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Applied Process Control by Michael Mulholland

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1Introduction

1.1 The Idea of Control

Plant and animal life relies on numerous control mechanisms. Here one thinks of an ‘open-loop’ causal system in which cause (input) generates effect (output). Then the ‘control’ part operates around this in order to modify the effect (Figure 1.1).

A flowchart depicting feedback control mechanism, where on the left-hand side are rectangles placed vertically, denoting inputs 1–M, pointing arrows (rightward) at a bigger rectangle denoting system. From system various rightward arrows point at rectangles denoting outputs 1–N (top to bottom). A dotted arrow from output j points at a hexagon denoting decision and from here an arrow points at input i.

Figure 1.1 Feedback control mechanism.

All autonomous entities need ‘feedback’ paths like this. One might shut a door to reduce the noise level, eat to reduce hunger or turn the car steering wheel to keep in a lane. The control decision can be discrete, such as when the geyser thermostat switches on or the reserve bank adjusts the prime lending rate in order ...

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