measurement and the analysis areas and can be easily adapted and upgraded in already existing infrastructures. Electric telemetry methods are further divided depending on the transmission channel that they use as wire telemetry and wireless (or radio) telemetry. Wire telemetry is technologically the simplest solution. The limitations of wire telemetry are the low bandwidth and low transmission speed that it can support. However, it is used when the transmission wires can use the already existing infrastructure, as in most electric power lines that are also used as wire telemetry carriers. Wireless telemetry is more complex than wire telemetry, as it requires a final radio-frequency (RF) stage. Despite its complexity, it is widely used because it can transmit information over longer distances; thus, it is used in those applications in which the measurement area is not normally accessible. For most applications, the wireless nature of the system is implied when referring to telemetry. The largest area that led to the development of telemetry systems arose from defense and aerospace applications, specifically the development of rockets and ballistic missiles. Designers of these systems needed to monitor a large amount of data, while the rocket was in flight, and this task could only be achieved with sending the data wirelessly.