77 Telemetry 77.1 Introduction to Telemetry 77.2 Measuring and Transmitting 77.3 Applications of Telemetry Power Sources. Power Plants 77.5 Transmitters and Batteries 77.6 Receivers and discriminators 77.7 Antennas and Total System Operation 8 Calibration 77.9 Telemetry Frequency Allocations 77. 10 Telemetry Antennas 77.11 Measuring and Transmitting 77.12 Modulating and Multiplexing Conrad H. Hoeppner 77 13 Passive Telemeters The Johns Hopkins University 77.14 The Receiving Station 77.1 Introduction to Telemetry Telemetry, or measurement at a distance, takes many and varied forms. It may use the principles of radio, electricity, optics, mechanics, or hydraulics to convey measurements made at one place to indicators, actuators, recorders, or computers at another. By far the most popular telemetry systems are electrical and use radio or wire links to convey information. In this respect, all of the considerations in the foregoing chapters on com munications apply, as well as considerations of antennas, power supplies and convertors, heat removal, and radio frequency interference. Additional considerations that are unique to telemetry are treated here The deeper an instrumented vehicle probes into the remote reaches of outer space, the more technologically spectacular seem the achievements of telemetry. There is still something exciting and uncanny about performing measurements of a physical quantity at a distant location and precisely reproducing them at a more convenient place for reading or recording them. Yet the vast distances spanned by telemetry signals are less challenging technically than the stubborn problems of almost sheer inaccessibility in some industrial applications to the quantities being measured. Signals from a missile-launched space probe soaring toward the sun are often easier to obtain than measurements from inside a stolid, earthbound motor only a foot or two away. To find the temperature of the spinning rotor, housed in a steel casing and surrounded by a strong alternating magnetic field, may require more ingenuity to transcend the operating environment than taking measurements from the most distant instrument payload speeding through the unaccommodating environment of space. The technology that has produced missile and space telemetry is also spawning new forms of industrial radio telemetry, capitalizing on the development of new transducers, powerful miniature radio transmitters, improved self-contained power sources, and better techniques of environmental protection. Simply enough, to telemeter is to measure at a distance. First, at the remote point, is needed a transducer, a device that converts the physical quantity being measured into a signal, usually an electrical one, so that it c 2000 by CRC Press LLC© 2000 by CRC Press LLC 77 Telemetry 77.1 Introduction to Telemetry 77.2 Measuring and Transmitting 77.3 Applications of Telemetry Power Sources • Power Plants 77.4 Limitations of Telemetry 77.5 Transmitters and Batteries 77.6 Receivers and Discriminators 77.7 Antennas and Total System Operation 77.8 Calibration 77.9 Telemetry Frequency Allocations 77.10 Telemetry Antennas 77.11 Measuring and Transmitting 77.12 Modulating and Multiplexing 77.13 Passive Telemeters 77.14 The Receiving Station 77.1 Introduction to Telemetry Telemetry, or measurement at a distance, takes many and varied forms. It may use the principles of radio, electricity, optics, mechanics, or hydraulics to convey measurements made at one place to indicators, actuators, recorders, or computers at another. By far the most popular telemetry systems are electrical and use radio or wire links to convey information. In this respect, all of the considerations in the foregoing chapters on com￾munications apply, as well as considerations of antennas, power supplies and convertors, heat removal, and radio frequency interference. Additional considerations that are unique to telemetry are treated here. The deeper an instrumented vehicle probes into the remote reaches of outer space, the more technologically spectacular seem the achievements of telemetry. There is still something exciting and uncanny about performing measurements of a physical quantity at a distant location and precisely reproducing them at a more convenient place for reading or recording them. Yet the vast distances spanned by telemetry signals are less challenging technically than the stubborn problems of almost sheer inaccessibility in some industrial applications to the quantities being measured. Signals from a missile-launched space probe soaring toward the sun are often easier to obtain than measurements from inside a stolid, earthbound motor only a foot or two away. To find the temperature of the spinning rotor, housed in a steel casing and surrounded by a strong alternating magnetic field, may require more ingenuity to transcend the operating environment than taking measurements from the most distant instrument payload speeding through the unaccommodating environment of space. The technology that has produced missile and space telemetry is also spawning new forms of industrial radio telemetry, capitalizing on the development of new transducers, powerful miniature radio transmitters, improved self-contained power sources, and better techniques of environmental protection. Simply enough, to telemeter is to measure at a distance. First, at the remote point, is needed a transducer, a device that converts the physical quantity being measured into a signal, usually an electrical one, so that it Conrad H. Hoeppner The Johns Hopkins University