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| Gain on process rather than error In applications with high gain, a step change can result in a sudden, large movement in the valve. • Not as severe as the derivative effect, but still can upset the process • Solution: let gain act only on process rather than error. Derivative on process rather than error A step change in the setpoint results in a step change in the error. • The derivative term acts on the rate of change of the error. • The rate of change of a step change is very large. • An operator step change of the setpoint would cause a very large change in the output, upsetting the process. • Solution: let derivative act only on process rather than error. |
go to chapter 4: Additional PID Concepts