Motor position sensing is a critical application in a number of systems. Galvanically isolated sensors for motor position sensing are strongly favored in both industrial and extreme-environment applications. Two examples of these sensors are resolvers and linear variable differential transformers (LVDTs). Both of these utilize a transformer with a primary and two secondary windings whose coupling constants are variable with either shaft angle (for the resolver) or position (for the LVDT). These sensors are utilized by driving the primary winding with a sinusoidal signal and measuring the relative amplitudes of the secondary winding outputs. The resulting output waveforms have wide range (up to ±20 V for some applications), and are usually ground-referenced. It is thus critical to have a signal-conditioning interface circuit that can sense voltages across wide ranges and convert them to voltages that a standard integrated circuit can process.

A wide-input-range signal-conditioning interface is disclosed for use in extreme environments. This signal-conditioning interface uses on-chip resistors to convert the large voltage input signals to currents, which are then processed and converted back to voltage for further operations.

A wide-temperature, wide-input-range sensor at the time of this reporting did not exist in the literature. This innovation allows this operation to take place near the motor and sensor in the ambient environment, reducing noise and power.

Wide-temperature and extreme-environment electronics are crucial to future missions. These missions will not have the weight and power budget for heavy harnesses and large, inefficient warm boxes. In addition, extreme-environment electronics, by their inherent nature, allow operation next to sensors in the ambient environment, reducing noise and improving precision over the warm-box-based systems employed today.

Many industrial systems rely on precise motor control for correct operation. This innovation facilitates motor control in extreme and robust environments by providing an interface through which galvanically isolated sensors can be more readily measured.

This work was done by Jeremy A. Yager, Edward H. Kopf Jr., and Mohammad Mojarradi of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48501


This Brief includes a Technical Support Package (TSP).
Wide-Input-Range Signal-Conditioning Input Interface for Motor Position Sensing in Extreme Environments

(reference NPO48501) is currently available for download from the TSP library.

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