US Patent 7461562 Process device with density measurement

A process variable transmitter for measuring a process variable of a process fluid in a vessel includes first and second pressure couplings arranged to receive a first pressure and a second pressure of process fluid in the vessel. These pressures are related to the density of the process fluid. A sensor provides a sensor output related to the process fluid in the vessel. Measurement circuitry is configured to calculate a calculated process variable of the process fluid in the vessel based upon the first and second pressures and the sensed process variable.