Neutral zone (control theory)

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When a controller operates in discontinuous mode around a setpoint (for example turning an airconditioner on above a certain room temperature and turning it off below that temperature) there can be frequent undesirable oscillations between on and off (sometimes referred to as 'chatter') when the variable is close to the setpoint. To solve this problem a neutral zone can be implemented between two set points (high and low) with the controller taking no action as long as the temperature is in the neutral zone. According to Curtis (see Reference below) "The existence of such a Neutral Zone is an example of desirable hysteresis in a system."

In the above figure the controller will take no action as long as the measured error is between − Δe_p and + Δe_p.

For more information concerning Neutral zones or Controller modes, please refer to Johnson's book.

Note: a neutral zone is also called a deadband.

[edit] References

• Johnson, Curtis D. "Process Control Instrumentation Technology", Prentice Hall (2002, 7th ed.)