Performance assessment of class 1E pressure transmitters subjected to environmental stresses

An experimental investigation into the performance of Class 1E electronic pressure transmitters exposed to environments within and beyond the design basis has been conducted. Emphasis was placed on determining the instruments' failure and degradation modes in separate and simultaneous environmental exposures. Five unaged ITT Barton Model 763 pressure transmitters were tested. Each transmitter was exposed to a unique environment. Evaluation of transmitter response showed that temperature is the primary environmental stress affecting performance. Large errors were observed at the onset of accident environment exposure. These errors decreased with time-at-temperature. We believe the source of these errors to be a common-mode design weakness in the transmitter's calibration potentiometers resulting from a dielectric property temperature dependency. The modification recommended by the manufacturer to reduce this temperature effect proved to work reasonably well in the long term. A second potential common failure mode which activates slowly with time-at-temperature was also identified. We believe this failure mechanism is catalyzed by the presence of a specific lubricant used in the production of some potentiometers. The transmitters tested proved to be exceptionally hard to radiation effects and there appeared to be no significant synergistic effects between radiation and temperature. The observed responses of the transmitters offer support for the position forwarded by IEEE 381-1977 recommending that electronic modules be aged to varying degrees of advanced life before testing. (orig.)