Terry Blevins of Emerson Process Management has an excellent blog on modeling and process control. Hist post of August 8th has some interesting things to say about process gain and how it can be optimized with FOUNDATION fieldbus. Process gain is often called the "sensitivity of the process", and shows how the PV reacts in responses to changes in controller output (CO). Blevins asserts that, from a process control perspective, process gain should be constant.
Blevins states that it is not always possible to change valve characteristics to compensate for changes in process gain during commissioning because of the time and expense involved. If you have a FOUNDATION fieldbus installation, however, the block structure of FOUNDATION technology allows you to use a characterizer block between the PID and analog output blocks. You can achieve a consistent response to load disturbances and setpoint changes even if the final control element has non linear installed characteristics. Read the rest of the post to get the whole story:
Terry Blevins Modeling and Control Blog: Commissioning Control Systems -- Installed Characteristics