Signal Processing of Multiplexed Optical PWM Signals for Sensor Arrays in Nuclear Environments

Abstract

The actionable data provided by the sensor arrays located throughout a plant provide a holistic online indication of reactor operation. Thus, these data greatly benefit the safe and effective generation of terrestrial nuclear power. This array includes sensors for monitoring coolant flow and pressure, temperature and heat transfer, radiation levels, structure health monitoring, and other critical parameters for reactor operation. Although sensors that measure these parameters have been developed, the electronics used in the pre-amplification and analog-to-digital conversion of the small signals they produce are extremely sensitive and susceptible to damage from the high temperatures and radiation environments present within nuclear reactors when power is being generated. The small signals from sensors in nuclear power plants are transmitted over long cable runs, which introduce dispersion artifacts into the signals of interest and electromagnetic interference (EMI) from lighting fixtures, pumps, mains electricity, and other e quipment. To overcome these challenges, a front-end digitization (FREND) system was developed that uses radiation-tolerant electronics to multiplex, amplify, and optically encode signals from an array of sensors for transmission over an optical fiber to mitigate dispersion and EMI artifacts from long runs of electrical cabling. To recover the optically transmitted data, this paper describes a signal processing scheme based on 1D template matching to an indexing channel, which is demonstrated to have an effective bit depth of 9.2 bits (1%). This scheme was validated in proof-of-concept nonnuclear testing, and preliminary experimental results show good agreement between the measured optical output and sensor input signals. While results of irradiation testing is not discussed in this work, it will be presented and analyzed in subsequent publication. The FREND system represents a low-loss data link between sensors in nuclear environments and data acquisition hardware aimed at improving the signal-to-noise ratio of data acquired from these sensors to provide better information to operators and researchers.