Editing Proportional–integral–derivative controller (section)

====Steady-state error====

The '''steady-state error''' is the difference between the desired final output and the actual one.<ref>{{Cite book| title = Instrument Engineers' Handbook: Process control and optimization | first = Béla G. | last = Lipták | edition = 4th | publisher = CRC Press | year = 2003 | isbn = 0-8493-1081-4 | page = 108}}</ref> Because a non-zero error is required to drive it, a proportional controller generally operates with a steady-state error.{{efn|The only exception is where the target value is the same as the value obtained when the controller output is zero.}} Steady-state error (SSE) is proportional to the process gain and inversely proportional to proportional gain. SSE may be mitigated by adding a compensating [[biasing|bias term]] to the setpoint AND output or corrected dynamically by adding an integral term.