We have a Rosemount DP level transmitter installed on a bridle on the side of a distillation column. It tends to read consistently with the installed sightglass for long periods of time, but will experience episodes where it deviates quite badly. The Bridle is open to both the liquid and vapor side of the sump. I was wondering if anyone knew of any issues that would make the levels deviate. The nozzles on the complete system are steam traced to prevent freezing in the system.