The plant installed sanitary pressure transmitters
on various process lines using them for control input to move product throughout various process stages. The ambient environment was very humid and temperatures on the surface of the transmitter would cycle from quite warm, >90°F to cool, <60°F. Even though all transmitters were certified as NEMA 4X rated, over time many of the incumbent transmitters would slowly fill up with water and fail. Investigation revealed pressure differentials from ambient were created by the cycling temperature changes. When the transmitter cooled, warm humid air would slowly be drawn into the enclosure and then condense. Brand new transmitters were failing in as little as 6 months and maintenance inspections were showing measurable water ingression within the first month of service.