Keywords: nuclear power plants, NPP, noise analysis, pressure transmitters, nonlinear dynamics, nuclear reactors, nuclear energy, nuclear technology, nuclear science, inner silicone oil loss, oscillation symmetry, amplitude probability, Rosemount transmitters
When a pressure transmitter leaves the linearity: the Rosemount Case
When a Rosemount pressure transmitter experiences the inner silicone oil-loss syndrome, it loses its linear behaviour. In such a case, the response time is not unique; as a consequence, focusing the sensor surveillance to the response time, as required by the technical specifications of the nuclear plant, might have no sense. In which way is the sensor dynamic not linear? Answering this open question is the main objective of this work. A bilinear model can explain most of the features of the noise signal. A more elaborated model is built in order to explain the results of the deterministic experiments. The corresponding non-linear differential equation is solved exactly for the step response, and an approximate expression is found for the anomalous response time. When the driving term of the dynamic is not a step, the differential equation is solved approximately using the Picard iteration procedure. It gives some light on why the oscillations lose symmetry or why the amplitude probability of the noise signal shows skewness.