These are the most commonly used devices to measure the pressure at the base of a tank. When a DP transmitter is used for the purpose of measuring a level, it will be called a level transmitter.
To obtain maximum sensitivity, a pressure capsule has to be used, that has a sensitivity range that closely matches the anticipated pressure of the measured liquid.
However, system pressures are often much higher than the actual hydrostatic pressure that is to be measured.
If the process pressure is accidentally applied to only one side of the DP capsule during installation or removal of the DP cell from service, over ranging of the capsule would occur and the capsule could be damaged causing erroneous indications.