A process pressure transmitter system includes a process pressure transmitter housing and a process pressure sensor in the process pressure transmitter housing. A metal flange is configured to mount to a process vessel which carries a process fluid. An isolation diaphragm attaches to the metal flange and is exposed to the process fluid through an opening in the process vessel. The isolation diaphragm comprises a polymer diaphragm bonded to a metal face of the metal flange. A capillary passageway carries a fill fluid from the isolation diaphragm to thereby convey a process pressure to the pressure sensor.