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A Glossary for Systems Biology

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INTEGRAL CONTROL

see also

adaptation, robustness, proportional control, differential control, PID control

Meaning

Systems Theory:

Control action is proportional to the control error integrated over time. The control error is defined as the difference between the set point and the process output.

Explanation

``Proportional control normally gives a system that has a steady-state error. Integral action is introduced to remove this. [...] The idea is simply that control action is taken even if the error is very small provided that the average of the error has the same sign over a long period.'' [7] This enables the controller to correct for accumulation of small errors over time (cumulative error). Integral control is often referred to as the 'memory' of a controller.

Examples

Biology:

• bacterial chemotaxis: Chemotactic cells move along concentration gradients of attracting or repelling substances to reach the area of optimal conditions. Integral feedback control ensures the robustness of adaptation in this mechanism. [63]; see also Chapter 'Recommended Readings'.

Systems Theory:

• A heating system controlled by a thermostat is one well-known example of integral feedback control.[63]

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