The differential pressure measurement principle states that differential pressure (also shown as DP or ∆p), is the difference between two applied pressures. For example, if the pressure at point A equals 100psi and the pressure at point B equals 60psi, then the differential pressure is 40psi (100psi – 60psi).

Differential Pressure (DP) transmitters measure the difference between two pressures. They use a reference point called the low-side pressure and compare it to the high-side pressure. Ports in the instrument are marked high-side and low-side. The DP reading can be either negative or positive depending on whether the low-side or high-side is the larger value. A DP transmitter can be used as a gauge pressure transmitter if the low-side is left open to the atmosphere.