NASA’s Glenn Research Center is offering a sensor and actuator networking innovation applicable to smart vehicle or component control. This innovation requires no additional connectivity beyond the wiring providing power. This results in lower system weight, increased ease and flexibility for system modifications and retrofits, and improved reliability and robustness. The technology was specifically designed for harsh, high-heat environments, but has applications in multiple arenas. The device is compatible with most communication protocols.
The innovation consists of both a device and a technique. The device is radiation hard, and capable of withstanding temperatures up to 225 °C using available silicon-on-insulator semiconductor components. The technique is a method of modulating a signal to be placed on a DC power bus.
The signal is modulated by on-off keying, and uses capacitive coupling. The demodulation is accomplished using an asynchronous quadrature detection technique. The technique relies on a quasi-discrete Fourier transform that occurs by using the quadrature components of the carrier frequency as generated by the microcontroller, and as a function of the selected crystal frequencies driving its oscillator. The detected signal is changed into a direct current using an absolute value circuit containing no diodes (diodes can’t operate at high temperatures). The local power for the circuit is derived from a 5-volt regulator whose input is the supply rail. The data imposed upon the supply rail does not substantially present itself upon the local power rail of the circuit, because the lower excursions are above the dropout voltage of the regulator and also within the regulator’s power supply rejection specifications.
The device can draw power for itself and associated sensors and actuators from an existing power bus, communicate with similar devices or a central processor by placing a signal on the same power bus, make smart decisions within its operational loop, and affect control outputs to associated sensors and actuators. There is no limit to the number of sensors/actuators that could be placed in the network. All of this can be accomplished in a high-heat (up to 225 °C) environment with a bandwidth range of 1500 bps, ideal for environments such as jet engines, smelting operations, or deep drilling.
The ability to draw power and communicate over a power bus reduces weight and mass. With less wiring, the risk of interconnection breakdown and failure diminishes. In addition, the system is less susceptible to noise because it operates in a lower, unused frequency spectrum — it can withstand a noise-to-signal ratio of 20 dB. This innovation’s simplicity and off-the-shelf components make it suitable for multiple applications.
Potential applications include use in jet engines, oil field services, power turbines, biomedical devices, nuclear power plants, factory automation, and solar power collectors.