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Chapter 5
Other Controller Features


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.