we have Differential Pressure Transmitter connected to the De-ethanizer tower and the High Tap is at the bottom and the Low Pressure Tap is at the top of the tower. the transmitter located at the top, and High connected to the high, and low to the low, and it give negative reading. the transmitter is calibrated correctly. tube is 1/2" 316SS.

 

Fluid has probably collected on the low side. During startup the overhead stream is much richer and it's not unusual for that to happen as the process cools down. Consider using remote diaphragm seals to eliminate the possibility of that happening.

> we have Differential Pressure Transmitter connected to the
> De-ethanizer tower and the High Tap is at the bottom and the
> Low Pressure Tap is at the top of the tower. the transmitter
> located at the top, and High connected to the high, and low
> to the low, and it give negative reading. the transmitter is
> calibrated correctly. tube is 1/2" 316SS.