What does a DP cell measure to determine liquid level?

• A. Pressure between two points
• B. Temperature difference
• C. Liquid density
• D. Flow velocity

Answer: (A)

A DP cell measures the pressure difference between two points in the liquid. That differential pressure comes from the hydrostatic head of the liquid column, so it is directly related to the height of liquid above the lower tap (proportional to rho times g times height). By reading this pressure difference, you can infer the liquid level. Temperature difference, density, or flow velocity aren’t what the sensor directly measures; density or temperature may affect how you convert the reading to level, but the DP cell’s job is to sense the pressure Difference between two points.