Level measurement using hydrostatic head

The most common type of level measurement is based on measuring the hydrostatic head in a vessel using a differential pressure measurement. This approach typically works well as long as there is a large difference between the density of the light and heavy phases. This approach usually has relatively fast measurement dynamics, since it is based on a pressure measurement. Level measurements typically have repeatability of approximately 1%. 

The tank is open to the atmosphere therefore, it is necessary to use only the high pressure (HP) connection on the AP transmitter. The low pressure (LP) side is vented to the atmosphere therefore, the pressure differential is the hydrostatic head, or weight, of the liquid in the tank. The maximum level that can be measured by the AP transmitter is determined by the maximum height of liquid above the transmitter. The minimum level that can be measured is determined by the point where the transmitter is connected to the tank. 

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