Glossary · Automation fundamentals, platforms and components
Process gain
Also known as: Steady-state gain, Plant gain
German: Prozessverstärkung
In control engineering, process gain is the ratio of the steady-state change of a process variable to the change of the manipulated variable that caused it. Together with dead time and time constant it characterizes the process dynamics used for controller tuning.
- Automation components
In one sentence
Process gain is the steady-state change of a process variable divided by the change in the controller output that caused it.
Example
Opening a steam valve from 40 % to 50 % raises the tank temperature by 6 K at steady state, so the process gain is 0.6 K per percent.
How it applies
- Engineering: Tuning methods for PID loops use process gain, Time constant and dead time from a step test. A high gain calls for a smaller controller gain to avoid oscillation.
- Commissioning: Measure the gain around the normal operating point: many processes are nonlinear, so the gain at low load can differ strongly from that at full load.
- Documentation: Record step-test results (operating point, step size, resulting gain) in the loop documentation, so later retuning starts from known values.
Process gain vs. controller gain
Process gain belongs to the plant and is measured. Controller gain (proportional gain) is a tuning parameter set in the controller. The loop gain is roughly their product, which is why a change in process gain, for example after a valve replacement, can destabilize a well-tuned loop.