closed tank level calibration Abu dhabi
Closed Vessels and Differential Pressure Devices
• Pressure above the liquid in closed vessels affects the pressure measured at the bottom.
• To measure the true level, vessel pressure must be subtracted from the measurement.
• A pressure tap at the vessel is connected to the LP side of a DP transmitter, resulting in differential pressure proportional to the liquid height multiplied by the specific gravity.
• Differential pressure devices require a constant head on the external or reference leg.
• Two methods are commonly available: Dry leg and Wet leg.
• Dry leg: If gas above the liquid doesn't condense, the impulse piping to the low side of the transmitter remains empty. Zero suppression is necessary to offset the constant static head.
• Wet leg: If gas above the liquid condenses, the pipe is filled with a reference fluid with a higher specific gravity than the liquid in the vessel.