arteries are available solidly encapsulated in epoxy resin to withstand almost as rugged environments as the telemeter itself. In a moving or rotating application, stationary magnets can be placed so that they generate electricity in a moving coil and are used to provide automatic power generation. If this method is not feasible, a stationary coil can be placed in the vicinity of the transmitter and fed electrical energy at a high frequency, so that its field can easily couple into a me coil in almost any environment. The station even encompassing a whole room; usually only one turn of wire is necessary. The stationary coil may also be made extremely small, 14 to 12 in. in diameter, and coupled to the end of a rotating shaft. These power supplies and coil configurations are standard available units Power plants In power plants, coal is fed in turn to a number of hoppers by conveyor belt. a tripper on the conveyor belt diverts the coal into a particular hopper until it is full. Either an operator or a mechanical sensing device determines when the hopper is full, and a signal is transmitted to the conveyor to move onto the next hopper. Before telemetering equipment was in use, costly accidents could occur if the operator should be away momentarily or if the sensor failed to function As much as six tons of coal a minute could overflow onto the power station floor 6 To prevent this, pressure switches are installed in the tripper chute to activate a radio transmitter if coal ks up into the tripper. The transmitter sends its signal to a receiver located at the conveyor belt and sounds an alarm. This type of control is difficult if not impossible to achieve by wired power connections because the tripper is moving and because the corrosive coal dust atmosphere attacks the wires. For this reason, a radic transmitter equipped with long-life batteries is mounted on the tripper. The receiver at the control end powered by ac Subcarrier tone( frequency) coding is used to eliminate the effects of interference and noise, giving positive protection at all times 77. 4 Limitations of Telemetry The preceding paragraphs describe a number of the requirements placed upon telemetry systems by the transducers and quantities being measured. Unfortunately, the development of telemetry has not been such to satisfy all requirements, and in many cases the telemetry system seriously limits the measurement. A compromise is therefore required between telemetry capabilities and the requirements of measurement. The ortcomings and limitations of the telemetry system place restrictions upon measurements above and beyond those encountered in the laboratory when the telemeter is not used In the first place, an electrical output from the measuring device is required in order that the measurement may be placed on a radio link. Consequently transducers that produce an electrical output on one form or another are necessary. Also, the telemetry system may not be perfectly stable down to zero frequency(dc), and transducers and methods of measurement must be chosen to minimize the effects of drift. Overmodulating the subcarrier, or the time-division multiplexer, may also affect adjacent channels, as well as produce erroneous data in its own channel. If various measuring devices are switched, the switching transients must be minimized, or the accuracy of the telemetry system may be impaired. When mechanical commutators or time multiplexers are used, the measurement of the time occurrence of the event, such as the impact of cosmic particles or the receipt of a guidance pulse, is made more difficult and the time ambiguity of the multiplexed system is a serious limitation The measurement of a large number of parameters requires extensive and bulky equipment, unless the be combined in groups of similar inputs to minimize the signal conditioning required. This fact generally dictates a relatively standard transducer rather than an optimum one for each particular mea surement The bandwidth of the measurement, or the frequency with which the measured quantity changes, is also eriously limited by the telemeter. In the FM/FM telemeter, the permissible bandwidth varies from a relatively low value on the lower-frequency subcarriers to a reasonably high value on the high-frequency subcarriers. The bandwidth of the measurement must not exceed the subcarrier bandwidth limitations or sidebands will be generated in adjacent channels, thereby reducing the accuracy of other measurements (if multiplexed),or interference with adjacent RF signals will be caused e 2000 by CRC Press LLC© 2000 by CRC Press LLC batteries are available solidly encapsulated in epoxy resin to withstand almost as rugged environments as the telemeter itself. In a moving or rotating application, stationary magnets can be placed so that they generate electricity in a moving coil and are used to provide automatic power generation. If this method is not feasible, a stationary coil can be placed in the vicinity of the transmitter and fed electrical energy at a high frequency, so that its field can easily couple into a moving coil in almost any environment. The stationary coil ring may be large, even encompassing a whole room; usually only one turn of wire is necessary. The stationary coil may also be made extremely small, 1⁄4 to 1⁄2 in. in diameter, and coupled to the end of a rotating shaft. These power supplies and coil configurations are standard available units. Power Plants In power plants, coal is fed in turn to a number of hoppers by conveyor belt. A tripper on the conveyor belt diverts the coal into a particular hopper until it is full. Either an operator or a mechanical sensing device determines when the hopper is full, and a signal is transmitted to the conveyor to move onto the next hopper. Before telemetering equipment was in use, costly accidents could occur if the operator should be away momentarily or if the sensor failed to function. As much as six tons of coal a minute could overflow onto the power station floor. To prevent this, pressure switches are installed in the tripper chute to activate a radio transmitter if coal backs up into the tripper. The transmitter sends its signal to a receiver located at the conveyor belt and sounds an alarm. This type of control is difficult if not impossible to achieve by wired power connections because the tripper is moving and because the corrosive coal dust atmosphere attacks the wires. For this reason, a radio transmitter equipped with long-life batteries is mounted on the tripper. The receiver at the control end is powered by ac. Subcarrier tone (frequency) coding is used to eliminate the effects of interference and noise, giving positive protection at all times. 77.4 Limitations of Telemetry The preceding paragraphs describe a number of the requirements placed upon telemetry systems by the transducers and quantities being measured. Unfortunately, the development of telemetry has not been such as to satisfy all requirements, and in many cases the telemetry system seriously limits the measurement. A compromise is therefore required between telemetry capabilities and the requirements of measurement. The shortcomings and limitations of the telemetry system place restrictions upon measurements above and beyond those encountered in the laboratory when the telemeter is not used. In the first place, an electrical output from the measuring device is required in order that the measurement may be placed on a radio link. Consequently, transducers that produce an electrical output on one form or another are necessary. Also, the telemetry system may not be perfectly stable down to zero frequency (dc), and transducers and methods of measurement must be chosen to minimize the effects of drift. Overmodulating the subcarrier, or the time-division multiplexer, may also affect adjacent channels, as well as produce erroneous data in its own channel. If various measuring devices are switched, the switching transients must be minimized, or the accuracy of the telemetry system may be impaired. When mechanical commutators or time multiplexers are used, the measurement of the time occurrence of the event, such as the impact of cosmic particles or the receipt of a guidance pulse, is made more difficult and the time ambiguity of the multiplexed system is a serious limitation. The measurement of a large number of parameters requires extensive and bulky equipment, unless the parameters can be combined in groups of similar inputs to minimize the signal conditioning required. This fact generally dictates a relatively standard transducer rather than an optimum one for each particular mea￾surement. The bandwidth of the measurement, or the frequency with which the measured quantity changes, is also seriously limited by the telemeter. In the FM/FM telemeter, the permissible bandwidth varies from a relatively low value on the lower-frequency subcarriers to a reasonably high value on the high-frequency subcarriers. The bandwidth of the measurement must not exceed the subcarrier bandwidth limitations, or sidebands will be generated in adjacent channels, thereby reducing the accuracy of other measurements (if multiplexed), or interference with adjacent RF signals will be caused