A gauge pressure (GP) transmitter compares a process pressure against local ambient air pressure. Example Industrial Applications: Open tank level, Line pressure, and Blanket pressure in a tank.
Differential Pressure (DP) transmitters measure The Difference between two pressures. They use a referent 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.
Absolute pressure (AP) transmitter measure relative to perfect (full) vacuum pressure (absolute zero pressure); therefore, AP transmitters are not affected by fluctuations in the local atmospheric pressure. All absolute pressure measurements are positive.
Fieldbus transmitters accurately measure differential, gauge, or absolute pressure.