feedback control

electronics A control system which monitors its effect on

the system it is controlling and modifies its output

accordingly. For example, a thermostat has two inputs: the

desired temperature and the current temperature (the latter is

the feedback). The output of the thermostat changes so as to

try to equalise the two inputs.

Computer disk drives use feedback control to position the

read/write heads accurately on a recording track. Complex

systems such as the human body contain many feedback systems

that interact with each other; the homeostasis mechanisms that

control body temperature and acidity are good examples.

(1996-01-02)